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ENGLISH FOR BIOLOGY
ENGLISH FOR BIOLOGY
Ho Chi Minh City University of Industry - HUI
Institute of Biotechnology and Food Technology
Assessment:
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Credit point: 2
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Assessed as: Graded
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Note: There is compulsory school attendance.
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UNIT 1: CELLS AND TISSUES
GROUP 1
THE CELL
Almost everything in the world is made up of smaller things. Houses are built out of individual bricks and
pieces of wood. Cars are built out of pieces of metal, plastic, and rubber. Think about your cell. What parts
make up your cell?
The Cell Theory
One very important similarity among all living things is that they are made of cells, the smallest units of life.
In 1838, two biologists, Schleiden and Schwann, studied many cells and made some conclusions. From their
observations they developed what is known as the Cell Theory. Since then, this theory has been central to our
understanding of biology. This theory states that:
1. All life forms are made from one or more cells. Some organisms, like bacteria or paramecium, are only
one cell big. These are called unicellular organisms (uni-=one). Other organisms are multicellular: that means
they are made up of more than one cell (multi-=more than one). For example, the human body consists of
billions of cells!
2. Cells only arise from pre-existing cells. A cell can make copies of everything it has inside it, then divide
itself in two, making two new cells. This process is called mitosis, or cell division. In this way, organisms can

keep growing or replace damaged or old cells. For example, the formation of new cells is what allows your
body to grow, or what replaces your damaged skin when you fall and skin your knee, making you good as
new!
3. The cell is the smallest form of life. There is nothing smaller that is alive, and life requires what is inside
a cell. For example, the molecules that make up the parts of the cell, such as sugars, fats and proteins are not
alive. The separate regions of the cell are not alive on their own. Life can only be reduced down to the cellular
level-thus cells are the smallest unit of life!
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The Cell and Its Organelles
Even the cell is made up of smaller parts. These parts are called organelles (little organs). They divide up all
the work that the cell has to do. In the human body, we have different organs to do different jobs that help us
live: for example, our lunges help us breathe while our brain helps us think. It’s the same in a cell: the different
organelles have different jobs, and together they help the cell live.
In a unicellular organism, one cell does all the jobs the being needs to survive, and the cell divides up these
jobs among its organelles. In multicellular organisms, many cells come together to make a living being. Just
like in unicellular organisms, the cells of a multicellular organism have organelles which divide up the cell’s
work
1. Nucleus. The nucleus is the control center of the cell. It houses all
the genetic information, DNA in the form of chromatin, that tells the
cell what to do. DNA is like the recipe for the cell: all the instructions
are there, and the organelles of the cell help to read it and build the
final products: proteins! When the cell reads its DNA recipe in its
nucleus, it converts these instructions to another form called
messenger RNA (mRNA), which is like translating from one language to another in a process called
transcription.
2. Endoplasmic reticulum (ER). The ER is like a little maze of tubes that are hollow inside. Add a few cake
sprinkles right next to the ER. These are ribosomes. After mRNA is made in the nucleus, it is sent to the
ribosomes on the ER. The ribosomes are responsible for reading the mRNA message and making the proper
protein according to its instructions. This process is called

translation. As a protein is made, or “translated,” the ribosomes
pushes it into the maze of the ER. A second type of ER, called the
smooth ER is where fats are formed. It is called smooth ER
because it has no ribosomes on it.
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3. The Golgi body. The proteins made by the ribosomes that are
inside the ER are sent to the Golgi for finishing touches and
distribution. Here, the protein may be packaged or changed: it’s
like putting the paint on a car being made in a factory before it is sent out to the car dealer!
4. Mitochondria are often referred to as the powerhouses of the cell, for it is within them that energy is
released from organic molecules by the process of Cellular respiration. This energy is needed to keep
the individual cells and the plant functioning as a
whole. Carbon skeletons and fatty acid chains are also
rearranged within mitochondria, allowing for the
building of a wide variety of organic molecules.
Mitochondria are numerous and tiny, typically
measuring from 1 to 3 or more micrometers in length and
having a width of roughly one half micrometer; they are
barely visible with light microscopes. They appear to be in
constant motion in living cells and tend to accumulate in
groups where energy is needed.
5. To the lysosome, which is full of molecules that can break down cellular waste. Lysosomes are the garbage
dumps of the cell—they break down waste and dispose of it properly. Lysosomes are relatively large vesicles
formed by the Golgi. They contain hydrolytic enzymes that could destroy the cell.
6. How does the cell stay together? They are housed in a double-layered coating called the plasma
membrane that gives the cell its shape. This membrane helps control what goes in and out of the cell, and
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helps protect the cell from damaging things in the environment. The cell membrane functions as a semi-

permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced
chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development
of the lipid bilayer model (also referred to as the fluid-mosaic model). The most common molecule in the
model is the phospholipid, which has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. These
phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic
heads on the inner and outer surfaces of the membrane.
7. Ribosomes are the sites of protein
synthesis. They are not membrane-bound
and thus occur in both prokaryotes and
eukaryotes. Eukaryotic ribosomes are
slightly larger than prokaryotic ones.
Structurally the ribosome consists of a small
and larger subunit. Biochemically the
ribosome consists of ribosomal RNA
(rRNA) and some 50 structural proteins.
Often ribosomes cluster on the endoplasmic
reticulum, in which case they resemble a
series of factories adjoining a railroad line
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UNIT 2: DNA STRUCTURE
GROUP 2:
INTRODUCTION
Our genes are made of deoxyribonucleic acid (DNA). This remarkable molecule contains all the information
necessary to make a cell, and DNA is able to pass on this information when a cell divides. This chapter
describes the structure and properties of DNA molecules, the way in which our DNA is packaged into
chromosomes, and how the information stored within DNA is retrieved via the genetic code.
THE STRUCTURE OF DNA
Deoxyribonucleic acid is an extremely long polymer made from units called deoxyribonucleotides, which are
often simply called nucleotides. Figure 4.1 shows one deoxyribonucleotide, deoxyadenosine triphosphate.

Note that deoxyribose, unlike ribose, has no OH group on its 2’carbon. Four bases are found in DNA; they
are the two purines adenine (A) and guanine (G) and the two pyrimidines cytosine (C) and thymine (T) (Fig.
4.2). The combined base and sugar is known as a nucleoside to distinguish it from the phosphorylated form,
which is called a nucleotide. Four different nucleotides join to make DNA. They are 2’-deoxyadenosine-5’-
triphosphate (dATP), 2’-deoxyguanosine-5’-triphosphate (dGTP), 2’-deoxycytidine-5’-triphosphate (dCTP),
and 2’-deoxythymidine-5’-triphosphate (dTTP).
DNA molecules are very large. The single chromosome of the bacterium Escherichia coli is made up of two
strands of DNA that are hydrogen-bonded together to form a single circular molecule comprising 9 million
nucleotides. Humans have 46 DNA molecules in each cell, each forming one chromosome. We inherit 23
chromosomes from each parent. Each set of 23 chromosomes encodes a complete copy of our genome and
is made up of 6 × 10
9
nucleotides (or 3 × 10
9
base pairs—see below). We do not yet know the exact number
of genes that encode messenger RNA and therefore proteins in the human genome. The current estimate is in
the range of 30,000. Table 4.1 compares the number of predicted messenger RNA genes in the genomes of
different organisms. In each organism, there are also approximately 100 genes that code for ribosomal RNAs
and transfer RNAs.
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.
Figure 4.3 illustrates the structure of the DNA chain. As nucleotides are added to the chain by the enzyme
DNA polymerase, they lose two phosphate groups. The last (the α phosphate) remains and forms a
phosphodiester link between successive deoxyribose residues. The bond forms between the hydroxyl group
on the 3’carbon of the deoxyribose of one nucleotide and the α-phosphate group attached to the 5’ carbon of
the next nucleotide. Adjacent nucleotides are hence joined by a 3’–5’phosphodiester link. The linkage gives
rise to the sugar–phosphate backbone of a DNA molecule. A DNA chain has polarity because its two ends are
different. In the first nucleotide in the chain, the 5’ carbon of the deoxyribose is phosphorylated but otherwise
free. This is called the 5’ end of the DNA chain. At the other end is a deoxyribose with a free hydroxyl group

on its 3’carbon. This is called the 3’end.
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The DNA Molecule Is a Double Helix
In 1953 Rosalind Franklin used X-ray diffraction to show that DNA was a helical polymer. James Watson
and Francis Crick demonstrated, by building three dimensional models, that the molecule is a double helix
(Fig. 4.4). Two hydrophilic sugar–phosphate backbones lie on the outside of the molecule, and the purines and
pyrimidines lie on the inside of the molecule. There is just enough space for one purine and one pyrimidine in
the center of the double helix. The Watson–Crick model showed that the purine guanine (G) would fit nicely
with the pyrimidine cytosine (C), forming three hydrogen bonds. The purine adenine (A) would fit nicely with
the pyrimidine thymine (T), forming two hydrogen bonds. Thus A always pairs with T, and G always pairs
with C. The three hydrogen bonds formed between G and C produce a relatively strong base pair. Because
only two hydrogen bonds are formed between A and T, this weaker base pair is more easily broken. The
difference in strengths between a G–C and an A–T base pair is important in the initiation and termination of
RNA synthesis. The two chains of DNA are said to be antiparallel because they lie in the opposite orientation
with respect to one another, with the 3’-hydroxyl terminus of one strand opposite the 5’-phosphate terminus of
the second strand. The sugar–phosphate backbones do not completely conceal the bases inside. There are two
grooves along the surface of the DNA molecule. One is wide and deep—the major groove—and the other is
narrow and shallow—the minor groove (Fig. 4.4). Proteins can use the grooves to gain access to the bases.
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The Two DNA Chains Are Complementary
A consequence of the base pairs formed between the two strands of DNA is that if the base sequence of one
strand is known, then that of its partner can be inferred. A G in one strand will always be paired with a C in the
other. Similarly an A will always pair with a T. The two strands are therefore said to be complementary.
Different Forms of DNA
The original Watson–Crick model of DNA is now called the B-form. In this form, the two strands of
DNA form a right-handed helix. If viewed from either end, it turns in a clockwise direction. B-DNA is the

predominant form in which DNA is found. Our genome, however, also contains several variations of the B-
form double helix. One of these, Z-DNA, so-called because its backbone has a zig-zag shape, forms a left-
handed helix and occurs when the DNA sequence is made of alternating purines and pyrimidines. Thus the
structure adopted by DNA is a function of its base sequence.
GROUP 3: DNA AS THE GENETIC MATERIAL
Deoxyribonucleic acid carries the genetic information encoded in the sequence of the four bases—adenine,
guanine, cytosine, and thymine. The information in DNA is transferred to its daughter molecules through
replication (the duplication of DNA molecules) and subsequent cell division. DNA directs the synthesis of
proteins through the intermediary molecule RNA. The DNA code is transferred to RNA by a process known as
transcription. The RNA code is then translated into a sequence of amino acids during protein synthesis. This is
the central dogma of molecular biology: DNA makes RNA makes protein.
Retroviruses such as human immunodeficiency virus, the cause of AIDS, are an exception to this rule. As their
name suggests, they reverse the normal order of data transfer. Inside the virus coat is a molecule of RNA plus
an enzyme that can make DNA from an RNA template by the process known as reverse transcription.
PACKAGING OF DNA MOLECULES INTO CHROMOSOMES
Eukaryotic Chromosomes and Chromatin Structure
A human cell contains 46 chromosomes (23 pairs), each of which is a single DNA molecule bundled up with
various proteins. On average, each human chromosome contains about 1.3 × 10
8
base pairs (bp) of DNA. If
the DNA in a human chromosome were stretched as far as it would go without breaking it would be about 5
cm long, so the 46 chromosomes in all represent about 2 m of DNA. The nucleus in which this DNA must be
contained has a diameter of only about 10μm, so large amounts of DNA must be packaged into a small space.
This represents a formidable problem that is dealt with by binding the DNA to proteins to form chromatin.
As shown in Figure 4.5, the DNA double helix is packaged at both small and larger scales. In the first stage,
shown on the right of the figure, the DNA double helix with a diameter of 2 nm is bound to proteins known
as histones. Histones are positively charged because they contain high amounts of the amino acids arginine
and lysine and bind tightly to the negatively charged phosphates on DNA. A 146 bp length of DNA is wound
around a protein complex composed of two molecules each of four different histones—H2A, H2B, H3, and
H4—to form a nucleosome. Because each nucleosome is separated from its neighbor by about 50 bp of linker

DNA, this unfolded chromatin state looks like beads on a string when viewed in an electron microscope.
Nucleosomes undergo further packaging. A fifth type of histone, H1, binds to the linker DNA and pulls the
nucleosomes together helping to further coil the DNA into chromatin fibers 30 nm in diameter, which are
referred to as 30-nm solenoids. The fibers then form loops with the help of a class of proteins known as
nonhistones, and this further condenses the DNA (panels on left-hand side of Fig. 4.5) into a higher order set of
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coils in a process called supercoiling.
In a normal interphase cell about 10% of the chromatin is highly compacted and visible under the light
microscope. This form of chromatin is called heterochromatin and is the portion of the genome where
no RNA synthesis is occurring. The remaining interphase chromatin is less compacted and is known as
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euchromatin.
Chromatin is in its most compacted form when the cell is preparing for mitosis, as shown at the top left of
Figure 4.5. The chromatin folds and condenses further to form the 1400- nm-wide chromosomes we see under
the light microscope. Because the cell is to divide, the DNA has been replicated, so that each chromosome
is now formed by two chromatids, each one a DNA double helix. This means the progeny cell, produced by
division of the progenitor cell, will receive a full set of 46 chromosomes. Figure 4.6 is a photograph of human
chromosomes as they appear at cell division.
Prokaryotic Chromosomes
The chromosome of the bacterium E. coli is a single circular DNA molecule of about 4.5 ×10
6
base pairs.
It has a circumference of 1 mm, yet must fit into the 1-μm cell, so like eukaryotic chromosomes it is coiled,
supercoiled, and packaged with basic proteins that are similar to eukaryotic histones. However, an ordered
nucleosome structure similar to the “beads on a string” seen in eukaryotic cells is not observed in prokaryotes.
Prokaryotes do not have nuclear envelopes so the condensed chromosome together with its associated proteins
lies free in the cytoplasm, forming a mass that is called the nucleoid to emphasize its functional equivalence to
the eukaryotic nucleus.

Plasmids
Plasmids are small circular minichromosomes found in bacteria and some eukaryotes. They are several
thousand base pairs long and are probably tightly coiled and supercoiled inside the cell. Plasmids often code
for proteins that confer resistance to a particular antibiotic. In Chapter 7 we describe how plasmids are used by
scientists and genetic engineers to artificially introduce foreign DNA molecules into bacterial cells.
Viruses
Viruses rely on the host cell to make more viruses. Once viruses have entered cells, the cells’ machinery is
used to copy the viral genome. Depending on the virus type, the genome may be single- or double-stranded
DNA, or even RNA. A viral genome is packaged within a protective protein coat. Viruses that infect bacteria
are called bacteriophages. One of these, called lambda, has a fixed-size DNA molecule of 4.5 × 10
4
base
pairs. In contrast, the bacteriophage M13 can change its chromosome size, its protein coat expanding in
parallel to accommodate the chromosome. This makes M13 useful in genetic engineering
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UNIT 3: VIRUSES
GROUP 4:
The Discovery of Viruses
The border between the living and the nonliving is very clear to a biologist. Living organisms are cellular
and able to grow and reproduce independently, guided by information encoded within DNA. the simplest
creature living on earth today that satisfy these criteria are bacteria. Even simpler than bacteria are viruses.
As you will learn in this section, viruses are so simple that they do not satisfy the criteria for “living.” Viruses
possess only a portion of the properties of organisms. Viruses are literally parasitic” chemicals, segments of
DNA or RNA wrapped in a protein coat. They cannot reproduce on their own, and for this reason they are not
considered alive by biologists. They can, however, reproduce within cells, often with disastrous results to the
host organism. Earlier theories that viruses represent a kind of halfway point between life and nonlife have
largely been abandoned. Instead, viruses are now viewed as detached fragments of the genomes of organisms
due to the high degree of similarity found among some viral and eukaryotic genes. Viruses vary greatly in
appearance and size. The smallest are only about 17 nanometers in diameter, and the largest are up to 1000

nanometers (1 micrometer) in their greatest dimension (figure 33.2). The largest viruses are barely visible with
a light microscope, but viral morphology is best revealed using the electron microscope. Viruses are so small
that they are comparable to molecules in size; a hydrogen atom is about 0.1 nanometer in diameter, and a large
protein molecule is several hundred nanometers in its greatest dimension.
Biologists first began to suspect the existence of viruses near the end of the nineteenth century. European
scientists attempting to isolate the infectious agent responsible for hoof-and-mouth disease in cattle concluded
that it was smaller than a bacterium. Investigating the agent further, the scientists found that it could not
multiply in solution—it could only reproduce itself within living host cells that it infected. The infecting agents
were called viruses. The true nature of viruses was discovered in 1933, when the biologist Wendell Stanley
prepared an extract of a plant virus called tobacco mosaic virus (TMV) and attempted to purify it. To his great
surprise, the purified TMV preparation precipitated (that is, separated from solution) in the form of crystals.
This was surprising because precipitation is something that only chemicals do—the TMV virus was acting like
a chemical off the shelf rather than an organism. Stanley concluded that TMV is best regarded as just that—
chemical matter rather than a living organism.
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Within a few years, scientists disassembled the TMV virus and found that Stanley was right. TMV was not
cellular but rather chemical. Each particle of TMV virus is in fact a mixture of two chemicals: RNA and
protein. The TMV virus has the structure of a Twinkie, a tube made of an RNA core surrounded by a coat of
protein. Later workers were able to separate the RNA from the protein and purify and store each chemical.
Then, when they reassembled the two components, the reconstructed TMV particles were fully able to infect
healthy tobacco plants and so clearly were the virus itself, not merely chemicals derived from it. Further
experiments carried out on other viruses yielded similar results.
GROUP 5:
The Nature of Viruses
Viral Structure
All viruses have the same basic structure: a core of nucleic acid surrounded by protein. Individual viruses
contain only a single type of nucleic acid, either DNA or RNA. The DNA or RNA genome may be linear
or circular, and single-stranded or double-stranded. Viruses are frequently classified by the nature of their
genomes. RNA-based viruses are known as retroviruses.

Nearly all viruses form a protein sheath, or capsid, around their nucleic acid core. The capsid is composed
of one to a few different protein molecules repeated many times (figure 33.3) In some viruses, specialized
enzymes are stored within the capsid. Many animal viruses form an envelope around the capsid rich in
proteins, lipids, and glycoprotein molecules. While some of the material of the envelope is derived from the
host cell’s membrane, the envelope does contain proteins derived from viral genes as well.
Viruses occur in virtually every kind of organism that has been investigated for their presence. However, each
type of virus can replicate in only a very limited number of cell types. The suitable cells for a particular virus
are collectively referred to as its host range. The size of the host range reflects the coevolved histories of the
virus and its potential hosts. A recently discovered herpes virus turned lethal when it expanded its host range
from the African elephant to the Indian elephant, a situation made possible through cross-species contacts
between elephants in zoos. Some viruses wreak havoc on the cells they infect; many others produce no disease
or other outward sign of their infection. Still other viruses remain dormant for years until a specific signal
triggers their expression. A given organism often has more than one kind of virus. This suggests that there
may be many more kinds of viruses than there are kinds of organisms—perhaps millions of them. Only a few
thousand viruses have been described at this point.
Viral Replication
An infecting virus can be thought of as a set of instructions, not unlike a computer program. A computer’s
operation is directed by the instructions in its operating program, just as a cell is directed by DNA-encoded
instructions. A new program can be introduced into the computer that will cause the computer to cease what
it is doing and devote all of its energies to another activity, such as making copies of the introduced program.
The new program is not itself a computer and cannot make copies of itself when it is outside the computer,
lying on the desk. The introduced program, like a virus, is simply a set of instructions. Viruses can reproduce
only when they enter cells and utilize the cellular machinery of their hosts. Viruses code their genes on a single
type of nucleic acid, either DNA or RNA, but viruses lack ribosomes and the enzymes necessary for protein
synthesis. Viruses are able to reproduce because their genes are translated into proteins by the cell’s genetic
machinery. These proteins lead to the production of more viruses.
Viral Shape
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Most viruses have an overall structure that is either helical or isometric. Helical viruses, such as the tobacco

mosaic virus, have a rodlike or threadlike appearance. Isometric viruses have a roughly spherical shape whose
geometry is revealed only under the highest magnification.
The only structural pattern found so far among isometric viruses is the icosahedrons, a structure with 20
equilateral triangular facets, like the adenovirus shown in figure 33.2. Most viruses are icosahedral in basic
structure. The icosahedron is the basic design of the geodesic dome. It is the most efficient symmetrical
arrangement that linear subunits can take to form a shell with maximum internal capacity.
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UNIT 4: STEM CELL
GROUP 6:
Since the isolation of embryonic stem cells in 1998, labs all over the world have been exploring the possibility
of using stem cells to restore damaged or lost tissue. Exciting results are now starting to come in. What is a
stem cell? At the dawn of a human life, a sperm fertilizes an egg to create a single cell destined to become
a child. As development commences, that cell begins to divide, producing a small ball of a few dozen cells.
At this very early point, each of these cells is identical. We call these cells embryonic stem cells. Each one
of them is capable by itself of developing into a healthy individual. In cattle breeding, for example, these
cells are frequently separated by the breeder and used to produce multiple clones of valuable offspring. The
exciting promise of these embryonic stem cells is that, because they can develop into any tissue, they may
give us the ability to restore damaged heart or spine tissue (figure 19.24). Experiments have already been tried
successfully in mice. Heart muscle cells have been grown from mouse embryonic stem cells and successfully
integrated with the heart tissue of a living mouse. This suggests that the damaged heart muscle of heart attack
victims might be reparable with stem cells, and that injured spinal cords might be repairable. These very
promising experiments are being pursued aggressively. They are, however, quite controversial, as embryonic
stem cells are typically isolated from tissue of discarded or aborted embryos, raising serious ethical issues.
Tissue-Specific Stem Cells
New results promise a neat way around the ethical maze presented by stem cells derived from embryos. Go
back for a moment to what we were saying about how a human child develops. What happens next to the
embryonic stem cells? They start to take different developmental paths. Some become destined to form nerve
tissue and, after this decision is taken, cannot ever produce any other kind of cell. They are then called nerve
stem cells. Others become specialized to produce blood, still others muscle. Each major tissue is represented

by its own kind of tissue-specific stem cell. Now here’s the key point: as development proceeds, these tissue-
specific stem cells persist. Even in adults. So why not use these adult cells, rather than embryonic stem cells?
Transplanted Tissue-Specific Stem Cells Cure
MS in Mice
In path finding 1999 laboratory experiments by Dr. Evan Snyder of Harvard Medical School, tissue-specific
stem cells were able to restore lost brain tissue. He and his coworkers injected neural stem cells (immediate
descendants of embryonic stem cells able to become any kind of neural cell) into the brains of newborn mice
with a disease resembling multiple sclerosis (MS). These mice lacked the cells that maintain the layers of
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myelin insulation around signal conducting nerves. The injected stem cells migrated all over the brain, and
were able to convert themselves into the missing type of cell. The new cells then proceeded to repair the
ravages of the disease by replacing the lost insulation of signal-conducting nerve cells. Many of the treated
mice fully recovered. In mice at least, tissue-specific stem cells offer a treatment for MS.
The approach seems very straightforward, and should apply to humans. Indeed, blood stem cells are already
routinely used in humans to replenish the bone marrow of cancer patients after marrow-destroying therapy.
The problem with extending the approach to other kinds of tissue specific stem cells is that it has not always
been easy to find the kind of tissue-specific stem cell you want.
GROUP 7:
Transplanted Stem Cells Reverse Juvenile
Diabetes in Mice
Very promising experiments carried out in 2000 by Dr. Ammon Peck and a team of researchers at the
University of Florida concern a particularly vexing problem, that of type 1 or juvenile diabetes. A person with
juvenile diabetes lacks insulin-producing pancreas cells, because their immune system has mistakenly turned
against them and destroyed them. They are no longer able to produce enough insulin to control their blood
sugar levels and must take insulin daily. Adding back new insulin-producing cells called islet cells has been
tried many times, but doesn’t work well. Immune cells continue to destroy them. Peck and his team reasoned,
why not add instead the stem cells that produce islet cells? They would be able to produce a continuous supply
of new islet cells, replacing those lost to immune attack. Because there would always be cells to make insulin,
the diabetes would be cured.

No one knew just what such a stem cell looked like, but the researchers knew they come from the epithelial
cells that line the pancreas ducts. Surely some must still lurk there unseen. So the research team took a bunch
of these epithelial cells from mice and grew them in tissue culture until they had lots of them. Were the stem
cells they sought present in the cell culture they had prepared? Yes. In laboratory dishes the cell culture
produced insulin in response to sugar, indicating islet cells had developed in the growing culture, islet cells that
must have been produced from stem cells.
Now on to juvenile diabetes. The scientists injected their cell culture into the pancreas of mice specially bred
to develop juvenile diabetes. Unable to manufacture their own insulin because they had no islet cells, these
diabetic mice could not survive without daily insulin. What happened?
The diabetes was reversed! The mice no longer required insulin. Impatient to see in more
detail what had happened, the researchers sacrificed the mice and examined the cells of
their pancreas. The mice appeared to have perfectly normal islet cells. One might have
wished the researchers waited a little longer before terminating the experiment. It is not clear
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whether the cure was transitory or long term. Still, there is no escaping the conclusion that injection of a
culture of adult stem cells cured their juvenile diabetes. While certainly encouraging, a mouse is not a human,
and there is no guarantee the approach will work in humans. But there is every reason to believe it might. The
experiment is being repeated now with humans. People suffering from juvenile diabetes are being treated with
human pancreatic duct cells obtained from people who have died and donated their organs for research. No
ethical issues arise from using cells of adult organ donors, and initial results look promising.
Transplanted stem cells may allow us to replace damaged or lost tissue, offering cures for many disorders that
cannot now be treated. Current work focuses on tissue-specific stem cells, which do not present the ethical
problems that embryonic stem cells do.
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UNIT 5:
Mutations are changes in the genetic message
GROUP 8:
Mutations Are Rare But Important

The cells of eukaryotes contain an enormous amount of DNA. If the DNA in all of the cells of an adult
human were lined up end-to-end, it would stretch nearly 100 billion kilometers—60 times the distance
from Earth to Jupiter! The DNA in any multicellular organism is the final result of a long series of
replications, starting with the DNA of a single cell, the fertilized egg. Organisms have evolved many
different mechanisms to avoid errors during DNA replication and to preserve the DNA from damage.
Some of these mechanisms “proofread” the replicated DNA strands for accuracy and correct any
mistakes. The proofreading is not perfect, however. If it were, no variation in the nucleotide sequences
of genes would be generated.
Mistakes Happen
In fact, cells do make mistakes during replication, and damage to the genetic message also occurs,
causing mutation (figure 18.2). However, change is rare. Typically, a particular gene is altered in
only one of a million gametes. If changes were common, the genetic instructions encoded in DNA
would soon degrade into meaningless gibberish. Limited as it might seem, the steady trickle of change
that does occur is the very stuff of evolution. Every difference in the genetic messages that specify
different organisms arose as the result of genetic change.
The Importance of Genetic Change
All evolution begins with alterations in the genetic message: mutation creates new alleles, gene
transfer and transposition alter gene location, reciprocal recombination shuffles and sorts these
changes, and chromosomal rearrangement alters the organization of entire chromosomes. Some
changes in germ-line tissue produce alterations that enable an organism to leave more offspring, and
those changes tend to be preserved as the genetic endowment of future generations. Other changes
reduce the ability of an organism to leave offspring. Those changes tend to be lost, as the organisms
that carry them contribute fewer members to future generations.
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Evolution can be viewed as the selection of particular combinations of alleles from a pool of
alternatives. The rate of evolution is ultimately limited by the rate at which these alternatives are
generated. Genetic change through mutation and recombination provides the raw material for
evolution.
Genetic changes in somatic cells do not pass on to offspring, and so have less evolutionary

consequence than germ-line change. However, changes in the genes of somatic cells can have an
important immediate impact, particularly if the gene affects development or is involved with regulation
of cell proliferation.
GROUP 9:
Kinds of Mutation
Because mutations can occur randomly anywhere in a cell’s DNA, mutations can be detrimental, just
as making a random change in a computer program or a musical score usually worsens performance.
The consequences of a detrimental mutation may be minor or catastrophic, depending on the function
of the altered gene.
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Mutations in Germ-Line Tissues
The effect of a mutation depends critically on the identity of the cell in which the mutation occurs.
During the embryonic development of all multicellular organisms, there comes a point when cells
destined to form gametes (germline cells) are segregated from those that will form the other cells
of the body (somatic cells). Only when a mutation occurs within a germ-line cell is it passed to
subsequent generations as part of the hereditary endowment of the gametes derived from that cell.
Mutations in Somatic Tissues
Mutations in germ-line tissue are of enormous biological importance because they provide the raw
material from which natural selection produces evolutionary change. Change can occur only if there
are new, different allele combinations available to replace the old. Mutation produces new alleles, and
recombination puts the alleles together in different combinations. In animals, it is the occurrence of
these two processes in germ-line tissue that is important to evolution, as mutations in somatic cells
(somatic mutations) are not passed from one generation to the next. However, a somatic mutation
may have drastic effects on the individual organism in which it occurs, as it is passed on to all of
the cells that are descended from the original mutant cell. Thus, if a mutant lung cell divides, all
cells derived from it will carry the mutation. Somatic mutations of lung cells are, as we shall see, the
principal cause of lung cancer in humans.
Point Mutations
One category of mutational changes affects the message itself, producing alterations in the sequence

of DNA nucleotides (table 18.1 summarizes the sources and types of mutations). If alterations involve
only one or a few basepairs in the coding sequence, they are called point mutations. While some point
mutations arise due to spontaneous pairing errors that occur during DNA replication, others result from
damage to the DNA caused by mutagens, usually radiation or chemicals. The latter class of mutations
is of particular practical importance because modern industrial societies often release many chemical
mutagens into the environment.
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Changes in Gene Position
Another category of mutations affects the way the genetic message is organized. In both bacteria and
eukaryotes, individual genes may move from one place in the genome to another by transposition.
When a particular gene moves to a different location, its expression or the expression of neighboring
genes may be altered. In addition, large segments of chromosomes in eukaryotes may change their
relative locations or undergo duplication. Such chromosomal rearrangements often have drastic
effects on the expression of the genetic message.

Exercises
A. Complete the below passages with the appropriate words:
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a. suffering b. scientists c. a host cell (tế bào chủ) d. human viruses e. genome
f. incapable of g. envelop h. made of
Exercise 1:
VIRUSES:
Viruses occupy a unique space between the living and nonliving worlds. On one hand they are (1)………
the same molecules as living cells. On the other hand they are (2)…………… independent existence, being
completely dependent on a host cell to reproduce. Almost all living organisms have viruses that infect them.
(3)…………. include polio, influenza, herpes, rabies, ebola, smallpox, chickenpox, and the AIDS (acquired
immunodeficiency syndrome) virus HIV (human immunodeficiency virus). Viruses are submicroscopic (siêu
hiển vi) particles consisting of a core of genetic material enclosed within a protein coat called the capsid.

Some viruses have an extra membrane layer called the (4)…………… . Viruses are metabolically inert
until they enter (5) ……………., whereupon the viral genetic material directs the host cell machinery to
produce viral protein and viral genetic material. Viruses often insert their (6)……………… into that of the
host, an ability that is widely made use of in molecular genetics. Bacterial viruses, called bacteriophages are
used by (7) …………… to transfer genes between bacterial strains. Human viruses are used as
vehicles for gene therapy. By exploiting the natural infection cycle of a virus such as adenovirus, it is possible
to introduce a functional copy of a human gene into a patient (8)…………… from a genetic disease such
as cystic fibrosis.
Vocabulary:
Genome (n): Bộ gen - The total genetic content contained in a haploid set of chromosomes in eukaryotes,
in a single chromosome in bacteria, or in the DNA or RNA of viruses. An organism's genetic material.
Host cell (n): tế bào chủ - In biology, a host is an organism that harbors (cho ẩn náu) a virus or
parasite.
Parasite (n): vât ký sinh
Submicroscopic (adj): siêu hiển vi.
protein coat (n): lớp bọc protein
gene therapy (n): liệu pháp gene - Gene therapy is a rapidly growing field of medicine in which genes
are introduced into the body to treat diseases.
Adenoviruses (n) - Adenoviruses are DNA viruses (small infectious agents) that cause upper respiratory
tract infections and other infections in humans.
Exercise 2
a. guanine and cytosine b. involved c. H bonds d. complementary e. consisting
f. ribose g. complementarity h. RNAs i. base j. protein k. contacted l. formed
Like (1)………………………., deoxyribonucleic acids (DNAs) are polymeric molecules (2)………………………. of
nucleotide building blocks. Instead of (3)…………………………, however, DNA contains 2_-deoxyribose, and the
uracil base in RNA is replaced by thymine. The spatial structure of the two molecules also differs. The first evidence
of the special structure of DNA was the observation that the amounts of adenine and thymine are almost equal in
every type of DNA. The same applies to (4) ……………………………… The model of DNA structure formulated
in 1953 explains these constant base ratios: intact DNA consists of two polydeoxynucleotide molecules (“strands”).
Each base in one strand is linked to a (5)…………………………… base in the other strand by H-bonds. Adenine is

complementary to thymine, and guanine is complementary to cytosine. One purine base and one pyrimidine base are
thus (6)……………………… in each base pair. The (7)…………………………….of A with T and of G with C can
be understood by considering the (8)……………………….that are possible between the different bases. Potential
donors are amino groups (Ade, Cyt, Gua) and ring NH groups. Possible acceptors are carbonyl oxygen atoms (Thy,
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Cyt, Gua) and ring nitrogen atoms. Two linear and therefore highly stable bonds can thus be (9)…………………….in
A–T pairs, and three in G–C pairs.
Exercise 3
a. nucleotides b. a double helix c. information d. hydrogen bonds
e. backbone f. DNA g. polymers h. a new chain i. enzymes j. protein k. replicated l. formed
DNA and RNA are long linear (1)………………………… , called nucleic acids, that carry (2)
………………………………… in a form that can be passed from one generation to the next. These macromolecules
consist of a large number of linked (3)……………………………… , each composed of a sugar, a phosphate, and a
base. Sugars linked by phosphates form a common (4)……………………………, whereas the bases vary among four
kinds. Genetic information is stored in the sequence of bases along a nucleic acid chain. The bases have an additional
special property: they form specific pairs with one another that are stabilized by (5)………………………………….
The base pairing results in the formation of (6)………………………………, a helical structure consisting of two
strands. These base pairs provide a mechanism for copying the genetic information in an existing nucleic acid
chain to form(7)………………………. Although RNA probably functioned as the genetic material very early in
evolutionary history, the genes of all modern cells and many viruses are made of (8)………………… DNA is (9)
………………… by the action of DNA polymerase (10)……………………… These exquisitely specific enzymes
copy sequences from nucleic acid templates with an error rate of less than 1 in 100 million nucleotides.
Exercise 4:
a. The sugar–phosphate backbone b.DNA double helix C. do occur d.passed
e. cell survival f. genetic material DNA
The (1)………………. must be faithfully replicated every time a cell divides to ensure that the information
encoded in it is (2)………… unaltered to the progeny cells. DNA molecules have to last a long time
compared to RNA and protein. (3)………… of DNA is a very stable structure because there are no free
hydroxyl groups on the sugar— they are all used up in bonds, either to the base or to phosphate. The

bases themselves are protected from chemical attack because they are hidden within the (4) …………….
Nevertheless, mutations (5)………… in the DNA molecule, and cells have had to evolve mechanisms
to ensure that mutation is kept to a minimum. Repair systems are essential for both (6)………… and to
ensure that the correct DNA sequence is passed on to daughter cells.
Vocabulary:
Hydroxyl – OH group (n): nhóm OH
Progeny (n): con cái, con cháu, dòng dõi.
Backbone (n): khung sườn
DNA double helix: chuỗi xoắn kép DNA
Daughter cell (n): tế bào con - Either of the two identical cells that form when a cell divides.
Exercise 5:
a. expressed b. mRNA c. RNA d. encoding e. Transcription
(1)…………… is the process whereby the information held in the nucleotide sequence of DNA is transferred
to RNA. The three major classes of (2)………… are ribosomal RNA (rRNA), transfer RNA (tRNA), and
messenger RNA (mRNA). All play key roles in protein synthesis. Genes (3)………… mRNAs are known as
protein-coding genes. A gene is said to be (4)……………. when its genetic information is transferred to (5)
………… and then to protein.
Vocabulary:
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Express (v) –expression (n): biểu hiện, gene expression (n): biểu hiện gene.
Transcript (v) – transcription (n): phiên mã
Sequence (v,n) – sequencing (n): xác đònh trình tự - DNA sequencing technique.
Protein - coding gene (noun phrase)
Gene (n) – genetic (adj)
Exercise 6:
DNA CLONING
a. introduce into (transfer into) b. proteins c. produced d.DNA cloning e. the human genetic
material f.properties g.interested h. four nucleotides i. interest
j.DNA k. identical l. population

Since DNA molecules are composed of only (1) ………… , their physical and chemical (2) ………. are very
similar. Hence it is extremely difficult to purify individual species of (3)………… by classical biochemical
techniques similar to those used successfully for the purification of (4) ………. However, we can use (5)
……….to help us to separate DNA molecules from each other. A clone is a (6) ………… of cells that arose
from one original cell and, in the absence of mutation, all members of a clone will be genetically (7) ……….
If a foreign gene or gene fragment is (8) …………. a cell and the cell then grows and divides repeatedly,
many copies of the foreign gene can be (9) ……… , and the gene is then said to have been cloned. A
DNA fragment can be cloned from any organism. The basic approach to cloning a gene is to take the
genetic material from the cell of (10)……… , which in the examples we will describe is a human cell, and to
introduce this DNA into bacterial cells. Clones of bacteria are then generated, each of which contains and
replicates one fragment of (11) ……… The clones that contain the gene we are (12)…………. in are then
identified and grown separately. We therefore use a biological approach to isolate DNA molecules rather
than physical or chemical techniques.
Vocabulary:
Introduce into =transfer into (v)
Replicate (v) ->replication (n): tạo bản sao.
Isolate (v) – isolation (n): tách chiết.
Isolating molecules = isolation of molecules.
Exercise 7:
GM CROPS:
a. suffer b. four genes c. the dagmage d. nutritionally enhanced crops
e. presence f. GM crops g. world’s population, h. insecticide i. the health j. vital nutrients
The arguments about the value of (1) ………. and (2) ………… they cause the environment will continue
for a long time. These have largely concerned plants that produce (3)…………… and plants that are
resistant to herbicide. Almost unnoticed in the maelstrom of claim and counterclaim has been the use of
genetic engineering to produce (4) ………… Rice is a staple food in many countries but lacks many (5)
………… About 800 million children (6) ……… from vitamin A deficiency, which can result in blindness
and a weakened immune system. In an attempt to overcome this severe nutritional deficiency, a group
of Swiss scientists have engineered the rice endosperm to produce provitamin A (beta-carotene). This is
converted in the body to vitamin A. (7)……………. were introduced into the rice endosperm, three genes

from the daffodil and one from the bacterium Erwinia. These genes code for all the proteins needed to make
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