Lecture Human anatomy and physiology - Chapter 3: Cells (part d)

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College

CHAPTER

3

Cells: The
Living Units:
Part D
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Cell Cycle
• Defines changes from formation of the cell
until it reproduces
• Includes:
• Interphase
• Cell division (mitotic phase)

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Interphase
• Period from cell formation to cell division
• Nuclear material called chromatin
• Four subphases:
• G1 (gap 1)—vigorous growth and metabolism
• G0—gap phase in cells that permanently cease

dividing
• S (synthetic)—DNA replication
• G2 (gap 2)—preparation for division
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G1 checkpoint
(restriction point)
S
Growth and DNA
synthesis
G1
Growth

M

G2
Growth and final
preparations for
division

G2 checkpoint

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Figure 3.31


Interphase

Centrosomes
(each has 2
centrioles)

Nucleolus
Interphase

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Nuclear
envelope

Plasma
membrane

Chromatin

Figure 3.33


DNA Replication
• DNA helices begin unwinding from the
nucleosomes
• Helicase untwists the double helix and
exposes complementary chains
• The Y-shaped site of replication is the
replication fork
• Each nucleotide strand serves as a template
for building a new complementary strand
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DNA Replication
• DNA polymerase only works in one direction
• Continuous leading strand is synthesized
• Discontinuous lagging strand is synthesized in
segments
• DNA ligase splices together short segments of
discontinuous strand

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DNA Replication
• End result: two DNA molecules formed from
the original
• This process is called semiconservative
replication

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Chromosome

Free nucleotides

DNA polymerase

Old strand acts as a
template for synthesis

of new strand

Leading strand

Old DNA
Helicase unwinds
the double helix and
exposes the bases
Replication
fork
Adenine
Thymine
Cytosine
Guanine

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Two new strands (leading and lagging)
synthesized in opposite directions
Lagging
strand

DNA polymerase Old (template) strand

Figure 3.32