The science of nutrition 4th edition thompson manore vaughan chapter 06

Chapter 6 Lecture

Chapter 6:
Proteins: Crucial
Components of
All Body Tissues

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What Are Proteins?
• Proteins: large, complex molecules found in
tissues of all living things
• Dictated by genetic material (DNA)
• Contain carbon, hydrogen, oxygen, nitrogen
• Made from 20 different amino acids

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Amino Acids
• Nine essential amino acids
• Cannot be produced in sufficient quantities to
meet physiological needs
• Must be obtained from food
• Nonessential amino acids
• Can be synthesized in sufficient quantities

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Amino Acids (cont.)
• Transamination
• Transfer amine group from an essential
amino acid to a different acid group and side
chain (R group)
• Conditionally essential amino acid
• Nonessential amino acid becomes essential
• Phenylketonuria (PKU): tyrosine becomes a
conditionally essential amino acid that must
be provided by the diet

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How Are Proteins Made?
• Proteins are long chains of amino acids
• Peptide bonds join amino acids together
forming dipeptides, tripeptides, oligopeptides,

and polypeptides
• Gene expression is the process by which cells
use genes to make proteins
• Gene: segment of deoxyribonucleic acid
(DNA) that serves as a template for the
synthesis (expression) of a particular protein

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How Are Proteins Made? (cont.)
• Transcription: messenger RNA copies the
genetic information from DNA in the nucleus
• Translation: the genetic information carried by
mRNA is translated into the amino acid
sequence of a protein at the ribosome

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How Are Proteins Made? (cont.)

• Protein turnover
• Existing proteins are degraded to provide the
building blocks for new proteins
• Amino acid pool includes amino acids from
food and cellular breakdown

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How Are Proteins Made? (cont.)
• Protein organization determines function
• Primary structure: sequential order of the
amino acids
• Secondary structure: spiral shape from twist
in amino acid chain
• Tertiary structure: unique three-dimensional
shape maintained by hydrogen bonds and
disulfide bridges; determines protein's
function
• Quaternary structure: polypeptides bond to
form larger proteins (globular or fibrous)
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© 2017 Pearson Education, Inc.

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Protein Denaturation
• Proteins uncoil and lose their shape
• Damaging substances: heat, acid, base, heavy
metal, alcohol
• Protein function is lost
• Denatured enzyme
• High fever
• Blood pH out of normal range
• During digestion

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Protein in the Diet
• For protein synthesis, all essential amino acids
must be available to the cell
• Limiting amino acid
• Essential amino acid that is missing or in the
smallest supply
• Slows down or halts protein synthesis
• Inadequate energy consumption
• Limits protein synthesis

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Protein in the Diet (cont.)

• Incomplete protein (low quality): insufficient
essential amino acids
• Does not support growth and health
• Complete protein (high quality): sufficient
amounts of all nine essential amino acids
• Derived from animal and soy protein

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Protein in the Diet (cont.)
• Mutual supplementation: combine two or more
incomplete protein sources to make a complete
protein
• Complementary proteins: two or more foods
are combined to supply all nine essential amino
acids for a complete protein

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Protein Digestion
• Protein digestion begins in the stomach
• Hydrochloric acid denatures protein strands and
converts inactive enzyme pepsinogen into its
active form pepsin
• Pepsin: enzyme begins breakdown down of

proteins into short polypeptides and amino acids
• Gastrin: hormone controls hydrochloric acid
production and pepsin release

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Protein Digestion (cont.)
• Digestion continues in the small intestine
• Pancreatic enzymes (proteases) complete
protein digestion
• Trypsin
• Chymotrypsin
• Carboxypeptidase
• Special sites (small intestine) transport amino
acids, dipeptides, tripeptides

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