Proteins are made up of amino acids and perform many essential functions in the body. They serve as structural materials, forming parts of tissues and providing strength. Proteins also act as enzymes, catalyzing biochemical reactions and allowing processes like digestion. Additionally, proteins function as regulators through roles like transporting molecules, balancing fluids, and stimulating growth via hormones. The document discusses how the 20 amino acids are used to build proteins through DNA transcription and translation, and how dietary protein intake influences protein synthesis and breakdown in the body.

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Protein: Amino
Acids
Chapter 6

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The Chemist’s View of Proteins
• Proteins contain:
• Carbon, hydrogen,
oxygen, nitrogen
• Amino acids
• Carbon
• Hydrogen
• Amino group
• Acid group
• Side group or side
chain

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Proteins Made of Amino Acids
• Proteins more complex than carbohydrates or
fats
• Twenty amino acids
• Different characteristics
• Essential amino acids
• Must be supplied by the diet
• Nonessential amino acids
• Body can synthesize
• Conditionally essential amino acids

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Amino Acids
Essential Amino Acids Nonessential Amino Acids
Histidine (HISS-tuh-deen)
Isoleucine (eye-so-LOO-seen)
Leucine (LOO-seen)
Lysine (LYE-seen)
Methionine (meh-THIGH-oh-neen)
Phenylalanine (fen-il-AL-ah-neen)
Threonine (THREE-oh-neen)
Tryptophan (TRIP-toe-fan, TRIP-toe-fane)
Valine (VAY-leen)
Alanine (AL-ah-neen)
Arginine (ARJ-ih-neen)
Asparagine (ah-SPAR-ah-geen)
Aspartic acid (ah-SPAR-tic acid)
Cysteine (SIS-teh-een)
Glutamic acid (GLU-tam-ic acid)
Glutamine (GLU-tah-meen)
Glycine (GLY-seen)
Proline (PRO-leen)
Serine (SEER-een)
Tyrosine (TIE-roe-seen)
These 20 amino acids can all be commonly found in proteins. In addition, other amino acids do not occur in proteins
but can be found individually (for example, taurine and ornithine). Some amino acids occur in related forms (for
example, proline can acquire an OH group to become hydroxyproline).

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Examples of Amino Acids

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Proteins
• Peptide bonds link amino acids
• Condensation reactions
• Amino acid sequencing
• Primary structure – chemical bonds
• Secondary structure – electrical attractions
• Tertiary structure – hydrophilic and hydrophobic
• Quaternary structure – two or more polypeptides

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Condensation of Two Amino
Acids to Form a Dipeptide

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Amino Acid Sequence of
Human Insulin

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The Structure of Hemoglobin

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Denaturation of Proteins
• Disruption of stability
• Uncoil and lose shape
• Stomach acid
• Examples
• Cooking an egg
• Curdling of milk
• Stiffening of egg whites

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Protein Digestion
• Mouth
• Stomach
• Hydrochloric acid denatures proteins
• Pepsinogen to pepsin
• Small intestine
• Hydrolysis reactions
• Peptidase enzymes

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Protein Digestion in the GI
Tract
PROTEIN
Mouth and salivary glands
Chewing and crushing moisten protein-rich foods and
mix them with saliva to be swallowed.
Stomach
Hydrochloric acid (HCI) uncoils protein strands and
activates stomach enzymes. Then enzymes on the
surface of the small intestinal cells hydrolyze these
peptides and the cells absorb them.
Small intestine and pancreas
Pancreatic and small -intestinal
enzymes spin polypeptides further:
Polypeptides are converted to tripeptides, dipeptides,
and amino acids using pancreatic and intestinal
proteases.
Then enzymes on the surface of the small intestinal
cells hydrolyze these peptides and cells absorb them:
Peptides are turned into amino acids by intestinal
tripeptidases and dipeptidases. The amino acids are
then absorbed.
HYDROCHLORIC ACID AND THE DIGESTIVE
ENZYMES
In the stomach:
Hydrochloric acid (HCI)
• Denatures protein structure
• Activates pepsinogen to pepsin
Pepsin
• Cleaves proteins to smaller polypeptides and some free
amino acids
• Inhibits pepsinogen synthesis
In the small intestine:
Enteropeptidase
• Converts pancreatic trypsmogen 10 trypsin
Trypsin
• Inhibits trypsinogen synthesis
• Cleaves peptide bonds next to the amino acids lysine and
arginine
• Converts pancreatic procarboxypeptidases to
carboxypeptidases
• Converts pancreatic chymotrypsinogen to chymotrypsin
Chymotrypsm
• Cleaves peptide bonds next lo the amino acids
phenylalanine, tyrosine, tryptophan, methionine, asparagine.
and histidine
Carboxypeptidases
• Cleave amino acids from the acid (carboxyl) ends of
polypeplides
Elastase and collagenase
• Cleave polypeptides into smaller polypeptides and tripeptides
Intestinal tripeptidases
• Cleave tripeptides to dipeptkies and amino acids
Intestinal dipeptidases
• Cleave dipepttdes to amino acids Intestinal
aminopeptidases
• Cleave amino acids from the amino ends of small
polypeplides (oligopeptides)

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Protein Absorption
• Transport into intestinal cells
• Uses of amino acids by intestinal cells
• Unused amino acids transported to liver
• Enzyme digestion
• Predigested proteins

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Protein’s Role in DNA
• Uniqueness of each person
• Amino acid sequences of proteins
• Genes – DNA
• Diet
• Adequate protein
• Essential amino acids

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Protein Synthesis

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Process of Protein Synthesis
• DNA template to make mRNA
• Transcription
• mRNA carries code to ribosome
• Ribosomes: protein factories
• mRNA specifies sequence of amino acids
• Translation
• tRNA
• Sequencing errors

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Sickle Cell Compared with
Normal Red Blood Cell
Aminoacidsequenceof normalhemoglobin:
Val----His----Leu—Thr—Pro---Glu---Glu
Aminoacidsequenceof sickle-cellhemoglobin:
Val---His---Leu---Thr---Pro---Val---Glu

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Gene Expression
• Gene expression and protein synthesis
• Capability of body cells
• Each type of cell makes only the protein it needs
• Dietary influence on gene expression
• Disease development

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Proteins as Structural
Materials and Enzymes
• Building blocks for most body structures
• Collagen matrix
• Filled with mineral crystals for bones or teeth
• Replacement of dead or damaged cells
• Enzymes
• Break down, build up, and transform substances
• Catalysts

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Enzyme Action

21. Stepped Art -
Enzyme Action
Enzyme Enzyme Enzyme
A
B
BA
BA
New
compound
The separate compounds,
A and B, are attracted to
the enzyme’s active site,
making a reaction likely.
The enzyme forms a
complex with A and B.
The enzyme is
unchanged, but A and B
have formed a new
compound, AB.

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Roles of Proteins
• Hormones
• Messenger molecules
• Transported in blood to target
tissues
• Regulators of fluid balance
• Edema
• Acid-base regulators
• Attract hydrogen ions
• Transporters
• Specificity

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Examples of Hormones and
Their Actions
Hormones Actions
Estrogen and
testosterone
Responsible for gender
characteristics
Oxytocin and prolactin Support lactation (see
Chapter 15)
Progesterone Supports pregnancy (see
Chapter 15)
Growth hormone Promotes growth
Insulin and glucagon Regulate blood glucose
(see Chapter 4)
Thyroxin Regulates the body's
metabolic rate
(see Chapter 8)
Calcitonin and
parathyroid hormone
Regulate blood calcium
(see Chapter 12)
Aldosterone,
angiotensin, renin,
and antidiuretic
hormone
Regulate fluid and
electrolyte balance
(see Chapter 12)

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An Example of a Transport
Protein

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More Protein Roles
• Antibodies
• Defend body against disease
• Specificity
• Immunity – memory
• Source of energy and glucose
• Starvation and insufficient carbohydrate intake
• Other roles
• Blood clotting
• Vision

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Preview of Protein Metabolism
• Protein turnover
• Continual production and destruction
• Amino acid pool
• Exists within cells and circulating blood
• Amino acids released during protein breakdown
• Used for protein production
• Used for energy if stripped of nitrogen

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Nitrogen Balance
• Zero nitrogen balance
• Nitrogen intake equals nitrogen output
• If body synthesizes more than it degrades:
• Positive nitrogen status
• Protein is added
• State in growing infants, children, and others
• If body degrades more than it synthesizes:
• Negative nitrogen status
• State of starvation or severe stress

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Other Uses for Amino Acids
• Making other compounds
• Tyrosine used to make epinephrine and
norepinephrine
• Tryptophan precursor for niacin and seratonin
• Energy and glucose
• Wasting of lean body tissue
• Adequate intake of carbohydrates and fats

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Making Fat from Amino Acids
• When energy and protein exceed needs
• Carbohydrate intake is adequate
• Can contribute to weight gain
• Deaminating amino acids
• Stripped of nitrogen-containing amino group
• Ammonia
• Keto acid

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Deamination and Synthesis of
a Nonessential Amino Acid

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Using Amino Acids to Make
Nonessential Amino Acids
• Cells can build essential or nonessential
amino acids
• Breakdown of proteins
• Keto-acids
• Liver cells and nonessential amino acids
• Converting ammonia to urea
• Liver – ammonia and carbon dioxide
• Dietary protein

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Transamination and Synthesis
of a Nonessential Amino Acid

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Urea Synthesis

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Excreting Urea
• Liver releases urea into blood
• Kidneys filter urea out of blood
• Effect of liver disease
• Effect of kidney disease
• Protein intake and urea production
• Water consumption

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Urea Excretion

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Protein Functions in the Body
Structural materials Proteins form integral parts of most body tissues and provide strength and
shape to skin, tendons, membranes, muscles, organs, and bones.
Enzymes Proteins facilitate chemical reactions.
Hormones Proteins regulate body processes. (Some, but not all, hormones are
proteins.)
Fluid balance Proteins help to maintain the volume and composition of body fluids.
Acid-base balance Proteins help to maintain the acid-base balance of body fluids by acting as
buffers.
Transportation Proteins transport substances, such as lipids, vitamins, minerals, and
oxygen, around the body.
Antibodies Proteins inactivate foreign invaders, thus protecting the body against
diseases.
Energy and glucose Proteins provide some fuel, and glucose if needed, for the body's energy
needs.
Other The protein fibrin creates blood clots; the protein collagen forms scars; the
protein opsin participates in vision.

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Protein Quality Factors
• Digestibility
• Other foods consumed
• Animal versus plant proteins
• Amino acid composition
• Essential amino acid consumption
• Nitrogen-containing amino groups
• Limiting amino acid

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Reference and
Complementary Proteins
• Reference protein
• Requirements of preschool-age children
• High-quality proteins
• Animal proteins
• Plant proteins
• Complementary proteins
• Low-quality proteins combined to provide
adequate levels of essential amino acids

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Complementary Proteins
Ile Lys Met Trp
Legumes ✓ ✓
Grains ✓ ✓
Together ✓ ✓ ✓ ✓
In general, legumes provide plenty of isoleucine (Ile) and
lysine (Lys) but fall short in Methionine (Met) and
tryptophan (Trp). Grains have the opposite strengths
and weaknesses, making them a perfect match for
legumes.
Black beans and rice, a favorite
Hispanic combination, together provide
a balanced array of amino acids.

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Health Effects of Protein
• Protein deficiency
• Consequences
• Protein-energy malnutrition
• Marasmus and kwashiorkor
• Heart disease
• Animal-protein intake
• Homocysteine levels
• Coffee’s role
• Arginine levels

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Other Effects of Protein
• Cancer
• Protein-rich foods; not protein content of diet
• Adult bone loss (osteoporosis)
• Increase in calcium excretion
• Protein-to-calcium ratio
• Weight control
• Kidney disease
• Acceleration of kidney deterioration

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Recommended Intakes of
Protein
• Need for dietary protein
• Only source of essential amino acids
• Only practical source of nitrogen
• 10 to 35 percent of daily energy intake
• RDA for adults
• 0.8 grams per kg of body weight per day
• Infant and child needs slightly higher
• Assumptions in setting the RDA
• Adequate energy

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From Guidelines to Groceries
• Protein foods
• One ounce delivers about seven grams of protein
• USDA Food Patterns
• Recommended sources
• Milk and milk products
• Fruits, vegetables, and grains
• Read food labels
• Current United States intakes
• Moderation

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Protein and Amino Acid
Supplements
• Building muscle
• Muscle work versus protein supplements
• Protein powders
• Athletic performance
• Whey protein
• Amino acid supplements
• Potential risks associated with intake
• Lysine and tryptophan

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Nutritional
Genomics
Highlight 6

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Nutritional Genomics,
continued
• Study of how nutrients influence gene activity
• New field
• Nutrigenetics
• How genes influence activity of nutrients
• Focuses on:
• Human genome
• Human proteome

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Nutritional Genomics
Illustrated

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The Human Genome
1. The human genome is a complete set of
genetic material organized into 46
chromosomes, located within the nucleus
of a cell.
2. A chromosome is made of DNA and
associated proteins.
3. The double helical structure of a DNA
molecule is made up of two long chains of
nucleotides. Each nucleotide is composed
of a phosphate group, a 5-carbon sugar,
and a base.
4. The sequence of nucleotide bases (C, G,
A, T) determines the amino acid
sequence of proteins. These bases are
connected by hydrogen bonding to form
base pairs—adenine (A) with thymine (T)
and guanine (G) with cytosine (C).
5. A gene is a segment of DNA that includes
the information needed to synthesize one
or more proteins.

49. Stepped Art–
The Human Genome
Cell
2. Chromosome
3. DNA
4.
4. Gene
1. Nucleus

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A Genomics Primer
• DNA
• 46 chromosomes
• Nucleotide bases
• Gene expression
• Genetic information to protein synthesis
• Gene presence versus gene expression
• Epigenetics
• How environmental factors affect gene
expression
• DNA methylation

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Nutrient Regulation of Gene
Expression

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Genetic Variation and Disease
• Genome variation
• About 0.1 percent
• Goal of nutritional genomics
• Customize recommendations to fit individual
needs
• Single-gene disorders
• Phenylketonuria (PKU)
• Mutation of a single gene

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Multigene Disorders
• Study expression and interaction of multiple
genes
• Sensitive to environmental influences
• Example: heart disease
• Single nucleotide polymorphisms (SNPs)

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Clinical Concerns
• Healthcare ramifications of understanding the
human genome
• Discover genetic predisposition to specific
diseases
• Develop “designer” therapies
• Create new medications for each genetic variation
• Increase understanding of nutrition’s influence on
biological disease pathways