NUTR207 Class 10

proteins part 1

What are the building blocks of proteins?

Amino acids

What elements make up amino acids?

Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur

What two groups are part of every amino acid’s structure?

An amine group and an acid group

What part of an amino acid makes it unique?

Its side chain (R group)

How many amino acids are there in total?

20

What are essential amino acids?

Amino acids not made by the body and must be obtained from food

What are non-essential amino acids?

Amino acids that the body can make or recycle (also come from food)

What are conditionally essential amino acids?

Amino acids that must be obtained from food only in special situations (e.g., PKU, newborns)

List the 9 essential amino acids.

Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine

What forms the backbone of a protein?

Amine group + acid group

What determines the function of an amino acid?

The size, shape, and chemical properties of its side chain

What type of bond links amino acids together?

Peptide bond

How do amino acids build proteins?

By linking via peptide bonds to form long chains of amino acids

How can proteins become functional?

When several strands cluster together, or when a metal ion/vitamin activates them

Describe the primary structure of a protein.

The amino acid sequence determined by genes; linked by peptide bonds

Describe the secondary structure.

Twisting or folding due to weak attractions between R groups; provides strength

Describe the tertiary structure.

Overall 3D folding; shaped by hydrophilic/hydrophobic interactions and disulfide (S–S) bonds

Describe the quaternary structure.

Interactions between two or more polypeptide chains

What determines a protein’s amino acid sequence?

Heredity (genetic code)

What is the term for all proteins produced by the body?

The proteome

Why do different amino acid combinations matter?

They produce different proteins with unique functions (over 1 million types)

What are single-gene disorders?

Inherited mutations present at birth (e.g., PKU, sickle cell anemia, cystic fibrosis)

What are multigene disorders?

Chronic diseases caused by several genes and environmental interactions (e.g., CHD)

What are SNPs (single nucleotide polymorphisms)?

Small genetic variations that may affect health or disease risk

How can inherited variations in amino acid sequences affect health?

They can alter protein function, leading to disease or dysfunction

What enzyme is non-functioning in PKU?

Phenylalanine hydroxylase

What happens when phenylalanine hydroxylase doesn’t work?

Phenylalanine (PHE) is not converted (hydroxylated) to tyrosine (TYR)

What builds up in the body due to PKU?

Phenylalanine and phenylketones

What damage does PKU cause?

Damages the developing brain

How is PKU detected?

Through neonatal screening programs

What is the medical nutrition therapy for PKU?

Keep PHE and phenylketones low, and treat tyrosine (TYR) as an essential amino acid

What gene is affected in cystic fibrosis?

CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene

How does a person inherit cystic fibrosis?

They must inherit two copies of the mutated CFTR gene (one from each parent)

What is the main defect caused by CFTR mutation?

Poorly functioning chloride channel

What are the main symptoms of cystic fibrosis?

Thick mucus in lungs leading to infections and breathing issues

What treatment helps with digestion in CF?

Pancreatic enzyme replacement (oral coated enzymes)

What is the cornerstone of CF treatment?

Medical Nutrition Therapy – supports growth and immune function

Where and when was the CFTR gene first identified?

Hospital for Sick Children, 1980s

How many CFTR polymorphisms are now known?

About 2000

What surgical option may be used in advanced CF?

Lung transplant

What happens when a cell makes a protein?

The gene for that protein has been “expressed”

How do nutrients influence gene expression?

Nutrients can activate or silence genes, affecting which proteins are made

Example of nutrients influencing gene expression?

Iron abundance stimulates hemoglobin synthesis

What is nutritional genomics?

The study of interactions between genes and nutrients

What are the two branches of nutritional genomics?

Nutrigenetics and nutrigenomics

What does nutrigenetics study?

How genes influence the activity and metabolism of nutrients

What does nutrigenomics study?

How nutrients influence the activity of genes (includes epigenetics)

How can nutrients affect gene expression?

• Directly interact with genetic signals that turn genes on or off

• Indirectly via substances generated during metabolism

What does activating or silencing a gene do?

Increases or decreases the synthesis of specific proteins

How do changes in gene expression affect health?

By influencing which proteins are made, affecting cellular function and overall health

What is protein denaturation?

Irreversible change in protein shape/structure

What causes protein denaturation?

• Agitation

• Heat

• Acid or base

• Heavy metal salts

• Alcohol

• Digestion

• Radiation

What is denaturation the first step of?

Destruction of a protein’s structure

What happens to protein in the stomach?

• Denatured by HCl (acid)

• Pepsin hydrolyzes peptide bonds

• Results in single amino acids and peptides

What happens to protein in the small intestine?

• Pancreatic bicarbonate inactivates pepsin

• Pancreatic enzymes (trypsin, chymotrypsin) break peptide bonds

• Intestinal peptidases further break peptides into amino acids, dipeptides, and tripeptides

Where does protein absorption occur?

In the small intestine

In what forms are proteins absorbed?

As single amino acids, dipeptides, and tripeptides

What happens to di- and tripeptides during absorption?

They may be broken into amino acids on the cell surface or inside the cell

Do all amino acids use the same absorption sites?

No, there are separate sites for different amino acid types → competition

After absorption, where do amino acids go?

To the liver via the hepatic portal vein

What happens to amino acids in the liver?

• Used by the liver

• Or released into the blood for other cells

How do cells use absorbed amino acids?

• To build new proteins

• Or for energy

Does the body store excess amino acids?

No, the body does not store protein or amino acids

What happens to protein-rich foods in the mouth and salivary glands?

They are chewed, crushed, and moistened with saliva to be swallowed.

Does protein digestion begin in the mouth?

No, it begins in the stomach.

What does hydrochloric acid (HCl) do in the stomach?

Denatures protein structure.

What enzyme does HCl activate in the stomach?

Pepsinogen → Pepsin.

What is the function of pepsin?

Cleaves proteins into smaller polypeptides and some free amino acids.

What does pepsin inhibit in the stomach?

Pepsinogen synthesis.

What enzymes from the pancreas and small intestine continue protein digestion?

Pancreatic and intestinal proteases

What do pancreatic and intestinal proteases split polypeptides into?

Tripeptides, dipeptides, and amino acids.

What enzyme activates trypsin from trypsinogen in the small intestine?

Enteropeptidase.

What are the functions of trypsin?

• Inhibits trypsinogen synthesis

• Cleaves peptide bonds next to lysine and arginine

• Converts procarboxypeptidases to carboxypeptidases

• Converts chymotrypsinogen to chymotrypsin.

What is the function of chymotrypsin?

Cleaves peptide bonds next to phenylalanine, tyrosine, tryptophan, methionine, asparagine, and histidine.

What is the function of carboxypeptidases?

Cleave amino acids from the acid (carboxyl) ends of polypeptides.

What do elastase and collagenase do?

Cleave polypeptides into smaller polypeptides and tripeptides.

What do intestinal tripeptidases do?

Split tripeptides into dipeptides and amino acids.

What do intestinal dipeptidases do?

Cleave dipeptides into amino acids.

What do intestinal aminopeptidases do?

Cleave amino acids from the amino (NH₂) ends of small polypeptides.

What is the final product absorbed by intestinal cells?

Amino acids.

How are amino acids absorbed into intestinal cells?

Amino acids require carrier proteins to cross cell membranes in the small intestine.

What is the main function of amino acid carriers?

To transport amino acids from one side of the cell membrane to the other.

What can happen when large doses of one amino acid are taken as a supplement?

It can cause amino acid competition, where one amino acid type limits the absorption of others that use the same carrier system.

Why do amino acid supplements sometimes create nutrient imbalances?

Because the amino acid in highest concentration will be absorbed preferentially, reducing absorption of others.

What is the implication of amino acid competition for supplements?

Taking single amino acids in excess can interfere with the absorption of other essential amino acids.

What are the main roles of protein in the body?

• Supporting growth and maintenance

• Building enzymes and hormones

• Building antibodies

• Maintaining fluid and electrolyte balance

• Maintaining acid-base balance

• Providing energy

• Supporting blood clotting and other vital processes

How do proteins support growth and maintenance?

They provide the amino acids needed to build new tissues and repair damaged ones.

What is the role of proteins in enzyme and hormone production?

Proteins act as enzymes that speed up chemical reactions and as hormones that regulate body functions.

How do proteins support immunity?

By building antibodies that defend the body against pathogens.

How do proteins help maintain fluid and electrolyte balance?

They attract water, keeping fluid distributed evenly inside and outside cells.

How do proteins maintain acid-base balance?

They act as buffers to prevent drastic changes in pH by accepting or releasing hydrogen ions.

How can proteins serve as an energy source?

When carbohydrate and fat stores are low, proteins can be broken down to produce energy.

What role do proteins play in blood clotting?

They form fibrin, which creates blood clots to prevent excessive bleeding.

Why must amino acids be continuously available in the body?

Because proteins in red blood cells, muscles, intestinal cells, skin, hair, and nails are constantly being replaced.

What are enzymes made from, and what do they do?

Enzymes are proteins that build, break down, or transform substances (e.g., amino acids into glucose).

What is the role of hormones made from proteins?

They act as messenger molecules released by glands to restore normal body conditions.

Give examples of protein-based hormones.

Insulin, glucagon, and serotonin (from tryptophan).

What other compounds are synthesized from amino acids?

Tyrosine is used to make epinephrine, norepinephrine, and the thyroid hormone thyroxine.

What do antibodies do?

They detect and attack foreign invaders like bacteria, viruses, and toxins.

What is special about antibody function?

Each antigen triggers the formation of a specific antibody, creating molecular memory (immunity).