Chapter 11: Proteins: Amino Acids and Peptides Part 1

Individuals with PKU must not consume phenylalanine (since it is not synthesized). Tyrosine is a byproduct of phenylalanine. When no Phe is available, additional Tyr must be consumed to meet the body’s needs (conditionally essential AA).

• Soybeans

• Must be heat processed for several hours to destroy toxic compounds that prevent the complete digestion of proteins

• Low in methionine

Cereal: Lysine
Others: Tryptophan, Threonine

• Whole-wheat bread + peanut butter

• Rice and red beans

• Refried beans and corn tortilla

• Hummus (chickpeas + sesame seeds)

AA with nonpolar side chains, positioned toward the outsides of the molecules, allowing them to attract cholesterol molecules

Serine, threonine, tyrosine (causes a polar nature)

Carbon, Hydrogen, Oxygen, Nitrogen, usually Sulfur

Iron, Copper, Phosphorus, Zinc

Amino acids

• Side chain of C and H

• Carboxyl group (COOH)

• Amine group (NH2)

Acid: carboxyl group
Base: amine group

carbonyl carbon and amide nitrogen combine and form a peptide bond through condensation (released water)

Chain of amino acids bound together by peptide bonds.

100 to 150 AA

1) By their nutritional use

2) By the chemical nature of their side chain

Dispensable/nonessential: made by the body (11)

Indispensable/essential: not made by the body and must be supplied by the diet (9)

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

Certain conditions prevent the body from producing enough dispensable AA and they have to be obtained from the diet
(not in healthy individuals)

Complete: contain all the indispensable AA
Incomplete: grains and vegetables are short one or more of the essential AA

Combining sources (ex: beans + rice)

• Nonpolar

• Uncharged polar

• Positively charged

• Negatively charged

Nonpolar sidechains

AA with neutral sidechains

Positively and negatively charged

1) Number of amino acids
2) Order in which they combine
3) Interaction of the sidechain

The order the amino acids occur in the sidechain; results from chain of peptide bonds.

Refers to the shape of sections of the protein

Refers to the 3D structure of an entire AA chain

1) Helix: repeating coil
2) Random coil: tangled and twisted
3) Pleated sheet: like a paperfan

1) Globular proteins do not form gel networks (do not hold water)
2) Fibrous proteins form gel networks, long elastic, usually made from helix-shaped strands

Form between the H-atom of one chain and the hydroxyl group of another

• Basic to the stability of 2nd and 3rd structures

| - Make some proteins water soluble

Covalent bonds between 2 protein molecules at side chains with sulfur

The more stable disulfide bonds, the more stable the molecule

Sodium hydroxide (Lye)

Form between sidechains that are nonpolar

• Caseins in milk (cheese curds)

| - Whey, by-product of cheese production

The iron binding protein pigment in muscle that provides colour

Bright Red: when O molecule is attached
Purplish: when O molecule is not attached
Brown: after prolonged exposure to O

The reversible process of adding and removing oxygen.

| Oxidation adds oxygen, Reduction removes it

added during the curing process to preserve meats

ham and bacon, very stable, pink-red colour

Any change in the shape of a protein molecule without breaking the peptide bonds