Amino acids, peptides & proteins

Zwitterionic form

The form where the carboxyl group is deprotonated (-COO⁻) and the amino group is protonated (-NH₃⁺), resulting in no net charge.

Isoelectric point (pI)

The pH at which the amino acid has no net charge.

Cationic form

At low pH (≤ 1.0), where both the amino and carboxylic acid groups are protonated.

Anionic form

At high pH (≥ 12.0), when both the carboxyl and amino groups are deprotonated.

What happens to functional groups as pH rises?

≤ 1.0 - All groups protonated.

1.0<pH<pI - Protonated R (if ionizable) and amino group, deprotonated carboxyl group

pI<pH<12.0 - Protonated amino group, deprotonated carboxyl, and R group (if ionizable)

≥ 12.0 - All groups deprotonated

Aromatic properties

Absorbs light in the UV region. Helps in detecting and quantifying proteins without destroying them.

R/S vs D/L

R/S - Calculated by functional groups

D/L - Determined by comparing to D or L glyceraldehyde from most oxidized to least oxidized

Peptide bonds are formed by

Formed by a CONDENSATION reaction

What happens/ leaves during peptide bond formation

The oxygen of the carboxyl group and two hydrogens of the amino group combine and leave to form water.

Where is the peptide bond formed between?

Formed between the carbon of the carboxyl group of one aa and the nitrogen of the amino group of the second aa.

The amino (N) terminus is located

on the end of a free amino group (not involved in peptide bond formation), LEFT

The carboxy (C) terminus is located

on the end of a free carboxyl group (not involved in peptide bond formation), RIGHT

Regulatory protein examples (3)

Peptide and protein hormones

Allosteric enzymes

Initiation factors

Transport protein examples (3)

Membrane transporters

Hemoglobin

Serum albumin

Storage protein examples (4)

Myoglobin

Ferritin

Ovalbumin

Casein

Structural protein examples (5)

Collagen

Alpha keratin

Beta keratin

Cytoskeletal protein fibers

Tubulin, actin, and spectrin

Contractile and motile protein examples (3)

Actin and myosin

Tubulin

Dynein and kinesin

Scaffold proteins

Act as bridges to form supramolecular complexes

Protective protein examples (4)

Antibodies

Hemostasis cascade

Toxins

Keratins

Stress proteins

allow abiotic survival

Stress protein examples (3)

Cytochrome P450

Metallothionein

Heat shock proteins (HSP)

Exotic protein examples

Glue proteins