Biochemistry 1: Peptides and Proteins

Question 1

characteristics of proteinogenic amino acids

Answer 1

20 alpha amino acids

alpha carbon is chiral (except glycine)

all chiral amino acids in eukaryotes are L-amino acids

all have S absolute configuration (except cysteine)

Question 2

amphoteric

Answer 2

at low pH, amino acid is protonated

at high pH, amino acid is deprotonated

Question 3

pKa

Answer 3

the pH where [protonated species] = [deprotonated species]

above, species is deprotonated

below, species is protonated

Question 4

zwitterion

Answer 4

amphoteric (acts as acid or base)

compound with no net electric charge

Question 5

isoelectric point (pI)

Answer 5

pH of the zwitterion

= (pKa of deprotonated species + pKa of protonated species) / 2

Question 6

alpha helix

Answer 6

protein secondary structure

helix that rotates clockwise around central axis

H bonds between O in C=O and N in NH3 in residues down the chain

side chains point outwards

Question 7

beta-pleated sheet

Answer 7

protein secondary structure

can be parallel or antiparallel

H bonds between O in C=O and N in NH3 in adjacent chains

Question 8

categories of proteins

Answer 8

fibrous, globular, molten globules (intermediate states in protein folding)

Question 9

denaturation

Answer 9

caused by heat and solutes (bases, detergents)

heat - causes increase in kinetic energy

solutes - disrupt interactions or solubilize proteins