Lesson 2

Question 1

what percentage of proteins are found within a cell

Answer 1

~ 14%

Question 2

what 3 roles do proteins play in cells

Answer 2

(1) structure
(2) enzymes
(3) immune response

Question 3

r-groups are classified based on

Answer 3

the chemical nature of the side chain

Question 4

are most amino acids an L or D isomer

Answer 4

L

Question 5

are most amino acids S or R

Answer 5

S –> one exception for cystine (R)

Question 6

what is the only amino acid that can form disulfide bonds (bridge) –> a stabilizing interaction in the 3D structure of a protein

Answer 6

cystine

Question 7

at pH 1, describe the protonation states of both the N and C terminals

Answer 7

at pH 1, both the N and C terminals are protonated

Question 8

at pH 7…

Answer 8

“zwitterion”
N-terminal is protonated, C-terminal is deprotonated

Question 9

acidic charged amino acids

Answer 9

aspartate (aspartic acid)
glutamate (glutamic acid)

Question 10

charged amino acids (basic)

Answer 10

lysine
arginine
histidine

Question 11

ionizable side chains

Answer 11

aspartic and glutamic acid
histidine
cystine
tyrosine
lysine
arginine

Question 12

ionizable side chains with +1 charge at acidic conditions

Answer 12

histidine
lysine
arginine
amino group on N-terminal

Question 13

ionizable side chains with neutral charge at acidic conditions

Answer 13

aspartic and glutamic acid
cystine
tyrosine
carboxyl group on C-terminal

Question 14

pk1

Answer 14

pH where carboxylic acid group is 50% ionized: 50 COOH and 50% COO-

Question 15

pk2

Answer 15

pH where alpha amino group is 50% ionized: 50% NH3 and 50% NH2

Question 16

pI

Answer 16

pH where net charge = 0
= 1/2 (pki +pkj)