2.2 - Protein Structure

Question 1

amino acid group at acid pH

Answer 1

protonated

Question 2

carboxyl group at basic pH

Answer 2

ionised

Question 3

amino acid group and carboxyl group at neutral pH (2)

Answer 3

1. amino acid group = protonated
2. carboxyl group = ionised

(total charge = 0)

Question 4

amino acid ion state at physiological pH

Answer 4

zwitterions

Question 5

zwitterions

Answer 5

molecules that contain both positively and negatively charged functional groups with an overall charge of 0

Question 6

amino acid shape

Answer 6

chiral

Question 7

chiral

Answer 7

asymmetric in such a way that the structure and its mirror image are not superimposable

Question 8

amino acid form in biological systems

Answer 8

L form

Question 9

peptide bonds

Answer 9

linkage of carboxyl group of one amino acid to amine group of another, with elimination of a water molecule

Question 10

why are peptide bonds planar?

Answer 10

due to sharing of electrons

Question 11

Trans-peptide group

Answer 11

R groups at opposite ends

Question 12

Cis-peptide group

Answer 12

R groups next to each other

Question 13

why is the core amino acid chiral in 19/20 amino acids?

Answer 13

because it has 4 different groups

Question 14

stereoisomers

Answer 14

same molecular formula and atomic connectivity, but their atomic arrangement in space is different

Question 15

which amino acid cant exist as a stereoisomer?

Answer 15

glycine-R=hydrogen atom

Question 16

Enantiomers (2)

Answer 16

amino acids can be:
1. L (left)
2. D (right)

Question 17

amino acid enantiomers found in proteins in living organisms

Answer 17

L amino acids

Question 18

enantiomers

Answer 18

two stereoisomers related to each other by a reflection (mirror images of each other, which are non-superimposable)

Question 19

number of amino acid combinations for a 100 residue protein

Answer 19

20^100

Question 20

amino acid classes (5)

Answer 20

1. non-polar
2. polar
3. acidic
4. basic
5. generic

Question 21

how are amino acids abbreviated?

Answer 21

three letter and one letter abbreviations

e.g. Alanine, Ala, A

Question 22

unique properties of glycine (2)

Answer 22

1. side chain is - H
2. glycines occur in tightly packed protein regions

Question 23

unique properties of proline (3)

Answer 23

1. introduces “kink” in chain
2. can form ‘cis’ backbone
3. difficult to fit into category, shares many properties with aliphatic amino acids

Question 24

what increases the hydrophobicity of amino acids?

Answer 24

more CH

Question 25

amino acids with aromatic R groups (3)

Answer 25

1. Phe 2. Tyr 3. Trp

Question 26

feature of aromatic amino acids

Answer 26

absorb UV light

Question 27

wavelength of light absorbed by Trp and Tyr at neutral Ph

Answer 27

280nm

Question 28

wavelength of light absorbed by Phe at neutral pH

Answer 28

260nm

Question 29

how are disulfide bonds formed? (2)

Answer 29

1. side chains d cysteine contain highly reactive thiol group 2. two thiol groups form disulfide bond

Question 30

effect of oxidising/reducing environments on disulfide bonds (2)

Answer 30

1. formed in oxidising environments 2. broken in reducing environments

Question 31

purpose of disulfide bridge

Answer 31

link distant amino acids

Question 32

cytochrome c

Answer 32

protein found in all aerobic organisms and protein sequences from distantly related species such as mammals and bacteria (similar enough to conclude proteins are homologous)

Question 33

what does the globin gene encode for?

Answer 33

haemoglobin

Question 34

haemoglobin in adults

Answer 34

iron containing heme molecule surrounded by 4 globin proteins (2 a-globins and 2 B-globins)

Question 35

how does sickle cell anaemia result from defective haemoglobin? (2)

Answer 35

1. haemoglobins stick together 2. RBCs damaged

Question 36

what causes sickle cell anaemia?

Answer 36

single mutation (significant change to protein structure and RBC structure as a result)