Amino Acid Structures: Secondary

Question 1

What are the secondary structures?

Answer 1

Alpha helices, beta sheets, coiled coils

Question 2

Alpha helices have a _________ backbone.

Answer 2

coiled

Question 3

Are the backbones of alpha helices usually R handed or L handed?

Answer 3

R handed (only sometimes L handed)

Question 4

How are alpha helices stabilized?

Answer 4

H-Bonds b/t carbonyl oxygen

and amide hydrogen four residues away

Question 5

How any residues are there per turn?

Answer 5

3.4

Question 6

Alpha helices rise ____ Angstroms per amino acids.

Answer 6

1.5

Question 7

Alpha helices rise ____ Angstroms per helical turns

Answer 7

5.4

Question 8

cut off length for most alpha helices?

Answer 8

45 Angstroms

Question 9

What residues are not commonly found in alpha helices?

Answer 9

a. branched chain amino acids - Val, Thr, Iso
b. hydrogen binding side chains - Ser, Asp, and Asn
c. Proline lacks a “free” NH group

Question 10

Beta sheets consists of two or more ________ which can be ________ or _______.

Answer 10

Beta strands, parallel, anti-parallel

Question 11

In Beta Sheets, the R-groups are pointing ________ from the backbone.

Answer 11

away

Question 12

What stabilizes Beta strands?

Answer 12

H-bonds between carbonyl oxygen and amide hydrogen from different strands

Question 13

What is the primary component of wool and hair?

Answer 13

keratin

Question 14

What are two examples of coiled coils?

Answer 14

keratin and collagen

Question 15

25% of total protein in the human body

Answer 15

collagen

Question 16

collagen is a fibrous component of ______

Answer 16

skin
bone
tendon
cartilage
teeth

Question 17

What does collagen consist of?

Answer 17

3 helical polypeptide chains

Question 18

collagen has __ residues per turn

Answer 18

3

Question 19

What amino acid is every 3rd base in collagen?

Answer 19

Gly

Question 20

What is abundant in collagen?

Answer 20

hydroxyproline (Hyp) and proline

Question 21

collagen consists of 3 repeats of ________________.

Answer 21

Gly, proline and hydroxyproline

Question 22

There are no _________ hydrogen bonds within the helix of collagen.

Answer 22

intrastrand

Question 23

What two things stabilize collagen?

Answer 23

a) Interstrand hydrogen bonds between the strands;
i.e., the hydrogen of the α-amino group of Gly with the carbonyl oxygen on an different peptide (chain).
b) Steric repulsion of the pyrrolidine rings of proline
and hydroxyproline (oriented outward away from
the helix)

Question 24

Importance of Vitamin C (ascorbate) and Scurvy

Answer 24

1) Hydroxyproline is essential for the stability of collagen
2) Prolyl hydroxylase synthesizes hydroxyproline from proline.
a) Requires a Fe2+ (ferrous) ion to activate O2 in the reaction.
b) In the formation of hydroxyproline, Fe2+ becomes
oxidized to Fe3+ (ferric) and prolyl hydroxylase become
inactive.
3) Vitamin C reduces Fe3+ (ferric) ion back to Fe2+ (ferrous)
ion.
4) Humans are unable to synthesize vitamin C and must acquire
it from their diet.
5) Lack of vitamin C in the diet can lead to a disease called
“scurvy” which results from less-stable collagen.
This leads to skin lesions, blood vessel fragility, and bleeding
gums, loss of teeth, and periodontal infections.

Question 25

What is the structure of keratin?

Answer 25

Two, right-handed α-helices intertwined to form a single

left-hand “superhelix”

Question 26

How are the keratin alpha helices held together?

Answer 26

van der Waals forces, ionic interactions, and disulfide bonds