Amino Acid Structures: Secondary Flashcards
What are the secondary structures?
Alpha helices, beta sheets, coiled coils
Alpha helices have a _________ backbone.
coiled
Are the backbones of alpha helices usually R handed or L handed?
R handed (only sometimes L handed)
How are alpha helices stabilized?
H-Bonds b/t carbonyl oxygen
and amide hydrogen four residues away
How any residues are there per turn?
3.4
Alpha helices rise ____ Angstroms per amino acids.
1.5
Alpha helices rise ____ Angstroms per helical turns
5.4
cut off length for most alpha helices?
45 Angstroms
What residues are not commonly found in alpha helices?
a. branched chain amino acids - Val, Thr, Iso
b. hydrogen binding side chains - Ser, Asp, and Asn
c. Proline lacks a “free” NH group
Beta sheets consists of two or more ________ which can be ________ or _______.
Beta strands, parallel, anti-parallel
In Beta Sheets, the R-groups are pointing ________ from the backbone.
away
What stabilizes Beta strands?
H-bonds between carbonyl oxygen and amide hydrogen from different strands
What is the primary component of wool and hair?
keratin
What are two examples of coiled coils?
keratin and collagen
25% of total protein in the human body
collagen
collagen is a fibrous component of ______
skin bone tendon cartilage teeth
What does collagen consist of?
3 helical polypeptide chains
collagen has __ residues per turn
3
What amino acid is every 3rd base in collagen?
Gly
What is abundant in collagen?
hydroxyproline (Hyp) and proline
collagen consists of 3 repeats of ________________.
Gly, proline and hydroxyproline
There are no _________ hydrogen bonds within the helix of collagen.
intrastrand
What two things stabilize collagen?
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)
Importance of Vitamin C (ascorbate) and Scurvy
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.
What is the structure of keratin?
Two, right-handed α-helices intertwined to form a single
left-hand “superhelix”
How are the keratin alpha helices held together?
van der Waals forces, ionic interactions, and disulfide bonds
