Lecture 5: fibrous proteins

Question 1

alpha-keratins are essentially all ____

Answer 1

alpha-keratins are essentially all alpha-helical

Question 2

the “sticky strip” is on the surface of the helix in _____ and is from _____ ; it allows for ____

Answer 2

the sticky strip is on the surface of the helix in an alpha-keratin and is from the hydrophobicity of a and d [in 7 residue pseudorepeat] ; it allows for coiled-coil formation

Question 3

coiled-coil formation [define] ; driving force is ____

Answer 3

= helices slowly winding around each other

- driven by the hydrophobic effect

Question 4

components of a strand of hair [inc. order] (4)

Answer 4

coiled-coils dimerize to form protofibrils → 11 protofibrils associate to form a microfibril → multiple microfibrils form a macrofibril → many macrofibrils in a strand of hair

Question 5

____ cause interactions between protofibrils

Answer 5

disulfide bonds cause interactions between protofibrils

Question 6

rearrangement of disulfide bonds

Answer 6

reducing agent breaks disulfide bonds → hair changes shape → heat and oxidizing agent reform the disulfide bonds in a new arrangment

Question 7

structure of fibroin

Answer 7

anti-parallel beta-sheet

Question 8

the repeating unit of fibroin is ____ and the side chains are ____ because _____

Answer 8

• (ser-gly-ala-gly)

- side chains are alternating big and small because glycine has a small side chain

Question 9

what causes fibroin to be flexible?

Answer 9

intersheet forces [VDW] are individually relatively weak but collectively very strong

Question 10

fibroin (is/ is not) stretchy and very strong

Answer 10

fibroin is not stretchy but is very strong

Question 11

repeating unit of tropocollagen

Answer 11

(gly-X-Y) where usually X = proline and Y = hydroxyproline

Question 12

the secondary structure of tropocollagen is ____

Answer 12

the secondary structure is helical but not an alpha-helix

Question 13

tropocollagen is a (R/ L-handed) helix and is (more/ less) extended than an alpha-helix

Answer 13

a L-handed helix and is more extended than an alpha-helix

Question 14

there are no intra-chain H-bonds in _____ because ____

Answer 14

no H-bonds in tropoollagen because the carbonyls and amides are farther apart

Question 15

the peptide bond planes of tropocollagen are (parallel/ perpendicular) to the helical axis

Answer 15

perpendicular to axis

Question 16

super helix bundle (3)

Answer 16

• 3 interwound L helices
• stabilized by interchain H-bonding
• gly alone fits into central position where chains approach each other closest

Question 17

collagen is stabilized by ___ and ____; these (increase/ decrease) with age and cause ____

Answer 17

collagen is stabilized by site-specific hydroxylations and post-transitional cross-links; cross-links increase with age and causes skin to lose elasticity and bones to become brittle

Question 18

formation of hydroxyproline or hydroxylysine

Answer 18

ascorbate [vitamin C] and hydroxylase

Question 19

cross-link formation requires ____ for lysil oxidase activity → a deficiency weakens ____

Answer 19

requires copper; a copper deficiency weakens collagen

Question 20

vitamin C deficiency means

Answer 20

a lack of enzymes to perform -hydroxy conversions → fewer H-bonds → weakened collagen