protein structure and function

Question 1

Examples of Silk Proteins

Answer 1

1. Collagen
2. Elastin
3. Keratin
4. Silk Fibroin

Question 2

▪ insoluble, extracellular (found outside the cell)

Answer 2

Collagen

Question 3

▪ very strong due to aldol crosslinks (covalent bond)

▪ found in all animals

Answer 3

Collagen

Question 4

▪ most abundant in the human body

Answer 4

Collagen

Question 5

▪ essential in all connective tissues e.g. cartilage, bone, tendons, ligaments, and skin

Answer 5

Collagen

Question 6

▪ triple helical structure (tropocollagen) stabilized by

Answer 6

aldol crosslinks

Question 7

▪primary structure of collagen

Answer 7

repeating tripeptide (Gly-X-Y) where X is usually Pro and Y is usually hydroxyproline

Question 8

they also exhibit H-bonding because of hydroxyproline

Answer 8

Collagen

Question 9

they are not α-helical; just helical

Answer 9

Collagen

Question 10

– excessive collagen synthesis

Answer 10

Fibrosis

Question 11

▪ overproduction of type 1 collagen in lungs reduces the lung’s ability to expand for air intake and interferes with normal breathing; scarring of lungs

Answer 11

Pulmonary fibrosis

Question 12

▪ excessive deposition in liver leads to scar tissue formation due to overconsumption of alcohol; may lead to cirrhosis

Answer 12

Liver fibrosis

Question 13

caused by insufficient collagen production where skin and tendons are weak and easily stretched producing loose joints and hyperextensive limbs

Answer 13

Ehler’s-Danlos (Rubberman syndrome)

Question 14

▪ type 1 procollagen molecules fail partially or completely to assemble into triple helices and are therefore degraded.
▪ reduced amount of collagen leads to fragile bones; easily fractured

Answer 14

Osteogenesis Imperfecta (Brittle bone syndrome)

Question 15

▪ found predominantly in walls of arteries, lungs, intestines, skins, etc.

Answer 15

Elastin

Question 16

▪ structural proteins that gives elasticity to the body’s tissues and organs

Answer 16

Elastin

Question 17

MW of elastin

Answer 17

72 kDA

Question 18

AAs in elastin

Answer 18

Small nonpolar

A,V, L,G

Question 19

▪WHY hydrophobic elastin molecules “slide and stretch” over one another

Answer 19

to maintain structural integrity and provide recoil

Question 20

▪ elastin protein molecules are crosslinked by WHAT TYPE OF BONDS

Answer 20

covalent bonds

Question 21

tough, fibrous, insoluble protein that makes up the skin, hair and nails

Answer 21

KERATIN

Question 22

also found in claws, hooves, feathers and horns

Answer 22

KERATIN

Question 23

human hair is __% cysteine;

Answer 23

14

Question 24

the more disulfide bridges present, the _ curly

Answer 24

more

Question 25

Soft Keratin –____disulfide bonds

Hard Keratin – ____disulfide bonds

Answer 25

soft - less

hard-more

Question 26

• most abundant protein in vertebrates

- has 3 polypeptide chains wrapped around each other in a ropelike twist or triple helix

Answer 26

collagen

Question 27

collagen fibers are both intra and intermolecularly linked by covalent bonds formed by reactions of ______ residues

Answer 27

lysine and histidine

Question 28

side chains of collagen are on the __ of the triple-helical molecule

Answer 28

surface

Question 29

in collagen, the AA which facilitates formation of the helical conformation of each alpha chain because it causes kinks

Answer 29

Proline

Question 30

in collagen, the AA which fits into the restricted spaces where the 3 chains come together

Answer 30

Glycine

Question 31

in collagen, the AA important in stabilizing the triple-helical structure because it maximizes interchain H-bond formation

Answer 31

Hydroxyproline

Question 32

*In collagen, Every 3rd position must be occupied by _

Answer 32

glycine.

Question 33

300 nm, 1.5 nm in diameter

• held together by H-bonds (involving Hyp/P)
• MW: 300, 000
• each strand has 800 AA residues

Answer 33

tropocollagen

Question 34

• precursor: tropoelastin
• linear polypeptide with about 700 AA, primarily small and nonpolar (A, V, L, G)
• also rich in protein and lysine, but contains only little hydroxylysine and hydroxyproline

Answer 34

elastin

Question 35

formed by 3 allysyl side chains + 1 unaltered lysyl side chain from the same or neighboring peptide
-produces elastin

Answer 35

desmosine cross-link

Question 36

– group of specialized proteins that contain heme as a tightly bound prosthetic group

Answer 36

Hemeproteins

Question 37

has 8 alpha-helical regions and no beta-pleated sheet regions

• 2 polar histidine residues are found in the interior (F8 and E7)
• proximal histidine (F8) binds directly to the iron of heme
• distal histidine (E7) does not directly interact with heme group, but helps stabilize binding of oxygen to the ferrous iron

Answer 37

myoglobin

Question 38

prosthetic group of myoglobin

Answer 38

heme group

Question 39

= complete destruction of tertiary structure

Primary structure determines tertiary structure.

Answer 39

Denaturation + reduction of disulfide bonds

Question 40

• The 2 alpha chains and the 2 beta chains are identical.
• Many of the AA of alpha chain, beta chain and myoglobin are homologous (same AA in same position).
• must bind strongly to oxygen and release oxygen easily
• gives up O2 easily in capillaries, where need for it is great
• different quaternary structures in the bound and unbound forms

Answer 40

hemoglobin

Question 41

-has 4 heme groups, so it can bind 4 oxygen molecules

Answer 41

hemoglobin

Question 42

when one oxygen molecule is bound, it becomes easier for the next to bind

Answer 42

Positive cooperativity –

Question 43

IS the oxygen binding ability of myoglobin affected by the presence of H+ and CO2?

Answer 43

No!