Proteins

Question 1

What are the two modified amino acids in collagen?

Answer 1

hydroxyproline

hydroxylysine

Question 2

What is required for Hydroxyproline and Hydroxylysine synthesis?

Answer 2

Vitamin C is a required cofactor for their enzymatic generation

Question 3

Which are the two ketogenic amino acids

Answer 3

lysine

leucine

Question 4

Which are the four aa that can be keto or gluco

Answer 4

isoleucine
tryptophan
tyrosine
phenylalanine

Question 5

Which aa strengthen collagen?

Answer 5

Hyp

Hyl

Question 6

How does Hyp and Hyl strenghten collagen?

Answer 6

Interstrand covalent crosslinks between Hyl and Lys

Hyp - interstrand Hydrogen bonding

Question 7

Prolyl hydroxylase

Lysyl hydroxylase

Answer 7

convert Proline to Hyp
convert Lysine to Hyl
respectively
Both enzymes require vitamin C

Question 8

Consequence of VitC deficiency?

Answer 8

Scurvy - reduced strength of collagen fibrils

Question 9

Gamma Carboxyglutamate?

Answer 9

modified form of glutamate - carboxylated

Important in prothrombin membrane targeting

Question 10

Gamma glutamyl carboxylase

Answer 10

TM protein that carboxylates glutamate to form Gla

- vitamin K dependent!!!

Question 11

How does carboxylating glutamate influence protein?

Answer 11

enables chelation of Ca2+ –> conformational changes

Question 12

Prothrombin uses____ to target membrantes?

Answer 12

Gla

Gamma carboxyglutamate

Question 13

2 ways to degrade protein

Answer 13

Proteosomal targeting - via ubiquitination (ATP dependent)

Lysosomal degradation (ATP independent)

Question 14

Which AA is ubiquitinated?

Answer 14

it appears lysine

Question 15

proteolytic degradation of proteins in stomach

Answer 15

via pepsin - only N terminal side of aromatic aa

Question 16

proteolytic degradation of proteins in intestine?

Answer 16

trypsin (activated by enteropeptidase)
chymotrypsin (activated by trypsin)
(both serine proteases)

carboxypeptidase A and B
(both metalloproteases activated by enteropeptidase)

Question 17

aminotransferase

Answer 17

transfer amino groups

Question 18

aminotransferase Keq

Answer 18

near 1 (so reversible and mainly directed by concentration of substrate and product)

Question 19

what is the major goal of transamination?

Answer 19

produce Aspartate and NH3 for the urea cycle

Question 20

where are aminotransferases located?

Answer 20

mainly in the cytosol of liver, kidney, intestine, and muscle cells

Question 21

What do increased levels of aminotransferases tell us?

Answer 21

LIVER DAMAGE/DISEASE
Especially
alanine aminotransferase
aspartate aminotransferase

Question 22

Transamination feeds?

Answer 22

the urea cycle with aspartate (AST) and ammonia (via Glu dehydrogenase of glutamate post ALT)

Question 23

Aminotransferases require what con-enzyme?

Answer 23

PLP (derivative of vitamin B6) - hold amino-group by forming schiff base with aminotransferase

Question 24

What are the 4 control point for protein catabolism

Answer 24

1) Directionality of transamination (by ALT and AST)
2) N-acetylglutamate
3) Directionality of Glu dehydrogenase
4) ATP and GTP inhibit Glu Dehydrogensase — ADP and GDP activate

Question 25

Why is it important to get rid of ammonia via urea?

Answer 25

hyperammonemia is toxic - cerebral edema / coma / death

Question 26

NET UREA

Answer 26

3ATP + HCO3- + NH4+ +Aspartate –> 2ADP + AMP + 2Pi + PPi + fumerate + urea

Question 27

Two sources of nitrogen in urea cycle?

Answer 27

NH4+ and aspartate