Protein Metabolism II (Lecture 4 - Exam 3)

Question 1

Dietary proteins provide AAs, which are needed for what? (4 total)

Answer 1

(1) Muscle tissue

(2) Immune cell synthesis

(3) Plasma protein synthesis (keeps our blood in the proper osmolality and viscosity)

(4) Nitrogen containing non-protein compound synthesis

Question 2

Creatine: what is it synthesized from?

Answer 2

Can be obtained from food, mostly meat and meat products

It is synthesized from arginine and glycine and then methylated by SAM

Question 3

Why is creatine important?

Answer 3

It is the first line of energy used before muscle glycogen is broken down to produce ATP.

This allows someone who is going to do a quick sprint, to get energy more quickly than breaking down glycogen in muscle.

Question 4

In what form is creatine activated?

Answer 4

ACTIVATE = PHOSPHORYLATED by CREATINE KINASE in the MITOCHONDRIA, which can now function to phosphorylate an ADP to form ATP. This ATP is going to be used when muscle contract.

INACTIVE = UNPHOS

Question 5

Carnitine: what is it synthesized from?

Answer 5

Can be obtained from food, mostly in meat and meat products

It can also be synthesized from LYSINE

Question 6

What 5 other nutritional factors does carnitine require for synthesis?

Answer 6

(1) SAM

(2) IRON

(3) PLP

(4) VITAMIN C

(5) NIACIN

Question 7

What is the function of carnitine?

Answer 7

It helps with carrying the FAs across the MITO membrane and into the mito matrix to be oxidized through beta-oxidation.

Question 8

What is glutathione made from?

Answer 8

3 AA + ATP

GLUTAMATE
CYSTEINE
GLYCINE

Question 9

What is the function of glutathione?

Answer 9

Acts as a scavenger of free radicals, protects against oxidation and damage

Question 10

Which form of glutathione is reduced?

Answer 10

GSH

Question 11

Which form of glutathione is oxidized?

Answer 11

GSSG

Question 12

Glutathione peroxidase

Answer 12

Catalyzes the reaction of H202 (hydrogen peroxide) is degraded to H20.

Note this is SELENIUM dependent

Question 13

Glutathione reductase

Answer 13

The enzyme that reduces GSSG to GSH via NADPH as the reducing agent

Question 14

Histamine

Answer 14

Part of the inflammatory response of allergies

It is also partly involved in digestion, as histamine STIMULATES gastric acid secretion and can STIMULATE vasodilation

Question 15

Histidine decarboxylase

Answer 15

Enzyme that decarboxylates HISTIDINE —-> HISTAMINE

This enzyme is PLP dependent

Question 16

What is essential for serotonin biosynthesis?

Answer 16

TRYPTOPHAN

Question 17

What are 2 functions of serotonin?

Answer 17

(1) 90% located in the intestinal cells where it stimulates mobility.

(2) 5% Located in the CNS where it acts as a neurotransmitter

Question 18

Which side of the intestine secrete serotonin?

Answer 18

BOTH: basolateral & luminal side

Question 19

Explain the conversion of tryptophan to serotonin.

Answer 19

(1) Tetrahydrobiopterin is used as a co-factor, and it is converted to dihydrobiopterin with the HYDROXYLASE enzyme and the addition of 02. The product is 5-Hydroxytryptophan.

(2) AROMATIC AMINO ACID DECARBOXYLASE enzyme (PLP/B6) converts 5-Hydroxytryptophan to serotonin.

Question 20

Catecholamines

Answer 20

Includes dopamine and norepinephrine

REMEMBER: TYROSINE is the “parent compound”

Question 21

Epinephrine

Answer 21

synthesized from the methylation of norepinephrine in the ADRENAL GLAND

Question 22

Which compounds are released in response to emotional stimulation?

Answer 22

NOREPINEPHRINE & EPI

“Fight or Flight” response

Can also be released during times of low glucose or very cold temperatures

Question 23

What is required for the biosynthesis of catecholeamines from tyrosine?

Answer 23

1. PLP
2. VITAMIN C
3. COPPER
4. SAM

Question 24

Explain the pathway of catecholeamine biosynthesis.

Answer 24

(1) Tetrahydrobiopterin + O2 are utilized by the enzyme TYROSINE HYDROXYLASE. This converts tyrosine to L-Dopa.

(2) L-Dopa is decarboxylated, in a PLP-dependent reaction, which forms DOPAMINE.

(3) DOPAMINE HYDROXYLASE adds another hydroxyl group, forming NOREPINEPHRINE.

(4) SAM adds a methyl group to norepinephrine, forming epinephrine.

Question 25

What is porphyrin synthesized from?

Answer 25

Glycine (non-essential AA)

Question 26

How is glycine synthesized?

Answer 26

Glycine is considered non-essential AA because it can be biosynthesized from SERINE. Which can be synthesized from 3-phosphoglycerate (which is formed from glycolysis when glutamate donates it’s amino group to serine)

Question 27

Explain porphyrin synthesis.

Answer 27

Glycine and succinyl CoA combine (requires PLP/B6) to form ALA (alpha aminolevulinic acid) which will go on to form porphyrin

Question 28

What is the most abundant form of porphyrin?

Answer 28

HEME

Remember: Iron binds to the middle of the molecule, which is how oxygen is carried to the peripheral tissues.

Question 29

Where is heme found?

Answer 29

Hemoglobin
Myoglobin
Cytochromes (ETC)
P450 enzymes
Catalase
Nitric oxide synthase and peroxidase

Question 30

What AA is needed for histamine synthesis?

Answer 30

HISTIDINE