Nitrogen Metabolism

Question 0

Intracellular amino acids in the body are __________ than extracellular concentrations.

Answer 0

Higher

Question 1

What is the amino acid pool?

Answer 1

Abstraction describing the availability, distribution, and uses of amino acids.

Question 2

What are the inputs to the amino acid pool: digestion of dietary proteins?

Answer 2

Stomach digestion, pancreatic enzymes, intestinal processing, absorption of amino acids

Question 3

Protein digestion begins in the stomach. Which enzymes are involved and where do they come from?

Answer 3

HCl: secreted by parietal cells
Pepsinogen: secreted from chief cells
Pepsinogen is autocatalytic - a little pepsin will create more

Question 4

What are the pancreatic enzymes, where are they found and what do they do?

Answer 4

Enteropeptidase: found in the brush border - initiates proenzyme activation cascade
Trypsinogen: converted to trypsin which activates other peptidases
Endopeptidases: complete intestinal digestion - Chymotrypsin, elastase, Carboxypeptidases

Question 5

What are the enzymes associated with intestinal processing?

Answer 5

Aminopeptidases and dipeptidases: brush border enzymes

Intracellular peptidases target small absorbed peptides

Question 6

True or false…

Amino acids are stored in the body?

Answer 6

FALSE! Amino acids have no formal storage.

Question 7

True or false…

Ammonia is a neurotoxin.

Answer 7

TRUE! It is a neurotoxin, hence its need to be detoxified.

Question 8

Uric acid can be reduced by which vitamin?

Answer 8

Vitamin C

Question 9

What are the primary carbon skeletons that go to the Kreb’s cycle and ketone bodies?

Answer 9

a-Keto acids

Question 10

What is the secondary carbon skeleton the goes into the urea cycle?

Answer 10

Glutamate

Question 11

What are the neurotransmitters synthesized from amino acids?

Answer 11

GABA, Serotonin, Norepinephrine, purines & pyrimidines (nucleotides)

Question 12

What are the hormones synthesized from amino acids?

Answer 12

Melatonin & thyroxine

Question 13

What is the pigment synthesized from amino acids?

Answer 13

Melanin

Question 14

What lipid is synthesized from amino acids?

Answer 14

Sphingosine

Question 15

CoQ10 can regenerate which vitamin?

Answer 15

Vitamin E

Question 16

What are the redox products synthesized from amino acids?

Answer 16

Glutathione & Nicotinamide

Question 17

What are four end products that get excreted in the urine?

Answer 17

Uric acid, Creatinine, NH4+, and Urea

Question 18

What is the purpose of the urea cycle?

Answer 18

Detoxify the body of harmful ammonia

Question 19

In absorption of amino acids, co-transport of Na+ and amino acids into the brush border is driven by…

Answer 19

Low intracellular Na+

Question 20

What are absorption disorders and what is the defect?

Answer 20

Cystinuria and Hartnup’s disease; they are defects in intestinal and renal uptake of amino acids

Question 21

Which amino acids are specific for the only non-sodium dependent transporter?

Answer 21

Branched chain and aromatic amino acids

His, Met, Leu, Ile, Val, Phe, Tyr, Trp

Question 22

Trypsin is the “lynch pin” for for what three digestive enzyme conversion?

Answer 22

Chymotrypsinogen —–> Chymotrypsin
Proelastase —–> Elastase
Procarboxypeptidases —–> Carboxypeptidase

Question 23

What is the half-life range of protein?

Answer 23

A few minutes to several days

Question 24

What are hormonal influences on protein degradation and what action do they have?

Answer 24

Glucocorticoids and thyroid hormones - increase degradation

Insulin -decreases degradation and increases synthesis

Question 25

Proteases facilitate recycling of body proteins by which four mechanisms?

Answer 25

Cathepsins - lysosomes
Caspases - apoptosis
Metalloproteinases - extracellular matrix
Serine proteases - digestion and blood clotting

Question 26

What is ubiquitination and what is its function?

Answer 26

It is a small protein (~76 amino acids) that labels cytosolic proteins for destruction.

Question 27

What complexes breakdown ubiquitin-tagged proteins?

Answer 27

Proteasomes