Amino Acids I

Question 1

What are the branched chain amino acids and where are they metabolized

Answer 1

Valine, leucine and Isoleucine metabolized in skeletal muscles

Question 2

Provide examples of non-essential fatty acids

Answer 2

Cysteine, glutamine, glutamate

Question 3

What are Ornithine and Citrulline

Answer 3

Basic amino acids that don’t integrate into proteins but play roles in the urea cycle

Question 4

How are proteins degraded by ATP-dependent ubiquitin proteasome system

Answer 4

They are targeted for degradation and tagged with ubiquitin which attached with isopeptide bond. There are three enzymes involved
1. Activating enzyme activates Ub
2. Conjugating enzyme transfers activated Ub
3. Ligase binds Ub to substrate

Question 5

What is ATP-independent degradation enzyme system lysosomes

Answer 5

Autophagy or heterophagy

Question 6

What are the short lived proteins, long lived and structural stable proteins

Answer 6

Short lived are regulatory or misfolded proteins.
-Long lived most proteins (days to weeks)
- structurally stable and metabolically stable like collagen (months to years)

Question 7

Describe pepsin

Answer 7

Pepsin secreted by chief cells, endopeptidase, released as inactive zymogen or proenzyme because contains extra amino acids in sequence that prevent them from being active

Question 8

Explain co transport system of amino acids

Answer 8

Against concentration gradient. Amino acids absorbed via Na+ linked transport. Di and tripeptides are absorbed by H+ linked secondary transport. Free amino acids transported to small intestine to liver by portal vein by Na-independent facilitated diffusion

Question 9

What is enterokinase

Answer 9

Found in small intestine converts trypsinogen to trypsin. Trypsin activates a proteolytic cascade

Question 10

The first step of amino acid metabolism

Answer 10

Nitrogen removal. Alpha amino groups are removed (they protect amino acids from metabolism). We take the amino group to a-ketoglutarate producing a-keto acid and glutamate by aminotransferases.

Question 11

Glutamate dehydrogenase GDH

Answer 11

GDH uses NAD+ or NADPH as a coenzyme. High ammonia levels drive the reaction to glutamate.

Question 12

Aspartate aminotransferase (AST) (btw aminotransferases require pyridoxal phosphate vit B6)

Answer 12

Exception to the rule that aminotransferases funnel amino groups to form glutamate. Reversible enzyme. Transfers amino groups from glutamate to oxaloacetate, forming aspartate as a source of nitrogen in urea cycle

Question 13

NH3 combines with what?

Answer 13

With glutamate to form glutamine via glutamine synthase (needs one ATP). Then it’s hydrolyséd into glutamate and free ammonia. It’s then oxidatively deaminated by glutamate dehydrogenase forming a-ketoglutarate and a second NH3

Question 14

First step in urea cycle is carbamoyl phosphate formation by CPS I which is activated by NAG and Arginine. What’s next?

Answer 14

Citrulline formation. Carbomyl portion of carbamoyl phosphate is transferred to ornithine by OTC (ornithine transcarbamylase). Citrulline is transported to the cytosol. Ornithine is the cyclic one like oxaloacetate

Question 15

Urea cycle steps are carbomyl phosphate formation, Citrulline formation, argininosuccinate formation then its cleavage then arginine cleavage to ornithine and urea by what enzymes?

Answer 15

Arginase-1 is exclusive to liver
Arginase-2 in kidneys controls arginine availability for nitric oxide synthesis

Question 16

Arguninosuccinate cleavage? (Urea cycle)

Answer 16

Agininosuccinate lyase yields arginine and fumarate. Fumarate becomes malate. Malate either goes to TCA cycle or is changed into oxaloacetate then sent to aspartate

Question 17

Acquired hyperammonemia the result of?

Answer 17

Shunting of portal blood directly into the systemic circulation, bypasses the liver, severely impairing the conversion of ammonia to urea

Question 18

Congenital hyperammonemia, most common disorder?

Answer 18

X-linked OTC deficiency (orithinine transférase)