Chapter 6 Proteins

Question 1

How do amino acids enter the blood stream?

Answer 1

Transported across the basolateral membrane of enterocytes (sodium independent transporters), into the interstitial fluid where they enter the blood through the capillaries of the villi for transport into the portal veins leading to the liver and other tissues.

Question 2

Lysinuric protein intolerance

Answer 2

defects in the basic amino acid transporters in the kidneys, liver, and intestine. poor absorption of lysine, arginine, and ornithine

Question 3

Sodium dependent N system

Answer 3

prominent in the periportal cells of the liver and functions as an antiporter to take up sodium and glutamine in exchange for H+

Question 4

What is the primary organ for the uptake of most amino acids following a meal?

Answer 4

The liver

Question 5

What percentage of amino acids are up-taken from the portal blood?

Answer 5

Up-taken by the liver/ 50%-65% of amino acids

Question 6

What is the organ primarily catabolizes branched amino acids?

Answer 6

Primarily by the muscle and the heart.

Question 7

What percentage of the liver’s energy is derived from the oxidation of amino acids?

Answer 7

50%

Question 8

What two aminotransferases are the most active in the body?

Answer 8

alanine aminotransferase and aspartate aminotransferase.

Question 9

Alanine transaminated to ______

Answer 9

Pyruvate

Question 10

Glutamate transaminated to ______

Answer 10

a-ketoglutarate

Question 11

Aspartate transaminated to ______

Answer 11

oxaloacetate

Question 12

What three amino acids cannot undergo transamination to any appreciable event?

Answer 12

Lysine, histidine, and threonine

Question 13

Threonine deamination

Answer 13

occurs by threonine dehydratase, PLP, H2O

Question 14

Sources of ammonia

Answer 14

deamination reactions, ingestion and absorption of foods, generation by the bacterial lysis of urea and amino acids

Question 15

What enzymes remove ammonia/ammonium ions from body cells?

Answer 15

glutamate dehydrogenase, glutamine synthetase and carbamoyl phosphate synthetase I

Question 16

Rate limiting step f the urea cycle

Answer 16

arginiosuccinate synthetase; aspartate + Citruline

Question 17

Carbon skeletons can be used to generate

Answer 17

glucose, ketone bodies, energy, cholesterol, fatty acids.

Question 18

What are the first cells to receive dietary amino acids?

Answer 18

Intestinal cells

Question 19

Role of glutamine in intestinal cells

Answer 19

primary source of energy; stimulates gastrointestinal mucosa cell proliferation, enhances synthesis of heat shock proteins; synthesis of mucins (along w/threonine); produces ammonia and glutamate; intravenous nutrition; g.I tract uses 10 g of glutamine/day

Question 20

Role of glutamate in intestinal cells

Answer 20

1) synthesis of proline 2) synthesis of glutathione (via glycine and cysteine) 3) synthesizes ornithine (along with aspartate) 4) very little glutamate leaves the intestinal cells as glutamate and enters the portal blood

Question 21

Role of aspartate in intestinal metabolism

Answer 21

1) transaminated to generate oxaloacetate 2) used to synthesize ornithine 3) very little aspartate is found in portal blood

Question 22

Intestinal arginine metabolism

Answer 22

1) up to 40% of dietary arginine is oxidized in enterocytes (yields citruline and urea) 2)

Question 23

Intestinal Methionine and cysteine metabolism

Answer 23

1) 52% of methionine is metabolized in the gut 2) Cysteine used in the gut to make glutathione, but primarily is converted to taurine and lesser to pryruvate and sulfite

Question 24

The essential amino acids found in the greatest quantities in the endogenous AA pool are ____

Answer 24

threonine and lysine

Question 25

The non-essential amino acids found in the greatest quantities in the endogenous AA pools are ______

Answer 25

alanine, glutamine, glutamate, and aspartate w/ 80g of glutamine found in pool.

Question 26

What AA is the major transporter of ammonia in the body?

Answer 26

glutamine

Question 27

How much glutamine does the body produce/day?

Answer 27

40 to 80g

Question 28

What is glutamine synthetases role in extra-hepatic tissues?

Answer 28

catalyzes the use of ammonia or ammonium ions with glutamate.

Question 29

The immune system relies heavily on what amino acid?

Answer 29

glutamine

Question 30

What are the three branched chained amino acids?

Answer 30

Isoleucine, leucine, and valine. transamination occurs in the muscle, heart and kidneys (NOT the Liver)

Question 31

How are the a-keto acids produced by branch chained amino acids transported?

Answer 31

via serum albumin

Question 32

BCKAD

Answer 32

Branch chain a-keto acid dehydrogenase; catalyzes irreversible decarboxylation step

Question 33

Endogenous sources of proteins

Answer 33

desquaminated mucosal cells 50 g/day, digestive enzymes and glycoproteins 17g protein/day

Question 34

Protein digestion begins in the ____

Answer 34

stomach. HCl affects the quaternary, tertiary, and secondary structure of proteins.

Question 35

Pancreatic acinar cells

Answer 35

Secrete bicarbonate, water, electrolytes and zymogens in response to CCK and secretin excretion.

Question 36

Brunner glands

Answer 36

regions in small intestine; secretes mucins in response to cck and secretin.

Question 37

Process of Amino acid absorption

Answer 37

Sodium binds to brush border membrane proteins causing increasing affinity for the amino acid,

Question 38

Which occurs faster, peptide or amino acid transport?

Answer 38

Peptide transport. It appears that this is the fastest and most used method.