AA Metabolism

Question 1

What is the major proteolytic enzyme in the stomach?

What is the inactive form of this enzyme

Answer 1

Pepsin

Pepsinogen

Question 2

What cells in the stomach produce Pepsin

What cells produce HCL

Answer 2

Chief cells

Parietal cells

Question 3

How is pepsinogen activated?

Answer 3

HCl secreted by the stomach

Question 4

At low energy states what are AA converted to?

Answer 4

1. AA are converted to pyruvate and enter gluconeogenesis to form Glucose.
2. They can also be converted to Acetyl Coa to be oxidized in the CAC to H20 and C02.
3. They can form Ketone Bodies in times of starvation.

Question 5

In the low energy state are AA being synthesized?

Answer 5

No

Question 6

At high energy levels what is the fate of the blood pool of AA?

Answer 6

1. Glycogen can be formed after conversion to glucose.

2. Fatty Acids can be formed via conversion to Acetyl CoA

Question 7

What is the purpose of the AA pool?

6 Things

Answer 7

1. Ensures availability of AA to tissues for protein synthesis.
2. Vital Proteins listed in the next slide.
3. Generates glucose and ketone Bodies.
4. Can be oxidized in TCA cycle
5. They Mantain Blood pH
6. They can be made into Fatty Acids

Question 8

What are important structures derived from AA in the body?

Answer 8

Proteins, Neurotransmitters, Heme, Pyrimidines, Purines, Creatine Phosphate, Melanin, skin Pigment, Nucleotides, Nuclaic Acids,

Question 9

What is the average dietary protein intake per day?

What is the other source of AA for proteins in the body.

Answer 9

100 g / day

Protein turnover from AA found in the body. Proteins that have been degraded by endocytosis, phagocytosis, ubiquitin targeted degradation.

Question 10

What is the average turnover of endogenous protein?

Answer 10

3-600g / day

Question 11

What are common proteins that undergo synthesis and degradation frequently?

Answer 11

Heme, Muscle Protein, Digestive enzymes, Cells lining the GI tract.

Question 12

How are pancreatic enzymes activated?

Answer 12

When the pH of the intestines is raised from Bicarbonate release.

Question 13

Must digestive enzymes be activated?

Answer 13

Yes, digestive enzymes are produced as inactive precursors (Zymogens)

Question 14

How are pancreatic zymogens activated?

Answer 14

Enteropepsidase converts Trypsinogen to Trypsin…. Trypsin activates Chymotrypsinogen, Proelastase, Procarboxypepsidase,

Question 15

Can essential AA be synthesized?

What are two you should remember from lecture?

Answer 15

No

Methionine and Phenylalanine.

Question 16

What are nonessential AA?

Answer 16

Nonessential amino acids are synthesized from common metabolic intermediates or from other amino acids.

Question 17

What are Cysteine and Tyrosine produced from?

Answer 17

Methionine and Phenylalanine respectively.

Question 18

What gives rise to Kwashiorkor Syndrome?

Answer 18

Deficiency of an AA in the diet.

• Results in Decreases plasma concentration of Proteins. Albumin and Transferin indicate starvation.
• Increased interstitial fluid adema. due to increased osmotic pressure.
• Adema results in a distended belly
• Inability to produce digestive enzymes and replenish intestinal mucosa cells.

Question 19

What are the 4 fates of AA in the blood?

Answer 19

1. New Protein Synthesis
2. Conversion to Pyruvate and Acetyl CoA
3. Degraded to enter the urea cycle
4. Functional products, Signaling peptides, pyrimidine, purine, ect.

Question 20

What factors affect the rate of protein degradation?

Answer 20

1. Hormonal Control

2. Other methods (lyosomal degradation, protein denaturation)

Question 21

How is protein degradation hormonally regulated?

Answer 21

Glucocorticoids released from the adrenal glands increase protein degradation in the muscle tissue via an increase in ubiquitin production. and proteolysis via the proteosome pathway.

Excessive thyroid hormones increase protein turnover.

Insulin increases protein synthesis.

Question 22

What are two methods of non- hormonal regulation of AA

Answer 22

1. Lyosomes can be activated and will increase protein degradation.
2. Proteins can be denatured which will cause them to loose function.

Question 23

What amino acid sequence activates the ubiquitone- proteosome pathway?

Answer 23

PEST- Regions rich in Pro (P), Glu (E), Ser (S), and Thr (T)- short half life and degraded by ubiquitin-proteosome pathway

Question 24

What N-Terminal Residues will make a protein unstable?

Answer 24

N-terminal residues - The presence of Phe, Leu, Asp, Lys, or Arg at N-terminal makes protein unstable

Question 25

What is an example of oxidative damage to a protein?

Answer 25

Lys Oxidation

Question 26

How can proteins be modified?

Answer 26

Mutations and deletions

Question 27

What digestive enzymes are found in pancreatic secretions?

6

Answer 27

"B E C E E P"
Bicarbonate. -
Endopepsidase-
Chymotrypsin-
Elastase-
Exopeptidases-
Proteases-

Question 28

How can Cystic Fibrosis affect digestion?

Answer 28

Decreased Na+ secretion through CFTR channels results in extreamly thick secretions in the pancreas which will occlude the pancreatic ducts.

Question 29

What are the three ways AA are transported into the cells of the intestine?

Answer 29

1. Na Dependent Carrier transport
2. Facilitated Transport
3. y-Glutamyl Cycle in the intestine and kidney

Question 30

How does secondary active transport of AA using the Na+ gradient work?

Answer 30

1. Co-transport Na+ and the amino acids from the outside of the apical membrane to the inside is driven by low intracellular [Na+] that results from the pumping of Na+out of the cell by Na+/K+ ATPase
2. Facilitated transporters in the serosal membrane transport amino acids to portal vein.