Amino Acid Metabolism 1-2

Question 0

Pepsin:
What kind of peptidase activity does it have?
Optimal functioning pH and chemical makeup?

Answer 0

Endopeptidase activity – cleaves bonds INSIDE the proteins

Optimal pH 2 and has an aspartic acid in the active site

Question 1

What is the role of HCl in activating pepsinogen and aiding in peptide bond hydrolysis?

Answer 1

HCl secreted in the stomach denatures proteins, making them more susceptible to proteolysis
The acidity of the HCl also unblocks the active site of pepsinogen, allowing it to perform autocatalytic reactions of 46 a.a.’s on its N-terminus, turning it into its active form, pepsin –>pepsin can then activate more pepsinogen molecules

Question 2

Outline steps of zymogen activation in the small intestine

Answer 2

Chyme (peptides + acid) enters the intestine from the stomach and activates 2 hormones –> secretin and cholecystokinin
*secretin releases alkaline (HCO3- rich ) fluid to neutralize chyme
*cholecystokinin releases bile for fat absorption and also releases digestive zymogen, trypsinogen
Trypsinogen is cleaved by enteropeptidase and is activated into trypsin–> this activation sets off a cascade of zymogen activations of other digestive enzymes

Question 3

Draw non-polar amino acids

Answer 3

glycine
proline
methionine
alanine
valine
leucine
isoleucine

Question 4

Draw aromatic amino acids

Answer 4

Tryptophan
Tyrosine
Phenylalanine

Question 5

Draw polar amino acids

Answer 5

serine
cysteine
threonine
asparagine
glutamine

Question 6

Draw acidic amino acids

Answer 6

Aspartate

Glutamate

Question 7

Draw basic amino acids

Answer 7

lysine, arginine, histidine

Question 8

Describe transport of amino acids and peptides across intestinal mucosa

Answer 8

Amino acids and peptides both have specific transport mechanisms

• Amino acid transport requires energy from Na+ electrochemical gradient –transport systems have higher affinity for L-amino acids
• Peptide transport requires energy from H+ pump

Question 9

What else does the di-peptide transport system transport?

Answer 9

beta-lactam antibiotics (drugs in the aminopenicillin family)

Question 10

How do free amino acids get into portal circulation?

Answer 10

Facilitated diffusion

Question 11

Acute pancreatitis–
Cause?
Triggers?
Treatment?

Answer 11

Cause: premature activation of zymogens –> occurs inside the pancreas instead of in the intestines where it should happen normally
Triggers: alcohol, gallstones, infections
Treatment: analgesics for pain and a period of fasting (3-7 days) to avoid secretion of the enzymes
*TPN or tube feeding if that does not fix the problem

Question 12

Hartnup disease-
What is it?
Patient presentation?
Treatment?

Answer 12

Rare genetic defect that does not allow large, neutral amino acids to be transported into intestine or reabsorbed in the kidneys
Patient presents with malabsorption and presence of those a.a.’s in the urine; symptoms resemble pellagra
Treated with dietary supplements of niacin

Question 13

Celiac disease -
What is it?
Presentation?
Treatment?

Answer 13

Inappropriate immune response to alpha-gliadin, a protein in gluten
Results in decreased absorptive area of the small intestine, sometimes even losing the villi, resulting in a “flat” intestine
Patients present with nutrient deficiency and cramps/bloating due to bacteria fermentation
Treated with gluten free diet

Question 14

What is meant by the “amino acid pool?”

Answer 14

The sum of all intracellular and extracellular amino acids in the body’s circulation
Amounts to about 100g in adults
Most are used for energy protein synthesis

Question 15

What is Nitrogen balance?

The 2 irregular types?

Answer 15

Balance between Nitrogen coming in (dietary protein) and Nitrogen leaving the body (urea)
Positive N balance: Increase in body protein; occurs in pregnant women, growing children, adults recovering from illness
Negative N balance: Not enough protein intake to offset degradation; seen in wasting disease and starvation

Question 16

How much protein does an adult need?

Answer 16

Approx 400 g daily
Approx 300 of this is recycled into new proteins so only about 50-100 g are actually needed
Varies with age, activity, etc.

Question 17

What are the 10 essential amino acids?

Difference in essential amino acids in adults vs. infants?

Answer 17

Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine 
Methionine 
Histidine
**Arginine -- only essential in infants
Leucine
Lysine

Question 18

Why is arginine only essential in infants?

What else is arginine used for?

Answer 18

Synthesis of arginine cannot keep up with growth in infants

Arginine supplements also used for pressure ulcers – promotes tissue regrowth