Digestion & Absorption

Question 1

What is protein metabolism ?

Answer 1

Various biochemical processes involved in the synthesis of protein and amino acids and in the breakdown of proteins by catabolism.
I.e. can be anabolic or catabolic

Question 2

Organic monomeric units from which proteins are synthesized are called

Answer 2

Amino acids

Question 3

What is the basic function of protein?

Answer 3

It acts as an enzyme in and around the cell

Question 4

Which animal source of protein is not considered to be high class protein ?

Answer 4

Gelatin

Question 5

Peptidases (proteolytic enzymes) are divided into what and what ? Explain each.

Answer 5

Endopeptidases - hydrolyze the peptide bonds in the main polypeptide structure, breaking it down to amino acids e.g pepsin, trypsin, chymotrypsin.

Exopeptidases - hydrolyse the peptide bonds adjacent to the amino and carboxyl terminal residues. E.g carboxypeptidases, aminopeptidases.

Question 6

Protein digestion is divided into ?

Answer 6

Gastric
Pancreatic
Intestinal

Question 7

Protein Digestion begins chemically where?

Answer 7

The stomach

Question 8

Explain the gastric digestion of proteins

Answer 8

.Gastric juice secreted in stomach contains HCL and Pepsinogen
. HCL kills bacteria that may denature protein
. Pepsinogen is secreted as an inactive ZYMOGEN (has extra amino acids to prevent self destruction)
. It is activated by HCL or by the auto catalytic activity of already activated pepsin.
. Pepsin is an endopeptidase and hydrolyses peptide bonds to polypeptide chains and a few free amino acids

Question 9

What are the polypeptide hormones secreted when polypeptides enter the duodenum ?

Answer 9

CHOLECYSTOKININ and SECRETIN

Question 10

What are the 4 enzymes (inactive form) secreted by the pancreas for protein digestion.

Answer 10

1. Trypsinogen
2. Chymotrypsinogen
3. Procarboxypeptidases A&B
4. Proelastases

Question 11

What enzyme causes the activation of trypsin?

Answer 11

Enterokinase

Question 12

Explain the specificity of the active pancreatic proteolytic enzymes

Answer 12

TRYPSIN - hydrolyses peptide bonds of basic amino acids (Lys and Arg)
CHYMOTRYPSIN - hydrolyses peptide bonds of aromatic acids linking the amino group of another amino acid other than glutamate and aspartate
ELASTASE - hydrolyses peptide bonds adjacent to small neutral amino acids residues
CARBOXYPEPTIDASE- further degrades peptides into free amino acids and dipeptides.

Question 13

What are the two sources of proteins?

Answer 13

1) dietary proteins - 70-150g
2) endogenous proteins - 35 - 200g (as a result of protein synthesis)

Question 14

Enzymes involved in the hydrolysis of proteins are called

Answer 14

Peptidases

Question 15

Nutritional value or quality of a protein is determined by a combination of two factors

Answer 15

1) protein digestibility
2) essential amino acid content

Question 16

Infant stomachs produce an additional enzyme called __ which prevents the quick removal of milk from the stomach

Answer 16

Rennin or chymosin

Question 17

__ regulates the activity of intestinal proteolytic enzymes

Answer 17

Pancreatic trypsin inhibitor

Question 18

Carboxypeptidase A attacks _

Answer 18

Carboxyl terminal peptide linkages of polypeptides

Question 19

Carboxypeptidase B acts on __

Answer 19

It acts on peptide linkages adjacent to amino or basic amino acid residues

Question 20

What are the major enzymes of the mucosal secretions of the glands of Brunner and Lieberkuhn (in the intestine)

Answer 20

Aminopeptidases and dipeptidases

Question 21

Aminopeptidases are ___

Answer 21

1) non-specific for amino acids
2) do not hydrolyze didpeptides
3) are Mg2+ and Mn+
4) hydrolyze successive amino terminal residues for short peptides but not when there is a free carboxyl terminal in the area.

Question 22

Dipeptidases are __

Answer 22

1) specific for amino acids
2) complete digestion of dipeptides to free amino acids

Question 23

Prolinases ____

Answer 23

Hydrolyze peptides or dipeptides containing PROLINE or Hydroxyproline as N-terminals