Digestion & Absorption Flashcards
What is protein metabolism ?
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
Organic monomeric units from which proteins are synthesized are called
Amino acids
What is the basic function of protein?
It acts as an enzyme in and around the cell
Which animal source of protein is not considered to be high class protein ?
Gelatin
Peptidases (proteolytic enzymes) are divided into what and what ? Explain each.
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.
Protein digestion is divided into ?
Gastric
Pancreatic
Intestinal
Protein Digestion begins chemically where?
The stomach
Explain the gastric digestion of proteins
.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
What are the polypeptide hormones secreted when polypeptides enter the duodenum ?
CHOLECYSTOKININ and SECRETIN
What are the 4 enzymes (inactive form) secreted by the pancreas for protein digestion.
- Trypsinogen
- Chymotrypsinogen
- Procarboxypeptidases A&B
- Proelastases
What enzyme causes the activation of trypsin?
Enterokinase
Explain the specificity of the active pancreatic proteolytic enzymes
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.
What are the two sources of proteins?
1) dietary proteins - 70-150g
2) endogenous proteins - 35 - 200g (as a result of protein synthesis)
Enzymes involved in the hydrolysis of proteins are called
Peptidases
Nutritional value or quality of a protein is determined by a combination of two factors
1) protein digestibility
2) essential amino acid content
Infant stomachs produce an additional enzyme called __ which prevents the quick removal of milk from the stomach
Rennin or chymosin
__ regulates the activity of intestinal proteolytic enzymes
Pancreatic trypsin inhibitor
Carboxypeptidase A attacks _
Carboxyl terminal peptide linkages of polypeptides
Carboxypeptidase B acts on __
It acts on peptide linkages adjacent to amino or basic amino acid residues
What are the major enzymes of the mucosal secretions of the glands of Brunner and Lieberkuhn (in the intestine)
Aminopeptidases and dipeptidases
Aminopeptidases are ___
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.
Dipeptidases are __
1) specific for amino acids
2) complete digestion of dipeptides to free amino acids
Prolinases ____
Hydrolyze peptides or dipeptides containing PROLINE or Hydroxyproline as N-terminals
