TOPIC 10 PROTEIN METABOLISM OBJs Flashcards
basic structure of a protein
- Protein degradation occurs in two places:
- Stomach – starts in stomach and continues to the;
- Small intestine
_______ enzymes are responsible for degrading proteins
Proteolytic
- Two main types of proteolytic enzymes:
- Endopeptidases
- Exopeptidases - Break terminal peptide bonds, either at amino terminal end (aminopeptidase) or carboxy (carboxypeptidase) terminal end
- Endopeptidases -
Break bonds from interior of chain
Exopeptidases -
Break terminal peptide bonds, either at amino terminal end (aminopeptidase) or carboxy (carboxypeptidase) terminal end
Stomach
- Digestion in the stomach is facilitated by gastric juice which contains pepsinogen and hydrochloric acid (HCl)
- Pepsinogen is a zymogen (or proenzyme) = an inactive form of an enzyme
- When activated it becomes pepsin, which is an endopeptidase which cleaves on the COOH side of aromatic or bulky aliphatic groups
- Digestion in the stomach is limited by
- Short contact time
- Specificity of pepsin
what passes into small intestine
chyme
stomach digestion results in
polypeptide chains and digested mix (chyme)
- Chyme stimulates the release of two polypeptide hormones from the small intestine:
- Secretin – release stimulated by low pH
- Cholecystokinin – release stimulated by polypeptides
- Secretin
– release stimulated by low pH
- Cholecystokinin
– release stimulated by polypeptides
Both secretin and cholycystokin are
hormones
Both secretin and cholycystokin cause the release of
enteropeptidase
secretin also causes releases of
pancreatioc zygomens
Pancreatic zymogens:
- Trypsinogen
- Chymotrypsinogen
- Proelastase
- Pro-carboxypeptidase
- Pro-carboxypeptidase B
_____________ is the master switch that unleashes a cascade of proteolytic activity in the small intestine
Enteropeptidase
end result of digestion in small intestine
polypeptide chains are broken down into much smaller (oligopeptide) chains and free amino acids
- Mucosal cells also have two exopeptidases to further digest oligopeptides, which are:
- Aminopeptidase: Cleaves amino acids from the amino terminus
- Dipeptidase: Cleaves aromatic dipeptide pairs
- Inside epithelial cells, dipeptides are hydrolysed into ________
- Free amino acids are then released into the blood stream, and transported to the ____ by the portal vein
amino acids
liver
how many storage systems exist for amino acids
none
excess amino are utilised in
metabolism
3 roles of amino acids in metabolism:
- Involved in synthesis of proteins
- Metabolized to generate energy
- Converted to small active molecules
decarboxylation
amino acid is converted to small active molecules (active amine = become neurotrans or hormones)
in deamination and transaminaiton
amino acids are metabolized to generate energy
what are the two types of deamination
- Oxidative deamination – (redox reaction)
o Requires either NAD+ or FAD - Non-oxidative deamination
o Does not require NAD+ nor FAD
Explain the fate of active amines
hormone or neurotransmitter
Describe the fate of the α-keto acid that is produced from either deamination or transamination of an amino acid
- The new a-keto acid is metabolized to generate energy
Describe the two categories of transaminase (aminotransferase) enzyme
Non-specific transaminases
- Non-specific in their choice of amino acid
- e.g. glutamate transaminase
- the a-keto acid is metabolized to generate energy
Specific transaminases
- Specific in their choice of amino acid
- e.g. aspartate aminotransferase
- Oxaloacetate is metabolized to generate energy via the TCA cycle
Distinguish between ketogenic and glucogenic amino acids
- Acetyl CoA or acetoacetyl CoA
o ketogenic amino acids – ketogenesis involved in lipid metabolism - Pyruvate or a TCA cycle intermediate
o glucogenic amino acids – gluconeogenesis
- Explain the role of the Urea cycle and how it links to the TCA cycle
Fate of NH4 +
- Most cells cannot detoxify ammonia
- They produce alanine, glutamate or glutamine
- These amino acids can be transported to the liver or kidney, where the ammonia can be converted to non-toxic urea
- Via the urea cycle
- Urea is then excreted via the urine
