This document discusses protein and amino acid metabolism. It begins by explaining that proteins are polymers of amino acids and that sources of proteins include plants like cereals and beans as well as animals like milk, fish, meat and eggs. It then provides an overview of how dietary proteins are digested in the gastrointestinal tract through the action of proteolytic enzymes from the stomach, pancreas, and small intestine. The document concludes by outlining different pathways that amino acids can enter once absorbed, such as being used to form other amino acids, producing urea, or providing carbon skeletons and energy through various metabolic pathways in the liver.
3. *Proteins are polymers of amino acids
*Sources
Plants:as cereals and beans
Animals:as milk,fissh,meat and eggs.
General metabolismof proteins
Fasting feeding
((2-4 mg/dl) Amino acids (6-8
mg/dl
4. Amino acids
Dietary protein
Pepsin
Stomach
Polypeptides
and amino acids
Trypsin
Chymotrypsin
Carboxypeptidase
Elastase
Pancreas
To liver
Oligopeptides and amino acids
Aminopeptidases
Small intestine
Digestion of dietary proteins by the proteolytic enzymes of the
gastro-intestinal tract.
Tripeptidase
Dipeptidase
liver
5. OVERVIEW OF AMINO ACID
METABOLISM
ENVIRONMENT ORGANISM
Ingested
protein
Bio-
synthesis
Protein
AMINO
ACIDS
Nitrogen
Carbon
skeletons
Urea
Degradation
(required)
1
2 3
a
b
Purines
Pyrimidines
Porphyrins
c c
Used for
energy pyruvate
α-ketoglutarate
succinyl-CoA
fumarate
oxaloacetate
acetoacetate
acetyl CoA
(glucogenic)(ketogenic)
6. PROTEIN METABOLISM
During fasting (18h )
main source of energy(1g=4.1Kcal)
Generalmetabolismofaminoacids
*Each amino acid gives :
# Ammonia (NH3)
# Carbon skeleton
By removal NH3 from A.A. by 4 mechanisms
7. *Transamination: as (AST-ALT) except
threonine &lysine.
*Oxidative deamination:
removal of (H2&NH3)
1-Amino acid oxidase
2-L-glutamate dehydrogenase
9. 1)Form non-essential amino acids.
2)Glutamine synthesis(brain,liver,renal T. and muscle).
3)Producing urea(by urea cycle 90%).
4)Excretion in urine(upto 1gm/24h urine).
5)Traces in blood (upto 100 ug/dl).
Glutamate + NH3 + ATP GS Glutamine + ADP + Pi
10. CO2 + 2NH3 +3ATP UREA
UREA released into :
Blood----------------------(20-40 mg/dL) of serum.
(Urine------------------(20-40 g/24h urine collection
Reactions
First 2 reactions ---------- mitochondria.
The rest 3 reactions --------- cytoplasm.