The document provides an overview of protein metabolism. It discusses the key topics of: - Protein structure and functions in the body. - The amino acid pool and how tissues draw from and contribute to it. - The digestion of proteins in the body. - The two phases of protein metabolism - anabolism and catabolism. - The major catabolic pathways in the liver that break down amino acids including deamination, transamination, decarboxylation, and transmethylation. - The ornithine or urea cycle, which occurs primarily in the liver and converts ammonia into urea for excretion from the body.

1. PRESENTATION
ON
“PROTEIN METABOLISM”
PRESENTED BY-
ANISHA MUKHERJEE
M.Sc FIRST SEMESTER
BIOTECHNOLOGY
GUIDED BY-
Mrs. SABIHA NAZ MA’AM

2. CONTENTS
 Proteins
 Amino Acid Pool
 Digestion Of Proteins
 Protein Metabolism-
Anabolism
Catabolism
 Catabolic Phase Of Amino Acid
o Deamination- Oxidative & Non-Oxidative
o Transamination
o Decarboxylation
o Transmethylation
 Ornithine Cycle or Urea Cycle
• Energetics
• Fate of urea
• Disorders

3. PROTEINS
 Proteins are the polymers of amino acids which play a
crucial role in all biological processes.
 Most abundant organic molecules of the living
system.
 Proteins have many important biological functions:-
o Enzymes - biological catalysts
o Antibodies- defense proteins
o Transport proteins- carrier proteins
o Structural proteins- provides support
o Hormonal proteins- chemical-signaling molecules

4. Amino Acid Pool
• The amount of free amino acids distributed
throughout the body is called amino acid pool.
• All the tissues can draw freely any amino acid
from this pool when needed & can also
discharge amino acids into this pool by way of
breakdown of proteins
• There is a dynamic equilibrium between the
breakdown of proteins & formation of new
proteins.
• Sources of amino acid pool
Dietary protein
Breakdown of tissue protein
Biosynthesis of non-essential amino acids

6. DIGESTION OF PROTEINS

7. PROTEIN METABOLISM
• Protein metabolism denotes the various
biochemical processes responsible for the synthesis
& breakdown of proteins.
• PHASES OF METABOLISM
ANABOLISM CATABOLISM
 This is the building up or
biosynthetic phase of metabolism.
 Energy is required during
anabolism which is fulfilled by ATP
generated during catabolism.
 This is the biodegradative phase
of the metabolism.
 Energy is released during
catabolism by the breakdown of
complex molecules.

8. PHASES OF METABOLISM

9. CATABOLIC PHASE OF AMINO ACID
• The breakdown of amino acid is called catabolism.
• Most of the amino acids are converted into alpha-
keto acids by the removal of nitrogen in the form
of ammonia which is quickly transformed into
urea or some other amino acid.
• The catabolism of amino acids occurs by
following methods- MAJOR SITE- LIVER
 DEAMINATION
 TRANSAMINATION
 DECARBOXYLATION
 TRANSMETHYLATION

10. DEAMINATION
o DEFINITION:
Deamination is the removal of amino
groups from the amino acids with the
formation of keto acids & ammonia.
oTYPES:
It can be of two types:-
 Oxidative Deamination.
 Non-oxidative Deamination.

11. OXIDATIVE DEAMINATION
• The removal of amino group from amino acid with
the utilization of oxygen is called oxidative
deamination.
• There are two steps in the oxidative deamination:-
Oxidation (Dehydrogenation)
Hydrolysis
• SITE: Mitochondria of Liver and Kidney.
• ENZYMES: Amino acid oxidases(dehydrogenases).
• CO-ENZYMES: FAD(Flavin adenine dinucleotide) or
FMN(Flavin mono nucleotide).

12. OXIDATIVE DEAMINATION
STEP 1(OXIDATION / DEHYDROGENATION):-
• The first step is the oxidation of amino acid
resulting in the formation of an imino acid.
STEP 2 (Hydrolysis):-
• The imino acid undergo hydrolysis resulting in the
formation of keto acid and ammonia.

13. NON-OXIDATIVE DEAMINATION
• The removal of amino group from amino acid
without utilization of oxygen is called non-
oxidative deamination.
• Amino acids like Serine, Homoserine and
threonine undergo non-oxidative deamination.
• ENZYME- Dehydratase.
• CO-ENZYME- Pyridoxal phosphate.

14. TRANSAMINATION
• Transamination is a process of transfer of an
amino group from an amino acid to a alpha-keto
acid which results in the formation of a new
amino acid and a new keto acid.
• ENZYME- Transaminase or Aminotransferase.
• CO-ENZYME- Pyridoxal phosphate.
• MAJOR TISSUES- Liver, Heart, Kidney & Brain.

15. Salient Features of Transamination:-
• SUBSTRATES- Amino Acids
Almost all amino acids undergo transfer of
amino group to small or large extent.
• EXCEPTIONS-
Lysine, Threonine, Proline and Hydroxyproline
do not take part in transamination.
• REVERSIBLE REACTION-
Hence keto acid can be derived from amino acid
& amino acids can be obtained from keto acid.

16. DECARBOXYLATION
• This refers to the removal of carbon-dioxide from
the carboxyl group of amino acids.
• ENZYME- Decarboxylases.
• CO-ENZYME- Pyridoxal phosphate.

17. TRANSMETHYLATION
• The transfer of methyl group from active
methionine/SAM to an acceptor is called
transmethylation.
• Here there are two compounds involved:-
One donates methyl group known as methyl
donor.
Other accepts the methyl group known as
methyl acceptor.

18. TRANSMETHYLATION
• ENZYME- Transmethylases/Methyl
transferases.
• CO-ENZYME- Tetra hydro folate(THF)
• Vit B-12 is also involved in this reaction.
• Methionine has to be activated to S-adenosyl
Methionine (SAM) to donate the methyl
group.
• SAM acts as donor of methyl group to the
acceptor, so that acceptor is converted to
methyl acceptor.

20. Significance of Transmethylation
Transmethylation is an essential process since
many biological compounds becomes
functionally active only after methylation.
Transmethylation synthesizes biologically
important compounds like
Choline,Creatine,Epinephrine,Nor-epinephrine.

21. ORNITHINE CYCLE OR UREA CYCLE
• Discovered by Krebs and Henseleit in 1932.
• Hence it is also called Krebs-Henseleit cycle.
• The biosynthesis of urea from ammonia is called urea
cycle.
• Major Site- Liver(cytosol & mitochondria).
• Ammonia, the product of oxidative deamination
reaction, is highly toxic in even small amount & must
be removed from the body.

22. UREA CYCLE

23. ENERGETICS OF UREA CYCLE

24. FATE OF UREA