Metabolism includes all chemical processes within cells related to building up and breaking down molecules and functional operations. Energy metabolism deals with overall energy production, while anabolism involves forming larger molecules and catabolism breaking down larger molecules. Carbohydrate metabolism centers around glucose and related molecules. Glycolysis and the fate of pyruvate are described. Glycolysis generates ATP and NADH. Gluconeogenesis forms glucose from non-carbohydrates like lactate and pyruvate in the liver. Glycogen is synthesized from glucose for storage. Protein metabolism involves amino acid breakdown and synthesis, as well as protein biosynthesis and degradation. Lipid metabolism describes fatty acid types and oxidation through beta-oxidation within

1. METABOLISM
1
Compiled and Edited by
Dr. Syed Ismail
VN Marathwada Agricultural University,
Parbhani, Maharashtra, India

2. METABOLISM
 Metabolism Includes all the chemical processes within cells
and tissue that are concerned with their building up and
breaking down and their functional operations.
 Energy Metabolism is energy composition of metabolism
and deals with the overall energy production as per
requirement of the organisms.
 Anabolism: Process for union of smaller into larger
molecules or metabolism of tissue formation.
 Catabolism: process of tissue breakdown obviously is
primarily concerned with the splitting of the larger
protoplasmic molecules into the smaller ones.
2

3. Energy Metabolism
3

4. Carbohydrate Metabolism
 Carbohydrate metabolism in the animal body is
essentially the metabolism of glucose and of the
substances related to glucose in their metabolic
processes.
 Glucose occupies a central position in the metabolism of
plant, animals and may microbes.
 Glycolysis
 Fate of Pyruvate
4

5. Carbohydrate Metabolism
5

6. Glycolysis (EMP) pathway
Almost universal central pathway of glucose
 In glycolysis two ATP and two NADH molecules
are generated.
Two phases
 Primary Phase
Secondary phase
6

7. Primary Phase
7

8. Payoff phase
8

9. Summary of Glycolysis
Summary for glycolysis
ATPATP
{Glucose G6P F6PF1,6BP DHAP GAP} Preparatory Phase
NADH 2ATP  2ATP
{GAP1,3BPG 3PG2PG PEP Pyruvate} Payoff Phase
(Keep in mind that TWO of these molecules will actually be reacting in the biological pathway for each glucose molecule that entered it).
Hence, the net gain is of two molecules of ATP and two molecules of NADH in the process of glycolysis.
9

10. Acetylation
o Definition: Conversion of pyruvate into acetyl CoA is called
acetylation.
o Occurs in cytoplasm
o enzyme involved :
o Five Cofactors required: Thiamine pyrophosphate (TPP), Flavin
adenine dinucleotide (FAD), Coenzyme A (CoA–SH), Nicotinamide
adenine dinucleotide (NAD )and Lipoate.
o One NADH {Nicotinamide adenine dinucleotide (reduced)} is formed
during conversion
o It contains three enzymes –
o Pyruvate dehydrogenase (E1)
o Dihydrolipoyl transacetylase (E2)
o Dihydrolipoyl dehydrogenase (E3)
10

11. Acetylation
Remember
One NADH is produced during oxidation of pyruvate to Acetyl CoA
Acetyl CoA formed during acetylation enters into mitochondria and is intermediate key
compound and acts as a connecting link between glycolysis and Kreb’s Cycle.
Remember
One NADH is produced during oxidation of pyruvate to Acetyl CoA
Acetyl CoA formed during acetylation enters into mitochondria and is intermediate key
compound and acts as a connecting link between glycolysis and Kreb’s Cycle.
11

12. TCA CYCLE (Kreb’s Cycle)
o Definition: the citric acid cycle is a cyclical set of eight
reactions that accomplish the final steps of the breakdown of
glucose to carbon dioxide and water. Its actual starting point is
acetyl coenzyme A.
o Occurs in mitochondria
o Also called TCA or Kreb Cycle
12

13. TCA Cycle
13
SUMMARY OF TCA CYCLE
The reactions of TCA can be devided to 8 steps
(1) Condensation to form citrate by citrate synthase.
(2) Aconitase transformation to isocitrate through cis aconitase.
(3) Isocitrate dehydrogenated A Ketoglutarate & CO2 by isocitrate dehydrogenase.
(NAD+
---------- NADH + H+
)
(4) A Ketoglutarate oxidative decarboxylation succinyl Co A & CO2 by dehydrogenase complex.
(NAD+ ------ NADH + H+
)
(5) Succinyl Co A hydrolyzed to succinate by succinyl Co A synthesase (GDP ------ GTP)
(6) Succinate dehydrogenated to Fumarate by succinate dehydrogenase (FAD ----- FADH2)
(7) Fumarate to Malate by Fumarase. (+ H2O)
(8) Malate is Dehydrogenated by Malate dehydrogenase to Oxaloacetate.
SUMMARY OF TCA CYCLE
The reactions of TCA can be devided to 8 steps
(1) Condensation to form citrate by citrate synthase.
(2) Aconitase transformation to isocitrate through cis aconitase.
(3) Isocitrate dehydrogenated A Ketoglutarate & CO2 by isocitrate dehydrogenase.
(NAD+
---------- NADH + H+
)
(4) A Ketoglutarate oxidative decarboxylation succinyl Co A & CO2 by dehydrogenase complex.
(NAD+ ------ NADH + H+
)
(5) Succinyl Co A hydrolyzed to succinate by succinyl Co A synthesase (GDP ------ GTP)
(6) Succinate dehydrogenated to Fumarate by succinate dehydrogenase (FAD ----- FADH2)
(7) Fumarate to Malate by Fumarase. (+ H2O)
(8) Malate is Dehydrogenated by Malate dehydrogenase to Oxaloacetate.

14. Gluconeogenesis
o Definition: formation of glucose from non–
carbohydrate precursors like pyruvate and
related three and four carbon compounds.
o Important precursors of glucose in animals are
three carbon compounds such as lactate, pyruvate
and glycerol, as well as certain amino acids.
o Mainly occurs in liver
14

15. Conversion of pyruvate to glucose
First Bypass
 Conversion of pyruvate into phospho-enol-pyruvate.
 Here pyruvate is first transported from cytoplasm into
mitochondria. Then pyruvate is converted to
oxaloacetate by action of pyruvate carboxylase.
Mitochondrial membrane has not tranporter for oxaloacetate, before export to
the cytosol the oxaloacetate formed from pyruvate must be reduced to
malate by mitochondrial malate dehydrogenase, at the expense of NADH:
The malate leaves the mitochondrial membrane, and in the cytosol it is
reoxidized to oxaloacetate, with the production of cytosolic NADH:
The oxaloacetate is then converted to PEP by phospho-enol-pyruvate
carboxykinase. This Mg++ dependent reaction requires GTP
(Guanosine Tri-Phosphate) as the phosphoryl group donor.
15

16. Reverse of glycolysis
16

17. Conversion of F1-6DP into F6P
Second Bypass
 Enzyme – Fructose 1,6 biphosphatase, carries irreversible hydrolysis of the
C-1 phosphate (not phosphoryl group transfer to ADP)
 Fructose 6 phosphate is then reversibly converted to G6P.
Third bypass (conversion of G6P to Glucose)
 Enzyme – G6Phosphatase
Gluconeogenesis is expensive
Thus, Gluconeogenesis is not simply reversible of glycolysis
17

18. Glycogenesis
It is biosynthesis of glycogen from glucose, occurs
especially in skeletal muscle and liver
• The glucose units of the outer branches of glycogen enter to the
pathway through action of three enzymes; glycogen phosphorylase,
glycogen debranching, and phosphoglucomutase.
• Glycogen phosphorylase catalyzes the reaction in which
an (α1-4) glycosidic linkage between two glucose residues
at a non-reducing end of glycogen undergoes attack by
inorganic phosphate (Pi), removing the internal terminal
glucose residue as α-D-glucose 1 phosphate.
18

19. Contd….
• Glycogen phosphorylase acts repetitively on the
nonreducing ends of glycogen branches until it reaches a
point four glucose residues away from an (α 1-6) branch
point. Where its action stops. Further degradation by
glycogen phsophrylase can occur only after the
debranching enzyme, formally known as oligo (α 1-6) to
(α 1-4) glucantransferase, catalyzes two successive
reactions that transfer branches.
• Once these branches are transferred and the glucosyl
residue at C-6 is hydrolyzed, glycogen phosphorylase
activity can continue.
19

20. Contd….
• Glucose 1phosphate, the end product of the glycogen
phosphorylase reaction, is converted to glucose 6
phosphate by phosphoglucomutase, which catalyzes the
reversible reaction. The glucose 6 phosphate formed from
glycogen in skeletal muscle can enter glycolysis and serve
as an energy source to support muscle contraction.
20

21. Glycogenesis
21

22. Glycogenesis
22

23. Protein Metabolism
o Amino Acid Metabolism
o Biosynthesis
o Degradation
o Deamination
o Transamination, etc
o Urea Cycle
o Protein Biosynthesis and
Degradation
23

24. Amino Acids
 Which are Essential Amino Acids
e.g. L2T2MVIP
 Non Essential Amino Acids
e.g. A4G3SPTC
24

25. Oxidative Degradation
 Why does it Occur?
 During normal synthesis and degradation of cellular proteins,
some amino acids are released from proteins breakdown and
are not needed for new protein synthesis undergo oxidative
degradation.
 When amino acids exceed body’s need for protein synthesis.
 When carbohydrate is not available. starvation, diabetics, etc.
25

26. Transamination
 What does it mean?
 Transfer Amino group from amino acid to α-ketoacid (oxaloacetate, α-
ketoglutarate, pyruvate, etc).
 Site: Cytosol and Mitochondria
 Enzyme: Aminotransferase or Transaminase.
 Cofactor: Pyradoxal Phosphate.
 During Breakdown all amino acids are transferred to α-ketoglutarate
because only glutamate can undergo rapid oxidative deamination.
26

27. Deamination
 Amino acids are collected in liver in the form of the amino group
of glutamate molecules.
 These amino groups must next to be removed from glutamate to
prepare them for excretion.
 Glutamate is transported from cytosol to mitochondria where it
undergoes oxidative deamination catalyzed by glutamate
dehydrogenase.
 Dehydrogenase removed the amino group from glutamate and
ammonia formed enters the urea cycle and the carbon skeletons
(α-ketoacids) are all glycolytic and TCA cycle intermediate.
27

28. Nitrogen Balance
 Net daily loss of nitrogen (as urea) from the body, is usually to
about 35 – 55 gm protein lost each day.
 Positive nitrogen Balance: intake greater than loss. E.g.
growth, pregnancy, etc.
 Negative nitrogen balance: intake less than loss. E.g
Starvation, etc.
28

29. Urea Cycle
 Transmutation, Deamination leads to CO2+ NH4+
 Interacts with water and 2ATP to form Carbamoyl Phosphate.
29

30. Urea Cycle 30

31. Role of proteins as an energy source
31

32. Glucose – Alanine Cycle
 G-A cycle shows how carbon skeleton alternate between
protein and glucose.
 Alanine released by muscle is converted back to glucose in
the liver by gluconeogenesis. The glucose formed is taken
back to the muscle for use.
32

33. Biosynthesis of Non Essential Amino Acids
33

34. Protein Degradation
Two possible ways
 Ubiquitin Pathway:
degrade abnormal proteins and short-lived cytosolic
proteins.
 Located in cytosol.
 ATP dependent
 Losysomal pathway:
 Degrades long-lived membrane proteins and organelles,
for example mitochondria.
 ATP-Independent.
Located in lysosome.
 Cathepsin
34

35. Protein Biosynthesis
Involves Five Major Steps
Activation of Amino Acids
Initiation
Elongation
Termination
Folding and post-translation
processing
35

36. Lipid Metabolism
What are the fatty acids
Carboxylic acids with hydrocarbon chains
ranging from 4 to 36 carbons long (C4 to
C36)
CH3(CH2)nCH2CO2H
36

37. Classification of Fatty acids
Saturated fatty acids
Unsaturated fatty acids
37

38. Nomenclature
Usually referred by common names
– Carbon Skeleton Common name word origin
– 12:0 lauric acid laurus plant
– 14:0 myristic acid myristica genus
– 16:0 palmitic acid Palm plant
– 18:0 Stearic acid stear mean Hard fat
– 18:1 Oleic acid oleum meaning oils
– So on…………………..
Systematic Names: basis of their chain length and No. of double bond.
12:0 lauric acid Dodecanoic acid
14:0 myristic acid n-Tetradecanoic acid
18:1(9) Oleic acid 9-octadecenoic acid
18:2(9,12) linoleic acid ???????????????
18:3 (9,12,15) Linolenic acid ??????????????
20:4 (5,8,11,14) Arachidonic acid ???????????????
16:0 palmitic acid ???????????????
38

39. The Essential Fatty acids
Linoleic
Linolenic
Arachidonic acid
Else
– Scaly skin, stunted growth and increased dehydration.
39

40. Oxidation of Fats
Fatty acids are oxidized to carbon dioxide
and water at the liberation of large unit of
energy.
Oxidation is brought in mitochondria
Several Theories.
Mitochondrial oxidation of fatty acids takes
place in three stages.
– β Oxidation
– TCA
– ETC
40

41. β Oxidation
Knoop in year 1905
In β oxidation, fatty acids are breakdown to
acetyl CoA i.e. Glycolysis of Fatty acid.
Strictly Aerobic
Occurs in Mitochondria
Acetyl CoA produced goes to Kreb’s Cycle
while over production leads to Ketosis.
41

42. Transport of Fatty acids to Mitochondria
12 or fewer enter mitochondria without help
of membrane transporters.
14 or more can directly pass through
mitochondrial membrane – they must first
undergo three enzymatic reactions of
carnitine shuttle.
42

43. Carnitine Shuttle
1. Carboxyl group react with Coenzyme A to yield Fatty acyl-CoA.
Catalyzed by Acyl CoA synthetase.
2. Transesterification: catalyzed by carnitine acyltransferase I, leads
to formation of fatty acyl carnitine.
1. Occurs in outer membrane. Then transferred to inter-
mitochondrial membrane.
3. Transfer of fatty acyl group from carnitine to inter-mitochondira
Coenzyme A by Acyltransferase II.
FA + HS-CoA FA~CoA
Acyl CoA synthetase
FA~CoA + Carnitine Fatty Acyl-Carnitine
Acyl-transferase I
Fatty Acyl-Carnitine + HS-CoA Fatty Acyl CoA
Acyl-transferase II
43

44. Mechanism of Beta oxidation
5 steps
1.Activation of fatty acids by formation of
thioester of coenzyme A
2. Dehydrogenation in α and β position by Acyl-CoA
dehydrogenase. (FAD to FADH2)
3. Addition of water to double bond by Enoyl CoA
hydratase
4. Dehydrogenation of β Carbon
5. Thiolysis
44

45. β Oxidation of Saturated Fatty Acids
(Even Number - Palmitate)
Dehydrogenation
Addition of water
Dehydrogenation of β Carbon
Thiolysis
45

46. β Oxidation of Saturated Fatty Acids
(ODD Number)
 Odd in plant and Marine
 In same way and Even, but final
product is Propionyl-CoA which
enter different pathway.
 Propionyl Co A to D-
methylmalonyl CoA by
carboxylase.
 To L – methyl malonyl CoA by
Epimerase
 Final product is Succinyl CoA.
46

47. β Oxidation of Mono- unsaturated Fatty Acids
(Oleic Acid)
 Cis double bond between 9
and 10.
 Three cycle Passes without
problem.
 hydratase can not act on cis
but trans
 Isomerase Acts to convert
cis form to trans form.
 Rest of the reaction occurs
same as that of saturated
fatty acids.
47

48. Oxidation of Poly-Unsaturated Fatty Acids
 In β Oxidation of polyunsaturated fatty
acids, such as linoleic acid, translocation
of double bond is carried out with various
enzymes and further it is oxidized in
same way as that of monounsaturated
fatty acids.
48

49. Ketogenesis
 Acetyl Co A formed can either enter in TCA or undergo
conversion on the Ketone Bodies.
 Major ketones produced are Acetone, acetoacetate and β-
hydroxylbutyrate.
 Acetone is exhaled.
 Liver continuously produced while not utilized by TCA.
 Usually during starvation and diabetes mellitus, overproduction of
ketone bodies occurs.
 Increased blood levels of acetoacetate and β-hydroxylbutyrate
lowers blood pH, causing the condition known as acidosis.
 Blood Normally contains < 3 mg/100 ml of ketone bodies, while
in diabetics it can reach to extraordinary level of 90 mg/100 ml,
this condition called ketosis
49

50. Thank You!
50