Metabolism & Respiratory chain

1. Dr. Subir Kumar Mandal
MBBS, M.Phil (Biochemistry)

2. Overview of Metabolism
 Metabolism: The entire spectrum of chemical
reactions, occurring in living system are collectively
referred to as metabolism.
 Anabolism: It’s the synthetic process concerned with
synthesis of large, complex substances from small,
simple molecules with utilization of energy.
 Catabolism: It’s the breakdown process concerned
with break down of large complex substances into
smaller & simpler forms with or without the release
of energy e.g. Oxidation of glucose/fatty acid (here
energy is released), Glycogenolysis to glucose (here
no energy is released).

3. Overview of Metabolism
Purpose of metabolism:
 Release of energy from ingested food for cellular
work & maintenance of body temperature.
 Transformation of small organic compounds into
macromolecules.
Energy Metabolism
 It deals with metabolic pathways concerned with
liberation and storage of energy.

4. Paradigm of Metabolism
o Primary metabolism: This includes the digestion of
food materials into their absorbable units in
intestine & the equivalent processes within the cell
(e.g. lipolysis in adipose tissue, lysosomal
degradation of cellular contents etc.).
o Secondary metabolism: Here the end products of
primary metabolism undergo varieties of catabolic
& anabolic activities within the cell to synthesize
different biomolecules and to generate ATP &
reduced coenzymes through oxidative processes.
o Tertiary metabolism: Here the reduced coenzymes
are oxidized through respiratory chain with
production of ATP and water.

5. Bioenergetics
 It is the study of energy changes associated with
biochemical reactions. The reactions are broadly
classified as exergonic (energy releasing) and
endergonic (energy consuming).
 It describes the transfer & utilization of energy in
biological system.
 Free energy: It is the energy available to do work.
In exergonic reaction △G is negative and in
endergonic reaction △G becomes positive. Free
energy change (△G) becomes zero when a reaction
is at equilibrium. It is the amount of useful energy
obtained from a biochemical system & used to
perform work.

6. Energy Phosphate Compounds
o High energy compounds or energy rich compounds
are substances which possess sufficient free energy
to liberate at least 7 Cal/mol at pH 7.0
 Examples: Phosphoenol pyruvate, Carbamoyl
phosphate, C-AMP, 1,3-Bisphosphoglycerate,
Phosphocreatine, Acetyl phosphate, Pyrophosphate,
Acetyl CoA, ATP etc.
o Low energy compounds which liberate energy less
than 7.0 Cal/mol at pH 7.0
 Examples: ADP, Glucose 1-phosphate, Glucose 6-pho
sphate, Fructose 6-phosphate, Glycerol 3-phosphate.

7. Energy Phosphate Compounds
o High energy compounds possess high energy bonds
(acid anhydride bonds/phosphoanhydride bonds) in
their structures. Acid anhydride bonds are formed
by the condensation of two acidic groups or related
compounds.
o Free energy is liberated when these bonds are
hydrolyzed. The symbol ∼ is used to represent high
energy bonds i.e. ATP is written as AMP∼P∼P .

8. ATP-ADP cycle

9. Role of ATP in Bioenergetics
o ATP acts as an energy carrier in biological system &
serves as the mediator of biological energy transfer.
o It links the energy yielding (exergonic) & energy
requiring (endergonic) processes. ATP carries
energy from exergonic processes and then delivers
that energy to endergonic processes. So, ATP is
regarded as the energy currency of cell.

10. Carbohydrate Metabolism
o Important dietary carbohydrates:
 Starch
 Cellulose
 Lactose
 Sucrose

11. Intermediary Metabolism of Glucose
 Anabolic:
 Glycogenesis
 Gluconeogenesis
 Catabolic:
 Glycolysis (Embden-Meyerhof pathway)
 Glycogenolysis
 Hexose Monophosphate shunt (HMP shunt)
 Oxidation of Pyruvate to acetyl-CoA
 Tricarboxylic acid cycle (TCA cycle/Krebs cycle/Citric
acid cycle)
 Liver, muscle, adipose tissue & brain are main sites of gl
ucose metabolism.

12. Glucose Pool
o It is the total amount of glucose present in ECF.
o Blood glucose concentration is 4.5-5.5 mmol/L in
normal glucose pool.
o Glucose comes to glucose pool from dietary
carbohydrate, glycogenolysis & gluconeogenesis.
o Glucose is removed from glucose pool for
glycogenesis, amino acid synthesis, fat synthesis,
structural material synthesis, HMP shunt &
oxidation.
o About 10-20% glucose is oxidized from glucose
pool in HMP shunt and another 20% is used for
synthesis of structural materials like glycoprotein,
glycolipid, MPS etc.

13. Glucose Pool

14. Glucose Homeostasis
 It is the maintenance of normal glucose pool or
normal blood glucose concentration within the
narrow limit of 80-100 mg% in spite of its tendency
to become abnormal following meal and during
fasting/starvation.
 Normally the rate of glucose entry into the glucose
pool is equal to that of glucose removal from the
pool to maintain the normal blood glucose
concentration.
 Following meal blood glucose concentration tends
to increase & generally reach to the peak by 1h
which is called Postprandial hyperglycemia. Then
blood glucose level gradually comes down to
normal by about 2hrs after meal.

15. Glucose Homeostasis

16. Glucostatic Functions of Liver
 It is the intrinsic capacity of liver to maintain
normal blood glucose concentration & glucose pool
in spite of hyperglycemia and hypoglycemia
tendency following meal & fasting or starvation
respectively.
 The importance of the glucostatic functions of liver
is to maintain normal blood glucose concentration
through glucose homeostasis.
 Mechanism of glucostatic functions of liver:
 In hyperglycemia, liver reduces blood glucose
concentration to normal by using glucose for
glycogenesis and lipogenesis.
 In hypoglycemia, liver raised blood glucose
concentration to normal by producing glucose
through glycogenolysis and gluconeogenesis.

17. Metabolic fates of glucose
 Oxidation through glycolysis & HMP shunt pathway
 Storage of glycogen in liver & skeletal muscle
 Conversion to fat & storage in adipose tissue
 Conversion to amino acids
 Synthesis of structural materials e.g. glycoprotein,
glycolipid, MPS etc.

18. Types of metabolic reactions
The biochemical reactions are mainly of four types:
₪ Oxidation-reduction reaction.
₪ Group transfer.
₪ Rearrangement and isomerization.
₪ Make and break of carbon-carbon bonds.

19. Glycolysis
 Definition: Glycolysis is defined as the sequence of
reactions converting glucose or glycogen to
pyruvate /lactate with the production of ATP.
 Salient features:
 Substrate : Glucose
 Product : Pyruvate (in aerobic condition)
Lactate (in anaerobic condition)
 Site : All cells and tissues
 Compartment : Cytoplasm
 Nature : Catabolic
 Specialty : Can occur in both aerobic and in
anaerobic condition.

22. ATP production in glycolysis
(in aerobic condition)
Generation at substrate level : 4 ATP
Generation at respiratory chain : 6 ATP
Utilization : 2 ATP
Net ATP Production : 8 ATP

23. ATP production in glycolysis
(in anaerobic condition)
Generation at substrate level : 4 ATP
Utilization : 2 ATP
Net ATP Production : 2 ATP

24. Inhibitors of Glycolysis
 In vitro: By Fluoride. It inhibits the enzyme Enolase
of glycolysis. During blood glucose estimation,
commonly fluoride is used in test tube to prevent
glycolysis in blood sample
 In vivo: By Iodoacetate. It increases ATP & citrate
concentration.

25. Oxidation of Pyruvate to Acetyl-CoA

26. Salient features of oxidation of pyruvate to ac
etyl-CoA
 Substrate : Pyruvate
 Product : Acetyl CoA
 Site : All cells and tissues
 Compartment : Mitochondria
 Nature : Catabolic
 ATP production : 06 ATP from 2 pyruvate
 Significance : Linker of glycolysis with TCA cycle

27. Citric acid cycle
 Definition: TCA Cycle is the cyclical sequence of
reactions in mitochondria that oxidizes acetyl CoA
with production of reduced coenzymes & CO2.
 Salient features of TCA Cycle:
 Substrate : Acetyl CoA
 Product : Reduced Coenzymes, CO2 & GTP/ATP
 Site : All cells and tissues
 Compartment : Mitochondria
 Nature : Amphibolic
 Coenzyme needed : TPP, NAD, FAD, CoA, Lipoic acid
 ATP Production : 10/12 (for 1 molecule of Acetyl CoA)
 Specialty : Common metabolic pathway

31. TCA cycle & Respiratory Chain
 Citric acid cycle is an integral part of the process by
which much of the free energy liberated during the
oxidation of fuels is made available.
 During the oxidation of acetyl-CoA, coenzymes are
reduced and subsequently reoxidized in the
respiratory chain, linked to the formation of ATP
(oxidative phosphorylation).

34. Respiratory Chain

35. Respiratory Chain Inhibitors
 Complex-I: Barbiturates
 Complex-II: Malonate
 Complex-III: Antimycin-A, Dimercaprol
 Complex-IV: H2S,CO,CN

38. ATP production in TCA cycle
Generation at respiratory chain through
3 NAD2H : 9/7.5 ATP
Generation at respiratory chain through
1 FAD2H : 2/1.5 ATP
Generation at substrate level : 1 ATP
Total: 12/10 ATP per acetyl-CoA
 NAD2H=2.5 ATP, FAD2H=1.5 ATP 10 ATP
 NAD2H=3 ATP, FAD2H=2 ATP 12 ATP

39. Total ATP production from complete
oxidation of 1 mol glucose
In aerobic condition
• From glycolysis : 08/07
• From conversion of Pyruvate to acetyl CoA : 06/05
• From 2 turn of TCA cycle :24/20
Total ATP Production : 38/32
 In anaerobic condition glucose is incompletely oxidized to
lactate with net 2ATP productions because in absence of
oxygen TCA cycle & respiratory chain can’t work. So in
anaerobic condition only 2 ATP will be produced from eac
h mol of glucose.

41. Important Criteria of TCA Cycle
o OAA is the catalyst of TCA cycle
o TCA cycle is a common metabolic pathway
o TCA cycle is an amphibolic pathway

42. Sources & Fates of Pyruvate
 Sources:
 Glucose oxidation via glycolysis
 Lactic acid oxidation
 Catabolism of glucogenic amino acid
 Metabolic fates:
 Conversion to lactate
 Synthesis of alanine
 Synthesis of glucose
 Conversion to OAA
 Conversion to acetyl-CoA

43. Gluconeogenesis
 Definition: Gluconeogenesis is the process of
synthesis of glucose or glycogen from
noncarbohydrate precursors e.g. glucogenic amino a
cid, pyruvate, lactate, glycerol, intermediates of
TCA cycle, propionate.
 Salient features:
 Substrate: GAA, Glycerol, Pyruvate, Lactate
 Product: Glucose
 Site: Liver & Kidney
 Compartment: Mainly cytoplasm then mitochondria
 Nature: Anabolic
 ATP requirement: 6 ATP is needed
 Source of ATP: β- oxidation of fatty acid

47. Gluconeogenesis from glycerol

48. Gluconeogenesis from Propionate

49. Gluconeogenesis from pyruvate / lactate / differe
nt intermediates of TCA cycle

50. Gluconeogenesis from Glucogenic Ami
no acids.

51. Gluconeogenesis from Glucogenic Ami
no acids.
I. Amino acids entering gluconeogenic pathway
through pyruvate are : Alanine, Cysteine, Glycine,
Serine, Threonine & Tryptophan.
ii. Amino acids entering gluconeogenic pathway
through α-ketoglutarate are : Glutamate,
Glutamine, Histidine, Proline & Arginine.
iii. Amino acids entering gluconeogenic pathway
through Succinyl CoA are : Methionine, Valine,
Isoleucine.
iv. Amino acids entering gluconeogenic pathway
through Fumerate are : Phenylalanine, Tyrosine.
v. Amino acids entering gluconeogenic pathway
through Oxaloacetate are : Aspartate, Asparagine.

52. Gluconeogenesis from fat
▣Fatty acids on oxidation produce acetyl-CoA which
can’t be converted to pyruvate due to irreversibility
of this reaction. However, the glycerol released from
lipolysis and the propionate obtained from the
oxidation of odd chain fatty acids are good
substrates for gluconeogenesis.

53. Cory Cycle/Lactic acid cycle

54. Cory Cycle/Lactic acid cycle

55. Importance of Cory Cycle
 Prevents lactic acid accumulation & lactic acidosis.
 Lactic acid is disposed in liver through
gluconeogenic pathway. So congenital deficiency of
gluconeogenic enzymes leads to lactic acidosis.

56. Glucose-Alanine Cycle

57. Importance of Glucose-Alanine Cycle
 Allows muscle glycogen to contribute glucose
supply to blood during starvation.
 Allows transfer of NH2 from muscle to liver to
convert it into urea.

58. Sources of glucose by gluconeogenesis

59. Hexose Monophosphate Shunt
 Definition: HMP shunt is an alternative pathway to
glycolysis and TCA cycle for the oxidation of
glucose. However, HMP shunt is concerned with the
biosynthesis of NADPH and pentoses.
 Salient features:
 Substrate: Glucose 6-P
 Product: Ribose sugar, NADP2H
 Site: Liver, adipose tissue, RBC, gonads, adrenal
cortex, macrophage, lactating breast.
 Compartment: Cytoplasm
 Nature: Catabolic
 ATP involvement: No ATP is directly consumed or
produced.

62. Criteria of HMP Shunt
 It is called pentose phosphate pathway because it
synthesizes pentose phosphate.
 It is called alternative pathway of glucose oxidation.
 It is called HMP shunt because it branches from
glycolytic pathway at the level of glucose 6-P.
 It is called shunt because pentose formed from
glucose 6-P are recycled back to the mainstream of
glycolysis by conversion into glycolytic intermediates
(fructose 6-P & glyceraldehyde 3-P)

63. Importance of HMP Shunt
 Provides ribose sugar for synthesis of nucleotide
and nucleic acid.
 Provides NADP2H to-
 Help in reductive synthesis of fatty acid, steroid,
cholesterol etc.
 Support detoxifying functions of liver by
hydroxylation of toxic water insoluble aromatic/
aliphatic substance (e.g. drugs) into water soluble,
less toxic or nontoxic forms.
 Prevent hemolysis by facilitating anti oxidant
activity (neutralization of superoxides and free
radicals) in RBC.
 Help in synthesis of nitric oxide (NO) or endothelial
derived relaxing factor (EDRF).

64. Importance of HMP Shunt
 Facilitate superoxide and free radical production in
phagocytes through oxygen dependant
myeloperoxidase system to kill bacteria and other
pathogens.
 Help in reduction of H2O2.

65. Role HMP shunt in RBC
 Under the influence of different oxidants,
hemoglobin in RBC may turn into methemoglobin,
where ferrous iron of normal hemoglobin is
converted to ferric form by losing one electron
which is accepted by molecular oxygen to form
superoxide, causes lysis of RBC membrane and the
methemoglobin that is produced loses oxygen
carrying capacity. Therefore to save RBC, superoxide
must be metabolized to H2O and to maintain
normal hemoglobin function, methemoglobin
must be converted back to normal hemoglobin. For
these activities NADP2H Provided by HMP shunt is
needed. NADP2H maintains the concentration of
reduced glutathione that reduces H2O2
concentration in cell.

66. Clinical consequences of HMP Shunt pa
thway defects
 Hemolytic anemia due to G6PD deficiency.
 Chronic granulomatosis due to G6PD deficiency.
 G6PD deficiency and resistance to malaria.
 Wernicke-Korsakoff syndrome.

67. Glycogenesis
 Definition: Synthesis of glycogen from glucose.
 Salient features:
 Substrate : Glucose
 Product : Glycogen
 Site : 1. Liver 2. Skeletal Muscle
 Compartment : Cytoplasm
 Nature : Anabolic
 Branching enzyme: Glucosyl α-4-6 transferase
 ATP requirement : 3 ATP for each glucose added to
the growing chain of glycogen
molecule.

69. Advantage of storing glucose as gly
cogen
 Glycogen exerts less osmotic pressure and prevents
osmotic lysis of cell. Glucose at 400mmol/L
concentration exerts high osmotic pressure, but if
the same amount of glucose is stored as glycogen;
the glycogen concentration appears to be 0.01µmol
/L only, which have no osmotic effect at all.
 So in the form of glycogen large amount of glucose
can be stored within the cell without disturbing the
osmotic equilibrium of cell and ICF volume.
 Glycogen possesses high energy value than glucose.
 Glycogen does not diffuse out from its storage site
since it is colloid in nature.

70. Glycogenolysis
 Definition: Break down of glycogen to glucose is called
glycogenolysis.
 Salient features :
 Substrate : Glycogen
 Product : Glucose (in liver)
Glucose 1-P (in muscle)
 Site : Liver & Skeletal muscle
 Compartment : Cytoplasm
 Nature : Catabolic
 Debranching enzyme: Glycosyl 4:4 transferase (α-1,4 bond)
Amylo α-1,6 glucosidase (α-1,6 bond)
 ATP involvement : No ATP is used or produced

71. Glycogenolysis

72. Role of liver glycogen
Maintenance of blood glucose concentration.
 In hyperglycemia following meal, glycogenesis
occurs to reduce blood glucose concentration back
to normal. In hypoglycemia following fasting,
glycogenolysis occurs to raise blood glucose
concentration back to normal. After 12-24 hrs fast liver
glycogen is almost totally depleted.
Decreases catabolism of amino acid and increases
protein synthesis.
Provides protection to hepatocytes against various
toxic insults.
Increases the hepatic capacity for detoxification of
drugs, toxins etc.

73. Role of muscle glycogen
1. Provides energy to muscle
 For this, glycogen produces glucose 1-P which is
converted to glucose 6-P to get entry into
glycolytic pathway for oxidation.
2. Effect on blood glucose
 In hyperglycemia muscle glycogenesis tends to
reduce blood glucose concentration back to normal.
 In hypoglycemia role of muscle glycogen is
negligible, but it can provide small amount glucose
to blood via glucose - alanine cycle.

74. Glycogen Storage Disease
 Definition: A group of genetic disorders produced
due to the deficiency of enzymes concerned with
glycogen metabolism leading to failure of glycogen
mobilization or excess accumulation of normal or
abnormal type of glycogen in one or more tissues.

77. Metabolic fates of Glucose 6-P
 Oxidation via glycolysis and TCA cycle
 Glycogen synthesis
 Conversion to glucose
 Oxidation through HMP shunt
 Synthesis of glucuronic acid through uronic acid
pathway.

78. Sources and Metabolic fates of Acetyl CoA
Sources :
1. Oxidation of glucose by glycolysis
2. Oxidation of fatty acid by β-oxidation
3. Oxidation of amino acid.
Metabolic fates :
1. Oxidation in TCA cycle
2. Synthesis of fatty acid
3. Synthesis of cholesterol
4. Synthesis of ketone bodies
5. Donation of acetyl group in different biosynthetic
process.

79. Uronic Acid Pathway
 This is an alternative oxidative pathway for glucose
and is also known as glucuronic acid pathway.
 It is concerned with the synthesis of glucuronic acid,
pentoses and ascorbic acid (except in primates and
guinea pigs).
 Dietary xylulose enters uronic acid pathway through
which it can participate in other metabolisms.