Biochemistry

1. Metabolism of
Biomolecules(Glycolysis)

2. Metabolism
 Derived from Greek word “Metaballein” which means
to turn about, to change or to alter
 Inter-conversion of chemical compounds in body
 Different pathways, their inter-relationship and their
regulation
Significance
(Why do we need the process of metabolism?)
 Synthesis of essential substances (molecules)
 Degradation (oxidation) of certain molecules
 Provision of energy
 Conversion of toxic substances to non-toxic substances
(which can easily be excreted)

3. Pathways
1. Anabolic Pathways
 Synthesis of larger molecules from smaller molecules
 Endothermic (energy requiring) processes
e.g. gluconeogenesis, protein synthesis
2. Catabolic Pathways
 Breakdown of larger molecules (oxidative)
 Exothermic (energy yielding) processes e.g. Glycolysis
3. Amphibolic Pathways
Involved in synthesis as well as breakdown of molecules
 Act as link between anabolic & catabolic pathways
e.g. Citric acid cycle

4. Carbohydrate Metabolism
Revolves around the provision and fate of glucose
 Glycolysis
 Hexose mono-phosphate shunt
 Uronic acid pathway
 Gluconeogenesis
 Glycogenesis
 Glycogenolysis
 Citric acid cycle (common metabolic pathway)

5. Gluconeogenesis
Uronic Acid Pathway
Glycogenesis
glycogenolysis
Glc     CO2 + H2O
30 steps of controlled burning of Glc
Energy
Provision

6. Glycolysis
 Derived from Glycos – Sweet, Lysis – Breakdown
 Also known as Embden-Meyerhof Pathway or
Embden – Meyerhof-Parnas Pathway
 A ten step process occurring in cytosol
Glycolysis is a process in which
the glucose (or glycogen) is converted into pyruvate or lactate
Or
Oxidation of glucose to pyruvate or lactate is known as glycolysis

7. Significance / Importance
 Glycolysis is required by all cells & tissues
substantially for brain and totally for RBCs
 Major pathway for glucose utilization
 Fructose and Galactose are also metabolized through
this pathway
 Can provide energy (ATP) even in absence of oxygen
 Provides carbon skeleton for the synthesis of
non-essential amino acids
 Provides glycerol for the synthesis of fats

8. Entry of glucose into cells
 Glucose has to be transported from ECF into cells
 Carrier-dependent transport across membrane
 For muscle cells, heart cells & adipocytes GLUT4 (insulin dependent)
 For liver cells GLUT2 (insulin independent)
 For brain cells GLUT3 (insulin independent)
 For RBCs GLUT1 (insulin independent)
Site
 All enzymes required for glycolysis are present in the extra-
mitochondrial fraction of cell – CYTOSOL

9. Overall Reaction
Glc + 2NAD+ + 2ADP + 2Pi
Aerobic
2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O
Glc + 2ADP + 2Pi
Anaerobic
2 Lactate + 2ATP + 2H2O

10. Stages of Glycolysis
Two Stages
A. Preparatory Stage (ATP consuming) (priming & splitting)
i. Phosphorylation
ii. Cleavage to Glyceraldehyde-3-Phosphate
B. Oxidative stage (ATP producing)
Glyceraldehyde-3-P + NAD+ + 2ADP + 2Pi
Pyruvate (Lactate) + NADH + H+ + 2ATP

11. Glycolysis

13. Comparison of Glucokinase & Hexokinase
3. Km high, low affinity for Glc Km low, high affinity for Glc
Glucokinase Hexokinase
1. Liver (& pancreas) Only Extrahepatic cells (All Cells)
2. Specific for Glc Non-specific (all hexoses)
4. Not inhibited by G-6-P Allosteric inhibition by G-6-P

14. Glucokinase Hexokinase
5. Inducible enzyme;
 in fasting and diabetes,
 in fed state and by insulin
Non-inducible, Not very
much influenced by fasting,
feeding, diabetic state or
insulin level
Comparison of Glucokinase & Hexokinase
6. Main function is to clear
glucose from blood after
meals
Main function is to make
glucose available to tissues
at low glucose conc. in blood
(during fasting or starvation)

16. Reactions

19. Glycolysis - Summary
Glucose
2 Pyruvate
2 ATP
2 ADP
4 ADP
4 ATP
2 NAD
2 NADH + H
4 ADP
Glucose
2 Lactate
2 ATP
2 ADP
4 ATP

20. Bioenergetics
 AEROBIC GLYCOLYSIS
2NADH + H+ = 2 x 3ATP = 6 ATP
Substrate Level = 2 x 2 ATP = 4 ATP
____________________________________________
TOTAL = 10 ATP
Consumed = -2 ATP
____________________________________________
Net Balance = 8 ATP

21.  ANAEROBIC GLYCOLYSIS (e.g. RBC)
Substrate Level = 4 ATP
Consumed = -2 ATP
____________________________
Net Balance = 2 ATP
 RBCs (only when first site of ATP generation is bypassed)
Substrate Level = 2 ATP
Consumed = -2 ATP
____________________________
Net Balance = 0 ATP
Bioenergetics

22. This metabolite(2,3-BPG)
combines with Hb, causing a
decrease in its affinity for O2,
favouring the unloading of O2
even at low O2 pressure.

23.  Three reactions are exergonic; hence are
physiologically irreversible
 These are the major sites of regulation.
i. Hexokinase / Glucokinase
ii. Phosphofructokinase
iii. Pyruvate Kinase
Regulation – Rapid & short term
Key regulatory enzymes
Fed state
 Glc  Activation of these enzymes for Glc utilization

24. HORMONAL: (Slow and Long Term)
Affecting the amount of enzyme(s) synthesized
1. Fed sate   insulin   gene transcription 
ed synthesis of 3 (& other) enzymes   glycolysis
2. Starvation / DM   insulin ( glucagon) 
ed synthesis of enzymes   glycolysis
Regulation

25. 3. Epinephrine / glucagon   cAMP  activates
cAMP-dependet protein kinase   phosphorylation
(inactivation) of Pyruvate kinase  inhibits glycolysis
4.  AMP  Activates PFK-I   glycolysis
5.  Citrate and  ATP  inhibit PFK-I   ed Glycolysis
6. Hypoxia   ATP ( AMP)   glycolysis
Regulation

26. Inhibitors
1. Arsenite:
Competes with Pi to form I-arseno-3-P-glycerate
2. Iodoacetate / Iodoacetamide:
Binds with (& inactivates) Gly.3.P.DH  no further
glycolysis ( Gly.3.P is accumulated)
3. Fluoride – enolase

27. Entry of other hexoses into glycolysis
Galactose
Gal-1-Phosphate
Glc-1-Phosphate
Glc-6-Phosphate
Mutase
Glycolysis
Galactose
Galactokinase
ATP ADP
Mg+2
Gal-1-P-uridyl
transferase
UDP-Glc
UDP-Gal
UDP-Gal-4-epimerase

28. Galactosemia
When Galactose cannot be metabolized due to inherited
defect / deficiency of any of the following enzymes;
Galactokinase, Uridyl transferase (common deficiency)
or 4 – Epimerase
Galactose concentration in blood increases and is
converted into galactitol (polyol)
Gal-1-Phosphate concentration also increases (depletes
liver Pi) & may lead to liver failure, mental deterioration.

29. Fructose Fr-1-Phosphate
ATP ADP
Mg++
Fructokinase
DHAP + Glyceraldehyde
Fr-1-P
Aldolase
Glyceraldehyde -3-Phosphate
Fructose (Major pathway) (Liver)
Fructose Fr-6-Phosphate  Glycolysis
ATP ADP
Mg++
Hexokinase
Fructose (Minor pathway) (Liver)
ATP
ADP
Triose
Kinase
PTI
Glycolysis

30. Fructose (Major pathway) (Liver)
Fructokinase
 Its activity is not affected by fasting or by insulin
 Has low Km (high affinity for Fru)
 Absence leads to fructosuria
Fructose intolerance
 Due to absence or deficiency of Fru-1-phosphate aldolase
Fructose loading
 Fru   pyruvate  Acetyl CoA   FA  TAG  VLDL & LDL

31. Assignment
What is Metabolism?
Significance of Metabolism (in points)
Enumerate different types of Metabolic Pathways.
What is Glycolysis? (Complete definition)
Types of glucose transporters and their location in the body
Flow chart of Glycolysis with enzymes, coenzymes and cofactors.
Significance of Glycolysis( in points)
Differences between Hexokinase and glucokinase in tabulated form
Bioenergetics of Glycolysis both aerobic and anaerobic
Regulation of Glycolysis.(regulatory steps)
Inhibitors of glycolysis
Entry of galactose into glycolysis (STEPS)
Biochemical Aspects of Galactosemias
Entry of Fructose into glycolysis (Major and Minor Pathways)
Biochemical Aspects of Fructose intolerance
Write ten (10) MCQ’s on Glycolysis (each MCQ with five options)