Glyco = sugar
Lysis = splitting

Dietary polysaccharides and disaccharides undergo
hydrolysis to monosaccharides

Glycolysis
• Occurs in cytoplasm when glucose a hexose (6C) sugar is broken
down into two molecules of pyruvate (3C)
• Glycolysis involves ten individual steps, each catalysed by an
enzyme.
• Energy is released and there is a net production of 2 ATP
molecules.
• Reduced NAD is formed, which has the potential to produce
more ATP.
Glycolysis takes place in the cytosol of cells.
Glucose enters the Glycolysis pathway by conversion to
glucose-6-phosphate.
H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
1
6
5
4
3 2
glucose-6-phosphate

GLYCOLISIS
• Glycolisis oxidation of glucose energy
• It can function either aerobically or anaerobically
pyruvate lactate
• Occurs in the cytosol of all cell
• AEROBICALLY GLYCOLYSIS :
Pyruvate Mitochondria oxidized to
Asetil CoA Kreb’s Cycle
CO2 + H2O + ATP

2 Pyruvate (3C)
Glucose (6C)
2 ATP
2 ADP
4 ADP
4 ATP
2 NAD
2 NADH + H

• NADH + H+ and FADH2 enter ETC and produce;
NADH + H+ 3 ATP
FADH2 2 ATP
c
c
Glycolysis complete Reaction (Energetic)
Glucose  2Pyruvate + 2NADH+ 2ATP
2 NADH produce = 6 ATP
ATP produce = 2 ATP x 2 = 4 Atp
2 ATP Used = - 2 ATP
Total = 8 ATP

Regulation of Glycolysis:
Two types controls for metabolic reactions:
a) Substrate limited : When concentrations of reactant and products in the cell
are near equilibrium, then it is the availability of substrate which decides
the rate of reaction.
b) Enzyme-limited: When concentration of substrate and products are far away
from the equilibrium, then it is activity of enzyme that decides the rate of
reaction. These reactions are the one which control the flux of the overall
pathway.
There are three steps in glycolysis that have enzymes which regulate the flux of
glycolysis.
I. The hexokinase (HK)
II. The phoshofructokinase (PFK)
III. The pyruvate kinase

Pyruvate is first transported into
mitochondria via a specific transporter on
the inner membrane and then oxidized to
acetyl-CoA by the catalysis of pyruvate
dehydrogenase complex.

ATP

Citric Acid cycle or
Tricarboxylic Acid cycle
(TCA) or Krebs Cycle

3
An overview of
the citric acid cycle
None of the intermediates
are phosphorylated.
None of the intermediates
are phosphorylated
All are either di- or
tricarboxylic acids.
To regenerate
oxaloacetate.
all are either di- or
tricarboxylic acids.

CO2
Acetyl CoA
NAD+
Pyruvate
NADH

Overall Reaction:
acetyl-CoA+3NAD++FAD+GDP+Pi+2H2O
2CO2 + 3NADH + FADH2 +GTP+2H++CoA
Acetyl CoA
3 NAD
3 NADH + H
1 FAD
1 FADH2
1 ADP
1 ATP
2 CO2

TCA cycle (Energetics):
Acetyl CoA 2CO2 + 3NADH+ FADH2+ GTP
3 NADH produce = 9 ATP
1FADH2 produce = 2 ATP
1 GTP produce = 1 ATP
12 ATPs
But 2 acetyl Con A take part in reaction so,
2 x 12ATPs = Toatal =
24 ATP formed

Total yield of high energy ATP in
the aerobic catabolism of glucose?
Glycolysis:
glucose 2pyruvate + 2NADH+2ATP 8 ATPs
Pyruvate Dehydrogenase:
2pyruvate  2acetyl CoA + 2NADH 6 ATPs
TCA cycle:
acetyl CoA2CO2+3NADH+FADH2+GTP 2x12ATPs
OVERALL yield from glucose 38 ATPs

ENERGY RELATIONSHIPS

G° for oxidation of glucose to CO2 is 2,840 kJ/mole
 Much of this energy conserved as ATP
38 ATP X 30.5 kJ/mole ATP
=1,160 kJ/mole glucose
 This represents 41% conservation of the potential
energy available in glucose as ATP.