Glycolysis and krreb's cycle Biochemistry

1. Glycolysis and krebs cycle
MuhammadAmmar

2. glycolysis
INTRODUCTION:
 Glycolysis literally means "splitting sugars" and is the process of
releasing energy within sugars.
 In the presence of oxygen, glycolysis is the first stage of cellular
respiration
 Glycolysis takes place in the cytosol of the cell's cytoplasm.
 In glycolysis, glucose (a six carbon sugar) is split into two molecules
of the three-carbon sugar pyruvate

3. History of glycolysis:
 The pathway of glycolysis as it is known today took
almost 100 years to fully discover .The combined results
of many smaller experiments were required in order to
understand the pathway as a whole.
 The first steps in understanding glycolysis began in the
nineteenth century with the wine industry
 Louis Pasteur (1850s) fermentation occurs by the action
of living microorganisms
 Eduard Buchner(1890s) Discovered cell-free fermentation.
 Otto Meyerhof (1920s ) One of the main scientists
involved in completing the puzzle of glycolysis
 With all of these pieces available by the 1930s, Gustav
Embden proposed a detailed, step-by-step outline of
that pathway we now know as glycolysis.
Eduard buncher
Otto Meyerhof

4.  This multi-step process yields:
 two molecules of ATP (free energy containing
molecule),
 two molecules of pyruvate,
 and two "high energy" electron carrying molecules of
NADH.
 Glycolysis can occur with or without oxygen
 However, the next stage of cellular respiration
known as the citric acid cycle, occurs in the matrix of
cell mitochondria.

5. 10 STEPS OF GLYCOLYSIS
Step 1
 Glucose (C6H12O6) + hexokinase + ATP → ADP + Glucose 6-phosphate
(C6H13O9P)
Step 2
 Glucose 6-phosphate (C6H13O9P) + Phosphoglucoisomerase →
Fructose 6-phosphate (C6H13O9P)

6. Step 3
 Fructose 6-phosphate (C6H13O9P) + phosphofructokinase + ATP → ADP + Fructose 1, 6-
bisphosphate (C6H14O12P2)
Step 4
Formation of two sugar (isomers)
 Fructose 1, 6-bisphosphate (C6H14O12P2) + aldolase → Dihydroxyacetone phosphate
(C3H7O6P) + Glyceraldehyde phosphate (C3H7O6P)

7. Step 5
The enzyme triose phosphate isomerase rapidly inter-converts the
molecules dihydroxyacetone phosphate and glyceraldehyde 3-
phosphate. Glyceraldehyde 3-phosphate is removed as soon as it
is formed to be used in the next step of glycolysis.
 Dihydroxyacetone phosphate (C3H7O6P) Glyceraldehyde 3-phosphate
(C3H7O6P)
Net result for steps 4 and 5:
 Fructose 1, 6-bisphosphate (C6H14O12P2) ↔ 2 molecules of
glyceraldehyde 3-phosphate (C3H7O6P)

8. Step 6
Dehydrogenation:
 The enzyme triose phosphate dehydrogenase serves 2 functions
1) Transfers a hydrogen (H-) from glyceraldehyde phosphate to the oxidizing
agent nicotinamide adenine dinucleotide (NAD+) to form NADH.
 Triose phosphate dehydrogenase + 2 H- + 2 NAD+ → 2 NADH + 2 H+
2) . Next triose phosphate dehydrogenase adds a phosphate (P) from the
cytosol to the oxidized glyceraldehyde phosphate to form 1, 3-
bisphosphoglycerate
 Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde 3-phosphate
(C3H7O6P) → 2 molecules of 1,3-bisphosphoglycerate (C3H8O10P2)

9. Step 7
 2 molecules of 1,3-bisphoshoglycerate (C3H8O10P2) +
phosphoglycerokinase + 2 ADP → 2 molecules of 3-phosphoglycerate
(C3H7O7P) + 2 ATP
Step 8
 2 molecules of 3-Phosphoglycerate (C3H7O7P) +
phosphoglyceromutase → 2 molecules of 2-Phosphoglycerate
(C3H7O7P)
Step 9
 2 molecules of 2-Phosphoglycerate (C3H7O7P) + enolase → 2 molecules
of phosphoenolpyruvate (PEP)
Step 10
 2 molecules of phosphoenolpyruvate (C3H5O6P) + pyruvate kinase + 2
ADP → 2 molecules of pyruvate (C3H3O3
-) + 2 ATP

10. Cyclic view
of Glycolysis

11. Krebs cycle
Names:
The Citric Acid
Cycle
Tricarboxylic Acid
Cycle
Krebs Cycle
 Hans Adolf Krebs.
Biochemist; born in
Germany. Worked in
Britain. His discovery in
1937 of the ‘Krebs cycle’
of chemical reactions
was critical to the
understanding of cell
metabolism and earned
him the 1953 Nobel Prize
for Physiology or
Medicine.

12.  Conversion of pyruvate to activated acetate
This cycle involves a series of reactions :
 a substrate, Oxaloacetate, that is modified in every
reaction
 Acetyl–CoA, from which energy is extracted,
 energy transport reactants, which collect the
extracted energy
 the controlling enzymes, which regulate the steps of
the cycle.

13. 8 steps of krebs cycle
Step 1:
Citrate synthesis
The first step is to put energy into the system

14.  Step 2
Citrate loses a molecule of water and another is added. In the process, citric acid is
converted to its isomer isocitrate.
Enzyme: aconitase.
 Step 3
Isocitrate loses a molecule of carbon dioxide (CO2) and is oxidized forming the five-
carbon alpha ketoglutarate. Nicotinamide adenine dinucleotide (NAD+) is reduced to
NADH + H+ in the process.
Enzyme: isocitrate dehydrogenase.
 Step 4
Alpha ketoglutarate is converted to the 4-carbon succinyl CoA. A molecule of CO2 is
removed and NAD+ is reduced to NADH + H+ in the process.
Enzyme: alpha ketoglutarate dehydrogenase.
Step 5
in mitochondria, the enzyme links to the Succinyl–CoA and uses the energy from releasing
the coenzyme, to add a phosphate (P) to GDP to produce GTP.
Enzyme:Succinyl-CoA synthetase

15. Step 6
Succinate is oxidized and fumarate is formed. Flavin adenine dinucleotide (FAD) is
reduced and forms FADH2 in the process.
Enzyme: succinate dehydrogenase.
Step 7
A water molecule is added and bonds between the carbons in fumarate are
rearranged forming malate.
Enzyme: fumarase.
Step 8
Malate is oxidized forming oxaloacetate, the beginning substrate in the cycle.
NAD+ is reduced to NADH + H+ in the process.
 Enzyme: malate dehydrogenase.