glycolysis

GLYCOLYSIS

MSD

Definition

Derived from Greek wordGlykys = Sweet Lysis = splitting

The process in cell metabolism by which carbohydrates and sugars, especially glucose, are broken down, producing (C6H12O6) ATP and pyruvic acid and two "high energy" electron carrying molecules

of NADH.

Glucose = (C6H12O6)

Glycolysis

• Glycolysis is the stepwise degradation of glucose (and other simple sugars).

• Glycolysis is a paradigm of metabolic pathways.• Carried out in the cytosol of cells, it is unique, in that it can function

either aerobically or anaerobically, depending on the availability of oxygen and the electron transport chain.

05/01/2023 Biochemistry for medics 3


Overview of Glycolysis • Glycolysis consists of two phases-• In the first, a series of five reactions, glucose is broken down to two

molecules of glyceraldehyde-3-phosphate. • In the second phase, five subsequent reactions convert these two

molecules of glyceraldehyde-3-phosphate into two molecules of pyruvate.

• Phase 1 consumes two molecules of ATP. • The later stages of glycolysis result in the production of four molecules

of ATP.• The net is 4 – 2 = 2 molecules of ATP produced per molecule of glucose.


Overview of GlycolysisoMost of the details of

this pathway (the first

metabolic pathway to be

elucidated) were worked

out in the first half of the

20th century by the

German biochemists

Otto Warburg, G.

Embden, and O.

Meyerhof.

oIn fact, the sequence of

reactions in is often

referred to as the

Embden-Meyerhof

pathway.


Steps of Glycolysis

10 Steps involves in Glycolysis

Step 1• The enzyme hexokinase phosphorylates (adds a phosphate

group to) glucose in the cell's cytoplasm.

Step 2• The enzyme phosphoglucoisomerase converts glucose 6-

phosphate into its isomer fructose 6-phosphate.

Step 3• The enzyme phosphofructokinase uses another ATP molecule

to transfer a phosphate group to fructose 6-phosphate to form fructose 1, 6-bisphosphate.

Step 4• The enzyme aldolase splits fructose 1, 6-bisphosphate into

two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate and glyceraldehyde phosphate.

Step 5• The enzyme triose phosphate isomerase rapidly inter-converts

the molecules dihydroxyacetone phosphate and glyceraldehyde phosphate.

• Glyceraldehyde phosphate is removed / used in next step of Glycolysis.

• Net result for steps 4 and 5:

Fructose 1, 6-bisphosphate↔ 2 molecules of Glyceraldehyde phosphate (C3H5O3P1)

Step 6• enzyme triose phosphate dehydrogenase

• enzyme transfers a hydrogen (H-) from glyceraldehyde phosphate to (NAD+) to form NADH.

Triose phosphate dehydrogenase + 2 H- + 2 NAD+ → 2 NADH + 2 H+

• Next triose phosphate dehydrogenase adds a phosphate (P) from the cytosol to the oxidized glyceraldehyde phosphate to form

1, 3-bisphosphoglycerate.

TPD+ 2P + 2 glyceraldehyde phosphate → 2 molecules of 1,3-bisphosphoglycerate

Step 7• The enzyme phosphoglycerokinase transfers a P from 1,3-bisphosphoglycerate to a molecule of ADP to form ATP• This happen for each molecule of 1,3-biphosphoglycerate

Result in step 6: 2 molecules of 3-phosphoglycerate (C3H5O4P1) + 2 ATP

Step 8• The enzyme phosphoglyceromutase relocates the P from 3-phosphoglycerate

from the 3rd carbon to the 2nd carbon to form 2-phosphoglycerate.

2 molecules of 2-Phosphoglycerate (C3H5O4P1)

Step 9• The enzyme enolase removes a molecule of water from 2-

phosphoglycerate to form phosphoenolpyruvic acid (PEP).

Result: 2 molecules of C3H3O3P1

Step 10• The enzyme pyruvate kinase transfers a P from PEP to ADP to

form pyruvic acid and ATP

Result in step 10: 2 molecules of 2 ATP + 2NADH

Net energy ATP utilized ATP produced

2 ATP 2ATPFrom glucose to glucose -6-p.From fructose -6-p to fructose 1,6 p.

4 ATP (Substrate level phosphorylation) 2ATP from 1,3 DPG.2ATP from phosphoenol pyruvate

In absence of oxygen (anaerobic glycolysis)

6 ATPOr8 ATP

2ATP-From glucose to glucose -6-p.From fructose -6-p to fructose 1,6 p.

4 ATP (substrate level phosphorylation) 2ATP from 1,3 BPG.2ATP from phosphoenol pyruvate.

In presence of oxygen (aerobic glycolysis)

+ 4ATP or 6ATP(from oxidation of 2 NADH + H in mitochondria).

Energy Production of Glycolysis

Substrates produced by different reaction can enter glycolysis at different points. Eg. When an animal breakdown glycogen glucose 6 phosphate is produced, it can enter at second step. This means one less ATP is required for the pathway.


Inhibitors of Glycolysis

a) Arsenate and Iodoacetate- Inhibitors of Glyceraldehyde-3-P dehydrogenase

b) Bromo hydroxy acetone phosphate- Inhibitor of dihydroxy acetone phosphate

c) Fluoride- Inhibitor of Enolased) Oxamate- Inhibitor of Lactate dehydrogenase

glycolysis

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