Glycolysis

WHAT IS RESPIRATION:

Respiration is defined as "The oxidation and reduction processes which occurs in living cells during which organic food molecule is broken down and energy is released".

Respiration occurs inside the cell and it main purpose is to breakdown food molecule to release energy for living cells functions.

TYPES OF RESPIRATION:

There are two types of respiration;

1-AEROBIC RESPIRATION

2-ANAEROBIC RESPIRATION

AEROBIC RESPIRATION:

The type of respiration in which organic food molecules broken down completely into carbon dioxide and water and release energy in presence of oxygen is called Aerobic respiration.

This respiration give us more energy.

It occurs in Eukaryotes.

It needs oxygen molecule.

OVERALL REACTION OF AEROBIC RESPIRATION:

C6H12O6 + 6O2 = 6CO2 + 6H2O +36ATP

Glucose and oxygen are used and carbon dioxide and water are produced and energy is also released which is used in synthesis of ATP molecule(Energy rich molecule).

The overall reaction completed in 3 steps:Glycolysis,Krebs cycle and Electron transport chain.

ANAEROBIC RESPIRATION:

The incomplete breakdown of food molecule without the utilization of oxygen is called Anaerobic respiration.

It occurs in both eukaryotes and prokaryotes.

It release less energy.

It does not require oxygen for reaction.

There are two types of anaerobic respiration 1-Lactic acid fermentation 2-Alcoholic fermentation.

Now we will study the Aerobic respiration steps;

1-GLYCOLYSIS:

Glycolysis is the breakdown of glucose or hexose sugar molecule (6 C) into two molecule of pyruvate (3 carbon compound) and a net gain of 2 ATP molecules .

It occurs in cytosol(cytoplasm) of cell.

It is common step in both aerobic and anaerobic respiration.

It does not need free oxygen.

Glycolysis completes in two phases:Preparatory phase and oxidative phase.

1-PREPARATORY PHASE:

Preparatory phase is the phosphorylation of glucose by two ATP molecules.

1-Glycolysis starts when glucose react with ATP molecule.

2-ATP transfers energy and phosphate to glucose by kinase enzyme which results in formation of glucose 6-Phosphate and itself changed into ADP.

GLUCOSE + ATP = GLUCOSE 6 PHOSPHATE + ATP

3-Glucose 6-phosphate isomerize into Fructose 6-phosphate by isomerase enzyme.

GLUCOSE 6 PHOSPHATE = FRUCTOSE 6 PHOSPHATE

4-Fructose 6-phosphate reacts with another ATP molecule forming Fructose 1-6 biphosphate.

FRUCTOSE + ATP = FRUCTOSE 1-6 BIPHOSPHATE + ADP

5-Fructose 1-6 biphosphate splits into 3 carbon compound phosphoglyceraldehyde(PGAL) and Dihydroxy acteone phosphate (DAP).

6-Dihydroxy acetone phosphate also changes to PGAL.

Preparatory phase is also called as INVESTMENT PHASE because here 2 ATP used .

Preparatory phase change glucose molecule into 2 Molecule of PGAL.

2-OXIDATIVE PHASE:

It is 2nd phase of Glycolysis.

This phase occurs 2 time.

Also called as payoff phase.

In this phase first PGAL is oxidized to PGA (phosphoglycerate).

Hydrogen is removed from PGAL and the energy of oxidation result in formation of high energy phosphate bonds and the generation of ATP molecules.

This process begins when two hydrogen molecules are removed from PGAL and transfer to NAD(Coenzyme).Thus PGAL oxidized into PGA and NAD reduced into NADH2.This step occurs 2 time because at the end of Preparatory phase two PGAL were produced.This process is accompnied by addition of 2 phosphate which results in 1-3-biphosphoglycerate.

2PGAL + 2Pi = 2BPGA + 2H2

2NAD + 2H2 = 2NADH2

Each molecule of 1-3 biphosphoglycerate transfers high energy phosphate to ADP and results in formation of ATP molecule.

1-3 biphosphoglycerate + ADP = 3 Phosphoglycerate + ATP

In next 3 phoosphoglycerate converts into 2 phosphoenol pyruvate(PEP) with the elimination of one water molecule.

2PGA = PEP + H2O

In last step phosphoenol pyruvate reacts with ADP forming an ATP and pyruvic acid.This formation of ATP is called substrate level phosphorylation because high energy Phosphate transfer from substrate to ADP.

PEP + ATP = PYRUVIC ACID + ATP

Overall four ATP molecules are produced in oxidative phase but two ATP were used in preparatory phase so there is net gain of 2 ATP molecules in Glycolysis process.