Question

Be able to label any and all steps in: glycolysis, the citric acid cycle and oxidative

phosphorylation. Including (but not limited to): names of compounds, enzymes (for extra credit where stated), ATP produced, NADH and FADH₂ produced, and the role or importance of main molecules.

**Note: this is really three questions in one. Therefore, know how to label the sequences in 1. Glycolysis 2. The citric acid cycle and 3. Oxidative phosphorylation

.

Answer 1

According to the question asked labelling means a detail description or explanation as to what kind of reaction is occuring and enzymes.

1. Glycolysis:

This is a pathway where Oxidation (breaking up) of glucose occurs to give a 3 carbon compound pyruvate and to release energy.

Enzymes involved are extramitochondrial and this pathway is divided into 4 stages.

stage 1 : preparatory stage: uptake of glucose by cells and its phophorylation

Glucose is easily permeable into liver cell, In others insulin facilitates in skeletal muscles, cardiac muscles, diaphragm and adipose tissue.

at first the Glucose is phosphorylated to form glucose-6-phosphate( Irriversible). This reaction is a phosphorylation reaction catalyzed by glucokinase. This enzyme needs magnesium ions to get activated and ATP donates phosphate ion to become ADP.

This step is a commited step since it is important for several other pathways.

2. Glucose 6 phosphate is converted to fructose 6 phosphate. The enzyme is phospho hexose isomerase which involves an aldose-ketose isomerization.

3. Fructose 6 phosphate to fructose 1,6 biphospahte: Another phosphorylation occurs with ATP catalzed by phosphofructokinase to produce a symmetrical molecule. this reaction is irriversible and this enzyme is the Key enzyme which regulates the pathway.

STAGE:2

Splitting of symmetrical molecule.

Fructose1,6 biphosphate is split by an aldolase enzyme to give two molecules an aldotriose (glyceraldehyde 3 phosphate) and Ketotriose Di hydroxy acetone-p

This is reversible and the enzyme aldolase is a tetramer containng 4 subunits.

STAGE 3: energy yielding reaction :

This is an oxidation reaction

* Glyceraldehyde 3 phosphate to 1,3biphospho glycerate : Dihydroxy acetone phospate to 1,3biphospho glycerate is catalyzed by Glyceraldehyde 3 phosphate dehydrogenase a NAD+ dependent. NADH is a energy molecule.

* 1,3 biphosphoglycerate to 3 phosphoglycerate . this reaction is catalyzed by phosphoglycerate kinase , the high energy phospate bond donates phospate ion to ADP to form ATP.

This is an substrate level phosphorylation reaction with out participating in electron transport chain.

STAGE 4: Recovery of phophate ion from 3phsphoglycerate.

* 3phosphoglycerate is is converted into 2phosophoglycerate by the enzyme phosphoglycerate mutase

* conversion of 2phosphoglycerate to phosphoenolpyruvate by enzyme enolase. This enzyme needs the presence of mg++ and mn++ for the activity. The reaction involves dehydration and redistribution of energywithin the molecule raising the phosphate ion to the higher position or higher energy stste.

* Phosphoenol pyruvate to pyruvate:

pyruvate kinase enzyme plays the role. This is a sustrate level phosphorylation . In this stage two molecule of ATP are released.

The net gain of energy molecule ATP is 10-2= 8.