Glycolysis Pathway in Cellular Respiration

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Questions and Answers

Under which conditions is glucose split into two 3-carbon pyruvate molecules?

Anaerobic conditions

In the presence of glucose-6-phosphatase

Aerobic conditions (correct)

In the absence of insulin

Where do all the reaction steps of glycolysis take place?

Cytoplasm (correct)

Mitochondria

Endoplasmic reticulum

Nucleus

What is the significance of glycolysis in erythrocytes?

It provides energy for muscle contraction

It is the primary pathway for protein synthesis

It is the sole pathway for lipid synthesis

It is the only source of energy (correct)

What is the role of hexokinase in the glycolytic pathway?

It phosphorylates glucose to glucose-6-phosphate Signup and view all the answers

Which glucose transporter is under the influence of insulin?

Glucose transporter-4 (GluT4) Signup and view all the answers

What is the result of the hydrolysis of ATP in the first step of glycolysis?

The energy released is utilized for the forward reaction Signup and view all the answers

What is the significance of the glycolytic pathway in strenuous exercise?

It forms the major source of energy for muscles Signup and view all the answers

What is the significance of the glycolytic pathway in the synthesis of non-essential amino acids?

It provides carbon skeletons for synthesis Signup and view all the answers

Which enzyme is responsible for the phosphorylation of glucose in the initial step of glycolysis?

Glucokinase Signup and view all the answers

What is the result of the phosphorylation of glucose in the initial step of glycolysis?

Glucose is trapped within the cell and has to be metabolized Signup and view all the answers

What is the function of phosphohexose isomerase in glycolysis?

It isomerizes glucose-6-phosphate to fructose-6-phosphate Signup and view all the answers

What is the significance of phosphofructokinase in glycolysis?

It is the rate-limiting enzyme of glycolysis Signup and view all the answers

What is the result of the reaction catalyzed by aldolase in glycolysis?

Fructose-1,6-bisphosphate is cleaved into two 3-carbon units Signup and view all the answers

What is the function of phosphotriose isomerase in glycolysis?

It isomerizes dihydroxy acetone phosphate to glyceraldehyde-3-phosphate Signup and view all the answers

What is the net result of steps 4 and 4-A of glycolysis?

Glucose is converted into two molecules of glyceraldehyde-3-phosphate Signup and view all the answers

Which phase of glycolysis consists of steps 1, 2, and 3?

The preparatory phase Signup and view all the answers

Study Notes

Glycolysis (Embden-Meyerhof Pathway)

Glycolysis is the pathway where glucose is split into two 3-carbon pyruvate molecules under aerobic conditions, or lactate under anaerobic conditions, along with production of a small quantity of energy.
The word "glycolysis" is derived from the Greek words, glykys = sweet; and lysis = splitting.

Site of Reactions

All the reaction steps take place in the cytoplasm.

Significance of the Glycolysis Pathway

It is the only pathway that takes place in all the cells of the body.
Glycolysis is the only source of energy in erythrocytes.
In strenuous exercise, when muscle tissue lacks enough oxygen, anaerobic glycolysis forms the major source of energy for muscles.
The glycolytic pathway may be considered as the preliminary step before complete oxidation.
The glycolytic pathway provides carbon skeletons for synthesis of non-essential amino acids as well as glycerol part of fat.
Most of the reactions of the glycolytic pathway are reversible, which are also used for gluconeogenesis.

Glucose Entry into Cells

Glucose transporter-4 (GluT4) transports glucose from the extracellular fluid to muscle cells and adipocytes.
GluT4 is under the influence of insulin.
In diabetes mellitus, insulin deficiency hinders the entry of glucose into the peripheral cells.
GluT2 is the transporter in liver cells, and it is not under the control of insulin.

Steps of Glycolytic Pathway

Step 1 of Glycolysis

Glucose is phosphorylated to glucose-6-phosphate.
The enzyme is hexokinase (HK), which splits the ATP into ADP, and the Pi is added on to the glucose.
The energy released by the hydrolysis of ATP is utilized for the forward reaction.
Hexokinase is a key glycolytic enzyme and catalyses a regulatory step in glycolysis that is irreversible.
Hexokinase and glucokinase may be considered as iso-enzymes.

Step 2 of Glycolysis

Glucose-6-phosphate is isomerised to fructose-6-phosphate by phosphohexose isomerase.
This is readily reversible.

Step 3 of Glycolysis

Fructose-6-phosphate is further phosphorylated to fructose-1,6-bisphosphate.
The enzyme is phosphofructokinase (PFK), which is an allosteric, inducible, regulatory enzyme.
PFK is an important key enzyme of this pathway and catalyses an irreversible step.
This step is the rate limiting reaction in glycolysis.

Steps 4 and 4-A of Glycolysis

The 6-carbon fructose-1,6-bisphosphate is cleaved into two 3-carbon units; one glyceraldehyde-3-phosphate and another molecule of dihydroxy acetone phosphate (DHAP).
The enzyme is called aldolase, and this reaction is reversible.
Dihydroxy acetone phosphate is isomerised to glyceraldehyde-3-phosphate by the enzyme phosphotriose isomerase.
Thus, the net result is that glucose is now cleaved into 2 molecules of glyceraldehyde-3-phosphate.