Lecture 9 - Glycolysis Flashcards
(42 cards)
What is a metabolic pathway
A series of steps found in biochemical reactions that help convert molecules or substrates into different, more readily usable materials
What are the 2 types of metabolic pathway
Anabolic and Catabolic
What is an anabolic pathway
Small molecules are assembled into large ones …energy is required
What is a catabolic pathway
Large molecules are broken down into small ones … energy is released
What is glycolysis
Glycolysis is a series of reactions for the breakdown of Glucose (a 6-carbon molecule) into two molecules of pyruvate (a 3-carbon molecule) under aerobic conditions; or lactate under anaerobic conditions along with the production of a small amount of energy
What are aerobic conditions in the human body
whereby the heart and lungs are trained to pump blood more efficiently, allowing more oxygen to be delivered to muscles and organs.
What are anaerobic conditions
in the absence of oxygen, preventing normal life for organisms that depend on oxygen
What is the biochemical significance of glycolysis
It is a significant route for carbohydrate metabolism
* It takes place in all the cells of the body
* It is the only pathway that can act in an aerobic and anaerobic environment.
* Skeletal muscles can survive because of anaerobic glycolysis.
* Glycolysis is the only source of energy in erythrocytes.
* The majority of glycolytic pathway reactions are reversible, which is essential for gluconeogenesis or the formation of new glucose.
What is the clinical significance of glycolysis
Pyruvate kinase enzyme deficiency is an autosomal recessive disorder that causes haemolytic anemia.
* Arsenic replaces phosphate in glycolysis steps, which is why arsenic poisoning prevents ATP synthesis.
* Exercise intolerance is caused by muscle Phosphofructokinase deficiency
What are the 2 phases of glycolysis
Energy-requiring (preparatory phase) (steps 1-5)
Energy-releasing (payoff phase) (Steps 6-10)
Where does glycolysis occur
In the cytosol
What is the first step in glycolysis and what is its catalyst
Uptake and Phosphorylation of Glucose
Hexokinases (Mg2+ required)
Describe the uptake and Phosphorylation of glucose stage
- Glucose is phosphorylated to form glucose-6-phosphate.
Hexokinase
* Phosphate group is transferred from ATP to Glucose.
* It is an irreversible step
* Hexokinase has a high affinity for glucose
* Mg2+ is the cofactor in this reaction
* Hexokinase is a key glycolytic enzyme.
* Glucose is phosphorylated to form glucose-6-phosphate.
Glucokinase
* It is present in the liver, where it removes the glucose from the portal vein following a meal.
* Also present in pancreatic cells, where it releases insulin.
* It acts only when blood glucose is more than 100mg/dL.
* Glucokinase has a high affinity for glucose
What is stage 2 of glycolysis and what is the enzyme that catalyses it
Isomerization of Glucose-6-Phsphate to Fructose-6-Phosphate
Phosphoglucoisomerase
Describe the Isomerization of Glucose-6-Phsphate to Fructose-6-Phosphate
Glucose-6-phosphate is isomerized to fructose-6-phosphate by phosphohexose isomerase.
* For the reaction to take place, it needs the help of aldose-ketose isomerization using a catalyst phosphohexose isomerase.
* It causes the glucopyranose ring’s opening to a linear structure changing the structure of the furanose ring of fructose-6-phosphate.
What is step 3 in glycolysis and what is it catalysed by
Phosphorylation of F-6-P to Fructose 1,6-Biphosphate
Phosphofructokinase
Describe the Phosphorylation of F-6-P to Fructose 1,6-Biphosphate
Fructose-6-phosphate is further phosphorylated to fructose 1,6-bisphosphate.
* The enzyme is phosphofructokinase-1. It catalyzes the transfer of a phosphate group from ATP to fructose-6-phosphate.
* It will be the second irreversible step.
* It is a major regulatory step of glycolysis.
* One ATP is utilized in this step.
* Phosphofructokinase-1 is the key enzyme in glycolysis that regulates the breakdown of glucose.
* It is also called the bottleneck or committed step of glycolysis
Why is the Phosphorylation of fructose-6-phosphate important
Prevents re-formation of glucose-6-phosphate
Second phosphate one in each triose in step 4
What is step 4 of glycolysis
Cleavage of Fructose 1,6 Bisphosphate
Aldolase
Describe the Cleavage of Fructose 1,6-Biphosphate
The 6-carbon fructose-1,6-bisphosphate is cleaved into two 3-carbon compounds; one glyceraldehyde-3-phosphate (GAP) and another one is dihydroxyacetone phosphate (DHAP).
* The enzyme which catalyzes the reaction is aldolase. Since the backward reaction is an aldol condensation, the enzyme is called aldolase.
* The reaction is reversible.
What is step 5 of glycolysis and what is it catalysed by
Interconversion of the Triose Phosphates
Triose-phosphate isomerase
Describe the Interconversion of the Triose Phosphates
GAP is on the direct pathway of glycolysis, whereas DHAP is not. Hence Triose-phosphate isomerase converts DHAP into GAP useful for generating ATP. Thus net result is that glucose is now cleaved into 2 molecules of glyceraldehyde-3-phosphate.
* This reaction is rapid and reversible.
Why is the Isomerisation of DHAP to GAP important
Rapid and reversible reaction
Enables us to use both molecules in glycolysis
What is the acronym for Energy-requiring phase of glycolysis
PIPCI
Phosphorylation
Isomerisation
Phosphorylation
Cleavage
Isomerisation
