Lecture 24: Glucose as a fuel molecule 2 Flashcards
What are the two phases of glycolysis?
Energy investment phase:
- The molecule is split (1X6C to 2X3C) at the end of the investment phase
Energy payoff phase:
- After a conversion, both 3C molecules processed in the same way (making ATP profit)
In which molecules is energy conserved/captured in glycolysis?
Energy conserved in ATP and NADH
Why is ATP hydrolyzed in the activation of glucose?
ATP hydrolysis transfers a phosphate group to glucose, forming glucose-6-phosphate. This step increases glucose’s reactivity, traps it inside the cell, and lowers activation energy for subsequent metabolic reactions.
- The reaction involving glucose and phosphate being converted to glucose-6-phosphate is energetically unfavourable
- While the hydrolysis of ATP is energetically favourable
- Therefore, the hydrolysis of ATP can couple the glucose reaction to make it overall favourable
What are the two forms NAD can be in, and what does it carry?
NAD+ (oxidized form)
NADH (reduced form):
Carries:
2 x e, 1 x H+
Why is the oxidation of glyceraldehyde-3-phosphate essential for glycolysis to make an ATP profit?
The addition of phosphate is powered by oxidation of G-3-P, The addition of phosphate does not require ATP
It also produces an NADH
Thus is essential in making ATP profit in glycolysis
The ATP produced in glycolysis is produced by what type of reaction? What is the key aspect of this type of reaction?
ATP produced in glycolysis is generated through substrate-level phosphorylation.
The key aspect is the energy released from cleaving high-energy phosphate ester bond on the molecule (which has stored energy) can be used to add a P onto ADP making ATP without an external energy source like a proton gradient.
Why does arsenate prevent an ATP profit being made in glycolysis?
Arsenate (AsO4-3) substitutes for phosphate (PO4-3)
This generates 1-Arseno-3-phosphoglycerate
The Unstable arsenate, is hydrolyzed but the energy is not captured
ATP is therefore not synthesized by phosphoglycerate kinase
No net gain of ATP in glycolysis
What is the overall reaction for glycolysis?
Glucose + 2NAD+ + 2ADP + 2Pi ➔ 2 pyruvate + 2 NADH + 2ATP + 2H+
Glycolysis overall: ΔG0´= -73 kJ/mol
- Pathway is energetically favourable
- Some energy also converted into heat
What are the two possible fates of pyruvate in humans?
aerobic oxidation and Anaerobic glycolysis
Describe the fate of pyruvate under aerobic oxidation?
Occurs in the mitochondrial matrix:
Involves a Pyruvate dehydrogenase reaction:
- Multienzyme complex with lots of cofactors/ coenzymes
Net reaction is an oxidative decarboxylation:
- CO2 released (decarboxylation; 3C to 2C)
- pyruvate is oxidized, energy captured in NADH and used to add Coenzyme A (CoA) to two-carbon chain
Reaction:
Pyruvate + NAD⁺ + CoA → Acetyl-CoA + NADH + CO2
ΔG0´= -33 kJ/mo
Describe the fate of pyruvate under anerobic glycolysis?
Pyruvate is converted to Lactate:
- Pyruvate is reduced to lactate by the enzyme lactate dehydrogenase.
- This process (oxidation) regenerates NAD⁺, which is essential for maintaining glycolysis.
Reaction:
Pyruvate + NADH → Lactate + NAD⁺
Purpose:
- Ensures continued ATP production in the absence of oxygen.
Location:
-Occurs in muscle cells during intense exercise or in anaerobic organisms.
Key Point:
- Conversion to lactate prevents pyruvate accumulation and allows glycolysis to continue under anaerobic conditions.
What is the importance of Mg2+ in glycolysis?
Cofactor for Enzymes:
- Mg²⁺ is essential for enzymes like hexokinase and phosphofructokinase, which drive key steps in glycolysis.
Stabilizes ATP:
- It forms complexes with ATP, allowing for efficient energy transfer during reactions.
Substrate-Level Phosphorylation (SLP):
- Mg²⁺ is crucial for reactions that produce ATP through substrate-level phosphorylation, like those catalyzed by phosphoglycerate kinase and pyruvate kinase.
Overall Role:
- Supports enzyme function, stabilizes energy molecules, and is vital for ATP production in glycolysis.
Why is it important that lactate is produced in animals under anaerobic conditions?
Lactate production in animals under anaerobic conditions is important because it:
Regenerates NAD⁺:
- Allows glycolysis to continue producing ATP.
Maintains Energy Production:
- Enables cells to meet energy demands during low oxygen.
Prevents Pyruvate Buildup:
- Avoids disruption of cellular metabolism.
How is Coenzyme A (CoA) derived and what is its role?
Derived from pantothenic acid (vitamin B5)
Carries:
acyl groups (2 C to long C chains)
eg. CH3(CH2)nCH2COO
What two forms can Coenzyme A (CoA) be found in?
free coenzyme A: CoASH
acyl group attached: Acyl-CoA (AcCoA)
