Lecture 8. Metabolic Pathways and Glycolysis Flashcards
What is glycolysis?
A series of reactions starting with glucose and ending with pyruvate resulting in a small gain of ATP (2 molecules ATP for each glucose molecule)
What happens during the dialysis of yeast extract?
Dialysis is a fractionation method: Yeast lysate in bag (cellophane) stir in buffer for several hours
Dialysed yeast extract is inactive, activity restored by adding dialysate
What is zymase?
Large molecules (non-dialysable) inactivated by heat (proteins)
What is co-zymase?
Small molecules (dialysable) heat stable (substrates are coenzymes)
What does glycolysis require?
Phosphate and NAD⁺
Glycolysis equation
Glucose + 2 ADP + 2 Pi+ 2 NAD⁺→ 2 pyruvate + 2 ATP + 2 NADH + 2H⁺+ 2H₂O
Advantages of studying metabolic reactions in vitro
Study a purified enzyme in isolation
Completely defined (and readily modifiable) conditions
Direct, quantitative results
Disadvantages of studying metabolic reactions in vitro
Loss of compartmentation, spatial and temporal organisation; dilution
Instability or degradation of key components (e.g. lack of ATP consumption in H&Y extracts prevented Pi release, limiting glycolysis)
What is required to test metabolic reaction in vivo?
Measuring with assays and indicators or labelled compounds
Modifying with inhibitors (pharmacological) or mutations (genetic)
Advantages of studying metabolic reactions in vivo
In cells
Disadvantages of studying metabolic reactions in vivo
Can be hard to get quantitive data
Many variables so careful interpretation
What is the main difference between respiration and combustion?
Respiration involves a multistep energy conserving pathway, whilst all the energy from combustion is released at once
What are control points
Key steps in a metabolic pathway that are irreversible (strongly negative ΔG)
What is the key cofactor that carries energy in energy metabolism?
ATP
What are the key cofactors that carries electrons for oxidation of fuels in energy metabolism?
NAD⁺ and FAD
What is the key cofactor that carries electrons for reductive biosynthesis in energy metabolism?
NADPH
What is the key cofactor that carries 2-carbon groups in energy metabolism
CoA
What is NAD⁺?
Nicotineamide Adenine Dinucleotide
What is NAD⁺ derived from?
Niacin / Vitamin B₃
What is FAD?
Flavine Adenine Dinucleotide
Wat is FAD derived from?
Riboflavin / Vitamin B₂
How many stages of catabolism are there?
3
What is anabolism?
Building molecules
What is catabolism?
Breaking molecules
What is stage I of catabolism?
Large to smaller molecules not useful for energy production
What is stage II of catabolism?
Many products of stage I to Acetyl-CoA
Small amount of ATP produced
What is stage III of catabolism?
Acetyl group of Acetyl-CoA to CO₂
Majority of ATP produced
What controls catabolic pathways?
Energy
Are anabolic pathways simply a reversal of catabolic pathways?
No
Is glycolysis aerobic or anaerobic?
Anaerobic - evolved before atmosphere contained significant O₂
Where does glycolysis take place?
Cytosol
How many steps are there in glycolysis?
10
What is stage 1 of glycolysis also known as?
The investment stage
What happens in stage 1 of glycolysis?
2 ATP used
Phosphorylation keeps intermediates in the cell
What is stage 2 of glycolysis also known as?
The payout stage
What happens in stage 2 of glycolysis?
Oxidation
4 ATP produced
2 NADH produced
Requires NAD⁺ and Pi
What is the net gain of ATP per glucose
2
What happens when the cofactors run out in glycolysis?
Glycolysis stops
What is needed for the oxidation of G-3-P?
NAD⁺
How is NAD⁺ regenerated?
NADH transfers electrons to O₂, forming H₂O and regenerates NAD⁺
What is the fermentation product in animals?
Lactate
What is the fermentation product in plants and yeast?
Ethanol
What is glycolysis central to?
Glycolysis is central to carbohydrate breakdown in modern organisms
What steps in glycolysis are have a highly negative ΔG?
Steps 1, 3 and 10
Which step is the main regulatory point of glycolysis?
Step 3
How is glycolysis regulated?
Mainly by regulation of PFK
