Glycolysis Flashcards
What is the definition of metabolism?
Process through which living systems acquire and utilize the free energy they need to carry out their various functions
ex: breakdown of food, ATP synthesis, heat loss, chemical waste, work, organic wastes
What is the reaction and ∆G˚’ of the full breakdown of glucose?
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
∆G˚’ = -2,870 kJ/mol
What is the reaction and ∆G˚’ of the full breakdown of lipids?
C16H32O2 + 23 O2 → 16 CO2 + 16 H2O
∆G˚’ = -9,781 kJ/mol
What is the reaction and ∆G˚’ of the hydrolysis of ATP?
ATP + H2O → ADP + Pi
∆G˚’ = -32.2 kJ/mol
How many calories is 1 kJ?
1 kJ = 0.239 kcal
How could catabolism and anabolism be summarized?
Catabolism: complex → simple (exergonic)
Anabolism: simple → complex (endergonic)
*Both coupled with ATP hydrolysis
What are the 3 stages of metabolism?
- Polymers and complex lipids → monomeric intermediates
- Monomeric sugars, amino acids and lipids → simpler organic compounds
- Degradation or synthesis of inorganic compounds including CO2, H2O and NH3
What are futile cycles?
When 2 metabolic pathways run simultaneously in both directions
It is an example of how cells regulate many pathways
Ex: Fatty acid synthesis and degradation occurred simultaneously (use ATP) → no useful work done and all ATP consumed
Solution → do these reaction in separate compartement (acetyl-CoA → Fatty acids uses ATP in cytosol ///// Fatty acids → Acetyl-CoA releasing ATP in Mitochondria)
What are the major intermediates of glycolysis?
Polysaccharides → Monosaccharides → GLYCOLYSIS [Glucose → Glyceraldehyde-3-phosphate (ATP/NAD step) → pyruvate] → To fermentation of respiration
Which tissues are responsible for synthesis of glucose and responsible for glucose use as a primary energy source?
Tissues that synthesize glucose:
- Liver
- Kidney cortex
Tissues that use glucose as their primary energy source:
- Brain
- Muscle
- Kidney medulla
- Erythrocytes
- Testes
Where does glycolysis occur in the cell?
In the cytosol
What are the net starting materials and products of glycolysis?
- Glucose
Energy investment phase: - Invest 2 ATP (→ADP)
Energy generation phase (2 trise phosphates (3C)):
3. Produces 4 ATP (from ADP)
4. Produces 2 NADH (from NAD+)
5. 2 Pyruvates
Net:
Glucose → 2 pyruvates
2 ADP → 2 ATP
2 NAD+ → 2 NADH
What explains the fact that glycolysis is a fermentation? (reaction)
NADH produced ealier in the pathway is reoxidized to NAD+ by transfer of electrons to some electron acceptor → ensures that there is enough NAD+ available for the cell to continue to produce ATP via glycolysis under anaerobic conditions
Lactate dehydrogenase reaction:
Pyruvate + NADH + H+ ↔ L-lactate + NAD+
∆G˚’ = -25.1 kJ/mol
Lactate is then excreted
Fermentation rxn: a biochemical reaction that extracts energy from carbohydrates without using oxygen
What are the 10 steps fo glycolysis?
Energy Investment phase:
1. Phosphorylation (Hexokinase)
2. Isomerization (Glucose-6-phosphate isomerase)
3. Phosphorylation (phosphofructokinase)
4. Cleavage (aldolase)
5. Isomerization (Triose phosphate isomerase)
Energy Generation phase:
6. Oxidation and phosphorylation (Glyceraldehyde-3-phosphate dehydrogenase)
7. Substrate-level phosphorylation (phosphoglycerate kinase)
8. Isomerization (phosphoglycerate mutase)
9. Dehydration
10. Substrate-level phosphorylation (pyruvate kinase)
End with 2 pyruvates
What occurs in step 1 of Glycolysis?
Step 1 = Phosphorylation by Hexokinase
Glucose → (Hexokinase) → G6P
Uses 1 ATP to phosphorylate the 6th carbon of glucose → traps glucose inside the cell (glucose enters by selective transporter)
*Hexokinase has very high affinity (low Kd) so will phosphorylate very low amounts of glucose coming in.
- Also has sites for both reactions
*Needs to be coupled with ATP hydrolysis, just glucose + phosphate in the test-tube → no reaction
What occurs in step 3 of glycolysis?
Step 3 = Phosphorylation by Phosphofrutokinase
F6P → (Phosphofrutokinase) → FBP
Use 1 ATP molecule to phosphorylate 1st Carbon (double phosphorylated in 1th and 6th positions)
What occurs in steps 4 & 5 of Glycolysis?
4 - Cleavage (Aldolase)
5 - Isomerization (Triose phosphate isomerase)
Splits Fructose-1,6-Biphosphate (FBP) into 2x Glyceraldehyde-3-phosphate (GAP)
DHAP and GAP are in equilibrium → as soon as DHAP is made → directly goes to GAP
*GAP = 3C, 1x phosphorylated
What occurs in the 6th step of Glycolysis?
Oxidation and phosphorylation (Glyceraldehyde-3-phosphate-dehydrogenase)
GAP → (GAPDH) → 1,3-BPG
2 GAP (3-phosphate) + 2 Pi + 2 NAD+ → 2 BPG (1,3-phosphate) + 2 NADH
∆G > 0, BPG = 1st molecule with high phosphorylation transfer potential
What occurs in the 7th step of Glycolysis?
Step 7 = Substrate-level phosphorylation (phosphoglycerate kinase)
BPG + ADP → (PGK) → 3PG + ATP
(produced 1 ATP/BPG → 2 ATP/glucose)
How are steps 6 and 7 of glycolysis thermodynamically coupled?
Step 6 (making BPG) has ∆G > 0 so need to be driven by step 7 (making ATP)
Step 6 = + 6.3 kJ/mol
Step 7 = -17.2 kJ/mol
Step 6 + 7 = -10.9 kJ/mol → favourable
What occurs in the 9th step of glycolysis?
Step 9 = Dehydration (Enolase)
2PG (2-phosphate-glycerate) → (Enolase) → 2 PEP (phosphoenol-pyruvate) + 2 H2O
Step with the lowest ∆G → can be coupled withh step 10 which produced ATP
What occurs in the 10th step of glycolysis?
Step 10 = Substrate-level phosphorylation (pyruvate kinase)
PEP + ADP → (Pyruvate kinase) → Pyruvate + ATP
*Pyruvate kinase doesn’t phosphorylate PEP as the name would suggest
What are the main energy driving steps of Glycolysis?
RATE CONTROLLING STEPS/REACTIONS
Step 1: Glucose → (HK) → G6P
Step 3: F6P → (PFK) → FBP
Step 10: PEP → (PK) → pyr
What proportion of glucose energy is captured in ATP by glycolysis?
∆G˚’ of glucose oxidation = -2,870 kJ/mol
∆G˚’ of ATP hydrolysis = -64.4 kJ/mol (2x -32.2)
64.4/2,870 = 2%
How is Hexokinase regulated?
Product inhibition → negative feedback inhibition by G6P onto HK
How is phosphofructokinase activity regulated?
PFK is regulated by adenylate charges
F6P → FBP (phosphofructokinase):
- activated by F2,6BP, AMP, ADP
- Inhibited by ATP (bc ATP is required for phosphorylation), Citrate
FBP → F6P:
- inhibited by F2,6BP, AMP
A) PFK has 2 ATP binding sites:
1st site has high affinity for ATP → active site
2nd site has low affinity for ATP → allosteric regulator site, binds only when very high ATP levels and inhibits activity
B) F6P ↔ (PFK-2/FBPase-2) ↔ F2,6BP
- PFK-2 has kinase domain (uses ATP) + phosphatase domain (uses H2O)
What are the active sites of PFK?
Step 3: F6P → (PFK) → FBP
PKF has active sites for Mg-ADP and for F6P
Which enzymes are responsible for reverse of glycolysis in the 3 energy driving steps?
Inverse = Gluconeogenesis
Pyruvate → (Pyruvate carboxylase + PEPCK) → PEP
FBP → (FBPase) → F6P
G6P → (Glucose-6-phosphatase) → Glucose
How is the last step of glycolysis regulated?
Regulation of Pyruvate Kinase
PEP → (PK) → Pyruvate:
- Activated by F1,6BP (feedforward activation)
- Inhibited by ATP, Acetyl-CoA, Alanine
Pyruvate → (PEPCK + PC) → PEP:
- Activated by accumulation of Acetyl-CoA
