Glycolysis Flashcards
What is gain of electrons called?
Reduction
What is loss of electrons called?
Oxidation
What bonds in ATP provide cellular energy?
High-energy phosphate bonds between 2nd and 3rd phosphates only (not bond between phosphate and sugar!)
Where does glycolysis take place?
Cytoplasm
What is standard free energy?
ΔGo - the free energy that is released when reactants are at a standard state concentration (1M) and are allowed to come to equilibrium
What will happen in a reaction if ΔG < 0?
Reaction will proceed forward
What will happen in a reaction if ΔG > 0?
Reaction will go backwards
What will happen in a reaction if ΔG = 0?
Reaction will stay at equilibrium - no change
D-Glucose –> Glucose 6-phosphate
(Step 1)
What enzyme? What is significant? Significant products?
Glucokinase - in liver and pancreas
Hexokinase - in muscle
Exergonic reaction - highly favorable, regulated step
Lose ONE ATP
Glucose 6-phosphate –> Fructose 6-phosphate
(Step 2)
What enzyme? What is significant? Significant products?
Phosphoglucose Isomerase
Isomerization - very little change
Fructose 6-phosphate –> Fructose 1,6-biphosphate (Step 3)
What enzyme? What is significant? Significant products?
PFK - phosphofructose kinase
Highly regulated by metabolites/hormones
Lose ONE ATP
What kinds of signals inhibit PFK?
ATP-like signals (like citrate)
What kinds of signals stimulate PFK?
AMP-like signals (like fructose 2,6-bisphosphate or F2,6-BP)
Fructose 1,6-biphosphate –> Dihydroxyacetone phosphate –> Glyceraldehyde 3-phosphate
(Step 4)
What enzyme? What is significant? Significant products?
Fructose bisphosphate aldolase and Triosephosphate isomerase
Isomerization step - little change
Glyceraldehyde 3-phosphate –> 1,3-bisphosphoglycerate
(Step 5)
What enzyme? What is significant? Significant products?
(GAPDH) Glyceraldehyde phosphate dehydrogenase
Creates high-energy phosphate bond by replacing high-energy thioester bond and using Mg2+ cofactor
Creates TWO NADH
1,3-bisphosphoglycerate –> 3-phosphoglycerate
(Step 6)
What enzyme? What is significant? Significant products?
PGK (3-phosphoglycerate kinase)
Uses Mg2+ cofactor
Creates TWO ATP
Phosphoenol pyruvate (PEP) --> Pyruvate (last step)
What enzyme? What is significant? Significant products?
Pyruvate Kinase
Last, irreversible step of glycolysis
Creates TWO ATP
What are the functions of skeletal muscle?
Provide normal mvt, respond to stress w/ continued work output, adapt to short periods of anaerobic work
What is skeletal muscle’s metabolic role?
Generate ATP to drive muscle contraction, store food locally for immediate need, take metabolic precursors from other organs, serve as storage site for proteins
What is function of liver?
Regulates blood glucose, (absorbs excess glucose in fed state, makes glucose during fasted state), Responds metabolically to higher level hormonal control
What is liver’s metabolic role?
Store glucose as glycogen, convert excess energy to fat, convert and break down metabolites
What are the stimulatory and inhibitory signals in energy generation?
Stimulatory - low-energy AMP- like signals
Inhibitory - high-energy, ATP-like signals
What are the stimulatory and inhibitory signals in food storage?
Activators - ATP-like
Inhibitors - AMP-like
High levels of what molecule indicate that glycolysis is backed up? Why?
Glucose 6-phosphate - this molecule normally serves as feedback inhibition for hexokinase or glucokinase
What does hexokinase’s low Km say about its function?
It will be saturated at normal glucose levels in blood so muscles can get glucose regularly
What does glucokinase’s high Km say about its function?
Since it is in the liver, its job is to ensure blood glucose levels are regulated properly, thus it will only be saturated when blood glucose levels are very high
Describe hormonal regulation of PFK in liver.
1) High insulin/glucagon ratio causes decreased cAMP and reduced levels of protein kinase A.
2) Decreased protein kinase A favors dephosphorylation of PFK-2/FBP-2.
3) Dephosphorylated PFK-2 is active, whereas FBP-2 is inactive so fructose 2,6-bisphosphate forms.
4) Elevated fructose 2,6-bisphosphate activates PFK-1 which increases rate of glycolysis.
Describe hormonal regulation of PFK in skeletal muscle.
1) Epinephrine binds Beta-adrenergic receptor which causes decreased cAMP and protein kinase A levels.
2) Decreased protein kinase A favors dephosphorylation of PFK-2/FBP-2 at a different site, forming a distinct isoform of PFK-2 that does not lead to its deactivation.
3) Fructose 2,6-bisphosphate forms.
4) Elevated fructose 2,6-bisphosphate activates PFK-1 which increases rate of glycolysis.
What is the Cori Cycle?
Exercising muscles convert glucose to lactate. This lactate is taken up by the liver and reconverted to glucose using ATP (via gluconeogenesis). Glucose is released back into circulation
What are the four potential fates of pyruvate?
- Ethanol fermentation (anaerobic)
- TCA cycle (anaplerotic rxn, gluconeogenesis) - becomes oxaloacetate
- Anaerobic metabolism - becomes lactate
- TCA cycle (energy) - becomes Acetyl CoA
Which reaction of glycolysis is highly exergonic and favorable?
Glucose –> Glucose 6-phosphate (using hexokinase or glucokinase)
How is PFK regulated by F26BP?
F26BP is an AMP-like signal that activates PFK and inhibits F1,6-BPase, upregulating glycolysis.
What reaction can happen if someone lives at a high altitude? What enzymes are involved?
Mutase can convert 1-3 BPG to 2,3-BPG which binds to Hg and increases O2 off-loading to tissues. Phosphatase will get it back to 3-phosphoglycerate.
What are the net products of aerobic glycolysis?
2 NADH, 2 ATP, 2 pyruvate
How is pyruvate kinase regulated metabolically? Hormonally?
1) Metabolically: F 1,6-BP feed-forwards/activates PK
2) Hormonally: In liver, glucagon signaling increases CAMP levels, which increase PKA levels, which deactivates pyruvate kinase
What are the net products of anaerobic glycolysis?
2 ATP, 2 lactate
What enzyme is involved in anaerobic glycolysis?
Lactate dehydrogenase
What molecule is recycled in anaerobic glycolysis?
NADH
