Bull section Flashcards
How many reactions take place in glycolysis?
10
What is the product of glycolysis for one glucose molecule?
2 pyruvate
What is the first step in glycolysis?
Glucose enters the cell
-phosphorylated by hexokinase to form glucose-6-phosphate
- step uses ATP
- irreversible
What is the second step in glycolysis?
Glucose-6-phosphate is converted to fructose-6-phosphate via the enzyme phosphoglucose isomerase
- isomerization reaction
What is the third step in glycolysis?
Fructose-6-P is phosphorylated to form fructose-1,6-bisphosphate by the enzyme phosphofructokinase (PFK)
- this step is irreversible
- this step uses ATP
What is the fourth step in glycolysis?
Cleavage of fructose-1,6-bisphosphate to two different 3 carbon molecules.
Cleaved by enzyme aldolase
- produces one dihydroxyacetone phosphate and one glyceraldehyde 3 phosphate
What is the 5th step in glycolysis?
The dihydroxyacetone phosphate produced in step four is converted to glyceraldehyde 3 phosphate by triose phosphate isomerase - resulting in TWO total glyceraldehyde 3 phosphate (one from step 4 one from step 5)
What is the 6th step in gylcolysis?
glyceraldehyde 3 phosphate is oxidized by glyceraldehyde 3 phosphate dehydrogenase to form 1,3-bisphosphoglycerate
What is the 7th step in glycolysis?
1,3-bisphosphoglycerate undergoes substrate level phosphorylation by the enzyme phosphoglycerate kinase to form 3-phosphoglycerate AND ATP
What is the 8th step in glycolysis?
3-phosphoglycerate is converted to 2-phosphpoglycerate by phosphoglycerate mutaseW
What is the 9th step in glycolysis?
2-phosphoglycerate is converted to phosphoenolpyruvate (PEP) by the enzyme enolase
What is the 10th step in glycolysis?
Phosphoenolpyruvate is converted to pyruvate via pyruvate kinase, generating ATP , this reaction is irreversible
Is pyruvate production from glycolysis a spontaneous reaction? what is the delta G for the net pathway?
Yes it is spontaneous in cellular conditions, deltaG is -22kcal/mol
What are the three fates of pyruvate?
Can be converted into ethanol, lactate or acetyl CoA depending on the cells needs
Why would pyruvate be converted into ethanol? What are the two steps in this process?
Happens anaerobically in some organisms, fermentation- NAD+ is regenerated in the second step of the conversion - loses a CO2
Pyruvate is converted into acetaldehyde via pyruvate decarboxylase
- Acetaldehyde is converted into ethanol via alcohol dehydrogenase
Why would pyruvate be converted into lactate? What is the step in this pathway?
NADH is used to reduce pyruvate to lactate, regenerating NAD+
Pyruvate is converted into lactate via lactate dehydrogenase
This reaction also occurs in muscles when oxygen supply is limited requiring the muscles to function anaerobically for a short period of time
What happens when lactate builds up in the muscle?
Lactate lowers the ph of muscle which inhibits PFK which is the main regulatory point of glycolysis - slowing the ability for muscle to metabolize glucose and fatigue sets in
Why would pyruvate be converted to Acetyl CoA? What is the step in this pathway?
Because this is the pathway where the most energy is obtained from pyruvate - NAD+ not directly regenerated but is in the TCA cycle
- Pyruvate is converted to acetyl coa via the pyruvate dehydrogenase complex
Where do galactose and fructose enter glycolysis?
Galactose enters as glucose 6-p
Fructose enters IN LIVER as dihydroxyacetone phosphate and glyceraldehyde 3 phosphate
Why can high fructose consumption lead to diabetes?
because fructose enters glycolysis via the liver it bypasses the main regulatory enzyme of glycolysis - PFK, so excess acetyl coa is synthesized and converted into fats
What are the three regulatory enzymes in glycolysis?
Hexokinase, PFK and pyruvate kinase
What is special about glycolysis in the muscle?
Muscle glycolysis provices ATP used for muscle contraction - highly controlled by the energy state of the cell - ATP:AMP ratio
- More ATP available inhibits glycolysis
- heavily regulated by PFK which is controlled allosterically - ATP is allosteric inhibitor and decreases PFKs ability to bind to fructose 6p
- a drop in ph also inhibits PFK
- hexokinase is inhibited by its product - glucose 6p
-pyruvate kinase is allsterically inhibited by ATP and ACTIVATED by fructose-1,6-bisphosphate
- why? because fructose16bisphosphate is the product of PFK, meaning a rise in fructose16bisphosphate means that the cell is getting ready to be more active and produce more ATP
Why isn’t hexokinase the control point in glycolysis?
because glucose 6-p can enter other pathways and not just glycolysis
What is special about glycolysis in the liver?
main function is different than that of muscle- liver is needed to maintain blood glucose levels in the blood stream - does not need to contract
- PFK is still main point of regulation - however it is not regulated by ATP and pH like in muscle - instead uses Citrate as a major inhibitor of PFK in liver (since citrate is formed from acetyl coa, which is a product of pyruvate metabolism means that high level of citrate = biosynthetic porecusors are suffiencent)
- PFK needs to be activated to handle rise in blood glucose after a meal - turns some fructose 6p into fructose 26bisphosphate which is an allosteric activator of PFK accelerating glycolysis after a meal
- instead of hexokinase, liver uses glucokinase which has a 50fold higher Km (can handle a higher load) - glucokinase is NOT inhibited by glucose 6p meaning the liver does not waste glucose
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What are the three non carbohydrate precursors for gluconeogenesis?
Lactate
amino acids
glycerol
When is gluconeogenesis important?
during periods of fasting to keep blood sugar levels high
Where does gluconeogenesis occur in animals?
only in liver and kidney, mainly liver
How is lactate used as a gluconeogenic precursor?
Because pyruvate can be converted into lactate and the reaction is reversible, most of the lactate winds up in the liver and is converted back to pyruvate via lactate dehydrogenase and can enter gluconeogenesis
Where does glycerol enter the gluconeogenic pathway?
is taken up by the liver and converted into dihydroxyacetone phosphate