Glycolysis And Control Flashcards
What is glycolysis and what is the pathway called
Splitting of glucose into pyruvate x 2
The EMBDEN MAYERHOF PARNAS PATHWAY
Why is glycolysis important
Only source of energy in anaerobic respiration
Name the 3 stages of glycolysis
Investment
Splitting
Energy yield
How many ATP molecules are used / hydrolysed in investment and how many gained
2
4 are gained
What first happens to glucose and which enzyme is involved
Glucose is phosphorylated
Glucose 6 phosphate produced
Hexokinase enzyme uses atp hydrolysis to phosphorylate glucose
Why is it important for cells that glucose is phosphorylated
Phosphate is negatively charged which stops glucose leaking out of cells as much
What ion does hexokinase need and also any other enzyme to phosphorylate glucose etc
Mg++
Needed to stop the other 2 phosphates being hydrolysed (only 1 phosphate added)
Why is hexokinase better than glucokinase in phosphorylation of molecules like glucose
Because gluco kinase has a higher KM which means lower affinity to the molecules than hexokinase
Which carbon is phopshorylated on glucose by hexokinase atp hydrolysis
6 C
Forms CH2OPO3-
What happens to glucose 6 phosphate when produced by hexokinase
Isomerisation (change in structure)
Into fructose 6 phosphate
Explain the steps of how aldose sugar glucose 6 P turns into a ketose sugar fructose 6 P
The ring opens to form an exposed aldehyde group ( h c=o h)
This isn’t stable so forms an internal ester with C2OH
This forms a ketone
Then the C2 double O forms internal bond with another O
The ring closes to form a furanose 5C sugar
= fructose 6 phosphate (6c is phosphorylated)
What happens to fructose 1 phosphate (5c ring) after isomerisation
Phospho fructo kinase will phosphorylate C1 aswell as C6 (using atp hydrolysis and mg++)
Forms a fructose 1, 6 bisphosphate
Why does fructose 1 6 bisphosphate split into 2 x 3c molecules instead of being a furanose 5c ring
Because of the symmetry and the 2 negative charges on phosphates cause repulsion
What happens in splitting (include the 2 enzymes involved)
Fructose 1 6 bisphosphate (6c) is split into Dihydroxyacetone phosphate (x2)
BY ALDOSE ENZYME
this then converts to glyceraldahyde 3 phosphate (x2) 3C
This is done using triose phosphate isomerase
Which enzyme converts dihydroxyacetone phosphate 3C into glyceraldahyde 3 phosphate
Triose phosphate isomerase
What is the gain of ATP in the energy yield stage of glycolysis
2 for each glyceraldahyde 3 phosphate (x2) = 4
What is the first step in energy yield converting glyceraldahyde 3 phosphate
Glucose 3 phosphate dehydrogenase Enzyme
Allows conversion of NAD to NADH which oxidises(H removed from G3p)
G3p also gains a free phosphate to form
1,3 bisphosphoglycerate
Where are the phosphates located on 1,3 bisphoshoglycerate converted from G3P
C1 and C3
What is 1,3 bisphosphoglycerate converted to and how
3 phoshpoglycerate
Converted by removing a phosphate which binds to ADP to form a new ATP molecules (substrate level phosphorylation)
Which enzyme dephosphorylates 1,3 bisphosglycerate to form a new ATP molecule
Phosphoglycerate kinase
How does 3 phosphoglycerate turn into 2 phosphoglycerate
Phosphoglycerate mutase converts the PO group from C3 to C2 (central C)
What happens to 2 phosphoglycerate produced by phosphoglycerate mutase enzyme
It is converted to phosphoenolpyruvate
H2O is removed from it by enolase enzyme
Why is h20 removed from 2 phosphoglycerate
Increases energy production by adding another double bond
Which enzyme dephosphorylates phosphoenolpyruvate to produce ATP and pyruvate
Pyruvate kinase
How many substrate level phosphorylation are there in glycolysis
4
Why is controlling glycolysis important
To link supple of atp with demand or if needed for storage
To allow cells to respond to the environment
Which type of enzymes are used to control catabolic reactions
Rate limiting enzymes (slow rate of reactions)
How do you limit rate of enzymes (4 ways)
1- control amount of enzyme
2- allosteric inactivation of the enzyme
3- covalent modification via kinase or phosphatase
4- controlling enzymes access to substrate
How is enzyme access to substrate limited
Via compartmentalisation
Either substrate or enzyme stick to one area
Which 3 enzymes are controlled in glycolysis
Hexokinase
Phosphofructo kinase
Pyruvate kinase
How is hexokinase inactivated when too much Glucose 6 phosphate is present
Allosterically inactivated via negative feedback
Why is glucose 6 phosphate important
Because it is used as a glycogen store important for muscles etc
What allows phosphofructokinase activity (turning fructose 1 phosphate into fructose 1,6 bisphosphate)
Low ATP/energy levels
Adenylate cyclase production of AMP activates the phosphofructokinase
Which 3 things in too much presence stops phosphofructokinase
ATP (not needed anymore)
Low ph indicating too much lactate produced by pyruvate
Citrate increase in the Krebs cycle
How is pyruvate kinase action increased (phosphoenolpyruvate into pyruvate)
The accumulation of fructose 1 6 bisphosphate in the investment stage of glycolysis causes activation of pyruvate kinase
How does fructose 2 6 bisphosphate presence allow for activation of phosphofructokinase
It decrease PFK affinity for atp and citrate which decrease its activity
