Regulation Of Glycolysis Flashcards
Describe glucose
Glucose is polar and tiny.
It’s happy in the blood.
Where does glucose go if it can’t get into the cell?
If the glucose does not get into cells, it’ll go to the kidney. This isn’t good because it’s too big. You don’t want glucose in your urine.
Where does glycolysis take place?
Glycolysis takes place within the cytoplasm, immediately inside the cell
What happens when glucose approaches the outside of a cell?
Glucose will approach the membrane, get through the outside but repelled through the non-polar environment!
What does glucose need to enter the cell? And why can’t it go in by itself?
GLUT 1 - glucose transport proteins. These are tunnels to provide an opening for the size or glucose that is polar to pass through the membrane
GLUT moves to the cell surface
What happens to glucose when it’s in the cytosol?
Which enzyme acts on it?
Turns it into?
In the cytosol hexokinase acts on glucose and adds a phosphate (phosphorylates it) and turns it into G6P and now it has a negative charge
Describe the entry/exit for the GLUT transport protein
Entry and exit of the GLUT transport proteins contain many E amino acids — negatively charged glutamic acid.
GLUT is a 2-way tunnel.
Structure of GLUT tunnels
GLUT tunnels are primarily alpha helices
What happens when glucose enters the cell?
Glutamic acid at the entry and exit is negatively charged
Glucose is phosphorylated inside the cell, which is negatively charged
This means it can’t get out because negative and negative repel!
G6P is trapped!
This means the tunnel is still open for more glucose to come in and keep the G6P inside.
How is glucose phosphorylated?
if there is no hexokinase in the cell, glucose won’t get phosphorylated, so it can leave
Hexokinase is regulated
Don’t make hexokinase if we don’t want glucose in the cell
What do kinases do?
A kinase will put a phosphate on a molecule — the source is ATP
kinase uses ATP to phosphorylate
What needs to be in the active site of hexokinase in order to make G6P?
Can’t make G6P unless glucose is in the active site of hexokinase.
Talk about ADP and ATP
ATP turns into ADP + Pi
ADP is a lot more stable than ATP.
That third phosphate on ATP will come off if it slams into another molecule
Describe the reaction of glucose to G6P
Glucose to G6P reaction is not favourable — but the reaction of ATP to ADP + Pi is favourable and that helps offset reaction 1 (glucose to G6P)
Energy in G6P
G6P is less stable than glucose after ATP gave it a phosphate. There is potential energy stored in that G6P molecule
What is happening in steps 7 and 10 of glycolysis?
In steps 7 & 10 of glycolysis, we are making ATP.
The energy in 1,3 BPG and PEP have more energy contained in their phosphate than ADP so the phosphate pops off and we get ADP to ATP
Why are there so many steps in glycolysis
Energetics —
Regulation —
Which molecule uses ATP
Kinase (look for this)
First half generates ATP and the second half uses ATP
What sets these three enzymes apart?
They are irreversible reactions!!
These are the rate limiting steps. You can’t go back. They are regulatory points. Committed.
What do muscles need?
What do they do if they can’t get it?
ATP
When ATP is low, they can grab 2 ADPs and make ATP
AMP is byproduct
ADP + ADP >< ATP + AMP
When ADP levels go down, AMP goes up.
This is what muscles pay attention to, the ADP levels
What is feed forward stimulation?
F6BP will build up if pyruvate kinase isn’t activated
Pyruvate kinase is activated by fructose 6-bisphosphate
(Slide 12)
What can the liver do if glucose is high, but PFK isn’t keeping up?
Glucose is high
PFK is high but not keeping up
F26BP will complete with ATP and open the active site up (like AMP in the muscles). This is when F6P starts to build up and PFK can’t keep up, so it makes F26BP. It’s a kinase — adding a phosphate.
Slide 17
To reverse this, liver doesn’t have ATP to compete it out. So just turn this enzyme F26BP off/get rid of it by dephosphorylate and send it back to F6P. Need a phosphotase to do this. (Slide 18)
One protein can do this! PFK-2 has 2 enzyme active sites.
Describe what happens in the liver when glucose is high and PFK can’t keep up
Slide 21
Describe what happens in the liver when glucose is low and need to shut down PFK
Summarise glycolysis regulation during exercise
Summarise glycolysis regulation during rest
Summarise glycolysis regulation during rest
