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 happens after glycolysis?
After glycolysis :
If oxygen is present, will use the NADH as an electron transporter and further oxidation
If oxygen is not present, I need to generate NAD+
— Yeast will produce ethanol and NAD+ as byproduct)
— can produce lactate and make NAD+ from NADH
Major regulatory enzyme in glycolysis
Phosphofructokinase
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.
Where is glycolysis regulated?
Muscles
Liver
What is the trigger from the muscles to speed up glycolysis?
AMP levels building up
How do muscles know they need energy?
What will they do?
What is produced?
When ATP levels are low
Your muscles will use two ADPs to make ATP
ADP + ADP >< ATP + AMP
AMP will build up
AMP is the trigger to speed up glycolysis
Glycolysis won’t run when ATP levels are…..
We don’t run glycolysis when ATP levels are high.
Three main regulatory enzymes
Hexokinase
PFK
Pyruvate kinase
One direction reactions
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
In terms of ATP, when do we switch glycolysis off?
When energy needs are met (high ATP) — turn OFF glycolysis
When levels of …… are …. glycolysis is turned ON
When AMP is high — turn ON glycolysis because muscles need energy
Describe the two sites on PFK
Active site
Allosteric site
What binds here?
PFK has an active site for the substrate Fructose 6-phosphate + ATP = Fructose 6-bisphosphate
It also has an allosteric site: has affinity (can bind) for ATP and AMP and it’ll impact the function of this protein.
How do you know which it’ll bind? It depends on if we need energy or not:
ATP is the inhibitor if we have enough ATP. It blocks the active site when it binds to the allosteric site.
AMP is the activator because we need ATP. AMP kicks out the ATP.
Remember ADP + ADP > ATP + AMP
This is non-competitive inhibition
When ATP levels are low, what are AMP levels? Is PFK1 active or inactive?
ATP levels are low
AMP are high
PFK1 needs to be active
When ATP levels are high, what are AMP levels? Is PFK1 active or inactive?
ATP levels are high
AMP levels are low
PFK1 is inactive
What happens to hexokinase if there is excess G6P?
What does glucose do?
What happens to G6P?
Excess G6P shuts down hexokinase to stop bringing in the glucose.
Remember if glucose enters a cell and there is no hexokinase, it’ll head back out again.
G6P can be stored as glycogen
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)
Liver cares about what?
Liver cares about glucose.
It doesn’t care about energy (ATP) levels
Any glucose left over after used by brain/muscles will go to the liver.
Glucose needs to avoid the kidneys — cannot process here — too big!!
What happens in the liver if glucose is high?
If glucose is high — activate glycolysis — to break it down!
Controlled by insulin — hormone signal saying “glucose levels high”
What does the liver do when glucose is low?
Glucose is too low — stop glycolysis — don’t want to break any more down. Will send any remaining sugar to the brain.
Liver needs to synthesise:
1. Pull it from glycogen (glucagon) (storage)
2. Or from gluconeogensis (make it from scratch)
Why doesn’t the liver have AMP? And the muscles do?
Muscles have AMP because when they desperately need ATP they’ll use two ADPs to make ATP and AMP
Liver doesn’t make ATP !
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
Signal transduction
Look at the drawing of hormones and GPCR + audio
Lecture in week 9 picked up from slide 5 “sources of glucose”
Reference slide
