Lecture #27 - Glycolysis Flashcards
Overview of glycolysis:
- Splitting of what and what does it turn into?
- Ubiquitous pathway - what does this mean?
- Which part of the cell does it occur in?
- Which cells is glucose essential for in animals? Why? (2 of them)
- In what two molecules is energy conserved?
- How can pyruvate be further metabolised? What is the actual end product of the entire oxidation?
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Organisation of glycolysis
- How many phases and what happens in each
- Why have the first phase?
- How many ATP in/out and how about NADH?
Energy investment phase:
-_______ of glucose and conversion to 2 molecules of ______-3-phosphate and ____ ATP are USED in these reactions
Energy pay off phase:
-Conversion of _______-3-phosphate to ______ and coupled formation of ___ ATP molecules
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Th energy investment phase of glycolysis (energy investment):
- In your own words, describe the 5 first steps of it
Okay, so glucose comes in and hexokinase (or glucokinase - it’s an isoenzyme) attaches a phosphate group onto glucose to turn it into G6P. But this is energetically unfavourable (+14kJ/mol) so hexokinase couples it with ATP (so overall G is -16).
Then G6P is rearranged into F6P and this has a small G of +1.6 but it still goes in the right direction (doesn’t go back even though reverse reaction is favourable) because it’s a small +G and can be overcome by the concentration gradient; G6P is in high concentration and F6P is in low concentration gradient because being taken away for the next step of glycolysis and this concentration gradient is large enough to drive the reaction forward
After this, phosphofructokinase adds a phosphate to the CH2OH group up the top and this is also coupled with ATP hydrolysis to get a -G of -14kJ/mol (adding a high energy phosphate will take energy)
-putting these two phosphate group on will help it split and also high energy bonds formed so breaking them will release heaps of energy and give out ATP = substrate level phosphorylation
Now, aldolase will do an aldol cleavage on the FBP and form DAHB and G3P which each have a phosphate on them. G3P can carry on but DAHB can’t. DAHB needs to be converted to G3P and because these two are in equilibrium, since we’re taking G3P away, the equilibrium will lie to the right and the enzyme (trios phosphate isomerase) will convert DAHB to G3P and yeah.
Substrate level phosphorylation - what is it? In your own words
This is where the energy is coming from reaction to other products to couple and make ADP —> ATP. We’re using the energy of the reaction of other products to make ATP - the phosphate can come from the reactant or elsewhere.
Oxidation of G3P (after formation of the 2 G3Ps):
- What is it oxidised to?
- What is the co-enzyme?
- Does this require ATP? Where does the energy come from?
- So on each molecule, how many high ene bonds now? So how does this relate to the ATP formed at the end?
- Oxidised to 1,3-BPG
- NAD+ provides the oxidising power so itself becomes reduced
- No - energy from oxidation being used to add another phosphate. And energy is also captured by NADH which goes to oxidative phosphorylation
- 4 high energy bonds (2 on each G3P) and this is how we get 4 ATP formed in the end (net gain of 2)
Generation of 1st ATP (substrate level phosphorylation)L
- Which carbon with phosphate on 1,3-BPG is very reactive?
- What is the removal of this phosphate group used for and why?
- What happens to the phosphate?
- What makes a SLP?
- Which enzyme does this?
- Carbon #1 phosphate very reactive (has large -ve G so unstable and cleaved)
- Removal of phosphate releases energy that is used for SLP - makes ADP to ATP. It’s large -ve G + the +30 makes -19.3kJ/mol so coupled and make ATP
- The phosphate transfers from 1,3-BPG to ADP to make ATP
- This isn’t SLP because the phosphate it coming from the reactant but rather because you’re directly coupling the reaction of cleavage of the phosphate to the formation of ATP
- Phosphoglycerate kinase
Get 3-PG after
Arsenic poisoning:
- What does arsenic substitute?
- What is the resulting compound and As is _____
- Is ATP synthesised by phosphoglycerate kinase?
- In your own words explain what happens
So As substitutes for phosphate and this compound is unstable and hydrolyses. But can’t capture energy at SLP and this energy is lost as heat - glycolysis can continue but passed crucial step so you spend 2 ATP and get 2 ATP
After 1st ATP formed, what happens?
Rearrangement from 3-PG to PEP
Generation of 2nd ATP (SLP)
Describe what happens
Here we are turning from PEP to pyruvate and it’s done by pyruvate kinase (kinases usually phosphorylate but here it does the opposite - they didn’t bother to change the name after the discovered the truth)
The phosphate again comes from the reactant (PEP) to add to ADP to make ATP but what makes it SLP is the fact that ene from leaving that bond (between O and PO3 2-) is being used to phosphorylate ADP to make ATP
Couple the large -G of cleaving to the +30 of ADP to ATP
What is the overall reaction for glycolysis - 4 reactants and 4 products
What is the overall G and how does it help whole pathway?
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Fates of pyruvate
What if it’s aerobic conditions?
- what does it get converted to and why?
- where does this conversion occur?
- what is required? (several….)
- what is the reaction called and why? (3)
- what is the G?
- what is formed (____ ene bond)
What if it’s anaerobic conditions?
- what happens? (O2 lacking so…)
- what does pyruvate form?
- explain this
- what about aerobic
Okay so the last “explain this”
You make lactate from pyruvate because no point in trying to make acetyl CoA since won’t be able to do anything without the O2. So make lactate and in the process, you oxidise NADH to NAD+ (coenzyme & dehydrogenase means redox?). Pyruvate gets reduced and coenzyme gets oxidised.
We do this because coenzymes exist in low concentrations in the cell and anaerobic metabolism allows the regeneration of NAD+
-if don’t regenerate then nothing to provide oxidising power so glycolysis would shut down
With aerobic
-you still regenerate NAD+ via oxidative phosphorylation to feedback into glycolysis and continue the whole process. Fermentation also allows to regernate NAD+
