Energy I: Metabolism, ATP and Glycolysis Flashcards
What is catabolism?
The breakdown of complex molecules to release energy or carry out mechanical work.
What is anabolism?
The synthesis of new molecules from less complex components.
Why is ATP essential?
ATP is central to a cell and therefore the body’s energy provision. It can act as both an acceptor and donator of energy and is a short term reservoir of energy.
How is ATP resynthesised?
Through oxidative phosphorylation in the mitochondria.
How do glycolysis work?
First Glucose is phosphorylated to give glucose 6 phosphate however this cannot pass through the membrane of the mitochondria so it turns into fructose-6-phosphate (this reaction requires ATP to be hydrolysed into ADP and Pi).
Fructose-6-phosphate phosphorylates into fructose 1,6, bisphosphate (this reaction requires ATP to be hydrolysed into ADP and Pi).
Further reactions occur where this breaks down into glyceraldehyde 3 phosphate and dihydroxyacetone phosphate.
These then react to form into phosphoenol pyruvate (this reaction requires NAD+ to reduce into NADH and ADP forms a unit of ATP).
Finally, phosphoenol pyruvate turns into pyruvate (this reaction requires ADP to turn into ATP).
From glycolysis, what are the total amounts of product formed from one molecule of Glucose?
2 Pyruvate
2 NADH
2 ATP
What regulates glycolysis?
Enzymes catalysing irreversible reactions are potential sites for regulation. Activity of such enzymes can be regulated by:
- Reversible binding of allosteric effectors- don’t change the enzyme, only it’s ability for it to react.
- Covalent modification- most common is phosphorylation
- Transcription
What are the three kinases that are used in glycolysis?
- Hexokinase: regulated by their product like most enzymes in a negative way, this is regulated by glucose-6-phosphate.
- Phosphofructokinase: most important kinase as this is regulated by many more things; ATP, citrate, H+ ions, fructose 2,6 bisphosphate and AMP.
- Pyruvate kinase: this is inhibited by high levels of ATP
What does AMP do?
AMP stimulates phosphofructokinase and is generated by the metabolism of ADP (with ADP being generated by ATP being hydrolysed).
What happens if there are high concentrations of ATP?
High levels of ATP will inhibit phosphofructokinase (PFK) by lowering the affinity for fructose 6 phosphate. It also becomes inhibited by low pH. The inhibition of PFK will cause the inhibition of hexokinase.
How is glycolysis regulated in the liver?
- Regulation in the liver is more complex. The liver has two enzymes that can phosphorylate glucose. It has hexokinase and glucokinase. This is an enzyme which has a high Kt. Only active when glucose concentrations are hgh and allows the liver to regulate blood glucose.
- Normally G6PP usually inhibits hexokinase but not glucokinase. G6PP can be generated in the liver where there is a lot of glucose present.
- The glucose and glucose 6 phosphate present is not for energy but for storage molecules primarily glycogen and fatty acids.
- High concentrations of ATP inhibit PFK, PFK is inhibited by citrate and is stimulated indirectly by a build-up of F6P.
What is a similarity between exercising tissue and tumours?
They both rely on anaerobic respiration.
What is needed for a cell to gain ATP?
In order for a cell to gain ATP, whether it be an exercising tissue or tumour, NAD is needed and cannot be a limiting factor. If glycolysis continues, it will mean that NAD will become used up and will become a limiting factor, creating NADH untill NAD runs out.
How does the body overcome the issue when NAD has used up all NAD and it has become a limiting factor?
It generates lactate which is generated at the expense of NADH. The NADH is metabolised to give back NAD. By generating lactate, we are producing NAD and thus NAD is not the limiting factor anymore.
This shows the importance of lactate for exercising muscles and tumours.
NOTE: Lactate is acidic- the H+ ions will inhibit glycolysis and will need to be taken to the liver for it to be broken down.
What are tumours?
Fast growth of cells. As it develops it recruits blood vessels from neighbouring tissues. Often, the tumour will grow faster than the vessels are able to supply blood, meaning that the tumour will not receive that amount of oxygen it needs so it switches to glycolytic/anaerobic processes. Tumour cells are not as sensitive to lactate as other cells.
