Biochem week 8 - respectfully send help

Delta G

gibbs free energy - Energy within a system that is released in a reaction. occurs if negative change in temperature and high entropy therefore negative delta G

Entropy and enthalpy

a process is favoured if it creates an increase in chaos (high entropy) This causes a release of energy from the system. (enthalpy) (drop in temperature from the system) this is also favourable.

Gibbs free energy and equilibrium

equilibrium exists at point of lowest gibbs free energy. Biochemical reactions are held away from equilibrium so that the creation of substrates will occur as they are energetically favourable. metabolism pushes away from equilibrium so it can be reached again

ATP and equilibrium

ATP is relatively stable away from equilibrium, with more ATP than ADP causing it to be very far from equilibrium. therefore has a very negative delta g when reacting. Coupling reactions to ATP hydrolysis provides large amounts of energy release from the system therefore making the reaction energetically favourable.

Exergonic

a chemical reaction where the change in the free energy is negative

Endergonic

Endergonic reactions do not proceed spontaneously and require an input of energy

glycolysis

takes place in cytosol, produces 4 ATP, net gain 2ATP. Takes ATP ←> ADP reaction away from equilibrium. Also produce NADH, pyruvate for TCA cycle, connect energy supply and storage with other metabolism e.g. amino acid synthesis

Destabilisation of glucose

1: 2 ATP + Stable glucose = destabilise. 2: breakdown 6 carbon unit to 2 3 carbon units, 3: ATP generatopm

Trapping glucose

(almost) Irreversible phosphorylation reactions. glucose + ATP → glucose 6 phosphate. fructose 6 phosphate → fructose 1,6 phosphate

hexokinase

catalyses glucose → Glucose 6 phosphate. Does this by dissolving and burying substrate in active site so they are no longer surrounded by non polar water but instead polar amino acids. When ATP is hydrolysed the phosphate cannot go to water so is transferred to carbon on glucose. Adding a phosphate moves it out of equilibria of glucose trapping it in the cell.

Isomerisation of Glc-6-p to Frc-6-P

Phosphoglucose isomerarase catalyses the opening and restructuring of the ring with an aldose ketose exchange so that 1 carbon molecule sticks out either side of the oxygen on position 1. Amino acids interact to overcome energy barriers.

second phosphorylation of fructose 6-P to fructose 1,6-bisphosphate

catalysed by phosphofructokinase. ATP to make the reaction irreversible. product is unstable

breakdown to 3C units

Aldolase cleaves frc 1,6 bp into dihydroxyacetone-p and glyceraldehyde. triose p isomerase converts dihydroxyacetone to glyceraldehyde.

Triose p isomerase

equilibrium favours DHAP so conversion is not energetically favourable. fast removal of the product shifts the position in equilibrium so the reaction is more energetically possible

oxidation of glyceraldehyde 3-p

GA3-P dehydrogenase enzyme

GAP + inorganic phosphate → unstable 1,3 BPG by coupling it to energetically favourable oxidation of GAP to reduce NAD so it can form NADH

C-H bond on GAP breaks. electrons go to NAD to form NADH. Pi uses the free energy to bind to GAP

Cysteine sidechain S in active site forms thioester bond unstable intermediate with phosphate preventing free energy drop. therefore energetically possible to form acyl phosphate

13bisphosphoglycerate → ATP

1,3BPG +ADP + H+ → 3, phosphoglycerate + ATP. Phosphoglycerate mutase moves phosphate from 3 → 2 position so less stable. Enolase remove H2O → unstable phosphenolpyruvate. then easy for pyruvate kinase to phosphorylate ADP + pyruvate (enol form). In solute pyruvate → normal pyruvate distorting enzyme storing energy for ATP to drive phosphorylation. See summary on slides at the end of the day.