Glycolysis and glucose oxidation Flashcards
describe what excessive glucose is
hyperglycaemic – too much can lead to damage as glucose is reactive and can react with things
describe what too little glucose is
hypoglycaemic – don’t have enough energy to function
- Glucose can be stored in limited quantities as glycogen
how much of the brain uses glucose
- At present the brain is using 60% of blood glucose
how many grams of glucose is circulating
- Current have 4g of glucose circulating
glucose is a
6 carbon sugar
how is glucose taken into cells
- by facilitated transport across the membrane
- GLUT transporters
what does GLUT 1 do
constitiuvie glucose transporter (low Km) found in all cells
why does GLUT 1 have a low Km
low Km – refers to the concentration at which something gets saturated, a low Km means it saturates at a low concentration, ,this means you can only transport a low amount of glucose
what does Glut 2
liver/pancreas uptake (high Km)can act as a glucose sensor in the liver and pancreas
why does Glut 2 have a high Km
High Km this is found in the pancreas where it is involved in allowing the pancreas to sense blood glucose, this means that it cannot get saturated so it can sense a high range of glucose concentrations
what does Glut 4 do
glucose uptake in muscle and adipose (low Km) cellular location is controlled by insulin
what are the two locations that Glut 4 exist
exists as vesicles inside cytoplasm or exists by fusing with the membrane via insulin action
describe how Glut 4 controls how much glucose the cell takes up
- exists as vesicles inside cytoplasm or exists by fusing with the membrane via insulin action
- By changing where it is in the cell membrane or vesicles controls the amount of glucose the cell takes up
- These allow you to control whether a cell is taking up glucose or not
- When glucose concentration is high promotes adipose and muscle to take up glucose
what is the amount of Glut 4 in muscle membrane effected by
by exercise – they what to take up more glucose to get that energy
describe the mechanism of action of hexokinase and how it works
- Hexokinase takes an phosphate from ATP and puts it on glucose making glucose 6 phosphate
- GLUT cannot transport phosphorylated glucose so once the glucose is phosphorylated it cannot leave the cell
- If you don’t use up the glucose then you stop phosphorylating it
- Sensitive to feedback inhibition
- It is the investing energy in the system
what is the difference between hexokinase and glucokianse
- The difference between hexokinase and glucokinase is that glucokinase has an higher Km
describe glucokinase and its mechanism of action
- This is found in the liver and pancreas
- Higher Km and also specificity for glucose
- Not sensitive to feedback inhibition
- In pancreas the beta cells act as a sensory location controlled by GKRP
- Does the same reaction as hexokinase
how is gluckinase activated and inactivated
- When levels of glucose in the blood is low glucoskinase is bound to GKRP in the nucleus of the cell therefore it is inactive
- When sugar rises glucokinase is released into the cytoplasm and can form its action in glycolysis
descirbe the isomerisation step in glycolysis
- Rearranging the molecule to rearrange the energy
- Move from glucose to fructose – make further steps (e.g. moving to 3 carbons) chemically easier
- Glucose 6 phosphate is converted to fructose 6 phosphate
- This reaction is reversible
describe the phosplhofructokianse step in glycosides
- Highly controlled step
- Takes the phosphate of ATP and add it to fructose 6 phosphate to produce fructose – 1,6 – bisphosphate
what activates and inhibits phosphofurctokinase - 1
- high levels of ATP inhibit - this is because the cell no longer needs energy as there is a high concentration of ATP
- high levels of cirtirate inhibit as well for the same regions
- low for both what activate it
- high levels of fructose-2,6- bisphosphate cause activation
what is the action of phosphofructosekinase 2
- Fructose 2,6-bisphopshate is produced by the enzyme phosphofructokinase-2
- This activates phosphofructokinase 1
- When fructose -2,6 bisphosphate is high this means that phosphofructokinase 1 is high
how is fructose-1.6-bisphosphate converted from a 6 carbon product to 3 carbon
- Cleavage of fructose-1,6- bisphosphate, produces two 3 carbon products
- Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate
- Interconversion to form a single product of by glyceraldehyde-3-phosphate triose phosphate isomerase, therefore all the dihydroxyacetone phosphate is converted to glyceraldehyde-3-phosphate
- This is also a feed point for glycerol
describe how substrate level phosphorylation happen
- Up until this point glycolysis is a net user or ATP
- First ATP production comes from free phosphate in the cell
- This happens when 1,3-bisphosphoglycerate to 3-phsophoglycerate
- Enzyme is phosphoglycerate kinase (PGK) takes phosphate from 1,3-bisphosphoglycerate and attaches it to ADP making ATP
- Then further ATP production happens when 3-phosphoglycerate is converted to pyruvate this results in 2 molecules of ATP net production this is catalysed by pyruvate kinase
- This is driven via an unstable enol
what is NAD
an electron carrier
when is NAD produced
- It is produced when glyceraldehyde 3-phosphate is converted to 1.3-bisphosphglycerate via glyceraldehyde-3-phsophate dehydrogenase
- pyruvate is converted to lactate by lactate dehydrogenase in anaerobic conditions
how is NADH changed back to NAD in order to except more electrons
- In aerobic conditions this is done by electron transport chain
- In anaerobic conditions or cells without mitochondria this is regenerated by forming lactate, lactate is acidic and reduced pH, pyruvate is converted to lactate by lactate dehydrogenase
describe how glycerol enters the glycolysis pathway
- Metabolised into the liver to form di-hydroxy acetone phosphate
- Glycerol is converted to glycerol 3 phosphate via glycerol kinase which converts ATP to ADP, this is then converted to dihydroxyacetone phosphate by converting NAD to NADH
- This then is converted to GALP and goes down the rest of the glycolysis cycle
- Occurs in the liver as this is where the majority of fat metabolism occurs
- Net output is 1 ATP
describe how fructose can enter the glycolysis pathway
- This can be metabolised by hexokinase and form fructose-6 phopshate from here it continues in the normal glycolysis cycle
- Fructose is converted to fructose -1-phosphate this is done by fructokinase which causes ATP to be converted to ADP, then fructose-1-phosphate is converted to dihydroxyacetone phosphate and glyceraldehyde which is converted into glyceraldehyde 3 phosphate by aldolase B, it then completes the rest of glycolysis - this happens in the liver
- the net output is 2 ATP
- Fructose is converted to fructose -1-phosphate this is done by fructokinase which causes ATP to be converted to ADP, then fructose-1-phosphate is converted to dihydroxyacetone phosphate and glyceraldehyde which is converted into glyceraldehyde 3 phosphate by aldolase B, it then completes the rest of glycolysis - this happens in the liver
describe how pentose phosphate enters the glycolysis cycle
- An alternative pathway from glucose-6 phosphate
- Pathway is important for providing substrates for biosynthesis – this is for making things, it produced NADPH which is required for fat and steroid hormone synthesis as well as having a role in nucleotide biosynthesis
- Products of this pathway can be fed back into glycolysis as fructose-6-phospahte and glyceraldehyde-3-phosphate at two different points in the glycolysis cycle
