Glycolysis and glucose oxidation

Question 1

describe what excessive glucose is

Answer 1

hyperglycaemic – too much can lead to damage as glucose is reactive and can react with things

Question 2

describe what too little glucose is

Answer 2

hypoglycaemic – don’t have enough energy to function

- Glucose can be stored in limited quantities as glycogen

Question 3

how much of the brain uses glucose

Answer 3

• At present the brain is using 60% of blood glucose

Question 4

how many grams of glucose is circulating

Answer 4

• Current have 4g of glucose circulating

Question 5

glucose is a

Answer 5

6 carbon sugar

Question 6

how is glucose taken into cells

Answer 6

• by facilitated transport across the membrane

- GLUT transporters

Question 7

what does GLUT 1 do

Answer 7

constitiuvie glucose transporter (low Km) found in all cells

Question 8

why does GLUT 1 have a low Km

Answer 8

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

Question 9

what does Glut 2

Answer 9

liver/pancreas uptake (high Km)can act as a glucose sensor in the liver and pancreas

Question 10

why does Glut 2 have a high Km

Answer 10

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

Question 11

what does Glut 4 do

Answer 11

glucose uptake in muscle and adipose (low Km) cellular location is controlled by insulin

Question 12

what are the two locations that Glut 4 exist

Answer 12

exists as vesicles inside cytoplasm or exists by fusing with the membrane via insulin action

Question 13

describe how Glut 4 controls how much glucose the cell takes up

Answer 13

• • 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

Question 14

what is the amount of Glut 4 in muscle membrane effected by

Answer 14

by exercise – they what to take up more glucose to get that energy

Question 15

describe the mechanism of action of hexokinase and how it works

Answer 15

• 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

Question 16

what is the difference between hexokinase and glucokianse

Answer 16

• The difference between hexokinase and glucokinase is that glucokinase has an higher Km

Question 17

describe glucokinase and its mechanism of action

Answer 17

• 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

Question 18

how is gluckinase activated and inactivated

Answer 18

• 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

Question 19

descirbe the isomerisation step in glycolysis

Answer 19

• 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

Question 20

describe the phosplhofructokianse step in glycosides

Answer 20

• Highly controlled step

- Takes the phosphate of ATP and add it to fructose 6 phosphate to produce fructose – 1,6 – bisphosphate

Question 21

what activates and inhibits phosphofurctokinase - 1

Answer 21

• 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

Question 22

what is the action of phosphofructosekinase 2

Answer 22

• 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

Question 23

how is fructose-1.6-bisphosphate converted from a 6 carbon product to 3 carbon

Answer 23

• 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

Question 24

describe how substrate level phosphorylation happen

Answer 24

• 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

Question 25

what is NAD

Answer 25

an electron carrier

Question 26

when is NAD produced

Answer 26

• 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

Question 27

how is NADH changed back to NAD in order to except more electrons

Answer 27

• 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

Question 28

describe how glycerol enters the glycolysis pathway

Answer 28

• 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

Question 29

describe how fructose can enter the glycolysis pathway

Answer 29

1. This can be metabolised by hexokinase and form fructose-6 phopshate from here it continues in the normal glycolysis cycle
2. • 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

Question 30

describe how pentose phosphate enters the glycolysis cycle

Answer 30

• 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