Glycolysis and glucose oxidation Flashcards
How much of the glucose in blood does the brain use?
60%
What is the molecular formula for glucose?
C6H12O6.
Which hormones control glucose? Where are they made?
Insulin and glucagon
Made in Islets of langerhans
How is glucose stored
Glycogen
How is glucose trapped in the cell
Phosphate group is added to it
In what form does glucose enter the body? What are its possible fates?
Enters- G6P Possible fates: 1. Stored as glycogen 2. Used in pentose phosphate pathway to make nucleotides and steroid hormones 3. Broken down to form pyruvate
How an where can G6p be reformed
Gluconeogenesis
Reformed by pyruvate in the liver and kidneys
Is the glucose cell membrane hydrophobic or
hydrphylic
hydrophobic
Name of glucose transporters
GLUTS
How do GLUTS work?
Facilitate transport
Down concentration gradient
No ATP needed
Name the 3 main Glucose transporters
GLUT1
GLUT2
GLUT4
Location and function of GLUT1
Found- In all cells
Has a low Km- so works at top speed even at low glucose concentrations
Location and function of GLUT2
Found- Liver an pancreas only
Low Km- works slow at low-normal glucose concentrations
Works fast as concentration increases
Location and function of GLUT4
Found- muscle and adipose
Has a low Km
Controlled by insulin
How does insulin control GLUT4?
In skeletal muscle, GLUT4 transporters are bound to vesicles inside the cell. So glucose can not enter.
Insulin activation causes vesicles to move and merge with cell membrane. This exposes the GLUT4 transporters and allows glucose uptake
Effect of Exercise on GLUT 4?
Causes glute 4 vesicles to merge with the cell membrane to increase glucose uptake into muscle. Glucose concentration is reduced in the blood
Where is exercise good for diabetes?
Reduces glucose concentration in the blood as it stimulates increased uptake
What is the main goal in glycolysis?
Conversion of glucose into pyruvate
How many steps in glycolysis? What is special about the first and last 5 steps
10 steps
First 5- require ATP
Last 5- produce 4ATP, 2NADH,2 pyruvate
Describe the first step if glycolysis
Phosphorylation of glucose into G6P
PO4 is added
Catalysed by hexokinase
Requires ATP
Properties of Hexokinase
Found in all tissues
Phosphorylaes all 6 carbon molecules
G6P- negative feed back- High G6p= inhibited hexokinase
What happens when glucose concentration in the cell is high
Decreased concentration gradient, further uptake of glucose blocked
Reduced glucose conversion to G6P
Describe the alternative step 1- glucokinase
Converters ONLY glucose to G6P
Found in pancreas and liver
Has a high Km- responds quickly to increased glucose concentrations. Slow activity otherwise
No negative feed back
Function of glucokinase in the pancrease? What is the mechanism?
Acts as a sensor for glucose
Signals for insulin and glycogen production/ secretion
Low glucose concentration glucokinase is kept bound to nucleus by GKRP (glucokinse regulatory protein)
High glucose concentrations- Glucokinase dissociates from GKRP and acts in the cytosol
What are the differences between gluckinase and hexokinase?
Glucokinase- High KM Responds to changes in blood glucose Phosphorylates only glucose Acts as a glucose sensor Found only in pancreas and liver
Describe step 2 of Glycolysis
Isomerisation
G6P is converted into fructose-6-phosphate
from 6 carbon to a 5 carbon ring
Makes further reactions more energetically favourable
Describe step 3 of Glycolysis
Phosphorylation of F-6-P to F1-6-bisphosphate
Enzyme-Phosphofructokinase
ATP used
Rate limiting step:
PFK1- allosterically inhibited by ATP to AMP ratio. High ATP switches off glycolysis. High AMP stimulates PFK1
Citrate inhibits PFK1
PFK1- covalently inhibited by production of fructose,2,6,phosphate. High F,2,6P stimulates PFK1
Describe step 4 of Glycolysis
F1-6-bisphosphate is broken down to give 2 3 carbon chains
Enzyme-Aldose
First chain- Aldehyde-glyceraldehyde-3-phosphate
Second chain- Acetone-dihydroxyacetone-phosphate
Acetone converted into aldehyde as only aldehyde is used in glycolysis
Result- 2 Aldehyde-glyceraldehyde-3-phosphate
Name an alternative source of acetone and how it enters glycolysis
Glycerol from fat can be broken down into acteone. This is then converted into aldehyde in glycolysis
Enzyme- Isomerase
Location- only the liver (has the enzyme)
Describe step 6 of Glycolysis
Free inorganic phosphate is added to glyceraldehyde
Enzyme- Dehydrogenase
Product- Glycerate
By product- NADH
Use of NADH produced from glycolysis? Name another source of NADH
Generate NAD+ in crebs cycle
Lactic acid
Describe step 7 of Glycolysis
1,3,bisphosphate glycerate gives off 1 phosphate to produce ATP from ADP (substrate level phosphorylation)
Enzyme- Phosphoglycerate kinase
Describe step 8 of Glycolysis
Phosphate is shifted to middle carbon
Describe step 9 of Glycolysis
Hydrolysis
water molecule removed to produces PEP
PEP is also produced by gluconeogenesis.
Describe step 10 of Glycolysis
PEP is broken down to pyruvate Enzyme- pyruvate kinase. pyruvate feeds into Kreb’s cycle. ATP is produced substrate level phosphorylation
How does fructose feed into glycolysis?
Fructose (diet) can be matabolised by hexokinase to form F-6-P (step 3)
Main path is fructokinase produced in liver which metabolises fructose ultimately producing Glyceraldehyde (step 4)
Pentose phosphate pathway and glycolysis
Alternative pathway for G-6-P
makes nucleic acids, steroid hormones, fat
Important for NADPH production
The products from the pathway glyceraldehyde-3-phosphate and fructose-6-phosphate, can feed into glycolysis.
