Glucose Flashcards
What is the energy of ATP (hydrolysed to ADP)?
30.5kJ/mol (relatively low energy intermediate)
What is the energy of NADH (oxidized to NAD+)?
220kJ/mol (relatively high energy intermediate)
Anaerobic metabolism of glucose provides how many ATP?
2
Aerobic metabolism of glucose provides how many ATP?
32
What is glycogen?
Fasting reserve of glucose
Glucose and galactose are what kind of sugar?
Aldose
Fructose is what kind of sugar?
Ketose
How does glucose enter cells?
GLUT transporters: 1 (universal), 2 (liver and pancreas), 4 (muscle and adipose; insulin responsive)
Red blood cells are obligated to which form of metabolism?
Anaerobic (they have no mitochondria)
Anaerobic glycolysis produces
lactate
Gluconeogenesis
generates new glucose from glycerol or amino acids, NEVER FROM FAT
Which sugar is correlated with obesity?
High fructose in processed foods
What is the cellular substrate for ATPases?
Mg-ATP (more stable)
Most of the electrons generated in metabolism are stored in
NADH
The general formula for carbohydrates is
Cn(H2O)n
Monosaccharides have how many carbons?
3-7
Glucose has how many carbons?
6
Fructose has how many carbons?
6
D sugars in Fischer projections have
-OH of highest chiral carbon on right
How is the Fischer projection of glucose remembered?
All D except for 3 - all -OH groups are on the right except at carbon 3 (carbon 1 = aldehyde)
Why do fats have more energy than carbohydrates?
Carbohydrates contain O and tf are partially hydrated/oxidized reducing the amount of energy we get from burning them
Maltose
2 glucose
Where do circulation problems in diabetes arise from?
Glycation of blood vessels - amino groups in protein are susceptible to glycation by glucose, generating fructosamine. this makes vessels brittle and prone to clots, leading to blindness and gangrene requiring amputation
Fasting blood glucose
4-5mM
What is the renal threshold for glucose?
10mM - beyond this it comes out in urine
What is the cause of retinopathy in diabetes?
When blood glucose is elevated it damages the retinal capillary beds, causing aneurysms and haemorrhage that can cause blindness
What is the diagnostic indicator of glycation/uncontrolled high glucose levels in blood?
Hb-A1C = glycosylated red Hb; normally 3-5% of Hb but ~15%+ in diabetes
GLUT1 are located
ubiquitous
GLUT2 are located
liver, pancreatic islets, intestine
GLUT4 are located
muscle, fat, heart
What is the function of GLUT1 transporters?
Basal glucose uptake
What is the function of GLUT2 transporters?
liver and pancreas response to glucose: formation of glycogen and release of insulin, respectively
What is the function of GLUT4 transporters?
insulin signal tells GLUT4 (inactive precursor) to migrate to the cell membrane and let in glucose; if you become resistant to insulin or insulin depletes, GLUT4 stays within the cell starving it of glucose while glucose causes damage because it can’t get into cells
What happens to GLUT4 in diabetes?
low insulin or insulin resistance means there is no insulin signal to muscle, fat, heart cells that triggers movement of GLUT4 to the membrane to let glucose in - the cells are starved of glucose; glucose causes damage because it can’t get into cells
Glucose-6-phosphatase is active only in
liver (mostly) and kidney
What is the role of glucose-6-phosphatase?
release of free glucose made from glycogen
What determines glucose uptake by GLUT transporters?
insulin:glucagon
In starvation mode, the liver
takes stored glycogen and metabolises it to glucose, released by G6Pase
In the fed state where insulin goes up, the liver
takes up glucose and stores it as glycogen
What is the equation for glucose metabolism?
glucose + 2NAD+ +2ADP + 2Pi –> 2pyruvate + 2NADH + 2ATP + 2H20
What are the products of glycolysis?
2pyruvate, 2NADH, 2ATP, 2H20
How much energy from glucose is captured as ATP?
2.1% = 61kJ out of a total of 2.8MJ per mole of glucose
What is the committed step of glycolysis?
fructose-6-phosphate to fructose-1,6-biphosphate by PFK; PFK is only active when cells have low [ATP] because this step is energetically irreversible
What energy store is used for short-term bursts of activity (eg first ~5s of 100m dash)
phosphocreatine in muscle; produces ATP
Endurance activity depends on
fatty acids, ketone bodies, blood glucose (aerobic metabolism)
Lactate is converted to glucose in
the liver (Cori cycle)
What is the Cori cycle?
carbon cycling between glycogen in muscle and lactate, converted back to glucose in the liver
What cells depend on anaerobic glycolysis?
retinal cells, red blood cells
Why are there no mitochondria in the retina?
mitochondrial cytochromes absorb light
The brain requires how many grams of glucose per day?
120g
What are the carbon sources for gluconeogenesis?
lactate (post-exercise or anaerobic tissue eg RBCs), amino acids from protein breakdown, glycerol from mobilisation of triacylglycerides in adipose tissue (starvation)
Glycerol undergoes gluconeogenesis in the
liver; adipose tissue lacks glycerol kinase tf glycerol circulates to the liver
Lactose is made of
glucose and galactose (disaccharide)
Utilization of lactose requires
epimerisation of galactose (4-epimer) back to glucose
Galactosaemia is the failure of which enzymes?
galactokinase, galactose-1-phosphate uridylytransferase, epimerase
Sucrose is made of
glucose and fructose
What are the metabolic products of fructose?
dihydroxyacetone phosphate (DHAP) and glyceraldehyde (GAP)
What is the action of fructose on insulin?
none - it is an isomer of glucose that does not stimulate insulin release from the pancreas
What is the action of fructose on leptin?
none - it does not increase the production of leptin from fat cells
What are the general roles of insulin and leptin suppressed by fructose?
turning down apetite to control body weight
What is the action of fructose on ghrelin?
Does not suppress it ie hunger and appetite stay increased
Fructose increases which type of cholesterol?
LDL
