Lecture 28 - Glucose as a fuel molecule Flashcards
Glucose as a fuel molecule
Oxidised in glycolysis
All organsims (animals, plants, fungi and bacteria)
Glycolysis is usually cytoplasmic (other pathways are mitochondrial)
In mammals, all cells can use glucose as a fuel. Some cells rely on/preferentially use glucose
Glucose is essential as fuel for red blood cells …
Glucose is essential as fuel for red blood cells
As red blood cells mature, they lose their cellular contents and so one of the things that they loose Is the mitochondria. Since red blood cells do not have mitochondria they therefore lack the other pathways. All that red blood cells have is glycolysis to produce energy
Glucose is favoured fuel in the b…
Brain
Glucose is favoured fuel in the brain
Glucose can readily cross the blood/brain barrier but fats cannot (fats are bulky and therefore have difficulty getting across)
The human brain requires around 120g of glucose per day - the entire body requires about 160g per day so you can see that the brain takes the majority
Glucose is favoured fuel in the e….
Eyes
Glucose is the favoured fuel in the eye
Blood vessels (bringing oxygen and mitochondria would refract light in the optical path (lens, cornea) to retina. So the front go the eye is quite low in blood vessels so they are low in oxygen and they are also quite low in mitochondria therefore there is a limited amount of the pathways that they can achieve but they can still do glycolysis which is occurring in the cytoplasm.
Muscle and glucose as a fuel molecule
White muscle cells tend to use glucose whilst red muscle cells tend to use fats
Red muscle Long distance running Slow twice Fats as fuels Usually in aerobic conditions
White muscle Sprinting (high impact) Fast twitch Glucose as a fuel Work more under anaerobic conditions when we are working hard and can’t supply adequate oxygen. Anaerobic conditions means that the mitochondrial pathways are not working very well therefore they often use glucose through glycolysis in order to produce the energy that is required
Glycolysis overview
The splitting of glucose
Conversion of glucose (6C) to 2x pyruvate (3C)
Energy conserved in ATP and NADH
Pyruvate may be further metabolised aerobically or anaerobically
Organised into two phases
Activation of glucose
Getting the molecule into a form so that energy can be captured
Adding a phosphate on to glucose does three things
1- Causes the glucose to be negatively charged/polar therefore preventing it from leaving the cell
2- Causes the glucose to become less stable and more reactive and therefore it is more likely to complete the rest of the glycolytic pathway
3- creates a high energy bond that can be broken if energy is required
Two phases of glycolysis
Energy investment phase
Energy payoff phase
Splitting (6C to 3C) of molecule occurs at the end of the investment phase. After conversion, both the 3C molecules in this phase are processed the same way in order to create pyruvate
Energy investment phase
Putting energy in so that we get the molecule into a form where we can get the energy back out in the second phase. This phase involves the activation of glucose = Getting the molecule into a form so that energy can be captured
In glycolysis the way that we are getting energy is that we are using 2 ATP for this process
Splitting (6C to 3C) of molecule occurs at the end of the investment phase.
Energy payoff phase
Return on the investment. Making an ATP profit
In the energy payoff phase we are making a return on the investment and what happens is that we get 4 ADP phosphorylated to get 4 ATP so we make 4 ATP in the energy pay off phase (lost 2 ATP on the energy investment phase, so overall we have made a net gain of 2)
After conversion, both the 3C molecules in this phase are processed the same way to create pyruvate
In the energy investment phase, what are the 2 3-carbon molecules that are produced?
Glyceraldehyde-3-phosphate (G3P) Dihydroxyacetone phosphate (DHAP) (which needs to be converted to G3P first in order to be used
Splitting or aldolase reaction
DHAP is converted to G3P by triode phosphate isomerase (rearrangement)
Reaction is shown being close to equilibrium which doesn’t really make sense, you do not want to split up any of the adolase into G3P just for it to be converted into DHAP so what happens is that this reaction is at equilibrium when you just have these two products but you have to remember that this is part of a pathway so the G3P is metabolised by the next part which will cause increased in G3P conversion due to equilibrium principles. Continually making both but G3P is constantly being used which will drive the reaction from DHAP to G3P
Pathways for processing food molecules for ATP synthesis
Two key types of reaction
1-Phosphorylation of ADP to ATP
substrate level phosphorylation - direct (A + ADP — B+ATP), energy comes from substrate
Oxidative phosphorylation - indirect (reduced coenzymes)
2- Redox reactions - fuel molecules get oxidised
How to get a release of energy to drive substrate level phosphorylation?
One way to release the energy to drive a substrate level phosphorylation is the cleavage of a high-energy phosphate bond on the substrate - Put P on during activation however we need a net gain of ATP in glycolysis …
A key reaction for making an ATP profit - oxidation of …
Oxidation of glyceraldehyde-3-phosphate
NAD+ is reduced which provides the oxidising power
The addition of phosphate powered by the oxidation of G3P therefore does not require ATP because it instead uses energy released through the oxidation of the fuel molecule
