Week 5 - CHO metabolism Flashcards
What is the relevance of carbohydrate metabolism?
Instantaneous source of energy with/without oxygen.
Protein sparing - maintains muscle mass
Can be converted to fat for stored energy
Stored in the muscle and liver as glycogen - glycogen content 5x higher in the liber than the muscle.
Issues with too much sugar
Chronic inflammation, build-up of fat, affected by glycaemic control.
When working at VO2max how much energy comes from carbs?
Around 70% - when working at >85% VO2max.
What is glucose converted into in glycolysis? Why?
Glucose-6-phosphate, to lock in into the cell and stop it diffusing out.
Glucose-6-phosphate can be stored as glycogen or converted from glycogen back to GP6 when needed in extreme exercise or starvation.
What is glucose-6-phosphate converted to?
Pyruvic acid which becomes lactic acid (anaerobic) or acetyl CoA (aerobic).
What happens to acetyl CoA?
Enters the Krebs cycle to produce H+ ions, electrons and electron carriers which enter the electron transport chain in the mictochondria to covert ADP to ATP.
What is the role of electron carriers?
Convert ADP to ATP.
What is glycolysis?
Breakdown of glucose to two molecules of pyruvate
What is the link reaction?
Breakdown of pyruvate to acetyl CoA.
Give the three steps of glycolysis
Glucose is broken down into fructose diphosphate
This forms 2 molecules of glyceraldehyde-3-phosphate
These form 2 molecules of pyruvate.
What does glycolysis produce per glucose molecule?
2x ATP
2 NADH (electron carriers)
Is glycolysis aerobic or anaerobic?
Anaerobic - but the first step in an aerobic process.
Outline the link reaction
Connects glycolysis + Krebs cycle.
Pyruvate is oxidised to acetyl CoA by removal of hydrogen and CO2. Coenzyme A is added.
What is the Krebs cycle?
Breakdown of acetyl CoA to CO2.
Outline the Krebs Cycle
What does it produce?
Acetyl and oxaloacetate combine to form citrate.
Each cycle produces 1 ATP, 3 NADH and 1 FADH2, 3 CO2.
Doubled per molecule of glucose.
How can we measure changes in CHO metabolism at the whole body level?
RER >1 indicates we are using CHOs.
Control of blood glucose and glucose uptake
Low blood sugar (<4.9mmol) causes alpha cells of the pancreas to produce glucagon stimulating liver breakdown to try and increase blood sugar levels.
High blood sugar level (6.7mmol), beta cells produce insulin to try and stimulate muscle and fat cells to absorb glucose, skeletal muscle more critical.
Difference between glucose uptake after insulin and after exercise/contraction.
Insulin - PI3K dependent mechanism to induce translocation of GLUT-4.
Exercise - independent of PI3K, likely controls through Ca2+ release.
Why does exercise benefit T2D patients?
Exercise stimulated glucose uptake reversed in insulin-resistant muscle.
Exercise encourages uptake of glucose.
Effect lasts around 40minutes.
Exercise benefits the patient for 40 minutes, but insulin sensitivity lasts around 24hrs.
Adaptations to carbohydrate metabolism with training
Substrate utilisation….
increase in size and number of mitochondria.
Skeletal muscle better at storing triglycerides.
Fats used for longer,
Fatigue less.
Molecular adaptations
Enzymes in the Krebs cycle increase in concentration. Better at producing FADH2 and NADH.
What does the electron transport chain do?
Produces ATP with energy carried by FADH2 and NADH.
Glycogen depletion from muscle fibre types occurs in which order?
I, IIa, IIb - order of decreasing mitochondria content.
What does chemiosmosis do?
Pushing electrons along the chain forces the H+ ions into the intermembrane space.
Energy from the electron transport is used to pump H+ across the inner membrane of the mitochondria.
This creates a proton concentration gradient.
The backflow of H+ through ATP synthase (complex 5) is used to synthesise ATP from ADP and Pi.
In the ETC what does complex 1 do?
Receiver for NADH.
Main donators of electrons come from malate, glutamate, and palmitoyl CoA in food.
In the ETC what does complex 2 do?
FADH2 feeds into complex 2.
Succinate is the main foodstuff.
What happens at complex 3 in the ETC?
Transports 2 H+, this can happen twice so 4x H+ and 4x e-.
