Carbohydrate and glucose metabolism

13 important questions on Carbohydrate and glucose metabolism

How many glucose does the brain use each day?

120-150 gram

Why do brain/neuronal cells not have beta-oxidation?

Because they cannot absorb long chain fatty acids (myelin).

Why can we not make glucose from FA?

FA can be broken down to C2, this is a 'passenger' in the TCA cycle. To make glucose we need a 'car', which is a C4 molecule.
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What stimulates glucagon production?

Nerves and AA (not low glucose in pancreas).

Where do you find glucokinase and where do you find hexokinase? What is the difference between these two regarding Km and Vmax?

Glucokinase: liver and pancreas (high Km, high Vmax)
Hexokinase: other cells (low Km, low Vmax)

Why is glucokinase only present in the liver and pancreas?

Glucokinase is sensitive to changes in [glucose], this is needed in the liver since the liver only uses excessive amounts of glucose. So when [glucose] is high, glucokinase will be used in the liver.

What is the difference in the liver compared to other cells?

Other cells do not have G6Pase and therefore cannot release glucose back into the bloodstream.

What happens when a patient is lactose intolerant?

The osmotic pressure in the intestines is raised, causing water to move into the lumen of the intestines.
Lactose = glucose + galactose. Lactase cuts these two.

Where does aerobic glycolysis occur, what about anaerobic glycolysis?

Aerobic glycolysis: mitochondrium
Anaerobic glycolysis: cytoplasm

What happens if you eat a high protein meal?

Induction of glucagon production, leading to gluconeogenesis.

When is pyruvate used for the TCA cycle?

When there is an excess of glucose.

How is the TCA controlled via hormones?

Insulin activates PDH (pyruvate dehydrogenase complex): glucose to acetyl CoA
Glucagon inactivates PDH: glucose to gluconeogenesis

What is the pentose phosphate pathway (PPP)?

The PPP is a shunt for glycolysis, this produces 2 NADPH that can synthesise FA, reduce glutathione, and help with other reactions.

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