Carbohydrates 2 Flashcards
What are the main products of carbohydrate digestion?
Glucose, galactose and fructose.
How are glucose, galactose and fructose absorbed into the blood?
Glucose passes through a glucose sodium symport which works due to the high levels of sodium outside of the cell. The system works even when glucose levels are high in the blood and it’s working against its concentration gradient. Galactose transport works similarly.
Fructose is passed through a Glut5 channel protein along its concentration gradient.
How does glucose get trapped in the cell?
It travels in the blood to the liver or other tissues and is phosphorylated into glucose-6-phosphate by hepatocytes or other cells. This cannot travel out of the cell as Glut Transporters won’t recognise it.
How do glucokinase and hexokinase work when blood glucose levels vary?
When blood glucose is normal, other tissues have the glucose. When it’s high, the liver grabs the glucose and phosphorylates it so it’s trapped in the liver.
Hexokinase can grab glucose efficiently even at low glucose levels but the tissues are easily satisfied.
Which enzyme converts glycogen into glucose in the liver?
Glucose 6 phosphatase
How is glycogen synthesised?
Glycogen is formed by glycogenin covalently binging glucose from uracil diphosphate(UDP) glucose to form chains of around 8 glucose residues. Glycogen synthase takes over to lengthen the chains. These chains are then broken by glycogen branching enzyme to form branch points (a1-6).
How is glycogen mobilised?
Glucose monomers are removed from the end of the chains one at a time as glucose-1-phosphate by glycogen phosphorylase. A de branching enzyme removes a set of 3 glucose residues and attaches them at the end of the chain (transferase) and glucosidase removes the final glucose so it is free glucose. This leaves an unbranched chain to be acted upon how needed.
What is von Gierke‘s disease?
It’s a glucose-6-phosphatase deficiency so have a high glycogen in liver and low blood glucose (all glucose comes from diet). A high blood lactate due to it not being able to be converted to glucose. It is treated by regular carbohydrate feeding.
