Carbohydrates

Question 1

Absorption of monosaccharides

Answer 1

Glucose and Na (glucose transporter) enter the cell
Na is immediately removed to maintain conc. gradient
Glucose travels down conc. gradient into the blood

Question 2

Glucokinase

Answer 2

Found in the liver
High Km - only picks up glucose after a meal, when there is a lot
High Vmax - does this quickly

Question 3

Hexokinase

Answer 3

Other tissues

Low Km and low Vmax - low concentrations of glucose will be picked up but are quickly satisfied

Question 4

Glycogen synthesis

Answer 4

Glycogenin covalently binds Glc from uracil’diphosphate (UDP) -glucose to form chains of around 8 Glc residues
Glycogen synthase takes over and extends the Glc chains which are then broken down by glycogen branching enzyme and re-attached with alpha 1-6 bonds to give branch points

Question 5

Glycogen in the liver

Answer 5

[blood glucose] falls
Stored glucose
Glycogen => G-6-P
Glucose-6-phosphate turns G-6-P into glucose in the blood

Question 6

Glycogen in skeletal muscle

Answer 6

(No Glucose-6-phosphate)
Glycogen => G-6-P => lactate (glycolysis)
ATP is required for muscle contraction

Question 7

Glycolysis

Answer 7

Catabolic pathway that saves some potential energy from glucose/G-6-P by forming ATP through substrate level phosphorylation

Question 8

Lactate dehydrogenase

Answer 8

Lactate => pyruvate

Question 9

Pyruvate dehydrogenase

Answer 9

Pyruvate => acetyl CoA

Question 10

Fate of absorbed glucose

Answer 10

Glucose through intestinal epithelial cells into portal blood to the liver
Phosphorylated into glucose-6-phosphate by hepatocytes - trapped there as will no longer be recognised by GLUT transporters

Question 11

Glycosidic bonds

Answer 11

Link monomers of carbohydrates