Carbohydrates

Question 1

Name the Major monosaccharides

Answer 1

Glucose
Galactose
Fructose

Question 2

Name the major disaccharides

Answer 2

Maltose
Sucrose
Lactose

Question 3

Name the enzyme which is found in the liver. Has a high Vmax and Km.

Answer 3

Glucokinase
Picks up glucose when the conc is high eg after a meal.
The high vmax allows it to do it quickly in order for as much glucose to be trapped.

Question 4

Name the enzyme which has a low Km and Vmax, so that even at low concentration, it can bind to it.

Answer 4

Hexokinase

The low Vmax however means that the tissues it is found in, are quickly satisfied.

Question 5

What is Glycogen?

Answer 5

Glycogen is a polymer of glucose (α1→4) linked subunits with (α1→6) branches every 8 to 12 residues.

Question 6

Describe the synthesis of glycogen?

Answer 6

It does not form directly from glucose subunits. instead, Glycogenin starts by covalently binding glucose from UDP-glucose to form chains of approx, 8 subunits.

Glycogen synthase takes over from there and extends the chains until they are broken by the glycogen-branching enzyme to form the 1-6 branching points.

Question 7

Describe the degradation of glycogen?

Answer 7

During degradation, glucose subunits are removed one at a time from the non-reducing ends of the branches as G-1P by glycogen phosphorylase.

Question 8

Describe the function and process of glycolysis

Answer 8

Glycolysis is a cytoplasmic pathway that breaks down glucose into two three-carbon compounds and generates energy. Glucose is trapped by phosphorylation, with the help of the enzyme hexokinase. Adenosine triphosphate (ATP) is used in this reaction and the product, glucose-6-P, inhibits hexokinase

Question 9

What are the products of glycolysis?

Answer 9

Overall, the process of glycolysis produces a net gain of two pyruvate molecules, two ATP molecules, and two NADH molecules for the cell to use for energy

Question 10

Describe the energy requirements of Glycolysis?

Answer 10

Steps 1 and 3 = – 2ATP
Steps 7 and 10 = + 4 ATP
Net “visible” ATP produced = 2.

Question 11

State the chemical equation for glycolysis?

Answer 11

C6H12O6 + 2 NAD+ + 2 ADP + 2 P —–> 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+

Question 12

How many steps of glycolysis are there?

Answer 12

10

Question 13

What are the steps of glycolysis?

Answer 13

Step 1: Hexokinase
Step 2: Phosphoglucose Isomerase
Step 3: Phosphofructokinase
Step 4: Aldolase
Step 5: Triosephosphate isomerase
Step 6: Glyceraldehyde-3-phosphate dehydrogenase
Step 7: Phosphoglycerate kinase
Step 8: Phosphoglycerate mutase
Step 9: Enolase
Step 10: Pyruvate Kinase

Question 14

What is step 1 glycolysis?

Answer 14

Conversion of D- glucose into glucose-6-phosphate.

The enzyme that catalyzes this reaction is hexokinase.

Glucose is phosphorylated
through the 6’ carbon of the glucose, Mg is involved to help shield the negative charges from the phosphate group on the ATP molecule.

Question 15

What is step 2 glycolysis?

Answer 15

Rearrangement of G6P into F6P. Catalyzed by phosphate isomerase.

Step 2 is an isomerization reaction

Question 16

What is step 3 glycolysis?

Answer 16

Phosphofructokinase, with a magnesium as a cofactor, changes fructose-6-phosphate into fructose-1,6-biphosphate.

Mg is present to shield from negative charge of the ATP molecule.

Phosphofructokinase present to catalyze reaction.

Question 17

What is step 4 glycolysis?

Answer 17

Aldolase splits F1,6BP into 2 sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP).

FBP catalyzed by Aldolase which creates DHAP and GAP

Question 18

What is step 5 glycolysis?

Answer 18

Triosephosphate isomerase

The enzyme triosephosphate isomerase rapidly inter-converts the molecules dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP). Glyceraldehyde phosphate is removed/ used in the next step of glycolysis.

Question 19

What is step 6 in glycolysis?

Answer 19

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) dehydrogenates and adds an inorganic phosphate to glyceraldehyde 3-phosphate, producing 1,3-biphosphoglycerate.