Glycolysis

Question 1

What is the general scheme of absorption of carbohydrates in the digestive system?

Answer 1

1. Mouth: alpha amylase-> breaks down to starch dextrins, maltose, isomaltose, lactose and sucrose.
2. Stomach: low pH is not optmum for alpha amylase, hence, slows it down.
3. Pancreatic alpha amylase: Continues to work on starch dextrins to give isomaltose, maltose, sucrose and lactose.
4. Mucosal cell membrane bound enzymes: Maltase, Isomaltase, sucrase and lactase-> breakdown disaccharides to monosaccharides.
5. Intestines: Absorption of monosaccharides-> sent to liver through portal circulation.

Question 2

Arrange the rate of absorption of monosaccharides in the intestines in decreasing order.

Answer 2

Galactose> Glucose> Fructose

Question 3

What kind of transport enables absorption of glucose and galactose in the endothelial cells in the intestine?

Answer 3

Secondary Active Transport

Question 4

What are the fates of glucose?

Answer 4

1. Glucose to pyruvate through Glycolysis
2. Glucose to glycogen through Glycogenesis
3. Glucose to ribose (nucleic acid synthesis) and NADPH (lipid synthesis) through Ribose Phosphate Pathway.

Question 5

What is glycolysis?

Answer 5

Glycolysis is the breakdown of glucose into two pyruvate molecules under aerobic conditions and two lactate molecules under anaerobic conditions, aiming for ATP synthesis and the production of other intermediates.

Question 6

What is the goal of glycolysis?

Answer 6

1. Pathway for ATP synthesis
2. Production of other intermediates

Question 7

Where does glycolysis take place?

Answer 7

Cytoplasm of cells

Question 8

What is the significance of glycolysis?

Answer 8

1. It is the only pathway that takes place in all the cells of the body.
2. It is the only source of energy in cells like RBCs and skeletal muscle cells.
3. Anaerobic pathway of glycolysis is the source of energy in muscles cells that lack oxygen after strenuous exercise.
4. Prelimnary step before complete oxidation of glucose.
5. Carbon skeleton for the synthesis of non-essential amino acids and glycerol for lipid synthesis.
6. Most reactions are reversible and can hence be used for gluconeogenesis.

Question 9

What are the possible substrates of gluconeogenesis?

Answer 9

1. Pyruvate
2. Glucogenic amino acids
3. Lactate
4. Glycerol

Question 10

What transmembrane proteins are used for the transport of gluscose from ECF to tissue cells?

Answer 10

Facilitative Glucose Transporters (GluT)

Question 11

What kind of transport is used to transport glucose from ECF to tissue cells?

Answer 11

Facilitative diffusion

Question 12

What is the target tissue and function of GluT-1?

Answer 12

Target tissue- Brain, Kidney, RBC
Function- Glucose intake

Question 13

What is the target tissue and function of GluT-2?

Answer 13

Target tissue- Hepatocytic membrane
Function- Decrease blood glucose levels

Question 14

What is the target tissue and function of GluT-3?

Answer 14

Target tissue- Brain, Kidney
Function- Glucose intake

Question 15

What is the target tissue and function of GluT-4?

Answer 15

Target tissue- Heart, Skeletal Muscles, Adipose
Function- Insulin mediated glucose intake

Question 16

What is the target tissue and function of GluT-5?

Answer 16

Target tissue- Small intestine, Kidney, Sperm
Function- Glucose Intake

Question 17

How does insulin help in regulating blood sugar levels?

Answer 17

Insulin helps in the translocation of GluT-4 and brings it to the surface of cells, for the transportation of glucose.

Question 18

Why do Type 2 Diabetes mellitus patients suffer from insulin resistance?

Answer 18

GluT-4 is reduced in Type 2 DM patients that causes insulin resistance in muscle and fat cells.

Question 19

True or False:
Glucose uptake is half the normal in muscle cells of Type 2 DM patients.

Answer 19

True

Question 20

How many phases does glycolysis have?

Answer 20

2 phases:
1. Energy Investment Phase
2. Energy Generative Phase

Question 21

When does the Energy Investment phase end and Energy Generation phase begin?

Answer 21

When dihydroxyacetone phosphate is converted to Glyceraldehyde-3-phosphate, by the action of Triosphosphate Isomerase.

Question 22

What regulates the formation of Glucose to G-6-P?

Answer 22

The enzyme hexokinase and glucokinase (in liver and pancreas):
Inhibited- G-6-P, Glucagon
Stimulated- Insulin

Question 22

In which step of glycolysis does oxidative phosphorylation take place?

Answer 22

Glyceraldehyde 3-phosphate is converted to 1,3-bisphosphoglycerate through Glyceraldehyde 3-phosphate dehydrogenase.
-CHO is oxidised to -COO and phosphate group is added.
NAD+ is reduced to NADH

Question 22

Which steps of glycolysis involve investment of ATP molecules?

Answer 22

1. Glucose to G-6-P by Hexokinase
2. Fructose-6-phosphate to Fructose-1,6-bisphosphate by Phosphofructo kinase

Question 22

What regulates the formation of Fructose-6-phosphate to Fructose-1,6-bisphosphate?

Answer 22

The enzyme phosphofructokinase is: Inhibited- Citrate, ATP, H+, Glucagon Stimulated- AMP, Fructose-2,6-bisphosphate, Insulin

Question 23

What is the significance of 2,3-biphosphoglycerate in RBCs?

Answer 23

2,3-BPG stabilise the T-form or the deoxy form of Hb by binding to the positively charged amino acids in the beta-chain, hence decreasing Oxygen affinity. This shifts the O2 dissociation curve to the right.

Question 24

Which steps of the Glycolysis pathway generates ATP?

Answer 24

1. 2,3-BPG to 3-Phosphoglycerate by Phosphoglycerate kinase (2 ATP) 2. Phosphoenolpyruvate to pyruvate by pyruvate kinase (2 ATP)

Question 25

What regulates the formation of pyruvate from phosphoenol pyruvate?

Answer 25

The enzyme Pyruvate kinase is: Inhibited by- Glucagon Stimulated by- F-1,6-bisphosphate (in liver), Insulin

Question 26

What is the importance of phosphorylated intermediates in the Glycolytic pathway?

Answer 26

1. Help trap Glucose in the cell. 2. 2,3-bisphosphoglycerate and phosphoenolpyruvate give phosphate to convert ADP to ATP.

Question 27

How is glucose trapped in the cell?

Answer 27

1. Phosphorylation of glucose to G-6-P changes its 3D shape making it recognisable to enzymes. 2. Unrecognisable to Glucose transporters. 3. Charges it so it cannot pass through the plasma membrane.

Question 28

Where does anaerobic glycolysis take place?

Answer 28

1. RBCs 2. In skeletal muscle tissue cells during strenuous exercise. 3. Ischemic tissues (w/ blocked oxygen supply)

Question 29

How do NaF and Arsenate operate as inhiitors?

Answer 29

Arsenate- Prevents ATP formation NaF- Inhibits Enolase