Carbohydrates

Question 1

Clinical importance of glucose

Answer 1

1. Preferred source of energy for most of body tissues . Brain cells mainly derive from
   2.minimum amount of glucose required for normal functioning
2. Normal fasting plasma glucose level is 70 to 110mg/dL.
   (After heavy carbohydrate meal , 150mg/dL)

Question 2

Definition of glycolysis .
Site of reaction .

Answer 2

In glycolytic pathway glucose is converted to pyruvate or lactate along with production of small quantity of energy .
Site :All reaction steps take place in the cytoplasm

Question 3

Significance of glycolysis pathway

Answer 3

1. Only pathway in all cells of body
   2.only source of energy in erythrocytes .
2. Exercise , anaerobic glycolysis major source of energy for muscles
3. Primary step before complete oxidation
   5.provides carbon skeletons for synthesis of non-essential amino acids
   as well as glycerol part of fat
   6.most reaction of glycolysis pathway reversible , also used for gluconeogenesis

Question 4

Glucose entry into cells

Answer 4

Glucose transporter- 4 (GluT4) transports glucose from ECF to muscle cells and adipocytes .

Question 5

GluT4 translocase is under the influence of

Answer 5

Insulin
In diabetes mellitus, hinders the entry of glucose into peripheral cells

Question 6

A GluT not under the influence of insulin

Answer 6

GluT2 ( transporter in liver cells )

Question 7

The steps of glycolysis that are key enzymes

Answer 7

Step 1, 3 and 9
Hexokinase
Phosphofructokinase
Pyruvate kinase
These reactions are irreversible

Question 8

Reaction step of gyclosis that produce energy

Answer 8

6 and 9
Produces ATP

Question 9

Steps Coupled for regeneration of NAD+

Answer 9

5 , 10
NAD+ is converted to NADH+ H+

Question 10

Induction difference between hexokinase and glucokinase and other difference

Answer 10

Hexokinase - not induced
Glucokinase , induced by insulin and glucose
[occurence , km value (higher for glucokinase )
Affinity to substrate , specificity , induction , function]

Question 11

Difference in occurrence of hexokinase , glucokinase

Answer 11

Hexokinase - all tissues
Glucokinase - only in liver

Question 12

Define gluconeogenesis

Answer 12

It is the process by which glucose molecules are produced from non-carbohydrate precursors( lactate , glucogenic amino acids , glycerol part of fat and propionyl CoA derived from odd chain fatty acids )

Question 13

Non carbohydrate precursor of glucose

Answer 13

lactate , glucogenic amino acids , glycerol part of fat and propionyl CoA derived from odd chain fatty acids

Question 14

Site of gluconeogenesis

Answer 14

Mainly in the liver
Lesser extend in the renal cortex
Part,y mitochondrial, partly cytoplasmic

Question 15

Key gluconeogenic enzymes

Answer 15

1. Pyruvate carboxylase
2. Phosphoenol pyruvate carboxy kinase
3. Fructose 1 6 bisphosphatase
4. Glucose 6 phosphatase

Question 16

Carboxylase enzyme requires coenzyme what

Answer 16

Biotin

Question 17

AST

Answer 17

aspartate amino transferase

Question 18

Pyruvate is carboxylased to what by pyruvate carboxylase and it’s site

Answer 18

To oxaloacetate
Needs coenzyme biotin and energy by ATP hydrolysis
Site : mitochondria

Question 19

What transfers oxaloacetate to cytosol for further reactions

Answer 19

Malate aspartate shuttle .
Oxaloacetate converted to malate , transverse the membrane and reach cytoplasm .then reconverted

Question 20

Where is malate DH present

Answer 20

Mitochondria , cytoplasm

Question 21

Shuttle that operates for lactate substrate and why

Answer 21

Aspartate shuttle operates .
Sufficient NADH available in the cytoplasm by LDH reaction

Question 22

When alanine is the substrate , shuttle and why

Answer 22

Malate shuttle .
NADH required in the cytoplasm for gluconeogenesis

Question 23

The reaction that takes place after oxaloacetate reaches the cytoplasm

Answer 23

PEPCK enzyme converts oxaloacetate to PEP , by removing a molecule of CO2
GTP or ITP donate phosphate

Question 24

Which step circumvents the irreversible step of glycolysis catalyzed by Pyruvate kinase

Answer 24

Pyruvate to oxaloacetate to PEP

Question 25

What are the steps catalysed by glycolysis enzymes that convert PEP to fructose 1-6 bisphosphate (freely reversible )

Answer 25

Steps 8
7
6
5
4
2

Question 26

What bypasses the step of glycolysis catalysed by PFK(step 3 of glycolysis)

Answer 26

F16BP forms F6P
by enzyme F16BPase

Question 27

What isomerases the reaction between F6P and G6P

Answer 27

Hexophosphate isomerase

Question 28

Glucose 6 Phosphatase seen in gluconeogenesis

Answer 28

Enzyme is active in liver
Lesser extend in kidney and intestinal mucosa
Absent in muscle
The g6p is hydrolysed to free glucose by it

Question 29

Significance of gluconeogenesis

Question 30

How does fluoride inhibit glycolysis

Answer 30

Remove magnesium , manganese ion , inhibit enolase enzyme irreversibly and therefore glycolysis .
Fluoride is therefore added to blood for sugar estimatation to prevent metabolisation of glucose by blood

Question 31

Lactase enzyme is usually produced by . Highest levels are usually found after

Answer 31

Cells lining the small intestine
After birth , decline with age

Question 32

Confirmatory diagnosis of lactose intolerance is made by

Answer 32

Stool acidity test( infants and young children )
Measure the amount of acid in stool . Undihested lactose creates lactic acid and other fatty acids , glucose maybe present in sample

Question 33

Treatment of lactose intolerance

Answer 33

Lactase enzyme or tablets
Non lactose alternatives