1.04 - Carbohydrate Metabolism

Question 1

List the various fates of glucose

Answer 1

Glycogen (storage)
Glycoproteins (Structure)
Glycolipids 
GAGs (structure)
Ribose --> DNA/RNA
Pyruvate (+ ATP) --> Acetyl CoA --> TCA Cycle + ATP
TCA Cycle --> Amino Acids
Acetyl CoA --> Fatty Acids

Question 2

Describe Glycoproteins

Answer 2

Attachment of carbohydrates to a polypeptide
May be O- or N- linked
Facilitates:
 - Protein folding
 - Protein stability
 - Targeting
 - Anchoring
 - Secretion 
 - Cellular Recognition

Question 3

Describe Glycoaminoglycans

Answer 3

Main form of structural carbohydrates
Linear unbranched polymers of repeating disaccharides
Contain large negative charge die to presence of carboxyl or sulphate groups on the sugars
Provide viscosity, elasticity and high tensile strength

Question 4

What is Glycogenesis?

Answer 4

The formation of glycogen from glucose for storage. Occurs after meals

Question 5

What is Glycogenolysis?

Answer 5

Breakdown of glycogen stores to release glucose

Question 6

What organ is the major storage of glucose?

Answer 6

The Liver, and also muscle

Question 7

What is the glucose transporter in hepatocytes?

Answer 7

GLUT2

Question 8

What is Glycogen?

Answer 8

The glucose storage form in animal cells
A polymer of glucose residues linked by alpha-1-4 glycosidic bonds
Branching structure (via alpha 1-6 glycosidic bonds)

Question 9

Describe Glycogen formation

Answer 9

Glycogen synthase catalyses addition of glucose.

Addition occurs via UDP-Glucose

Question 10

Describe Glycogen breakdown

Answer 10

Glycogen phosphorylase catalyses glycogen degradation to release free glucose

Question 11

Describe Glycolysis

Answer 11

Glycolysis is the primary catabolic (oxidative) pathway for glucose
Occurs in the cytosol
Converts glucose to pyruvate
Links to the TCA cycle for complete oxidation
Occurs under aerobic and anaerobic conditions

Question 12

What are the products of Glycolysis?

Answer 12

Two molecules of Pyruvate
Two (net) molecules of ATP
NADH

Question 13

What are the major steps in glycolysis

Answer 13

Glucose –> Glucose-6-Phosphate
Fructose-6-Phosphate –> Fructose-1,6-Bisphosphate
Fructose-1,6-Bisphosphate –> 2x Gylceraldehyde-3-Phosphate
Gylceraldehyde-3-Phosphate –> 1,3-Bisphosphoglycerate
1,3-Bisphosphoglycerate –> 3-Phosphoglycerate
Phosphoenolpyruvate –> Pyruvate

Question 14

Describe the ‘Glucose –> Glucose-6-Phosphate’ reaction in glycolysis

Answer 14

Energy dependent step
Enzyme:
 - Hexokinase -  peripheral tissue
 - Glucokinase - hepatic
ATP --> ADP

Question 15

Describe the ‘Fructose-6-Phosphate –> Fructose-1,6-Bisphosphate’ reaction in glycolysis

Answer 15

Energy dependent step
1st committed step
Enzyme: Phosphofructokinase
Highly regulated step
ATP --> ADP

Question 16

Describe the ‘Fructose-1,6-Bisphosphate –> 2x Gylceraldehyde-3-Phosphate’ reaction in glycolysis

Answer 16

Split from a 6 carbon to a 3 carbon molecule

Question 17

Describe the ‘Gylceraldehyde-3-Phosphate –> 1,3-Bisphosphoglycerate’ reaction in glycolysis

Answer 17

Generation of NADH
Enzyme: Glyceraldehyde-3-Phosphate Dehydrogenase
Link to TCA Cycle (Via NADH)
Low [NAD] limits glycolysis

Question 18

Describe the ‘1,3-Bisphosphoglycerate –> 3-Phosphoglycerate’ reaction in glycolysis

Answer 18

ADP –> ATP

“Balances” loss of ATP earlier in process as two molecules produced here per glucose

Question 19

Describe the ‘Phosphoenolpyruvate –> Pyruvate’ reaction in glycolysis

Answer 19

ADP –> ATP
NET gain of 2 ATP per glucose
Enzyme: Pyruvate Kinase
Highly regulated step

Question 20

How is glucose trapped in cells?

Answer 20

By Glucokinase and Hexokinase

Question 21

Where do glycolysis occur?

Answer 21

Cytoplasm

Question 22

What structures does glucose provide the building blocks for?

Answer 22

Proteins
Lipids
Nucleotides