Biochemistry week 12

Question 1

What is the structure of glycogen

Answer 1

-Glycogen is a branched polysaccharide made of glucose molecules
- Contains two types of glycosidic linkages

Question 2

What is the function of gluconeogenic Precursors

Answer 2

Used to synthesize glucose

Question 3

Name the three key precursors

Answer 3

• Glycerol
  -Lactate
  -Glucogenic Amino Acids

Question 4

What is glycerol released from

Answer 4

TAG hydrolysis in adipose tissue

Question 5

What is Lactate released from

Answer 5

• Anerobic glycolyis in skeletal muscles and red blood cells

Question 6

What does glucogenic amino acids come from

Answer 6

• Hydrolysis of tissue proteins

Question 7

What are the 2 functions of glucagon regulations

Answer 7

Decreases fructose 2,6-bisphosphate:
Activates fructose 1,6-bisphosphatase (gluconeogenesis).
Inhibits PFK-1 (glycolysis).

Inhibits pyruvate kinase (PK):
Converts PK to its inactive form (phosphorylated).
Prevents PEP conversion to pyruvate, favoring gluconeogenesis.

Question 8

What is the function of Allosteric activation by Acetyl coA

Answer 8

• Acetyl CoA activates pyruvate carboxylase, directing pyruvate toward gluconeogenesis instead of the TCA cycle.

Question 9

Explain allosteric inhibition by AMP

Answer 9

AMP inhibits fructose 1,6-bisphosphatase, reducing gluconeogenesis.
AMP activates PFK-1, promoting glycolysis.

Question 10

Name the key proteins involved in the hydrolysis of glucose-6-phosphate to glucose in gluconeogenesis and their function

Answer 10

• Glucose 6-Phosphate Translocase: Transports glucose 6-phosphate into the endoplasmic reticulum (ER).
  -Glucose 6-Phosphatase: Removes the phosphate group from glucose 6-phosphate, yielding free glucose.

Question 11

What is the function of the acetyl coA in gluconeogenesis

Answer 11

Acetyl-CoA is an allosteric activator of pyruvate carboxylase.
-0The enzyme that catalyzes the conversion of pyruvate to oxaloacetate

Question 12

Where does glycogenesis occur

Answer 12

• In the cytosol

Question 13

How is UDP-Glucose formed in glycogenesis

Answer 13

• Formed from glucose-1-phosphate and UTP by the enzyme UDP glucose pyrophosphorylase

Question 14

What is the name of the enzyme that forms an a(1-4) linkage in glycogen

Answer 14

Glycogen Synthase

Question 15

Name what can act as a primer for starting a new chain from free glucose in Glycogenesis

Answer 15

-A fragment or glycogen can act as a primer
-If glycogen is absent a protein can act as a primer by accepting glucose from UDP -glucose

Question 16

What is the function of Glycogen Synthase

Answer 16

-Adds glucose units in a(1-4) linkages

Question 17

Why are the branches in glycogen highly branched and soluble

Answer 17

-As the branches in glycogen occur every 8 glycosyl residues.

Question 18

Explain how branches are formed in glycogenesis

Answer 18

The enzyme amylo - a(1-4)- a (1-6)-transglycosylase create branches.
It:
-Removes 6-8 glycosyl residues form the main chain and attaches them to another part of the chain via an a (1-6) linkage

Question 19

Name the 3 main steps in glycogenolysis

Answer 19

• Action of Glycogen Phosphorylase
  -Debranching enzyme
  -Conversion of glucose-1-phosphate

Question 20

What s the function of the Debranching enzyme in Glycogenolysis

Answer 20

Removes the 4 units remaining at the branches with 2 enzymatic activities

Question 21

What is the name of the 2 enzymatic activites that the debranching enzyme uses

Answer 21

• Glucosyl 4:4 transferase
• a(1-6)-glucosidase

Question 22

Why cant glucose-6-phopshate be converted into glucose in the muscles

Answer 22

-Lacks glucose 6-phosphatase, so glucose 6-phosphate cannot be converted to free glucose.

Question 23

In glycogenolysis how is glucose-6-phosphate converted into glucose

Answer 23

• Glucose 6-phosphate is transported to the ER via glucose 6-phosphate translocase.
  In the ER, it is dephosphorylated to glucose by glucose 6-phosphatase.

Question 24

What is the function of Glucosyl 4:4 Transferase as one of the debranching enyzmes

Answer 24

• It Transfers 3 Glucose residues to the non-reducing end of another chain, forming a new a(1-4) bond

Question 25

What is the function of a(1-6) Glucosidase

Answer 25

Hydrolyzes the final Glucose at the branch point, releasing free glucose

Question 26

What is the 2 functions of the enzyme Glycogen phosphorylase in glycogenolysis

Answer 26

• Cleaves a(1-4) bond to produce glucose-1-phosphate
  -Splits 4 glucosyl units away from a branch point forming a limit dextrin

Question 27

What happens in lysosomal degration in glycogenolysis

Answer 27

A small fraction of glycogen degraded by acid α(1→4)-glucosidase (acid maltase) in lysosomes.