Biochemistry week 12 Flashcards
What is the structure of glycogen
-Glycogen is a branched polysaccharide made of glucose molecules
- Contains two types of glycosidic linkages
What is the function of gluconeogenic Precursors
Used to synthesize glucose
Name the three key precursors
- Glycerol
-Lactate
-Glucogenic Amino Acids
What is glycerol released from
TAG hydrolysis in adipose tissue
What is Lactate released from
- Anerobic glycolyis in skeletal muscles and red blood cells
What does glucogenic amino acids come from
- Hydrolysis of tissue proteins
What are the 2 functions of glucagon regulations
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.
What is the function of Allosteric activation by Acetyl coA
- Acetyl CoA activates pyruvate carboxylase, directing pyruvate toward gluconeogenesis instead of the TCA cycle.
Explain allosteric inhibition by AMP
AMP inhibits fructose 1,6-bisphosphatase, reducing gluconeogenesis.
AMP activates PFK-1, promoting glycolysis.
Name the key proteins involved in the hydrolysis of glucose-6-phosphate to glucose in gluconeogenesis and their function
- 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.
What is the function of the acetyl coA in gluconeogenesis
Acetyl-CoA is an allosteric activator of pyruvate carboxylase.
-0The enzyme that catalyzes the conversion of pyruvate to oxaloacetate
Where does glycogenesis occur
- In the cytosol
How is UDP-Glucose formed in glycogenesis
- Formed from glucose-1-phosphate and UTP by the enzyme UDP glucose pyrophosphorylase
What is the name of the enzyme that forms an a(1-4) linkage in glycogen
Glycogen Synthase
Name what can act as a primer for starting a new chain from free glucose in Glycogenesis
-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
What is the function of Glycogen Synthase
-Adds glucose units in a(1-4) linkages
Why are the branches in glycogen highly branched and soluble
-As the branches in glycogen occur every 8 glycosyl residues.
Explain how branches are formed in glycogenesis
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
Name the 3 main steps in glycogenolysis
- Action of Glycogen Phosphorylase
-Debranching enzyme
-Conversion of glucose-1-phosphate
What s the function of the Debranching enzyme in Glycogenolysis
Removes the 4 units remaining at the branches with 2 enzymatic activities
What is the name of the 2 enzymatic activites that the debranching enzyme uses
- Glucosyl 4:4 transferase
- a(1-6)-glucosidase
Why cant glucose-6-phopshate be converted into glucose in the muscles
-Lacks glucose 6-phosphatase, so glucose 6-phosphate cannot be converted to free glucose.
In glycogenolysis how is glucose-6-phosphate converted into glucose
- 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.
What is the function of Glucosyl 4:4 Transferase as one of the debranching enyzmes
- It Transfers 3 Glucose residues to the non-reducing end of another chain, forming a new a(1-4) bond
What is the function of a(1-6) Glucosidase
Hydrolyzes the final Glucose at the branch point, releasing free glucose
What is the 2 functions of the enzyme Glycogen phosphorylase in glycogenolysis
- Cleaves a(1-4) bond to produce glucose-1-phosphate
-Stops 4 glucosyl units away from a branch point forming a limit dextrin
What happens in lysosomal degration in glycogenolysis
A small fraction of glycogen degraded by acid α(1→4)-glucosidase (acid maltase) in lysosomes.
