GI biochemistry Flashcards
What is glycogenesis?
Synthesis of glycogen
What is glycogenolysis?
Breakdown of glycogen into glucose
What is gluconeogenesis?
Synthesis of glucose from metabolic precursors
What type of glycosidic links form between glucose molecules in glycogen?
α1-4 glycosidic links in the main chain
α1-6 glycosidic links in the branches
What is glycogenin?
A protein attached to a glycogen primer containing 4+ glucose residues, allowing addition of glucose to glycogen chain
In the first step of glycogenesis, glucose is turned into _____
Glucose-6-phosphate
In the first step of glycogenesis, glucose-6-phosphate is formed by _____ and enzyme _____
ATP and hexokinase
In the second step of glycogenesis, G-6-P is transformed into ____ by enzyme _____
Glucose-1-phosphate by phosphoglucomutase
In the third step of glycogenesis, G-1-P is turned into _____ by ____ and _____
UDP-glucose by UDP-glucose pyrophosphorylase and UTP
In the last step of glycogenesis, glucose is added to the glycogen chain by enzyme ____
Glycogen synthase
What secondary product is made in the last step of glycogenesis?
UDP
Name a rate-limiting enzyme of glycogenesis
Glycogen synthase
Give the equation for glycogenolysis
[glucose]n + phosphate -> G-1-P + [glucose]n-1
What rate-limiting enzyme catalyses glycogen?
Glycogen phosphorylase
After glycogenolysis, G-1-P is turned into G-6-P. What happens to G-6-P in the liver?
G6P is de-phosphorylated, can enter the blood
After glycogenolysis, G-1-P is turned into G-6-P. What happens to G-6-P in the skeletal muscle?
G6P can’t be de-phosphorylated, so used in glycolysis and TCA cycle
When and where does gluconeogenesis occur?
After long periods or not eating eg overnight, occurs mostly in liver, some in kidneys
Gluconeogenesis is an energetically ______ process
Expensive
Explain the process of gluconeogenesis
Oxaloacetate is formed in mitochondria from precursor, which is an intermediate in the TCA cycle
What is the Cori Cycle?
Lactate as a precursor for GNG:
- GNG of lactate in the liver produces glucose
- Glucose travels in blood to the muscles
- Glycolysis of lactate occurs in muscles, reforming lactate
Name the precursors of glucose in GNG
Lactate
Amino acids
Glycerol
How are glycolysis and GNG regulated?
By precursors and by hormones eg glucagon and insulin
What does insulin activate/deactivate?
Activates glycolysis, activates glycogenesis. Deactivates gluconeogenesis
