15 Questions
What is the active form of glucose involved in glycogen synthesis?
UDP-glucose
What type of glycosidic bonds are present in glycogen at branching points?
$\alpha(1\rightarrow4)$ and $\alpha(1\rightarrow6)$
What is the rate-limiting step in glycogen synthesis?
Formation of $\alpha(1\rightarrow4)$ glycosidic bonds
What enzyme catalyzes branching in glycogen?
Branching enzyme
What is the product of glycogen breakdown by glycogen phosphorylase?
Glucose-1-phosphate
What is the primary linkage between glucose units in the main chain of glycogen?
α-1,4 glycosidic bonds
Which enzyme is responsible for the breakdown of glucose units from the non-reduced end of glycogen?
Glycogen phosphorylase
Where does intense glycogen synthesis occur?
Liver and muscle tissue
What is the substrate of glycogen synthesis?
UDP-glucose
How is glycogen breakdown in muscle different from that in the liver?
Glycogen is broken down to glucose 6-phosphate in muscle, and to free glucose in the liver
Which enzyme converts glucose-1-phosphate to glucose-6-phosphate in cells?
Phosphoglucomutase
What is the enzyme responsible for hydrolyzing glucose-6-phosphate to free glucose in the liver?
Glucose-6-phosphatase
Which hormone increases the synthesis of glycogen in the liver and skeletal muscle?
Insulin
What happens to glycogen synthase when it is phosphorylated?
It becomes inactive
Why can't muscle glycogen increase blood sugar levels?
Lack of glucose-6-phosphatase in muscles
Study Notes
Glycogen Metabolism: Key Concepts
- Free glucose from glycogenolysis in the liver is released into the bloodstream for other tissues' use.
- Liver glycogen stores fluctuate, increasing in the well-fed state and depleting during fasting.
- Muscle glycogen is minimally affected by short fasting periods and moderately decreased in prolonged fasting.
- Sugar nucleotides are crucial for various hexose transformation and polymerization reactions.
- UDP-Glucose, a sugar nucleotide, is formed by a condensation reaction between a nucleoside triphosphate and a sugar phosphate.
- Glycogen consists of α(1→4) glycosidic bonds and contains α(1→6) glycosidic bonds at branching points.
- Glycogen synthesis begins with glucose-6-phosphate, which is formed from free glucose by specific enzymes.
- The synthesis of glycogen involves UDP-glucose as the active form of glucose and requires energy from ATP and UTP.
- Glycogen synthesis is initiated by UDP-glucose, with glycogenin acting as a receptor for glucose residues when glycogen is depleted.
- The rate-limiting step in glycogen synthesis is the glycogen synthase step, which forms α(1-4) glycosidic bonds.
- Branching in glycogen occurs after at least 11 glucose units and is catalyzed by the branching enzyme.
- Glycogen breakdown involves glycogen phosphorylase breaking α-1,4 glycoside bonds, leading to the release of glucose-1-phosphate.
Test your knowledge of glycogen metabolism with this quiz. Explore key concepts such as glycogenolysis, glycogen synthesis, sugar nucleotides, and the enzymes involved in glycogen breakdown and synthesis.
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