Topic A2

Question 1

Glycogen metabolism, general

Answer 1

• Glycogen is the storage form of carbohydrates
  
  • It is a poor form of long-term bulk energy storage as compared with fat
• Glycogen is found in nearly every tissue
  
  • Greatest quantitative importance in muscle and liver
• The glycogen metabolism in the tissues has several parts:
  
  • Glycogenolysis
    
    • Degradation of glycogen through phosphorolysis
  • Glycogenesis
    
    • Synthesis of glycogen from carbohydrate precursors (monosaccharides)
  • Gluconeogenesis
    
    • Synthesis of glycogen from noncarbohydrate precursor

Question 2

Glycogenesis

Localization

Answer 2

• Liver
• Skeletal
• (Kidney)
• Cytoplasm

Question 3

Glycogenesis

Energy balance

Answer 3

• Hexokinase (glucokinase):
  
  • ÷1 ATP
• UDP-glucose pyrophosphorylase
  
  • ÷1 UTP (= ÷1 ATP)
• ÷2 ATP /glucose

Question 4

Glycogenesis

Regulation

Answer 4

• Glucokinase (hexokinase)
• Glycogen synthease
  
  • BG level (?)
• Adrenalin ⊖
• Glucagen ⊖
• Glucogen ⊕
• Ca²⁺ ⊖
• Transoglucosasle (???)

Question 5

Glycogenolysis

Principle

Answer 5

• Terminal nonreducing α (1→4) linkage of glycogen undergoes phosphorolysis
• Phosphorylisis: removal of the terminal glucose residue by attack of inorganic phosphate to yield glucose-1-P
  
  • Catalyzed by glycogen phosphorylase*

Question 6

Glycogenolysis

Localization

Answer 6

Cytoplasm of glycogen storing cells

Question 7

Glycogenolysis

Energy balance

Answer 7

0 ATP

Ø energy produced, but glucose-6-P created can be used in other cycles (Eg.: GL)

Question 8

Glycogenolysis

Regulation

Answer 8

• Glycogen phosphorylase*
  
  • Ca²⁺ ↑ (activator)
  • Glucose (inhibitor)
• Glucagon ⊕
• Adrenalin ⊕
• Insulin ⊖
• Allosteric - slow
  
  • Glucose in liver → Glycogen phosphorylase ↓
  • Ca²⁺ in muscles → Glycogen phosphorylase ↑