Adipose Tissue and Muscle Metabolism

Question 1

the majority of our energy reserve is _____ that contains __% of total energy

Answer 1

the majority of our energy reserve is adipose that contains 83% of total energy

Question 2

describe the enzymes involved in mobilization and synthesis of lipids

Answer 2

• mobilization = lipolysis
  
  • enzyme = hormone sensitive lipase
  • provide energy needs for the body
• synthesis = lipogenesis (esterification)
  
  • enzyme = lipoprotein lipase (LPL)
  • storage of TAG in adipocyte

Question 3

describe the precursor molecules for the synthesis of TAG

Answer 3

• glycerol 3-P
  
  • in adipocyte, glycerol 3-P is obtained from glycolysis via DHAP
  • in hepatocyte, glycerol 3-P may be obtained from glycerol or from glycolysis pathway
• fatty acids obtained from:
  
  • diet (chylomicrons)
  • liver (VLDL): de novo fatty acid synthesis in the liver, FA are then esterified to glycerol to form TAG

Question 4

contrast the pathways in how liver vs adipose can form glycerol 3-P

Answer 4

Question 5

describe what state causes synthesis of TAGs in adipocytes

Answer 5

• occurs in the well fed state
  
  • absorb glucose
  • chylmicrons
• high insulin/glucagon ratio
  
  • leads to an increase in adipocyte GLUT-4 transporters
    
    • glucose uptake into adipocytes
• VLDL synthesis in liver -> released into the blood

Question 6

describe the mobilization of TAG in adipocytes

Answer 6

• hydrolysis of stored TAG
  
  • catabolic; energy producing
• catalyzed by hormone sensitive lipase (HSL)
  
  • active when phosphorylated
    
    • epinephrine

Question 7

describe the function of white adipose tissue (WAT)

Answer 7

• distributed throughout body
• WAT reclaims some of the FA that it mobilizes
  
  • limits the amount of FA in the blood
• regulated energy storage

Question 8

describe the function of brown adipose tissue (BAT)

Answer 8

• large number of mt
  
  • specialized for FA oxidation and heat production
• multiple fat droplets
• thermogenin leads to mt uncoupling
  
  • ​proton gradient uncoupling leads to high activity of the ETC -> heat production

Question 9

describe leptin

Answer 9

• leptin secreted by adipocytes
• leptin mediates appetite suppression
  
  • has receptors in the hypothalamus

Question 10

does obesity cause decreased or increased leptin?

Answer 10

• leptin levels are normal/HIGH in obese patients
  
  • not a problem of the ob gene
• leptin induces expression of the UCP type channel

Question 11

describe the link between obestiy and insulin resistance

Answer 11

• altered adipokine profiles in obese patients contributes to insulin resistance
  
  • hyperglycemia
• the pancreas responds with increased insulin production
  
  • hyperinsulinemia
• increased HSL activity in the absence of insulin signaling
  
  • insulin is there BUT adipose cells don’t respond to it because of insulin resistance –> hypertriacylglyceronemia

Question 12

contrast between the 3 types of sketal muscle fibers

Answer 12

Question 13

describe the use of glycogen during anaerobic muscle contraction

Answer 13

• if starting with glycogen, 3 ATP per glucose units are obtained rather than 2
• type IIB fibers have higher levels of glycolytic enzymes to compensate
• G6P is used 12x faster in Type IIb fibers than in Type I fibers

Question 14

describe how AMP and Ca regulate gylcolysis and glycogen degradation

Answer 14

• AMP stimulates PFK-1
• AMP stimulates glycogen phosphorylase b (only in muscle)
• Increased Ca stimulates glycogen phosphorylase kinase which leads to the full activation of glycogen phosphorylase