Metabolism and regulation Flashcards
In the post-absorptive state what are the 3 main sources of glucose?
Glycogenolysis
Lipolysis
Protein breakdown
Where does glycogenolysis occur?
In the liver (directly) and in skeletal muscle (indirectly)
What is the mechanism involved in hepatic glycogenolysis?
Enzymatic conversion of glycogen to glucose
How does skeletal muscle indirectly produce glucose?
Glucose-6-phophate ATP, pyruvate and lactate. Lactate then processed by the liver which releases glucose into the blood (which can then be used)
How does lipolysis produce glucose?
Hydrolysis of triglycerides produce glycerol and fatty acids. Glycerol is converted enzymatically to glucose the liver.
How can protein break down produce glucose?
Amino acids converted by the alpha-keto acid to glucose in the liver
Define gluconeogenesis
The process of generating new molecules of glucose from non-carbohydrate sources
How is fat stored?
Within adipocytes which then form tissue called adipose tissue
What % of all energy stored in the body do triglycerides account for?
78%
Name 3 main functions of lipids
Energy reserves
Structural part of cell membranes
Hormone metabolism
Where are high density lipoproteins formed?
Liver
Where are low density lipoproteins formed?
Plasma
What is the main function of high density lipoproteins?
To remove excess cholesterol from the blood and tissue
What is the main function of low density lipoproteins?
To transport cholesterol to cells throughout the body.
A positive net gain in amino acids is called …
Anabolic
A negative net gain in amino acids is called …
Catabolic
What is the most common cause of a positive nitrogen balance?
Pregnancy
What is the most common cause of a negative nitrogen balance?
Malnutrition
Where and by what process is alanine converted to pyruvate?
Transamination occurs in the liver
What is produced when glutamate undergoes oxidative deamination?
Ammonium (NH4+) which quickly dissociates into ammonia (NH3)
Where are the enzymes utilised in the urea cycle found?
Cytosol of hepatocytes or the mitochondria (in the liver)
What is arginine cleaved by arginase to produce?
Urea and ornithine
Outline the urea cycle (provide key enzymes and substrates)
Arginine (+ arginase) >urea and ornithine.
Ornithine (+NH3 +CO2) > citrulline
Citrulline (+ammonia) >arginine
What happens if the urea cycle does not occur (/not at a sufficient rate)?
High levels of ammonia in the blood
