0224 Synthesis and use of ketones and cholesterol Flashcards
What are ketone bodies and when are they used How are ketone bodies synthesised What is cholesterol Synthesis of cholesterol Regulation of cholesterol synthesis Uses of cholesterol & its derivatives
What are some types of tissues that utilise ketone bodies
Brain cells, skeletal muscle, cardiac muscle and renal tissue
Where does ketone synthesis occur and why does it occur there
Ketones are synthesised in the liver. One of the reasons it is made in the liver is because it lacks the enzyme to break it down (keto-acyl-CoA transferase).
This means in times of starvation energy is getting to the sites it is needed most
How does oxaloacetate affect ketone body synthesis
Diversion of OAA in TCA to gluconeogenesis means more Acetyl-CoA is directed to ketone body synthesis
What are the 3 main types of ketone bodies
Beta-hydroxy-butyrate, acetoacetate and acetone (not really utilised)
Describe the process of ketone synthesis and the enzyme that differentiates it from cholesterol synthesis
Acetyl-CoA to Aceto-acetyl-CoA (thiolase), AAC to HMG-CoA (HMG CoA synthase), HMG-CoA to Acetoacetate (HMG CoA lyase). Acetoacetate gives rise to both acetone and beta-hydroxy-butyrate. The distinguishing enzyme is HMA-CoA lyase
Describe the process of ketone body utilisation and the key enzyme that is needed to break it down
B-hydroxy-butyrate to acetoacetate (b-hydroxy-But. dehydrogenase), AAto aceto-acetyl-CoA (keto-acyl-CoA transferase). AAC to acetyl-CoA (thiolase). The key enzyme (not found in liver) is keto-acyl-CoA transferase
Where does cholesterol synthesis occur
Cholesterol synthesis can occur anywhere but a large proportion of it occurs in the liver (25%)
Name the condition where ketone body synthesis greatly excedes the extra-hepatic need
Ketosis (or ketoacidosis). It leads to acidification of plasma
Describe some roles of Cholesterol
membrane structure (Lipoprotein membranes), Hormones (testosterone), Fat emulsification (bile acids and salts)
Where in the cell is cholesterol synthesised
in the cytosol
Where in the cell does Ketone body synthesis occur
In the mitochondria (hepatocytes)
Describe the process of cholesterol synthesis and the enzyme that differentiates it from ketone body synthesis
Acetyl-CoA to Aceto-acetyl-CoA (thiolase), AAC to HMG-CoA (HMG CoA synthase), HMG-CoA to mevalonate(HMG CoA reductase). The distinguishing enzyme is HMA-CoA reductase
How is Cholesterol synthesis regulated
By cellular [cholesterol], And the amount and acitvity of HMG-CoA reductase (insulin stimulates and glucagon inhibits)
What is the role of statins)? Hint: it is used to treat high cholesterol
Statins inhibits HMG-CoA reductase
How is cholesterol transported
Cholesterol is transported via lipoproteins
