Question

Biochemistry:

"I provide radiolabeled malonyl-CoA to liver cells."

Base on the sentence above, create a question (relatives to metabolic pathway in cell: gluconeogenesis, PHD, TCA cycle). After that, answer to your own question.

P/s: it's a complete question already. The requirement is: You have to think and create/make up your own question that relates to the sentences, then answer to the question you just made up.

Answer 1

I provide radio-labelled malonyl-CoA to liver cells, in which metabolic pathway does it gets incorporated?

• Fatty acid metabolism occurs in mitochondria and peroxisomes.
• Thus, to be oxidized, fatty acids should first enter the organelle, which is mediated by fatty acid protein transporters associated with the membrane surface.
• To enter the mitochondrial matrix, long chain fatty acids should be trans esterified and require coupling to carnitine.
• This is mediated by the carnitine palmitoyl-transferase I (CPT-I).
• CPT-I convert, long chain fatty acyl-CoA to long chain acylcarnitine.
• This allows the long chain fatty acid to be transported across the inner mitochondrial membrane with the aid of carnitine translocase (CAT).
• Palmitic acid or Hexadecenoic acid, is a long chain fatty acid. Thus, to enter the mitochondria for oxidation process, it requires CPT-I for its coupling with carnitine.
• Short chain fatty acid, like Octanoic acids can directly cross the mitochondrial membrane and does not require carnitine association or CPT-I enzyme.
• CPT-I is in turn inhibited by Malonyl-CoA.
• Thus, when there is high concentration of Malonyl-CoA, it acts as an inhibitor to enzyme CPT-I. As a result, long chain fatty acids, like Palmitic acid cannot be coupled to carnitine. So, it cannot enter the mitochondria for oxidation.
• The regulation of Malonyl-Co concentration is observed to be regulated by hormones insulin and glucagon.
• Thus, Malonyl co-A acts as signalling molecule for lipid partitioning and 2 -carbon donor for fatty acid chain formation.