Which of the following is multi-enzyme complex?
Correct Answer: Fatty acid synthase
Description: Ans. c (Fatty acid synthase). (Ref. Harper's biochemistry 27th ed. Pg. 238 Chapter 23)KEY STEPS OF FATTY ACID SYNTHESIS# Fatty acid entry into mitochondrion is via Camiitine shuttle.2# Fatty acid entry into cytosol is via Carnitine shuttle.# Fatty acid synthase is a polypeptide multi-enzyme complex.2# Acyl carrier protein is a integral part of this polypeptide complex and functions as CoA.# Being a single unit; great efficiency freedom from interference and co-ordinated synthesis of all enzymes encoded by a single gene as advantage of this fatty acid synthase multi-enzyme complex.# Another example of multienzyme complex is:- pyruvate dehydrogenase complex (complex contains 3 enzymes that require 5 cofactors).The Fatty Acid Synthase Complex Is a Polypeptide Containing Seven Enzyme Activities# In bacteria and plants, the individual enzymes of the fatty acid synthase system are separate, and the acyl radicals are found in combination with a protein called the acyl carrier protein (ACP).# However, in yeast, mammals, and birds, the synthase system is a multienzyme polypeptide complex that incorporates ACP, which takes over the role of CoA. It contains the vitamin pantothenic acid in the form of 4'-phosphopantetheine.# In mammals, the fatty acid synthase complex is a dimer comprising two identical monomers, each containing all seven enzyme activities of fatty acid synthase on one polypeptide chain. Initially, a priming molecule of acetyl-CoA combines with a cysteine --SH group catalyzed by acetyl transacylase.# Malonyl-CoA combines with the adjacent --SH on the 4'-phosphopantetheine of ACP of the other monomer, catalyzed by malonyl transacylase (reaction lb), to form acetyl (acyl)-malonyl enzyme.# It is liberated from the enzyme complex by the activity of a seventh enzyme in the complex, thioesterase (deacylase).# The free palmitate must be activated to acyl-CoA before it can proceed via any other metabolic pathway. Its usual fate is esterification into acylglycerols, chain elongation or desaturation, or esterification to cholesteryl ester.# In mammary gland, there is a separate thioesterase specific for acyl residues of C8, C10, or C12, which are subsequently found in milk lipids.
Category:
Biochemistry
Get More
Subject Mock Tests
Practice with over 200,000 questions from various medical subjects and improve your knowledge.
Attempt a mock test nowMock Exam
Take an exam with 100 random questions selected from all subjects to test your knowledge.
Coming SoonGet More
Subject Mock Tests
Try practicing mock tests with over 200,000 questions from various medical subjects.
Attempt a mock test now