ICAR AIEEA PG Plant Biotechnology 14 July 2023 Shift-1 Paper

Cardiolipin (diphosphatidylglycerol) structure and biosynthesis:

• Cardiolipin is a unique tetra-acyl phospholipid consisting of two phosphatidyl groups linked across a shared central glycerol bridge (1,3-bis(phosphatidyl)glycerol).
• In bacterial cardiolipin synthase, two phosphatidylglycerol molecules condense with the release of one free glycerol to yield cardiolipin.
• Cephalin is phosphatidylethanolamine, ceramide is a sphingosine linked to a fatty acid, and gangliosides contain complex oligosaccharide headgroups with sialic acid.

Biosynthesis of plant fructans:

• Fructans (such as inulin and levan) are non-structural storage carbohydrates found in temperate grasses, chicory, and Jerusalem artichoke.
• The biosynthesis of all plant fructans begins with sucrose ($G-F$) as the essential starter/primer molecule, where sucrose:sucrose 1-fructosyltransferase (1-SST) transfers a fructosyl residue from one sucrose molecule to another to synthesize the trisaccharide 1-kestose.
• Fructose polymers are successively extended by adding additional fructose residues onto this terminal sucrose core.

Enzyme cofactors and prosthetic groups:

• Nitrogenase contains the FeMo-cofactor ($[\text{Mo-7Fe-9S-C-homocitrate}]$), where homocitrate coordinates to the molybdenum atom -> (II).
• Nitrite reductase contains siroheme coupled to a $[4\text{Fe}-4\text{S}]$ cluster to transfer 6 electrons reducing nitrite to ammonium -> (I).
• Serine hydroxymethyltransferase is a PLP-dependent enzyme requiring Pyridoxal phosphate -> (III).
• Acetyl-CoA carboxylase requires covalently bound Biotin for carbon dioxide fixation during fatty acid synthesis -> (IV).