Lipid biosynthesis Flashcards
Lipids fulfill a variety of biological functions
- Energy __ (_)
- Constituents of _
- Anchors for __ (/)
- Cofactors for _ (__)
- Signaling __ (__, _)
- Pigments (__)
- Det__ (b_ s_)
- Tran__
- Ant__ (Vit __)
Lipids fulfill a variety of biological functions
- Energy storage (TG)
- Constituents of membranes
- Anchors for membrane proteins (IP2/PIP3)
- Cofactors for enzymes (Vit K)
- Signaling molecules (eicosanoids, IP3)
- Pigments (retinal)
- Detergents (bile salt)
- Transporters
- Antioxidants (Vit A)
What is the phase 1 of biosynthesis of Fatty Acids?
Biosynthesis of FA starts with activation which occurs through formation of Malonyl-CoA which is made of acetyl-CoA-> cells have to decide- whether to use Acetyl CoA for energy, for ketone body synthesis of FA synthesis
AcetylCoA becomes activated when it is converted to Malonyl CoA by Acetyl-CoA Carboxylase (ACC)- Carboxylates Acetyl CoA
What does ACC use to carboxylate Acetyl-CoA
bicarbonate ion and energy
What are the domains of ACC?
- Biotin carboxylase portion
- Biotin carrier domain
Transcarboxylase domai
- Biotin carrier domain
Describe how does ACC function
Biotin carrier protein has an arm that takes bicarbonate ion and transfer it to Acetyl- CoA via trans-carboxylation - biotin carboxylase function
Biotin arm is held by biotin carrier protein
Carboxylation of biotin arm is achieved by Biotin carboxylase portion
Once biotin is carboxylated, arm turns 180 degrees and shifts to the right domain- transcarboxylase domain- which has a docking mechanism for acetyl CoA
Docking domain takes the carboxyl group and adds it to Acetyl-CoA converting it to Malonyl-CoA
Describe types of fatty acid synthase
- Type I in vertebrates and fungi
- Type II in bacteria and plant
Describe FA synthase. When is it used?
Once Malonyl CoA is made it can go into FA synthesis FA synthase (doesn't use ATP) is used which is an enzymatic complex made out of 6 individual protein It always functions in a dimer - whenever synthesis occurs, there are always 2 copies - 2 FA are synthesized at a time
Describe phase 2 of FA synthesis
Phase 2: Addition of 2 carbons to fatty acyl chain
Acetyl CoA is needed which is captured by KS (ketoacyl ACP-synthase) domain of FA synthase from cytoplasm
Acetyl-CoA becomes attached to KS domain
Malonyl CoA attaches to ACP domain (acyl carrier protein- carries acyl chain that made)
Carboxyl group of Malonyl CoA interacts with Acetyl COA present on KS domain - Acetyl CoA and Malonyl CoA are put together
Now malonyl CoA has 2 carbons added to it-> chain grows by 2 carbons at ACP- site of chain growth. CO2 is produced
ACP receives Malonyl CoA
Reduction-Dehydration-Reduction occurs to turn unsaturated O-double bonded chain to unsaturated carbon-hydrogen chain
Growing chain of fatty acids has to be transferred to KS domain -> ACP is free to receive new malonyl CoA
2 more carbons can be added until 16 carbon chain is made-palmitate
What is the cite of the chain growth of FA synthase?
ACP domain (acyl carrier protein)
__ is the most common FA made by fatty acids synthase - can synthesized it a its max __
Palmitate is the most common FA made by fatty acids synthase - can synthesized it a its max capacity
What are the condition to make a fatty acid longer than 16C?
New enzymes are required to make a longer chain
Elongation does occur, but FA have to be transported to other compartments of the cell such as ER or mitochondria- sites of elongation
__ is a precursor for longer chain FA
Palmitate is a precursor for longer chain FA
Long-chain FA are produced in __ (also __)
Long-chain FA are produced in ER (also Mitochondria)
FA such as Palmitate (16:0) and Stearate (18:0) are desaturated by __by __
FA such as Palmitate (16:0) and Stearate (18:0) are desaturated by Fatty acyl-CoA desaturase by oxidative reactions
Are desaturase enzymes specific or versatile?
desaturase enzymes are specific for each length
What does (18:2Δ9,12) mean
18 carbon long
2 double bonds at carbon 9 and 12
What is special about linoleate?
Linoleate (18:2Δ9,12) cannot be synthesized in mammals (essential)
Arachidonate (20:4Δ5,8,11,14) is synthesized from linoleate