1. The process occurs similar to beta-oxidation, though in reverse. Important distinctions are noted below in a-f.
* a. Fatty acid synthesis up to palmitate occurs in the cytoplasm, but beta oxidation occurs in mitochondrial matrix. * b. Fatty acids are built using an acyl carrier protein (ACP), but beta oxidation uses CoA. * c. NADPH is used to donate electrons in synthesis, but NAD+ or FAD are used to accept electrons in oxidation in the mitochondrion. * d. A three carbon molecule, malonyl-ACP donates two carbons to the growing fatty acid chain - a carbon dioxide is lost in the process. Beta oxidations yield two carbon acetyl-CoA units. * e. Synthesis of fatty acids longer than 16 carbons occurs in endoplasmic reticulum or mitochondrion. Oxidation of fatty acids longer than 16 carbons begins in peroxisomes. * f. In fatty acid biosynthesis, a D-hydroxyl intermediate is formed at carbon #3. In fatty acid oxidation, an L-hydroxyl intermediate is formed at carbon #3.
2. Acetyl-CoA carboxylase catalyzes the addition of a carboxyl group to acetyl-CoA to form malonyl-CoA. The enzyme is regulated allosterically (inhibited by palmitoyl-CoA and activated by citrate) and by covalent modification (phosphorylation inhibits, dephosphorylation activates).
3. Fatty acid biosynthesis occurs in the cytoplasm and the fatty acids are built on a 'carrier' known as acyl carrier protein (ACP). The Co-A above is swapped for ACP to start the synthesis process. Acetyl-CoA gets into the cytoplasm from the mitochondrion by the citrate shuttle. Acetyl-CoA is linked to oxaloacetate in the mitochondrion to make citrate, which is transported out and then citrate is cleaved to yield acetyl-CoA and oxaloacetate in the cytoplasm.
4. Malonyl-ACP is the "adding block" for fatty acid biosynthesis. Acetyl-ACP is the starting block for fatty acid biosynthesis.
5. During fatty acid synthesis, decarboxylation of malonyl-ACP yields a two carbon addition to the growing fatty acid chain. The two carbons from malonyl-ACP go onto the carboxyl end of the growing chain.
6. The numerous enzymes of fatty acid biosynthesis are contained in a multi-enzyme complex called fatty acid synthase.
7. Fatty acids up to 16 carbons long are synthesized in the cytoplasm by the fatty acid synthase. Synthesis of fatty acids longer than 16 occurs in the endoplasmic reticulum (or mitochondrion) catalyzed by enzymes called elongases.
This course in general biochemistry is intended to integrate information about metabolic pathways with respiration (respiratory control) and initiate the student into a microscopic world where blueprints are made of deoxyribonucleic acids, factories operate using enzymes, and the exchange rate is in ATPs rather than Yens or Euros. Beyond explaining terms, and iterating reactions and metabolic pathways, this course strives to establish that the same principles that govern the behavior of the world around us also govern the transactions inside this microscopic world of the living cell. And by studying and applying these principles, we begin to understand cellular and bodily processes that include sensory mechanisms.
Topics include: 1. Lipids, Membranes and Transport 2. Electron Transport, Oxidative Phosphorylation and Mitochondrial 3. Transport Systems 3. Lipid Metabolism 4. Nucleotide Metabolism 5. DNA Replication 6. Transcription 7. Translation