Lipid biosynthesis is essential for plant cells, with lipids making up 5-10% of dry weight, primarily in membranes. Membranes are crucial for cell structure and function, and lipids are vital for processes like photosynthesis. Lipids also serve as carbon storage in seeds, up to 60% of dry weight, and are involved in cuticular lipids that protect plants. Lipids are defined by their insolubility in water and extraction by nonpolar solvents. The most abundant lipids in plant cells are derived from fatty acid and glycerolipid biosynthesis. The fatty acid biosynthesis pathway is a primary metabolic pathway found in all plant cells, essential for growth. Fatty acids are typically esterified to glycerol, forming glycerolipids. These lipids have nonpolar fatty acyl chains and polar headgroups, making them amphipathic and essential for membrane bilayers. Triacylglycerols (TAGs), formed when all three glycerol positions are esterified with fatty acids, are the major form of lipid storage in seeds. Fatty acid synthesis occurs in the plastid, unlike in animals and fungi, which produce fatty acids in the cytosol. Plants must export fatty acids from the plastid to other cell sites, and the cell must control this process. The main fatty acids in plants are 18:1, 18:2, 18:3, 16:0, and 16:3, which make up over 90% of the acyl chains in plant membranes. The fatty acid biosynthesis pathway begins with acetyl-CoA, derived from the acetyl-CoA pool in the plastid. This pool is maintained through various pathways, including mitochondrial PDH and free acetate transport. Acetyl-CoA carboxylase (ACCase) catalyzes the first reaction of fatty acid biosynthesis, converting acetyl-CoA and CO2 to malonyl-CoA. ACCase has two forms: a multifunctional structure in the cytosol and a multisubunit structure in the plastid. ACCase is a key regulatory enzyme in fatty acid synthesis, with different isozymes in plants. The prokaryotic form is found in plastids, while the eukaryotic form is outside the plastid. The prokaryotic form is involved in supplying malonyl-CoA for de novo fatty acid synthesis, while the eukaryotic form is involved in other pathways like cuticular lipid production and flavonoid biosynthesis. The fatty acid synthesis pathway involves several enzymes, including condensing enzymes, which are logical control points. The pathway produces saturated fatty acids, but most plant tissues have unsaturated fatty acids. The first double bond is introduced by stearoyl-ACP desaturase, a soluble enzyme unique to plants.Lipid biosynthesis is essential for plant cells, with lipids making up 5-10% of dry weight, primarily in membranes. Membranes are crucial for cell structure and function, and lipids are vital for processes like photosynthesis. Lipids also serve as carbon storage in seeds, up to 60% of dry weight, and are involved in cuticular lipids that protect plants. Lipids are defined by their insolubility in water and extraction by nonpolar solvents. The most abundant lipids in plant cells are derived from fatty acid and glycerolipid biosynthesis. The fatty acid biosynthesis pathway is a primary metabolic pathway found in all plant cells, essential for growth. Fatty acids are typically esterified to glycerol, forming glycerolipids. These lipids have nonpolar fatty acyl chains and polar headgroups, making them amphipathic and essential for membrane bilayers. Triacylglycerols (TAGs), formed when all three glycerol positions are esterified with fatty acids, are the major form of lipid storage in seeds. Fatty acid synthesis occurs in the plastid, unlike in animals and fungi, which produce fatty acids in the cytosol. Plants must export fatty acids from the plastid to other cell sites, and the cell must control this process. The main fatty acids in plants are 18:1, 18:2, 18:3, 16:0, and 16:3, which make up over 90% of the acyl chains in plant membranes. The fatty acid biosynthesis pathway begins with acetyl-CoA, derived from the acetyl-CoA pool in the plastid. This pool is maintained through various pathways, including mitochondrial PDH and free acetate transport. Acetyl-CoA carboxylase (ACCase) catalyzes the first reaction of fatty acid biosynthesis, converting acetyl-CoA and CO2 to malonyl-CoA. ACCase has two forms: a multifunctional structure in the cytosol and a multisubunit structure in the plastid. ACCase is a key regulatory enzyme in fatty acid synthesis, with different isozymes in plants. The prokaryotic form is found in plastids, while the eukaryotic form is outside the plastid. The prokaryotic form is involved in supplying malonyl-CoA for de novo fatty acid synthesis, while the eukaryotic form is involved in other pathways like cuticular lipid production and flavonoid biosynthesis. The fatty acid synthesis pathway involves several enzymes, including condensing enzymes, which are logical control points. The pathway produces saturated fatty acids, but most plant tissues have unsaturated fatty acids. The first double bond is introduced by stearoyl-ACP desaturase, a soluble enzyme unique to plants.