Lipids.docx

Lipids are defined as water insoluble with amphipathic parts found in variety of biological systems e.g., cell membranes. Fatty acid structure Contains a charged COOH group with a pKa of 4.5-5. Can be saturated (solid) or unsaturated (liquid) Can be branched. Generally, has an even number of carbon...

Lipids are defined as water insoluble with amphipathic parts found in variety of biological systems e.g., cell membranes. Fatty acid structure Contains a charged COOH group with a pKa of 4.5-5. Can be saturated (solid) or unsaturated (liquid) Can be branched. Generally, has an even number of carbon atoms present in the chain. Saturated= highly melting points which increases with length of the chain. Unsaturated= lower melting points. Forms ester bonds Most abundant mammalian cells are generally: Oleate (18:1) Palmitate (16:0) Stearate (18:0) Essential fatty acids Linoleate (18:2 Δ9, 12) Linolenate (18:3 Δ9, 12,15) Arachidonate Fatty acid derivatives Fatty acids can be modified to form chemical mediators. Many used as signalling molecules. Triglycerides 3 fatty acids joined to glycerol. Amphipathic Forms cell membranes Forms fat droplets within cells. Phospholipids Has a glycerol backbone. 2 fatty acyl groups- can be saturated, unsaturated or branched. Phosphate head groups Head group e.g., ethanolamine. Contains both polar (head groups) and non-polar parts= amphipathic. The carbon chain can be unsaturated and saturated with a general number of 12-20 carbon atoms. Group of enzymes called phospholipases hydrolyse phospholipids into fatty acids. A1- found in digestive systems and hydrolyses off the fatty acids. A2- pancreatic juice, venoms and hydrolyses off the fatty acids C- liberates diacylglycerol. D- converts phospholipids to phosphatides by hydrolysing the head group. Plasmalogens- another class of phospholipids Found within the CNS and bacterial membranes. Often contains ethanolamine or choline headgroup. Has vinyl linkage rather than ether linkage. Sphingolipids- type of lipid High concentration in CNS due to myelin sheath around the nerves Not generally present in bacteria Derives from a molecule called sphingosine. Structure of sphingosine Unbranched 18 carbon alcohol Trans double bond between C4-C5 Amino group at C2 OH groups at C1 and C3. Ceramide Fatty acyl group linked to sphingosine via amide bond. Metabolic precursor of all sphingolipids Gangliosides More complex form of lipid Has the addition of sugars, can be branched or linear. The sugars are important for antibody recognition and structural reasons. Steroids Found in eukaryotic and some bacterial membranes. Derives from Isoprene and squalene. Cholesterol- type of sterol Vital for membranes fluidity Less common in plants Absent in prokaryotic, fungi. Fatty acid synthesis Occurs in the cytosol- hydrophilic. Repetitive addition of two-carbon units growing hydrocarbon chains Acyl carrier proteins is attached to growing chain. Production of acetyl ACP and malonyl ACP Initiation- condensation of acetyl and malonyl groups to produce C4 precursor and CO2. Elongation- acyl group on ACP extended by C2 units from malonyl ACP. Includes reduction, dehydration and reduction reactions. Lipid synthesis