BY3BC1- Medical Biochemistry Lecture 6 - Blood Lipids LO- - Categorise Major groups of lipids - Difference between apoproteins and lipoproteins - Lipid biochemistry and metabolism - Lipid disorders and clinical disease - The role of the clinical biochemistry lab in analysing blood lipids - The treatment of dyslipidaemia Essential to life Major biomolecule lipids - Structural component of cells (plasma membrane) - Metabolic and hormone pathways (vitamin d absorption in fat capsules ) - Energy storage Major groups of lipids Fatty acids - Long C chain with COOH (carboxyl group) - Double bonds unsaturated between carbons, saturated fatty acids have no double bonds (no kink) - Metabolic fluids sored as triglycerides Triglycerides - Energy source storage - Glycerol backbone with 3 fatty acid residues Cholesterol - Absorbed by Diet and produced by the liver - Essential component of cell membranes provides rigidity
Lipoproteins - Transport lipid around the body - Solubility of lipids is increased to aid transport - Lipid and apoproteins join Apoproteins (apoproteins - lipid lacking) Insoluble lipids are transported into hydrophilic environments in the blood by "marrying" to a protein (apoprotein)= lipoprotein Apoproteins are multifunctional proteins: Intestine and liver A A1, A2, A4 and A5 B B48 and B100 C C1, C2 and C3 Liver Intestine (B48) and Liver (B100) - Maintain structural integrity of the lipoproteins once they've bound to alipid E E2, E3 and E4 Intestine, Liver and Macrophage - Regulate enzymes acting on lipoproteins (act as cofactors) - Receptor recognition Categorised alphabetically A, B, C, E with subgroups different are synthesized and produced in different regions e.g. A in intestine and liver. Defects cause dyslipidaemia Lipoproteins Marriage between a lipid and an apoprotein Three roles: - Interorgan fuel (releasing triglycerides) - Distribution - Maintain cholesterol pool (rich in cholesterol) Core of the lipoproteins rich of triglycerides and esters The apoprotein determines the lipoprotein class Apolipoprotein Cholesteryl ester Phospholipid Triglyceride Cholesterol
Key lipoprotein classes Variation in : Triglycerides, cholesterol, phospholipids and apoproteins 1. Chylomicrons 2. VLDL 3. LDL Composition 86% Triglyceride 5% Cholesterol 7% Phospholipid 2% Protein Major apoproteins A,, B4B, C2 and E 86% Triglyceride 5% Cholesterol 7% Phospholipid 2% Protein B100, C2 and E 6% Triglyceride 50% Cholesterol 22% Phospholipid 22% Protein B100 Mean Diameter (nm) 500 Density (g/mL) 0.93 Function 43 22 0.95 - 1.006 1.019-1.063 Main carrier of dietary triglycerides Main carrier of endogenously produced triglycerides Main carrier of cholesterol 4. HDL 4% Triglyceride 17% Cholesterol 25% Phospholipid 55% Protein A, and A2 8 1.063-1.210 Protective Phospholipid and protein percentage Mean diameter Extra reading: IDL 5 major groups. 1. Chylomicrons - largest and the least dense and are majority consist of triglycerides- function carry dietary triglycerides All shown in the above table Exogenous pathway- chylomicrons Absorb triglycerides in our diet and get packaged to chylomicrons in the small intestine, which associate with ApoB-48 and many other apoproteins forming a lipoprotein which leave via th lymphatic system and go into the blood. These chylomicrons are then in the blood and the