Introduction to Cell Biology & Biochemistry Lecture Notes PDF

Introduction to Cell Biology & Biochemistry Dr Alessandro Siani  Lecture overview: Biological functions of lipids Sterol and derivatives Lipidic hormones Lipidic vitamins Synthesis of lipids  Lipids Refers...

Introduction to Cell Biology & Biochemistry Dr Alessandro Siani  Lecture overview: Biological functions of lipids Sterol and derivatives Lipidic hormones Lipidic vitamins Synthesis of lipids  Lipids Refers to a collection of organic molecules of varying chemical composition:  Fatty Acids (Saturated and Unsaturated)  Glycerides (Glycerol-containing Lipids)  Nonglyceride Lipids (Sphingolipids, Steroids, Waxes)  Complex Lipids (Lipoproteins) Dr Alessandro Siani  Sterol derivatives  Biological functions of lipids Energy Source When oxidised, each gram of fat releases 9 kcal of energy, more than twice the energy released by oxidation of a gram of carbohydrate Energy Storage In the form of triglycerides (TAG) in adipocytes Cell Membrane Structural Components Phosphoglycerides, sphingolipids, and steroids Dr Alessandro Siani make up the basic structure of all cell membranes  Biological functions of lipids (II) Hormones Eicosanoids Steroid Hormones Vitamins Lipid-soluble vitamins (A,D,E, and K) Vitamin Absorption Dietary fat serves as a carrier of the lipid-soluble vitamins Dr Alessandro Siani Protection – fats as shock absorber Insulation – subcutaneous fat  Fatty acids derivatives as signals Eicosanoids can act as PARACRINE signals (that sounds like gibberish, doesn’t it?) Life hack: try to learn the roots that make up scientific terms. “Mixing and matching” roots is Dr Alessandro Siani much easier than learning every word from scratch!  Any Greek speakers here? Eicosanoids can act as PARACRINE signals Eíkosi, “twenty” Para, “nearby” Ekkrinei, “to secrete” Dr Alessandro Siani Simply put, eicosanoids are fatty acids derivatives with a 20-carbon chain, that are used to transmit a message in a localised area.  Fatty acids derivatives as signals Eicosanoids can act as PARACRINE signals Eicosanoids are derived from ARACHIDONIC ACID (any Italian speakers?) Eicosanoids are drug targets Dr Alessandro Siani Dr Alessandro Siani Eicosanoids as drug targets  Sterols and derivatives Sterol is a basis for a number of other lipids C D A B Polar head Hydrophobic ‘tail’ Dr Alessandro Siani  Sterols Amphipathic (contain polar and nonpolar parts) Planar (flat) No rotation around the carbon bonds C D A B Dr Alessandro Siani Polar head Hydrophobic ‘tail’ Dr Alessandro Siani Cholesterol is a sterol derivative  Bile salts Cholic acid Taurocholic acid Look at the structure of bile salts. Can you guess their function? Bile salts are amphipathic. This property allows them to emulsify dietary lipids allowing their solubilisation and Dr Alessandro Siani absorption. At a molecular level, they behave in a similar way to detergents (this does NOT mean you should drink washing up liquid!).  Steroid hormones Steroids are derived from sterol They act as cellular messengers Many drugs are steroid analogues Dr Alessandro Siani  Sex hormones Progesterone Dr Alessandro Siani  Corticosteroids Any idea what these two do? Dr Alessandro Siani Dr Alessandro Siani Steroid drugs These are synthetic analogs of steroid hormones, and are used to treat a variety of inflammatory and autoimmune disorders.  Vitamins Vitamins are either soluble in water or fats Water-soluble vitamins are: - B class (1, 2, 3, 5, 6, 7, 9, 12) - C Fat-soluble vitamins are: - A - D Dr Alessandro Siani - E - K Dr Alessandro Siani Vitamin A (Retinol)  Vitamin A (Retinol) Important in skin cells Also important in vision Eat your carrots!!! Dr Alessandro Siani  Eating lots of carrots gives you the ability to see in the dark!... does it, though? During WW2, to prevent the Germans finding out that Britain was using radar to intercept bombers on night raids, the Air Ministry issued press releases stating that British pilots were eating lots Dr Alessandro Siani of carrots to give them exceptional night vision.  Vitamin D Made from 7-dehydrocholesterol In turn is modified to 1,25-dihydroxycholecalciferol Dr Alessandro Siani Controls calcium metabolism Dr Alessandro Siani Vitamin D A lack of vitamin D or calcium is the most common cause of rickets Dr Alessandro Siani Vitamin K Is often used as an antidote against rat poison (e.g. coumarin) and as a treatment for anticoagulant (e.g. warfarin) overdose. Dr Alessandro Siani Making Lipids  Lipids are built from acetate Lipids are made from smaller units Acetate is converted to Acetyl-Coenzyme A (Acetyl-CoA) Fatty acids and sterols are then made from Acetyl-CoA Dr Alessandro Siani Dr Alessandro Siani Acetate Dr Alessandro Siani Acetyl-CoA Dr Alessandro Siani Malonyl-CoA is an intermediate Dr Alessandro Siani Fatty acids are built two carbons at a time  Palmitate is the precursor of fatty acids Fatty acid synthase makes Palmitate Palmitate is 16:0 Longer are made by fatty acid elongation systems Dr Alessandro Siani  Smooth Endoplasmic Reticulum Longer chain fatty acids are made in the smooth ER Part of the synthesis of phospholipids and cholesterol also takes place in the smooth ER Prokaryotic cells do not have an endoplasmic reticulum. Dr Alessandro Siani  Making Sterols Sterols are also made from acetate Isoprene (shown below) is an intermediate in the reaction Dr Alessandro Siani Dr Alessandro Siani  Confused? Today we learned that:  Lipids can act as signaling molecules  Eicosanoids and sterol derivatives are key classes of lipid hormones  Vitamins can be hydrophilic or hydrophobic (lipidic)  Natural or synthetic lipid hormones can be used for pharmaceutical purposes  Lipids are built from smaller building blocks Dr Alessandro Siani (Acetate and acetyl-CoA)  Palmitate is the precursor of fatty acids  Isoprene is the precursor of sterols