Molecular Components of Cells PDF

Chapter 2 Molecular Components of cells Reem Dakhil M1 Biochemistry (Lebanese University) M2 Physiology, Epigenetics, Differentiation, and Cancer (Université Grenoble Alpes)  II. Carbohydrates Functions ✓ Energetic ✓ Structural ✓ Cell ident...

Chapter 2 Molecular Components of cells Reem Dakhil M1 Biochemistry (Lebanese University) M2 Physiology, Epigenetics, Differentiation, and Cancer (Université Grenoble Alpes)  II. Carbohydrates Functions ✓ Energetic ✓ Structural ✓ Cell identity glycogen in animals cellulose in plant cell wall blood groups  II. Carbohydrates 1. Monosaccharides Definition ✓ aka “simple oses” ✓ Most are D-stereoisomers ✓ CnH2nOn (3≤n≤6) ✓ Less diverse than proteins since: - Only a few monosaccharaides can form polymers - Different types do not combine much (max 2) D-glucose C6H12O6  II. Carbohydrates 1. Classification of Monosaccharides ✓ By functional group - Aldoses (aldehyde group) - Ketoses (ketone group) ✓ By n 3: trioses – 4: tetroses – 5: pentoses – 6: hexoses Aldose pentose: ribose Aldose hexoses: glucose, galactose, mannose Ketose hexose: fructose ribose glucose galactose mannose fructose  II. Carbohydrates 2. Cyclic Oses ✓ n>4 → straight chain or cycle → cycle is more stable → or → Pyranoses (6C) & furanoses (5C) α β ✓ From intramolecular reaction between OH & aldehyde/ketone group ✓ α & β isomers: differ by orientation of OH that replaced the aldehyde/ketone - α: downward - β: upward ✓ Usually cyclic oses are switchable between α & β until polymerized.  II. Carbohydrates 4. Modification ✓ Osamines addition of amine group (---NH2) eg: glucose→glucosamine. galactose→galactosamine ✓ N-acetyl osamines addition of acetyl group (---COCH3) to the amine group eg: NAG: N-acetyl galactosamine ✓ Uronic acids acidification of CH2OH into COOH eg: NANA: N-Acetyl Neuraminic Acid (from mannose)  II. Carbohydrates 5. Dimers and Polymers ✓ Disaccharide: 2 oses joined by covalent bond “glycosidic bond” Its formation releases H2O - Saccharose = glucose + fructose - Lactose = glucose + galactose - Maltose = 2 glucose ✓ Oligosaccharide: short polymer of monosaccharaides can be branched / unbranched can be linked to proteins / lipids for maturation  II. Carbohydrates 5. Dimers and Polymers ✓ Polysaccharide (Glycan): long chain of monosaccharides branched / unbranched simple or modified oses Functions: Structural - cellulose in plant cell wall – peptidoglycans in bacterial cell wall Energetic - glycogen in muscles – starch in plants  II. Carbohydrates 5. Dimers and Polymers ✓ Homopolysaccharide: polymer of the same molecule - Starch & glycogen = branched polymers of α-D-glucose - Cellulose = unbranched polymer of β-D-glucose - Chitin = polymer of N-acetyl glucosamine, in insects shell ✓ Heteropolysaccharide: polymer of 2 diferent simple/modified oses - GAG = glucosamine + galactosamine - Hyaluronic acid = glucoronic acid + N-acetyl glucosamine - Chondroitin Sulfate = glucuronic acid + N-acetyl galactosamine - Keratan Sulfate = N-acetyl glucosamine + D-galactose  FS.I Partial 2020 13)b, 14)d, 15)a, 12)c, 13)b FS.I Partial 2019