Cytology Ch2.4 PDF - Molecular Components of Cells

Chapter 2 Molecular Components of cells Reem Dakhil M1 Biochemistry (Lebanese University) M2 Physiology, Epigenetics, Differentiation, and  Cancer (Université Grenoble Alpes) III. Lipids All are non-polar → insoluble in wate...

Chapter 2 Molecular Components of cells Reem Dakhil M1 Biochemistry (Lebanese University) M2 Physiology, Epigenetics, Differentiation, and  Cancer (Université Grenoble Alpes) III. Lipids All are non-polar → insoluble in water, soluble in non-polar solvents Functions Structural: phospholipids: component of cell membrane Energetic: triglycerides: stored in plants seeds & animal adipose tissue Communication: steroid hormones, eicosanoids, phosphatidylinositol 2 Types Saponifiable: have f.a, can undergo saponification reaction Non-saponifiable: no f.a, can not undergo saponification Saponification or NaOH III.  Lipids 1. Saponifiable Lipids a. Fatty Acids ✓ Amphipathic: 1 polar hydrophilic head (COOH) & nonpolar hydrophobic tail (hydrocarbon chain) ✓ Formula: CH3-(CH2)n-COOH (2≤n≤20) n is even ✓ Rarely occur free ✓ More energetic than carbs ✓ Differ by: length of chain & unsaturation degree (nb of C=C) → both affect membrane fluidity ✓ Saturated f.a.: no double bond, solid at room t◦ (Butyric acid, Myristic acid, Palmitic acid) ✓ Unsaturated f.a.: ≥1 double bond, fluid at room t◦ (Arachidonic acid, Linoleic acid, Oleic acid)  III. Lipids 1. Saponifiable Lipids b. Triglycerides / Triacylglycerols / neutral fats ✓ Neutral fats → no polar groups ✓ Glycerol + 3 f.a joined by ester bonds ✓ Diverse since many f.a types can form it ✓ Function: stored energy reserve ✓ Hydrolysis: by lipases or: by alkaline medium + heating  III. Lipids 1. Saponifiable Lipids c. Phospholipids ✓ Function: Structural (found in cell membranes) ✓ Amphipathic: 1 large polar head (phosphate) + 2 hydrophobic tails ✓ Glycerol-derived: Glycerophosphatides: Phosphate + glycerol + 2 f.a ✓ Sphingosine-derived: Sphingophospholipids: Phosphate + sphingosine + 1 f.a Found in myelin sheath (sphingomyelin) * Ceramide = sphingosine + f.a ✓ Choline, Serine, Ethanolamine, or Inositol can be added to increase head polarity  III. Lipids 1. Saponifiable Lipids d. Glycolipids ✓ Function: cell identity (blood group – immunity – cell-cell  recognition) → found on outer cell membrane ✓ - Glycerol-derived: in plants & bacteria (Sugar + glycerol + 2 f.a ) - Sphingosine-derived: in animals (Sugar + sphingosine + 1 f.a) ✓ - Cerebrosides: Sugar is a simple ose (eg: galactocerebroside in brain’s myelin sheath) - Gangliosides: Sugar is an oligosaccharide III. Lipids 1. Saponifiable Lipids e. Cerides ✓ Esters of f.a + “fatty alcohol” (long hydrocarbon chain ending with OH) ✓ In bee wax, leaf cuticle, cork III. Lipids 2. Non-saponifiable Lipids a. Terpenes ✓ Polymers of propene with cyclization at one end & (maybe) polar OH at the other → moderately amphipathic ✓ Vit. A, E, K & carotenoids (lycopene, carotene)  III. Lipids 2. Non-saponifiable Lipids b. Steroids cholesterol ✓ Cyclic molecules carrying different functional groups ✓ Functions: Communication: Steroid hormones (estrogen, progesterone, testosterone, corticosterone, adrenal hormones…) Vitamins: Vit. D for growth & bone development (synth in skin) Structural: Cholesterol in plasma membrane controls its fluidity (bidirectionally) *It’ a precursor for steroid hormones, vit. D, bile salts… (Found in animal products) III. Lipids 3. Hydrophobic Interactions Lipids are amphipathic→ water insoluble→ mixing forms heterogeneous mixtures ✓ Monolayers ✓ Bilayers: polar hydrophilic surfaces, hydrophobic center that prevents diffusion of  large hydrophilic molecules ✓ Micelles: sphere of hydrophilic surface & hydrophobic core ✓ Liposomes: long bilayer folded back → hydrophilic surfaces & lumen FS.I Partial 2020 FS.I Partial 2019 10. a 11. b 12. a 14. a 15. a 23. b 30. energetic