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BIO 330 Cell Biology Spring 2011 Lecture Outline Chemistry of the Cell I. The Importance of Carbon A. Basic nature of carbon Valence of 4 4 covalent bonds Single, double, and triple bonds B. High stability of carbon-containing molecules Breaking carbon-carbon bonds requires high energy C. Diversity of carbon-containing molecules Hydrocarbons Functional groups Negatively charged at pH 7.4 – carboxyl & phosphate Positively charged at pH 7.4 – amino Neutral at pH 7.4, but polar – hydroxyl, sulfhydryl, carbonyl, aldehyde D. Carbon-containing molecules can form stereoisomers Tetrahedral structure Asymmetry Biologically relevant Examples – L-alanine vs D-alanine; D-glucose II. The Importance of water A. Polarity Bond angle is critical, causes polarity (partial charges) Electronegative at oxygen end B. Cohesion Hydrogen bonds between water molecules Allows for: High surface tension High boiling point High specific heat High heat of vaporization C. Temperature-stabilizing capacity High specific heat Hydrogen bonds act as buffer for increased energy Buffer cells from heat released during chemical reactions High heat of vaporization Cooling effect of sweating, panting, etc. D. Universal solvent Most molecules in cells are polar = hydrophilic Some are nonpolar = hydrophobic Spheres of hydration BIO 330 Cell Biology Spring 2011 Lecture Outline III. The Importance of Selectively Permeable Membranes A. Physical composition Phospholipids Glycolipids Membrane proteins Sterols (cholesterol, ergosterol, phytosterol) Membrane lipids are amphipathic B. Fluid-mosaic model Lipid bilayer Proteins – may be embedded in or associated with the lipid bilayer Transport proteins Enzymes Receptors Electron carriers (e.g., mitochondrial membranes) C. Membranes are selectively permeable Very small molecules diffuse across membranes freely E.g., water, oxygen, carbon dioxide, ethanol, urea Large molecules cannot pass freely through membrane – need help Ions cannot pass freely through membrane – need help Transport proteins Hydrophilic channel Carrier IV. The Importance of Synthesis by Polymerization of Small Molecules A. Macromolecules Polymers of repeating subunits (monomers) B. Hierarchical structure of a cell Organic molecules Biological macromolecules Supramolecular structures Organelles / subcellular structures Cell C. Four types of macromolecules Protein Nucleic acid Polysaccharide Lipids Informational macromolecules – nucleic acids Structural / functional – protein Storage / structural – polysaccharides D. Stepwise polymerization of monomers BIO 330 Cell Biology Spring 2011 Lecture Outline 6 basic principles in polymerization 1 – Macromolecules are synthesized by stepwise polymerization of similar or identical small molecules (monomers) 2 – This occurs by condensation reactions (removal of water) 3 – Monomers must be activated prior to condensation 4 – Activation involves coupling of monomer to carrier molecule 5 – Energy needed for condensation reaction is delivered by ATP 6 – Macromolecules have inherent directionality E. Degradation of macromolecules Hydrolysis reactions use water to break bonds between adjacent monomers V. The Importance of Self-Assembly A. Self-Assembly of higher order structures The information required to fold macromolecules and to incorporate them into larger structures is inherent in the polymers themselves No further energy or input is required B. Protein self-assembly Polypeptide vs mature protein Native conformation vs denaturation vs renaturation Polypeptide folding is spontaneous Molecular chaperones assist assembly of some complex proteins Assisted self-assembly Examples of chaperones: heat shock proteins (Hsp70) C. Noncovalent bonds and interactions are involved in macromolecular folding Hydrogen bonds van der Waals interactions Hydrophobic interactions Ionic bonds D. Limits of self-assembly Some materials must be added to existing structures E.g., membranes, cell walls, chromosomes E. Hierarchical assembly advantages Chemical simplicity Only 30 small precursor molecules make up most of the cell 20 amino acids 5 nitrogenous bases 2 sugars 3 lipid molecules Efficiency of assembly Defects are detected early Defective subunits discarded instead of a whole protein / organelle