A look at macromolecules (Text pages 38-54) What is the typical chemical composition of a cell? (Source of figures to right: Madigan et al.

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1 A look at macromolecules (Text pages 38-54) What is the typical chemical composition of a cell? (Source of figures to right: Madigan et al Chemical Bonds Ionic Electron-negativity differences cause unequal distribution of electrons essentially creating ions. Molecules are held together by electrical attraction...na+ Cl Not of major significance among the important classes of bio-organic molecules Covalent (bond strength > 50 Kcal mole-1) More-or-less equal sharing of electrons between two atoms creating stable molecules Consequential in biological molecules Hydrogen bonds (bond strength <2 kcal mole-1) Weak charge based attraction between molecules Very common in biological systems. What are the major classes of biologically important molecules? Carbohydrates (Sugars) All have the general form CH2O o Example: C6H12O6 Can exist as o Monomers o Polymers Monomers joined to form a potentially very large molecule. Joined covalently by a glycosidic bond Sizes Disaccharides Trisaccharides Oligosaccharides (several monomers) Polysaccharides (many many monomers)

2 Substituted forms (sugar derivatives) o Uses Structural components of cells Nucleic acids Walls Energy Nature of the glycosidic bond influences function Alpha form Beta form 1--> 4 bond 1--> 6 bond o Why are these important? Polymeric sugars serve as energy reserves Polymeric sugars are structural components of cells They can form bonds with lipids and proteins resulting in otter complex structural materials Glycolipids Glycoproteins Many of which are on the cell surface and act as receptors.

3 Lipids and Fatty Acids Fatty acids o Long chain hydrocarbons with a carboxylic acid at one end and a methyl group at the other o Variable chain length o Variable degree of double bond controls degree of liquidity o Hydrophobic end vs. hydrophilic end Simple lipids o Fatty acids esterified to glycerol o Termed a neutral triglyceride Complex o Similar to triglyceride but additional material substituted to the glycerol backbone o Very important biologically as this modifies the polar nature of the fatty acids Uses o Structural components of cells o In some cases, energy reserves

4 Amino Acids and Proteins Amino acids are the monomers that comprise proteins (proteins are poly-amino acids) 20 common amino acids and a few unique to bacteria all have some things in common o carboxylic acid end o amino end o can bond end to end via the Peptide Bond to form complex molecules with three dimensional characteristics

5 Proteins Forms Structural (parts of physical nature of cells) Catalytic (enzymes) General convention of describing structure Primary : linear array of amino acids Secondary: nature of twists and folds o Alpha helix o Beta pleated sheet Tertiary: continued folding post secondary structure Quaternary: more than one polypeptide chain Structure determined by order of amino acids Degree of hydrogen bonding Structure can be denatured Gentle vs. harsh The concept of stereoisomers In cells, the L-form of stereoisomers is the form that is almost always in play.

6 Nucleotides and Nucleic acids Nucleic acids Monomers are nucleotides Forms are DNA and RNA Composition of nucleotides Ribose or deoxyribose Purine or pyrimidine base Phosphate How does this come together? Nucleoside vs nucleotide Uses As polymers that carry genetic information Carriers of chemical energy Reduction and oxidation mediators Regulatory molecules carriers of sugars for polysaccharide biosynthesis As carriers of genetic information DNA o Several million nucleotides in a polymer o Polymer double stranded A-T bonds G-C bonds o Held by hydrogen bonding o Strands are complementary and anti-parallel (Figure in lower right from: Lewin, B. 1990)

7 RNA o All single stranded (except in some viruses) o Can be highly folded and give the appearance of being double stranded o Forms of RNA Messenger (mrna) Produced fro DNA template (i.e. complementary) Signal stranded Essentially directs how amino acids are assembled to build proteins Transfer (trna) Carries appropriate amino acids from cytoplasm to mrna template Ribosomal (rrna) Mediates the assembly of a protein by interfacing with mrna and trna Except where indicated, tables and figures used in this section are from Madigan et al References: Madigan, M.T., J.M. Martinko, and J. Parker Brock Biology of Microorganisms, 10 th ed. Prentice Hall. Lewin, B Genes, 4 th ed. Cell Press Inc. Cambridge