The Chemistry of Microbiology Chapter 02 Revised

Atoms  Cells are the building blocks of LIFE  But… cells are made of molecules which are made of atoms  Atoms  the building block of matter  Element  composed of a single type of atom

Atomic Structure  Electrons  negatively charged particles circling the atom  Nucleus: contains neutrons and protons  Neutrons uncharged particles, mass of 1  Protons positively charged particles, mass of 1

Isotopes  Atoms that differ in number of neutrons in their nucleus are isotopes  Stable isotopes  Unstable isotopes Release energy = radioactive isotopes

Electron Configurations  Only the electrons of atoms interact, so they determine atom’s chemical behavior  Electrons occupy electron shells

Chemical Bonds  Outer electron shells are stable when they contain eight electrons  When atoms do not have 8 electrons in their outer shell they often interact by forming a bond  Three principal types of chemical bonds  Ionic bonds  Covalent bonds – Nonpolar and polar  Hydrogen bonds – weak forces that combine with polar covalent bonds

Ionic Bonds  Transfer of electrons from one atom to another  Atoms have either positive (cation) or negative (anion) charges  Cations and anions attract each other and form ionic bonds (no electrons shared)  Typically form crystalline ionic compounds known as salts orials/Water/PublicWaterSupply/images/nacl.jpg

 Covalent bond: Sharing of electrons  Non-polar covalent bonds  Shared electrons spend equal amount of time around each nucleus, no poles exist  Polar Covalent bonds  Unequal sharing of electrons  Most important polar covalent bonds involve hydrogen Allows for hydrogen bonding Covalent Bonds Non-polar bond Polar bond

160hbondwater.gif Hydrogen Bonds  Electrical attraction between partially charged H + and partial negative charge of another atom  Weak bonds but essential for life  Often hundreds of H-bonds form at once  Help to stabilize 3-D shapes of large molecules like DNA and protiens

Water  Most abundant substance in organisms  Most of its special characteristics due to two polar covalent bonds  Water molecules are cohesive – surface tension  Excellent solvent  Remains liquid across wide range of temperatures  Can absorb significant amounts of energy without changing temperature  Participates in many chemical reactions

Organic Macromolecules  Contain carbon = Organic  Atoms often appear in certain common arrangements – functional groups  Macromolecules  Lipids  Carbohydrates  Proteins  Nucleic Acids  Monomers – basic building blocks of macromolecules

Proteins  Monomer is the amino acid  21 amino acids in multiple combinations make up proteins  The 3D shape is very important to protein function  Side groups of the amino acids form the shape  A peptide bond (covalent bond) formed between amino acids  Functions  Cellular structure and enzymes, also regulation, defense and offense

Amino Acids The set-up of an amino acid Example amino acids:

Protein Structure Proteins form complex 3D structures. This structure determines the function of the protein. There are 4 levels of structure. Please appreciate their complexity! Level 1 Level 2 Level 1

Carbohydrates  Monomer = Monosaccharide  Functions  Ready energy source  Part of backbones of nucleic acids  Form cell wall

Carbohydrates  The monomer of a carbohydrate is the monosaccharide  Two monosaccharides can be joined to form a Disaccharide

Polysaccharides  Many monomers can be joined to form a polymer  Many monosaccharides join to form polysaccharides

Nucleic Acids  DNA is genetic material of all organisms and of many viruses  Carries instructions for synthesis of RNA and proteins Genes contain instructions for the synthesis of everything that makes up a cell and allows a cell to function  Nucleic acids also serve as energy carriers in biochemical pathways (ex: ATP, NADH)  The monomers that make up nucleic acids are nucleotides

Nucleotides  Composed of three parts 1. Sugar Deoxyribose (in DNA) Ribose (in RNA) 2. Nitrogenous Base Adenine (A) Guanine (G) Cytosine (C) Thymine (T) – only in DNA Uracil (U) – only in RNA 3. Phosphate = PO 4 One nucleotide

Nucleic Acid Structure  H-bonds form between complementary bases:  Cytosine and Guanine  Adenine and Thymine in DNA  Adenine and Uracil in RNA  DNA is double stranded in most cells  Two strands are complementary  Two strands are antiparallel  This is why DNA is called the double helix

ATP ATP has 3 phosphates (instead of 1 like DNA and RNA). ATP is the main energy carrier in cells.

Lipids  Contain fatty acids and are all hydrophobic  Technically lipids do not have a monomer but we will consider the fatty acid to be the monomer for lipids.  Four groups  Fats  Phospholipids  Waxes  Sterols

Fats

Phospholipids Hydrophilic polar head Hydrophobic fatty-acid tails

Waxes  Completely insoluble in water; lack hydrophilic head  Important in cell wall of Mycobacterium

Sterols Important in EUKARYOTIC membranes. Also, work as cell signaling molecules in eukaryotes.