start here_ch02_lecture

Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Lecture prepared by Mindy Miller-Kittrell, University of Tennessee, Knoxville

M I C R O B I O L O G YWITH DISEASES BY BODY SYSTEM SECOND EDITION

Chapter 2 The Chemistry of Microbiology


Atoms

• Matter – anything that takes up space and has mass

• Atoms – the smallest chemical units of matter


Atoms

• Atomic Structure

– Electrons – negatively charged subatomic particles circling a nucleus

– Nucleus – structure containing neutrons and protons

– Neutrons – uncharged particles

– Protons – positively charged particles


Atoms


Atoms

• Atomic Structure

– Element – composed of a single type of atom

– Atomic number – equal to the number of protons in the nucleus

– Atomic mass (atomic weight) – sum of masses of protons, neutrons, and electrons


Atoms


Atoms

• Isotopes

– Atoms of a given element that differ in the number of neutrons in their nuclei

– Stable isotopes– Unstable isotopes

– Release energy during radioactive decay


Atoms


Atoms

• Electron Configurations

– Only the electrons of atoms interact, so they determine atom’s chemical behavior

– Electrons occupy electron shells

– Valence electrons – electrons in outermost shell that interact with other atoms


Atoms


Chemical Bonds

• Valence – combining capacity of an atom– Positive if has electrons to give up– Negative if has spaces to fill– Stable when outer electron shells contain eight electrons

• Chemical bonds – attachment of atoms combined by sharing or transferring valence electrons

• Molecule – two or more atoms held together by chemical bonds

• Compound – a molecule composed of more than one element


Chemical Bonds

• Covalent Bond – sharing of a pair of electrons by two atoms

• Electronegativity – attraction of atom for electrons; the more electronegative an atom, the greater the pull its nucleus exerts on electrons


Chemical Bonds

• Nonpolar Covalent Bonds

– Shared electrons spend equal amounts of time around each nucleus

– Atoms with similar electronegativities– No poles exist– Carbon atoms critical to life; form four nonpolar covalent bonds

with other atoms– Organic compounds contain carbon and hydrogen atoms


Chemical Bonds


Chemical Bonds

• Polar Covalent Bonds

– Unequal sharing of electrons due to significantly different electronegativities

– Most important polar covalent bonds involve hydrogen– Allows for hydrogen bonding


Chemical Bonds


Chemical Bonds

• Ionic Bonds

– Occur when two atoms with vastly different electronegativities come together

– 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


Chemical Bonds


Chemical Bonds

• Hydrogen Bonds

– Weak forces that combine with polar covalent bonds– Electrical attraction between partially charged H+ and full or

partial negative charge on different region of same molecule or another molecule

– Weaker than covalent bonds but essential for life– Many help to stabilize 3-D shapes of large molecules


Chemical Bonds


Chemical Reactions

• The making or breaking of chemical bonds

• Involve reactants and products

• Biochemistry involves chemical reactions of living things


Chemical Reactions

• Synthesis Reactions

– Involve the formation of larger, more complex molecules– Require energy (endothermic) – Most common type is dehydration synthesis

– Water molecule formed– All the synthesis reactions in an organism are called anabolism


Chemical Reactions


Chemical Reactions

• Decomposition Reactions– Break bonds within larger molecules to form smaller atoms,

ions, and molecules– Release energy (exothermic)– Most common type is hydrolysis

– Ionic components of water are added to products– All the decomposition reactions in an organism are called

catabolism


Chemical Reactions


Chemical Reactions

• Exchange Reactions

– Involve breaking and forming covalent bonds, and involve endothermic and exothermic steps

– Involve atoms moving from one molecule to another

– Sum of all chemical reactions in an organism is called metabolism


Water, Acids, Bases, and Salts

• Water– Most abundant substance in organisms– Most of its special characteristics due to two polar covalent

bonds– Cohesive molecules – 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



• Acids and Bases– Dissociated by water into component cations and anions

– Acid – dissociates into one or more H+ and one or more anions

– Base – binds with H+ when dissolved into water; some dissociate into cations and OH-

– Metabolism requires relatively constant balance of acids and bases

– Concentration of H+ in solution is expressed using the pH scale

– Buffers prevent drastic changes in internal pH



• Salts– Compounds that dissociate in water into cations and anions

other than H+ and OH-

– Cations and anions of salts are electrolytes– Create electrical differences between inside and outside of

cell– Transfer electrons from one location to another– Form important components of many enzymes


Organic Macromolecules

• Functional Groups and Monomers– Contain carbon and hydrogen atoms– Atoms often appear in certain common arrangements –

functional groups– Macromolecules – large molecules used by all organisms

– Lipids– Carbohydrates– Proteins– Nucleic Acids

– Monomers – basic building blocks of macromolecules



• Lipids– Not composed of regular subunits, but are all hydrophobic

– Four groups– Fats– Phospholipids– Waxes– Steroids



• Waxes

– Contain one long-chain fatty acid covalently linked to long-chain alcohol by ester bond

– Completely insoluble in water; lack hydrophilic head



• Carbohydrates– Organic molecules composed of carbon, hydrogen, and oxygen

(CH2O)n

– Functions– Long-term storage of chemical energy– Ready energy source– Part of backbones of nucleic acids– Converted to amino acids– Form cell wall– Involved in intracellular interactions between animal cells



• Carbohydrates– Types

– Monosaccharides– Disaccharides– Polysaccharides



• Proteins– Mostly composed of carbon, hydrogen, oxygen, nitrogen, and

sulfur– Functions

– Structure– Enzymatic catalysis– Regulation– Transportation– Defense and offense



• Amino Acids– The monomers that make up proteins– Most organisms use only 21 amino acids in the synthesis of

proteins– Side groups affect how amino acids interact with one another

and how a protein interacts with other molecules– A covalent bond (peptide bond) is formed between amino acids

by dehydration synthesis reaction



• Nucleic Acids

– DNA and RNA: the genetic material of organisms– RNA helps form polypeptides



• Nucleic Acids– Nucleotides

– Monomers that make up nucleic acids – Composed of three parts

– Phosphate– Pentose sugar – deoxyribose or ribose– One of five cyclic nitrogenous bases



• Nucleic Acids– Nucleic acid structure

– H bonds form between C and G and between T and A in DNA– Two H bonds form between U and A in RNA

– DNA is double stranded in most cells and viruses– Two strands are complementary– Two strands are antiparallel



• Nucleic Acids– Nucleic acid function

– DNA is genetic material of all organisms and of many viruses– Carries instructions for synthesis of RNA and proteins;

controls synthesis of all molecules in an organism