LS1101-01 Instructor:王雯靜 Date: 09/29/99; 10/6/99

Chapter 2 The chemical context of life

1. Elements and compounds

Elements: a substance that cannot be broken down to other substances by chemical reactions

Chemical element: 92 in the nature

Life requires about 25 chemical elements: C, O, H, N (96% of living matter ). P, S, Ca K and a few other elements account for the remaining 4% of an organism’s weight

Compound: a substance consisting of two or more elements combined in a fixed ration. E.g. NaCl, salt

2. Atoms and molecules

(1) Atom: the smallest unit of matter that still retains the properties of an element. Each element consists of one kind of atom.

Nucleus: protons, neutrons

Electrons

Atomic number: protons

Mass number/atomic weight: protons + neutrons

(2) Molecules: 2 or more atoms held together by chemical bonds form a molecule.

(3) chemical bonds--

covalent bond

ionic bond

hydrogen bonding

(4) Chemical reactions

　

Chapter 3 Water and the fitness of the environment
  1. The polarity of water molecules results in hydrogen bonding: Water is a polar molecule
  2. Organisms depend on the cohesion of water:

    3. cohesion (transport water from their roots to their leaves in trees), surface tension

  3. Water moderates temperatures on earth: hydrogen bonds
  4. Oceans and lakes don’t freeze solid because ice floats: ice is less than liquid water
  5. Water is the solvent of life

　

Dissociation of water molecules

Acid and base

The pH scare

Buffers

　

The chemistry of life is sensitive to acidic and basic conditions.

　

Acid precipitation threatens the environment: pH<5.6 in the air of sulfur oxides and nitrogen oxides, air-polluting compounds composed of oxygen combined with sulfur or nitrogen + water—result in sulfuric and nitric acid.

　

Chapter 4 Carbon and the molecular diversity of life

The molecules of cells
  1. Organic compounds: compounds containing carbon are knows as organic compounds.

Methane

Ethane

Propane

Butane

　

ethene

butene: 1-butene, 2-butene

　

2. Functional groups:

-OH

-C=O

-COOH

-NH2

　

Chapter 5 The structure and function of macromolecules

Most macromolecules are polymers

Monomer →polymer

Condensation: loss of a water molecule

Dehydration reaction
  1. Carbohydrates

    2. (CH2O)n

    *monosaccharides: glucose, fructose

    C-OH and one C=O (aldose or ketose)

    Straight chain → ring form

    *Disaccharides: sucrose

    *Polysaccharides: polymers of a few hundred to a few thousand monosaccharides linked together

    (1) starch: (Glucose)n by alpha 1,4-glycosidic linkage

    amylose, amylopectin

    (2) glycogen: (glucose)n in animal

    (3) structural polysaccharides: cellulose and chitin

    cellulose: (glucose)n, beta-1,4 linkage

    chitin: (amino sugar) n, the hard outer covering in arthropods

    *Function:

    (1) energy stores, fuels, and metabolic intermediates

    (2) structural elements in the cell walls of bacteria and plants, and in the exoskeletons of arthropods

    (3) carbohydrates are linked to many proteins and lipids.

    (4) ribose and deoxyribose sugars form part of the structure framework of DNA and RNA

    　

  2. Lipids

They have little or no affinity for water: hydrophobic behavior of lipids

Lipids consist mostly of hydrocarbons. Smaller than true (polymeric) macromolecules, lipids are a highly varied group in both form and function. Lipids include waxes and certain pigments, but we will focus on the most important families of lipids: the fats, phospholipids, and steroids.

(1) fats: store large amounts of energy

triacylglycerol: 3 fatty acids, glycerol

saturated fatty acid and unsaturated fatty acid

(2) phospholipids: the major components of cell membranes

2 fatty acids, glycerol, one phosphate group, which is negative in electrical charge

(3) steroids: lipids characterized by a carbon skeleton consisting of four fused rings: cholesterol

Function: energy-storage molecules, make up the bulk of all of the membranes of a cell; hormones; others form waterproof coverings on both plant and animal bodies

　

3. Proteins: proteins are polymers of amino acids

amino acids: 20

peptide bond

four levels of protein structure

(1) primary structure: the unique sequence of amino acids of a protein

(2) secondary structure: spatial arrangement of amino acid residues that are near one another in the linear sequence; segments of the polypeptide chain coiled or folded in patterns; e.g. alpha helix: beta pleated sheet

(3) tertiary structure: spatial arrangement of amino acid residues that are far apart in the linear sequence

(4) quaternary structure: spatial arrangement of subunits that associate together

(5) Protein Folding: what determines protein conformation

　4. nucleic acids- informational polymers

(1) Nucleic acids store and transmit hereditary information

(2) A nucleic acid strand is a polymer of nucleotides

Phosphate–pentose sugar–nitrogenous base