Biology

• Bonding

  • Covalent bonding - sharing of electrons between two non-metals
  • Ionic bonding - transfer of electrons from a metal to a non-metal, forming positive and negative ions
  • Hydrogen bonding - weak attraction between opposite dipoles
• Monomer

  Smaller unit from which larger molecules are made
• Polymer

  Molecule made from a large number of monomers joined together in a chain
• Examples of monomers and polymers

  • Amino acid (monomer) - Protein (polymer)
  • Nucleotide (monomer) - DNA/nucleic acid (polymer)
  • Glucose (monomer) - Polysaccharide/carbohydrate (polymer)
• Hydrolysis

  Breaking a chemical bond using water
• Condensation

  Joining two molecules together, creating a chemical bond and eliminating another molecule (usually water)
• Monosaccharide

  Single sugar, monomer for carbohydrates
• Alpha glucose and beta glucose

  • Differ in the spatial arrangement of the hydrogen and OH group
  • Cannot be superimposed, like left and right hand
• Monosaccharides

  • Glucose
  • Galactose
  • Fructose
• Disaccharide

  Two monosaccharides joined together
• Polysaccharide

  Many monosaccharides joined together
• Starch

  • Polymer of alpha glucose, insoluble, branched for enzyme access
  • Glycogen - similar to starch but shorter, more branched, found in animal cells
• Cellulose

  • Polymer of beta glucose, long straight chains, provides structural support in plant cell walls
• Benedict's test

  Test for reducing sugars - monosaccharides and some disaccharides
• Iodine test

  Test for starch
• Lipid

  Insoluble in water, soluble in organic solvents, great store of energy
• Triglycerides

  • Made up of 3 fatty acids joined to glycerol by ester bonds
• Phospholipids

  • One fatty acid replaced by a phosphate group, have hydrophilic head and hydrophobic tail, form cell membranes
• Amino acid

  Contains a central carbon, amino group, carboxyl group, and variable side group (R group)
• Peptide bond formation

  Condensation reaction between amino and carboxyl groups of two amino acids, forming a dipeptide
• Protein structure

  • Primary - sequence of amino acids
  • Secondary - alpha helix, beta pleated sheet
  • Tertiary - further folding and bonding
  • Quaternary - multiple polypeptide chains
• Biuret test

  Test for proteins, detects peptide bonds
• Alpha helix

  Secondary structure of proteins formed by hydrogen bonds between the carbonyl oxygen and amino hydrogen of the polypeptide backbone
• Beta-pleated sheet

  Secondary structure of proteins formed by hydrogen bonds between polypeptide chains arranged in parallel or antiparallel layers
• Protein folding

  1. Alpha helices and beta-pleated sheets form

  2. Further folding occurs to give rise to tertiary structure

  3. Hydrogen bonding, disulfide bridges, ionic bonding between R-groups determine tertiary structure
• Quaternary structure

  The highest level of protein structure, involving the aggregation of more than one polypeptide chain
• Types of proteins

  • Fibrous proteins
  • Globular proteins (e.g. enzymes, hemoglobin)
• Enzymes

  Biological catalysts that lower the activation energy required for a reaction to take place
• Uncatalyzed reaction

  Reaction progress goes up and down, with a peak in energy required to start the reaction
• Enzyme-catalyzed reaction

  Enzyme lowers the activation energy needed for the reaction to start
• Enzyme specificity

  Enzymes have a specific and complementary active site shape that only binds to a narrow range of substrates
• Induced fit model

  The active site of an enzyme changes shape slightly to better accommodate the substrate, unlike the rigid lock-and-key model
• Measuring enzyme reaction rate

  1. Measure product formation or substrate depletion

  2. Plot changes over time (volume of gas, mass, color, pH)

  3. Qualitative (yes/no) or quantitative (using equipment) tests
• As temperature increases

  Enzyme reaction rate increases due to more collisions, but then decreases as enzyme denatures
• Enzyme optimum temperature

  The temperature at which an enzyme's reaction rate is maximized, before denaturation occurs
• pH

  The concentration of hydrogen ions in a solution, ranging from acidic (low pH) to alkaline (high pH)
• Extreme pH

  Disrupts ionic bonds in enzyme tertiary structure, causing denaturation
• Enzyme-substrate interaction

  1. Enzyme concentration too low - substrate is limiting

  2. Enzyme concentration high enough to saturate substrate

  3. Substrate concentration becomes limiting
• Competitive inhibition

  Inhibitor binds to the active site, preventing substrate binding
• Non-competitive inhibition

  Inhibitor binds elsewhere on the enzyme, changing the active site shape so substrate cannot bind