biological molecules

• Monomers

  Smaller / repeating molecules from which larger molecules / polymers are made
• Polymers

  Molecules made up of many identical / similar molecules / monomers
• Condensation reaction

  1. 2 molecules join together

  2. Forming a chemical bond

  3. Releasing a water molecule
• Hydrolysis reaction

  1. 2 molecules separated

  2. Breaking a chemical bond

  3. Using a water molecule
• Monosaccharides

  Monomers from which larger carbohydrates are made
• Common monosaccharides

  • Glucose
  • Fructose
  • Galactose
• Disaccharides

  Two monosaccharides joined together with a glycosidic bond
• Common disaccharides and monosaccharides from which they're made

  • Maltose (glucose + glucose)
  • Sucrose (glucose + fructose)
  • Lactose (glucose + galactose)
• Formation of disaccharides

  Two monosaccharides joined together with a glycosidic bond -

  Condensation reaction, releasing a water molecule
• Polysaccharides

  Many monosaccharides joined together with glycosidic bonds
• Formation of polysaccharides

  Many condensation reactions, releasing water molecules
• function of Starch

  Energy store in plant cells
• function of Glycogen

  Energy store in animal cells
• Test for reducing sugars

  1. Add Benedict's solution 2. Heat 3. positive =blue -> green/yellow/orange/red precipitate
• Test for non-reducing sugars

  1. Do Benedict's test (stays blue) 2. Heat with acid (to hydrolyse into reducing sugar) 3. neutralise with sodium bicarbonate 4. Heat with Benedict's. positive = green/yellow/orange/red precipitate
• Measure quantity of sugar in solution

  Filter and dry Benedict's precipitate, find mass of it
• Test for starch

  Add iodine dissolved in potassium iodide and shake. positive = blue —> black
• Lipids

  Two groups: triglycerides and phospholipids
• structure of a Fatty acid

  Variable R group - hydrocarbon chain (un/saturated) - COOH group
• Saturated fatty acid

  No C=C double bonds, all carbons fully saturated with hydrogen
• Unsaturated fatty acid


  One or more C=C double bonds, creating bends/kinks
• Phospholipids vs triglycerides 


  One fatty acid of triglyceride substituted by phosphate-containing group

  
• Test for lipids

  Add ethanol, shake, add water, positive = milky white emulsion
• 20 amino acids common in all organisms, differing only in R group
• Test for proteins

  Add biuret reagent, positive = blue —> purple
• Enzymes act as biological catalysts


  • Each enzyme lowers activation energy of reaction it catalyses
  • To speed up rate of reaction
• Describe the induced-fit model of enzyme action

  1. Substrate binds to (not completely complementary) active site of enzyme

  2. Causing active site to change shape (slightly) so it is complementary to substrate

  3. So enzyme-substrate complex forms

  4. Causing bonds in substrate to bend / distort, lowering activation energy
• Models of enzyme action

  • Initially lock and key model (now outdated) - Active site a fixed shape, complementary to one substrate
  • Now induced-fit model
• Specificity of enzymes

  • Specific tertiary structure determines shape of active site, dependent on sequence of amino acids (primary structure)
  • Active site is complementary to a specific substrate
  • Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
• Functions of DNA and RNA in living cells

  • DNA holds genetic information which codes for polypeptides (proteins)
  • RNA transfers genetic information from DNA to ribosomes
• Components of a ribosome

  RNA and proteins
• Differences between a DNA nucleotide and an RNA nucleotide

  DNA nucleotide: Pentose sugar is deoxyribose, Base can be thymine

  RNA nucleotide: Pentose sugar is ribose, Base can be uracil
• Describe how nucleotides join together to form polynucleotides

  1. Condensation reactions, removing water molecules

  2. Between phosphate group of one nucleotide and deoxyribose/ribose of another

  3. Forming phosphodiester bonds
• Describe the structure of DNA

  1. Polymer of nucleotides (polynucleotide)

  2. Each nucleotide formed from deoxyribose, a phosphate group and a nitrogen-containing organic base

  3. Phosphodiester bonds join adjacent nucleotides

  4. 2 polynucleotide chains held together by hydrogen bonds

  5. Between specific complementary base pairs - adenine / thymine and cytosine / guanine

  6. Double helix
• Many scientists initially doubted that DNA carried the genetic code because of the relative simplicity of DNA - a chemically simple molecule with few components
• RNA

  • Polymer of nucleotides (polynucleotide)
  • Each nucleotide formed from ribose, a phosphate group and a nitrogen-containing organic base
  • Bases - uracil, adenine, cytosine, guanine
  • Phosphodiester bonds join adjacent nucleotides
  • Single helix
• Structure of DNA related to its function

  • Two strands allow both to act as templates for semi-conservative replication
  • Hydrogen bonds between bases are weak, allowing strands to be separated for replication
  • Complementary base pairing allows accurate replication
  • Many hydrogen bonds between bases make it a stable / strong molecule
  • Double helix with sugar phosphate backbone protects bases / hydrogen bonds
  • Long molecule allows storage of lots of genetic information (that codes for polypeptides)
  • Double helix (coiled) structure is compact
• Semi-conservative replication ensures genetic continuity between generations of cells
• Watson and Crick

  Proposed models of the chemical structure of DNA and of DNA replication
• ATP

  Adenosine triphosphate