Topic 1 - Biological molecules & nucleic acids

• What is a condensation reaction


  Monomers are linked together to form polymer chains, with a water molecule formed in the process
• What is a hydrolysis reaction?

  The breaking down of polymers into monomers by the addition of water molecules
• What are the 3 main monosaccharide?

  • Glucose
  • Galactose
  • Fructose
• What is glucose?

  • A hexose sugar (6 carbons) that can form two isomers (α-glucose and β-glucose)
  • Alpha glucose molecules can bond together to form starch or glycogen
  • Beta glucose molecules can bond together to form cellulose
• What is starch?

  A mixture of two polysaccharides, amylose and amylopectin, used by plants to store excess sugar
• What is amylose

  • Made from α-glucose 1,4 – glycosidic bonds, compact coiling for efficient storage
  • Insoluble, doesn't affect water potential
• Amylopectin

  • Made from α-glucose 1,6 and 1,4 – glycosidic bonds, branched structure increases surface area for rapid hydrolysis
  • Insoluble, doesn't affect water potential
• Cellulose

  Made up of Beta glucose, forms long unbranched chains that can cross-link via hydrogen bonds to provide structural support in plant cell walls
• Cellulose

  • Provides rigid cell walls to prevent plant cells from bursting due to osmosis, maintaining turgidity for photosynthesis
• Glycogen

  Made up of α-glucose, a highly branched polysaccharide used by animals to store excess glucose
• Glycogen

  • Many branches to increase surface area for rapid hydrolysis, very compact for efficient storage, insoluble
• Lipids

  Insoluble in water but soluble in organic solvents, main groups are triglycerides and phospholipids
• Roles of lipids

  • Source of energy
  • Waterproofing
  • Insulation
• Triglycerides

  Consist of 1 glycerol molecule joined to 3 fatty acid chains via ester bonds, non-polar
• Fatty acids

  Long chain organic compounds that can be saturated, unsaturated, or polyunsaturated
• Phospholipids

  Consist of a glycerol molecule, a phosphate, and 2 fatty acid chains, polar head and non-polar tails allow them to form bilayers in cell membranes
• Proteins

  Large molecules made up of amino acids, with 20 different amino acids present in all life forms
• Levels of protein structure

  • Primary
  • Secondary
  • Tertiary
  • Quaternary
• Enzymes

  Biological catalysts that lower the activation energy of reactions, have a specific active site complementary to the substrate
• Induced fit model

  The active site of an enzyme changes shape slightly to mould around the substrate, putting strain on the substrate bonds and lowering activation energy
• Factors affecting enzyme activity

  • pH
  • Temperature
  • Concentration
• Competitive inhibition

  Inhibitors that bind directly to the active site of an enzyme, competing with the substrate
• The concentration of competitive inhibitors compared to the concentration of substrates determines the effect of enzyme activity
• If substrate concentration is increased, the effect of the competitve inhibitor is reduced as the inhibitor is not permanently bound to the active site
• Inhibitors

  Substances that directly or indirectly interfere with the function of the active site of an enzyme which leads to reducing its activity
• Types of inhibitors

  • Competitive inhibitors
  • Non-competitive inhibitors
• Competitive inhibitors

  • Bind directly to the active site of the enzyme
  • Have a molecule shape similar to that of the substrate, allowing them to bind directly to the active site
  • Compete with the substrate for the available active sites
• Non-competitive inhibitors

  • Attach themselves to an alternate binding site called the allosteric site
  • Alter the shape of the enzyme and therefore the shape of its active site
  • Substrate molecules are unable to fit into the enzyme, so it is unable to function
  • Increase in substrate concentration does not alter the enzyme activity because the substrate and the inhibitor are not competing
• Reducing Sugars Test

  1. Add excess Benedict's reagent to the sample and heat in a warm water bath and wait for a colour change

  2. If the reducing sugar is present a green/yellow/red precipitate is formed, if not the solution remains blue
• Non-Reducing Sugars Test

  1. Add dilute Hydrochloric acid and heat in a water bath (to break bonds and produce monosaccharides)

  2. Add an alkali to neutralise (NaOH)

  3. Conduct the test for reducing sugars
• Starch Test

  Add iodine to the sample, there will be a colour change from brown/orange to blue/black
• Proteins (presence of amino acids) Test

  1. Add excess biuret reagent to the sample, shake and leave at room temperature

  2. If there are amino acids present then a purple/lilac precipitate forms, if not the solution will remain blue
• Lipids (emulsion) Test

  1. Add ethanol to the sample then add water, shake for a minute

  2. If lipids are present, they will form a milky white emulsion (layer above the ethanol/water)
• Nucleotide

  Made up of a pentose sugar, a phosphate group and a nitrogenous base
• Ribonucleic Acids (RNA)

  Single polynucleotide chain with ribose as the pentose sugar and the organic bases can be adenine, uracil, guanine and cytosine
• Deoxyribonucleic Acids (DNA)

  • Double helix shape with deoxyribose as the pentose sugar and the nitrogenous bases are: adenine, thymine, guanine and cytosine
  • Made up of two nucleotide strands with hydrogen bonds between complimentary base pairs
• DNA Replication

  1. DNA helicase causes the two strands to unwind

  2. Free nucleotides bind to their complimentary bases on the template strands

  3. DNA polymerase creates phosphodiester bonds between the adjacent nucleotides on the phosphate backbone.

  4. Results in two identical strands of DNA, each containing half of the original strand (semi-conservative model)
• ATP

  • Phosphorylated macromolecule with three parts: adenine, ribose and a chain of 3 phosphates
  • Bonds between the phosphate groups are unstable and have a low activation energy, when these bonds are broken, they release a considerable amount of energy
• ATP Synthesis

  Addition of a phosphate molecule to ADP, can occur during photosynthesis, respiration, or phosphate group transfer
• Roles of ATP

  • Not a good long-term energy store due to the instability of the bonds between phosphate
  • Provides energy for metabolic processes, movement, active transport, secretion, and activation of molecules