Biological Molecules

• Alpha and beta glucose as well as fructose and galactose are monosaccharides.
• Carbohydrates are joined by glycosidic bonds, formed via a condensation reaction
• Disaccharides: maltose - 2x alpha glucose, lactose - alpha glucose and galactose, sucrose - alpha glucose and fructose
• Polysaccharides are, starch, glycogen (alpha glucose) and cellulose (beta glucose)
• Starch is: insoluble so it does not affect water potential, large so it cannot leave the cell, helical so it is compact, branched so it can be easily hydrolysed.
• Glycogen is highly branched starch.
• Cellulose is: long straight chains, beta glucose molecules alternate in a chain, joined by hydrogen bonds and an arbitrary unit is called a microfibril.
• Starch test: iodine turns blue/black if +ve
• Test for reducing sugar: benedict's sol. and heat in water bath. Brick red PPT should form.
• Test for non-reducing sugar: Boil with dilute HCl acid then neutralise with NaHCO3. Add Benedict's sol. and heat in water bath. Brick red PPT should form.
• Condensation reaction - joining of two molecules together, forming a bond and eliminating water.
• Fats are solid at room temperature, its bonds are saturated. Oils are liquid at room temperature, they have unsaturated bonds.
• Glycerol molecule

  
• Fatty acids - CH3(CH2)nCOOH
• A triglyceride is a molecule made up of three fatty acids and a glycerol joined by ester bonds.
• Triglycerides are hydrophobic and insoluble. Phospholipids though, are polar as they're both hydrophobic and hydrophilic.
• A phospholipid contains 2 fatty acid and a phosphate group, instead of 3 fatty acids.
• Emulsion test - add ethanol and shake well, add gently to water. White emulsion forms if positive.
• Protein monomer- amino acid

  
• There are 20 amino acids. They contain C, H, O, N and sometimes S.
• Amino acids join via peptide bonds in a condensation reaction.

  
• The primary structure, is the order or sequence of amino acids.
• The secondary structure, is the folding due to hydrogen bonds forming between certain amino acids. This leads to the formation of alpha helices and beta pleated sheets.
• The tertiary structure, is formed when more hydrogen bonds form, and also ionic bonds. If sulphur is present then disulphide bridges are also formed. This leads to more folding and the proteins 3D shape forms.
• The quaternary structure, is two or more polypeptide chains, often including a prosthetic group.
• Lock and Key Hypothesis- the substrate and enzyme active site have complementary shapes. Hence, they bind easily. This model was updated to the induced fit model of enzyme action.
• The Induced Fit Model - the active site and substrate are not initially complementary but, when they bind, the active site moulds around the substrate. This applies pressure to the bonds which bends them and therefore, lowers the activation energy.
• Test for proteins - add biuret solution, if positive, lilac ppt will form
• Competitive Inhibition- the substrate and CI are complementary in shape to the enzyme's active site as their similar in shape. The effect of the inhibitor can be overcome by increasing the substrate concentration.
• Non-Competitive Inhibition - the NCI binds away from the active site altering its tertiary structure so the substrate can no longer bind. So enzyme - substrate complexes cannot be formed. This cannot be overcome.
• Nucleotides are made up of a phosphate group, a pentose sugar and a nitrogenous base

  
• DNA: deoxyribose sugar and either an adenine, thymine, cytosine or guanine base.

  RNA: ribose sugar and either and adenine, uracil, cytosine or guanine base.
• Adjacent nucleotides are joined by phosphodiester bonds to form a sugar phosphate backbone.
• RNA forms a short, single strand.
• DNA, is a large double stranded molecule. The strands join by hydrogen bonds linking the bases.
• Adenine --> Thymine

  Cytosine --> Guanine
• 3 bases code for an amino acid.
• Strong due to many hydrogen and phosphodiester bonds, the 2 strands can unzip to replicate, it is large and helical in shape for storage, so that it can store a lot of genetic information, DNA is an information-carrying molecule.
• Semi Conservative Replication-

  • DNA helicase breaks the hydrogen bonds between the 2 strands which allows them to unzip.
  • Free floating nucleotides line up, via complementary base pairing, opposite the exposed bases on the 2 template strands.
  • DNA polymerase joins adjacent DNA nucleotides together via phosphodiester bonds. This forms the sugar-phosphate backbone.
  • The 2 strands wind up together - 1 original and 1 new strand hence, semi conservative replication
• ATP - Adenosine Triphosphate

  a nucleotide derivative

  • contains a nitrogenous base but it is always adenine
  • contains 3 phosphate groups rather just 1
  • the pentose sugar is always ribose