2.1.2 - Biological Molecules

• why is water a polar molecule?

  uneven distribution of charge within the molecule
• when two molecules join together with the removal of water

  condensation
• when two molecules are split apart by the addition of a molecule of water

  hydrolysis
• what enables the effective transport of water in tube-like transport cells?

  strong cohesion between molecules
• what happens because of strong cohesion?

  surface tension at the water-air boundary is high
• when is water at its maximum density?

  4 degrees
• what prevents the freezing of organisms?

  ice is less dense than water and floats on top to create an insulating layer
• why does water provide good support?

  it's incompressible
• what is glucose?

  a monosaccharide which is the main substrate for respiration
• what are carbohydrates?

  molecules which consist only of carbon, hydrogen and oxygen which are long chains of sugar units called saccharides
• what can monosaccharides join together to form?

  disaccharides and polysaccharides by glycosidic bonds formed in condensation reactions
• what is an isomer + what are the isomers of glucose?

  two molecules with the same molecular formula but differ structurally + alpha and beta glucose
• name three disaccharides and how they're formed

  maltose = condensation of two glucose molecules, sucrose = condensation of glucose and fructose, lactose = condensation of glucose and galactose
• how are glycogen and starch formed?

  condensation of alpha glucose
• how is cellulose formed?

  condensation of beta glucose
• what is glycogen?

  the main energy storage molecule in animals formed from many molecules of alpha glucose joined together by 1,4 and 1,6 glycosidic bonds
• features of glycogen

  it has a large number of side branches so glucose can be released quickly + it is a large but compact molecule which maximises the amount of energy it can store
• what is starch?

  it stores energy in plants and is a mix of two polysaccharides, amylose and amylopectin
• what is amylose?

  an unbranched chain of glucose molecules joined by 1,4 glycosidic bonds. amylose is coiled and is a very compact molecule
• what is amylopectin?

  branched and made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds. presence of many side branches means it is rapidly digested by enzymes and so energy is released quickly
• what is cellulose?

  composed of long, unbranched chains of beta glucose joined together by glycosidic bonds
• what are microfibrils?


  strong threads made of long cellulose chains joined together by hydrogen bonds and they provide structural support in plant cells
• what is the primary structure of a protein?

  the specific order of amino acids in a polypeptide
• why is primary structure important in a protein?

  it helps to determine the final 3D shape of the protein, which is crucial to its function
• what is the secondary structure?


  specific regions of the chain fold
• how is secondary structure formed?

  hydrogen bonds formed between the amino acids all along the polypeptide chain cause the chain to twist and fold into shapes
• name two types of secondary structure

  alpha helix and beta pleated sheet
• what does the type of secondary structure formed depend on?

  the primary structure in that region
• what is the tertiary structure?


  the overall 3D shape of a polypeptide chain
• steps in formation of polypeptide chain:

  1. chain folds into regions of secondary structure 2. once these regions form, the chain now continues folding to form the final tertiary structure
• what is the quaternary structure?

  the arrangement of individual subunits to form a larger 3D structure
• what is a prosthetic group?

  non-protein molecules which form part of a quaternary structure
• name an example of a prosthetic group

  the haem group in haemoglobin, binds to oxygen
• what are conjugated proteins?

  proteins with prosthetic groups
• what are lipids?

  biological molecules that are only soluble in organic solvents
• what are the two types of lipid?

  saturated, i.e no C=C bonds, and unsaturated, i.e containing C=C bonds
• what happens as the number of unsaturated bonds increases?

  the intermolecular bonds get weaker, resulting in a lower boiling point
• what state are saturated and unsaturated fats at when at room temperature?

  saturated are solids, and unsaturated are liquids
• what are triglycerides?

  lipids which are made up of one molecule of glycerol and three fatty acids joined by ester bonds which are formed in condensation reactions
• what are phospholipids?

  made up of two fatty acids and a phosphate containing group