Biological compounds

• Name the four key inorganic ions in living organisms


  Mg2+, Fe2+, Ca2+, PO4 3-
• What is the role of Mg2+ in plants?


  To produce chlorophyll
• What is the role of Fe2+ in animals?`


  It is found in haemoglobin and is involved in the transport of oxygen
• What is the role of PO4 3- in living organisms?


  To produce ADP and ATP.
• What is the role of Ca2+ in living organisms?


  To strengthen tissues such as bones and teeth in animals and cell walls in plants
• Why is water a polar molecule?


  O is more electronegative than H, so attracts the electron density in the covalent bond more strongly. Forms O delta - (slight negative charge) & H delta + (slight positive charge)
• Describe hydrogen bonding between water molecules


  Weak intermolecular forces of attraction form between a lone pair on a delta - O and a delta + H on an adjacent molecule.
• What is a metabolite?


  A molecule formed or used in metabolic reactions
• Describe the role of water as a metabolite.


  Water is a reactant in photosynthesis and hydrolysis reactions. Water is a product in aerobic respiration and condensation reactions
• Why is water's high specific heat capacity important for organisms?


  Water acts as a temperature buffer, enabling endotherms to resist fluctuations in core temperature and to maintain optimum enzyme activity
• Why is water's high latent heat of vaporisation important for organisms?


  When water evaporates, it has a cooling effect. This is important in homeostasis: organisms can lose heat through sweating or panting
• Why is water an important solvent for organisms?


  Water is a polar universal solvent, which enables chemical reactions to take place within cells, the transport of materials in the plasma and the removal of metabolic waste
• Why does water have a high surface tension?


  Due to the ordered arrangement and cohesion of molecules at the surface of water
• Why is the high surface tension of water important for organisms?


  Enables the transport of water and nutrients through plant stems and small blood vessels in the body

  Allows small insects to 'walk' on water
• What is a monosaccharide?


  Simple sugar

  General formula Cn(H2O)n
• Give some examples of monosaccharides


  Glucose, fructose, galactose
• Identify the monosaccharide


  Alpha glucose

  
• What is the name of the bond formed when two monosaccharides react?


  Glycosidic bond
• What is a disaccharide?


  Molecule formed by the condensation of two monosaccharides, forming a glycosidic bond

  Formula C12H22O11
• Give some examples of disaccharides and their monosaccharide constituents.


  Sucrose (glucose + fructose)

  Maltose (alpha glucose + alpha glucose)

  Lactose (glucose + galactose)
• What is a polysaccharide?


  A polymer of monosaccharides, formed by many condensation reactions
• Give some examples of polysaccharides


  Starch, glycogen, cellulose, chitin
• What is the function of starch?


  Energy storage in plants
• Describe the structure of starch.


  Polymer of alpha glucose molecules with two forms:

  Amylose: alpha 1-4 glycosidic bonds, unbranched

  Amylopectin: alpha 1-4 and 1-6 glycosidic bonds, branched
• What is the function of glycogen?


  Energy storage in animals
• How does the structure of glycogen relate to its function?


  It is highly branched enabling the rapid hydrolysis of glucose molecules
• Describe the structure and function of cellulose.


  Linear polysaccharide that is the main component of the cell wall in plants

  Consists of many beta glucose molecules joined by beta 1-4 glycosidic bonds

  Alternate glucose molecules rotated 180 degrees allowing hydrogen bonds between parallel chains, forming myofibrils
• Describe the structure and function of chitin.


  Linear polysaccharide found in the exoskeletons of insects as well as fungal cell walls

  Consists of many beta glucose molecules joined by beta 1-4 glycosidic bonds

  Alternate glucose molecules rotated 180 degrees allowing hydrogen bonds between parallel chains, forming myofibrils
• Explain how a triglyceride is formed.


  One molecule of glycerol forms ester bonds with three fatty acids via condensation reactions
• Relate the structure of triglycerides to their functions


  High energy to mass ratio: energy storage

  Insoluble hydrocarbon chain: used for waterproofing

  Slow conductor of heat: thermal insulation

  Less dense than water: buoyancy of aquatic animals
• What is a phospholipid?


  A type of lipid formed by the condensation of one molecule of glycerol, two molecules of fatty acid and a phosphate group
• Relate the structure of phospholipids to their functions.


  Glycerol backbone attached to two hydrophobic fatty acid tails and one hydrophilic polar phosphate head:

  - forms phospholipid bilayer in water: component of cell membranes

  - tails splay outwards: waterproofing
• What is the difference between saturated and unsaturated fats?


  Saturated have no C=C bonds and are solid at room temperature due to strong intermolecular forces

  Unsaturated have one or more C=C bonds and are liquid at room temperature due to weak intermolecular forces
• What is the difference between monounsaturated and polyunsaturated fatty acids?


  Monounsaturated contains one C=C bond

  Polyunsaturated contains more than one C=C bond
• What is meant by a low density lipoprotein (LDL)?


  Combination of triglycerides from saturated fats and protein

  Blocks receptor sites, reducing cholesterol absorption

  Known as 'bad' lipoproteins
• How do LDLs contribute to the risk of cardiovascular disease?


  The high blood cholesterol level caused by LDLs lead to formation of plaques
• Describe the general structure of an amino acid.


  Amino group (NH2)

  Variable side chain (R)

  Carboxyl group (COOH)

  H atom

  
• How are polypeptides formed?


  Many amino acid monomers join together in condensation reactions, forming peptide bonds (CONH)
• What is the primary structure of a protein?


  The individual sequence of amino acids in a protein
• What is the secondary structure of a protein?


  The local interactions of the amino acids in the polypeptide chain resulting in alpha helices or beta pleated sheets. Hydrogen bonds hold them in place