Core Concepts 1 - Biological Molecules

• Name the four key inorganic ions in living organisms.

  Magnesium ions (Mg2+)

  Iron ions (Fe2+)

  Calcium ions (Ca2+)

  Phosphate ions (PO43-)
• What is the role of Mg2+ in plants?

  Mg2+ is used to produce chlorophyll.
• What is the role of Fe2+ in animals


  Fe2+ is found in haemoglobin and is involved in the transport of oxygen.
• What is the role of PO43- in living organisms?

  PO43- is used to produce ADP and ATP
• What is the role of Ca2+ in living organisms?

  Ca2+ is used 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 𝛿- (slight negative charge) & H 𝛿+ (slight positive charge).
• Describe hydrogen bonding between water molecules.

  Weak intermolecular forces of attraction form between a lone pair on a δ- O and a δ+ 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. It 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.

  Glyceraldehyde, Ribose, Deoxyribose, α- and β-glucose, Fructose, Galactose.
• What is the name of the bond formed when two monosaccharides react?

  Glycosidic Bonds
• 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 many monosaccharides, formed by 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 a-glucose monomers

  - Two forms: Amylose and Amylopectin

  - Amylose: a-1,4 glycosidic bonds, unbranched

  - Amylopectin: a-1,4 and a-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.
• Explain how a triglyceride is formed.

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

  ● High energy:mass ratio = high calorific value from oxidation (energy storage).

  ● Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing.

  ● Slow conductor of heat = thermal insulation e.g. adipose tissue.

  ● 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 e.g. skin.
• What is the difference between saturated and unsaturated fats?

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

  - Unsaturated fats have one or more C=C bonds, and are liquid at room temperature due to weak intermolecular forces.
• Differentiate between monounsaturated and polyunsaturated fatty acids.

  - monounsaturated fatty acids contain one C=C bond

  - polyunsaturated fatty acids contain 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 LDL's contribute to the risk of cardiovascular disease?

  The high blood cholesterol level caused by LDL's leads to formation of atherosclerosis plaques.
• Describe the general structure of an amino acid.

  - Amine 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.
• Describe 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 the arrangements in place.
• Describe the tertiary structure of a protein.

  Folding of a protein to make a three-dimensional structure held in place by various interactions and bonds

  disulphide bonds, ionic bonds, hydrogen bonds, hydrophobic interactions
• Describe the quaternary structure of a protein.


  - Interactions of more than one polypeptide chain.

  - May involve addition of prosthetic groups, e.g. metal ions or phosphate groups.