Biological Molecules: Key Terms
- The key molecules that are required to build structures that enable organisms to function are:
- Carbohydrates
- Proteins
- Lipids
- Nucleic Acids
- Water
- Carbohydrates, proteins, lipids and nucleic acids contain the elements carbon (C) and hydrogen (H) making them organic compounds
- Carbon atoms are key to the organic compounds because:
- Each carbon atom can form four covalent bonds – this makes the compounds very stable (as covalent bonds are so strong they require a large input of energy to break them)
- Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur
- Carbon atoms can bond to form straight chains, branched chains or rings
- Carbon compounds can form small single subunits (monomers) that bond with many repeating subunits to form large molecules (polymers) by a process called polymerisation
- Macromolecules are very large molecules
- That contain 1000 or more atoms therefore having a high molecular mass
- Polymers can be macromolecules, however not all macromolecules are polymers as the subunits of polymers have to be the same repeating units
Carbohydrates
- Carbohydrates are one of the main carbon-based compounds in living organisms
- All molecules in this group contain C, H and O
- As H and O atoms are always present in the ratio of 2:1 (eg. water H2O, which is where ‘hydrate’ comes from) they can be represented by the formula Cx (H2O)y
- The three types of carbohydrates are monosaccharides, disaccharides and polysaccharides
Exam Tip
When discussing monomers and polymers, give the definition but also name specific examples eg. nucleic acids – the monomer is a nucleotide.
The Two Forms of Glucose
- The most well-known carbohydrate monomer is glucose
- Glucose has the molecular formula C6H12O6
- Glucose is the most common monosaccharide and is of central importance to most forms of life
- There are different types of monosaccharide formed from molecules with varying numbers of carbon atom, for example:
- Trioses (3C) eg. glyceraldehyde
- Pentoses (5C) eg. ribose
- Hexoses (6C) eg. glucose
- Glucose exists in two structurally different forms – alpha (α) glucose and beta (β) glucose and is therefore known as an isomer
- This structural variety results in different functions between carbohydrates
- Different polysaccharides are formed from the two isomers of glucose
Structure of polysaccharides table
Exam Tip
You must be able to recognise and draw the isomers of α and β glucose.