Molecules

• monosaccharides - single sugars. e.g. pentose (ribose and deoxyribose) and hexose (a-glucose, B-glucose and fructose)
• disaccharides - double sugars. e.g maltose (2 a-glucose molecules) and sucrose (a-glucose and a fructose)
• polysaccharides - amylose and amylopectin (plants) and glycogen (animals) are stores of a-glucose molecules

Bonds between a-glucose molecules:

• 1,4-glycosidic bonds 
• 1,6-glycosidic bonds - causes them to branch (amylopectin and amylose)

B-glucose molecules:

• many bond to produce cellulose
• straight chains
• linked together by hydrogen bonds - grouped to produce microfibrils
• each microfibril - 100s of cellulose molecules = immense tensile strength
• form cell wall of plant cell and prevent cell from bursting in dilute solutions

Triglycerides : lipids composed of 3 fatty acids joined to a glycerol by ester bonds

Fatty acids:

• saturated
• unsaturated - contains a double bond
• release energy in aerobic respiration

Phospholipids:

• glycerol + 2 fatty acids + phosphate
• glycerol/phosphate 'head' = hydrophilic
• fatty acid 'tails' = hydrophobic

• Amino acids joined by peptide bonds >>>> polypeptides
• 20 different amino acids, so infinite variety of polypeptides possible

Amino acids consist of a carbon atom with 4 groups attached:

• an amino group
• a carboxylic acid group
• a hydrogen atom
• a residue group (R-group)

Proteins have different levels of structure:

• Primary structure - sequence of amino acids
• Secondary structure - a-helix (colied) OR B-pleated sheets
• Tertiary structure - further folding of polypeptide, 3D shape. R-groups are held together by hydrogen bonds, hydrophobic interactions, ionic bonds and disulfide bonds.
• Quaternary structure - two or more polypeptide chains

Water molecules are dipolar, so neighbouring water molecules are linked by hydrogen bonds. The H-bonding of water molecules is known as cohesion. They are attracted to each other and surround ions and molecules with charged groups, which thus are dissolved by water.      Water is a good solvent caoable of dissolving a wide range of chemical substances

A solute dissolves in a solvent to produce a solution.

Role of ions and their atoms as components of biologically important molecules:

• Nitrate (NO3-) >> Nitrogen in the amino group of amino acids and the organic base of nucleotides produced in plants
• Sulfate (SO4 2-) >> Sulfur in the R group of the amino acid cysteine
• Phosphate (PO4 3-) >> In a range of important molecules: adenosine triphosphate, ATP; nucleotides and so nucleic acids; phospholipids
• Calcium (Ca2+) >> In calcium pectate, which contributes to the middle lamella of plant cell walls; in calcium phosphate in the bones of vertebrate animals
• Magnesium (Mg2+) >> In the chlorophyll molecule
• Iron (Fe3+) >> In the haemoglobin molecule