Module 1: Biological Molecules
2.1.1 Biological Molecules
a) Hydrogen bonding occurs between oxygen atoms and hydrogen atoms. The oxygen is electronegative (or delta negative) whilst hydrogen is electropositive (delta positive).
b) An amino acid contains the central atoms, carbon, nitrogen, nitrogen. Two hydrogen atoms are bonded to the nitrogen molecule. The first carbon has one hydrogen attached to it as well as the R group. The final carbon has one oxygen double bonded to it and an OH molecule. The R group is the variable group as there is no such thing as an 'R' element. In more simple amino acids it can represent a single hydrogen, whilst in other amino acids it can be a much more complex molecule.
c) Peptide bonds are formed when two amino acids join together. The OH molecule of one amino acid and a H atom from the other amino acid forms a water molecule and the double bonded oxygen atom joins the two molecules together. Peptide bonds are created in condensation reactions. This is when a water molecule is released from the formation of the bond. Two amino acids joined together forms a dipeptide molecule. A peptide bond is broken when a dipeptide splits into two amino acids. This is when a hydrolysis reaction happens. Hydrolysis reactions require a water molecule to be used up in the reaction. More than two amino acids joined together forms a polypeptide.
d) Primary structure is the specific sequence of amino acids that make up the protein.
e) Secondary structure is when the chain of amino acids coils to form an alpha helix or folds to form a beta pleated sheet. It is the hydrogen bonds that hold the secondary structure together. Although hydrogen bonds are generally weak, the sheer number of them gives the shape good stability.
f) Tertiary structure is the final 3D shape of a protein when the coils or pleats, begin to coil and fold themselves with chains of amino acids between them. Disulfide bonds- when two cysteine (amino acid containing sulfur) molecules are close together they can create a covalent bond. Ionic bonds- when oppositely charged amino acids are found close together an ionic bond can form. Hydrogen bonds- when slightly positive charged groups are found near slightly negatively charged groups hydrogen bonds form. Hydrophobic amino acids are found in the center of the molecule and hydrophillic amino acids are found on the outside of globular proteins.
g) Quaternary structure- proteins made up of more than one polypeptide chain or a polypeptide and an inorganic molecule.
Haemoglobin- four polypeptide sub-units, two are alpha chains, two are beta chains. It is a water soluble globular protein. It carries oxygen from the lungs to the tissues. Haemoglobin is found inside red blood cells.
h) Collagen-a fibrous protein. 3 polypeptide chains wound round each other and joined by hydrogen bonds. Collagen molecules also form covalent bonds between molecules called cross links. This is known as a collagen fibril. Many of these joined together is known as a collagen fibre. Provides mechanical strength- walls of arteries, tendons, bones, cartilage and connective tissue.
j) Monomers of carbohydrates are known as monosaccharides. There are two types of glucose (a six carbon monosaccharide). Alpha glucose contains the two OH groups at the bottom of the molecule whilst Beta glucose contains one OH molecule at the top and one at the bottom.
l) Two monosaccharides joined together is known as disaccharide. It is formed in a condensation reaction and forms a glycosidic bond. Glycosidic bonds are broken and two monosaccharides formed in a hydrolysis reaction. Polysaccharides are when more than two monosaccharides join together.

	Created by Laura Perry about 9 years ago

A Levels Biology (AS Biology) Note on OCR AS Biology- Biological Molecules, created by Laura Perry on 01/04/2015.