Lipids are made up of the elements carbon, hydrogen and oxygen but in different proportions to carbohydrates. The most common type of lipid is the triglyceride. Fats and oils are very similar in structure (triglycerides). At room temperature, fats are solids and oils are liquids. Triglycerides are made up of 3 fatty acid chains attached to a glycerol molecule.
In the fatty acid chains the carbon atoms may have single bonds between them making the lipid saturated. These are usually solid at room temperature and are called fats. If one or more bonds between the carbon atoms are double bonds, the lipid is unsaturated. These are usually liquid at room temperature and are called oils.
Proteins: There about 20 different amino acids that all have a similar chemical structure but behave in very different ways because they have different side groups. Hence, stringing them together in different combinations produces very different proteins.
Each amino acid has an amino group (NH2) and a carboxylic acid group (COOH). The R group is a different molecule in different amino acids which can make them neutral, acidic, alkaline, aromatic (has a ring structure) or sulphur-containing.
When 2 amino acids are joined together (condensation) the amino group from one and the acid group from another form a bond, producing one molecule of water. The bond formed is called a peptide bond.
Primary structure of proteins
The primary structure depends on the order and number of amino acid For e.g. Haemoglobin is made up of 4 polypeptide chains, each with a haemoglobin group attached. There are 146 amino acids in each chain. If just one of these is wrong, serious problems can arise (e.g. sickle cell anaemia).
Secondary structure of proteins
This is the basic shape that the chain of amino acids takes on. The 2 most common structures are the a-helix and the b-pleated sheets in a particular protein. This has a regular coiled structure like a spring, with the R groups pointing towards the outside of the helix. Hydrogen (H) bonds are relatively weak but because there are so many, the total binding effect is strong and stable.
Tertiary structure of proteins
This is the overall 3-D structure of the protein.
The shape of the protein is held together by H bonds between some of the R groups (side chains) and ionic bonds between positively and negatively charged side chains. These are weak interactions, but together they help give the protein a stable shape. The protein may be reinforced by strong covalent bonds called disulphide bridges which form between two amino acids with sulphur groups on their side chains.
Quaternary structure of proteins
If a protein is made up of several polypeptide chains, the way they are arranged is called the quaternary structure.
Structure of RNA: Ribonucleic acid (RNA). The chain of nucleotides is formed in exactly the same way as in DNA, but the molecule has some very important differences:
1. It is a single stranded molecule.
2. The pyrimidine Thymine never occurs but is always replaced by Uracil, another pyrimidine.
3. It is much smaller than DNA.
4. It comes in three different forms, ribosomal, transfer and messenger.
Ribosomal RNA is 80% of the total RNA in a cell. It is involved with the formation of ribosome’s and is therefore important as the site of protein synthesis in a cell.
Transfer RNA is a clover leaf shaped molecule and is up to 15% of the total RAN in the cell. It is involved in carrying the amino acids through the cytoplasm to their correct places in a growing polypeptide chain.
Structure of DNA. DNA is a polymer of nucleotides: are made up of a phosphate, a sugar – deoxyribose, a base - adenine, guanine, thymine or cytosine.
In DNA the sugar is always the same but each nucleotide will have only of the four nitrogenous bases. The phosphate sugar and base are linked together.
DNA is a macromolecule polymer made of subunits called nucleotides. The nucleotides are arranged in two chains which are coiled into a spiral shape called a double helix.
As with all nucleotides, those in DNA have three parts. These are a pentose sugar called deoxyribose, a phosphate group and a nitrogenous base.
The sugar and the phosphate are exactly the same in every nucleotide, but the base varies. There are four bases in DNA and each nucleotide contains one of them. The bases are called Adenine, Guanine, Thymine and Cytosine. (A,G,T and C for short).
The order of the nucleotides means that the bases they contain are in a certain order, it is this order which forms the genetic code.
Words 1000 exactly.
Bibliography
I got my source of information from:
- Biology:- AQA Specification A:- Bill Indge, Martin Rowland, Margaret Baker
- School class room notes.
