This week we have been learning all about proteins, in particular a group of proteins called amino acids.
Every amino acid has a central carbon atom with four different chemical groups attatched to this atom, they are:
- The amine group (-NH2)
- A carboxyl group (-COOH)
- A hydrogen atom (-H)
- And an R group which is different for each different enzyme.
In addition to learning about the structure of an amino acid, we have been learning about the structure of proteins and the formation of bonds.
Peptide bonds - Amino acid monomers combine to form a dipeptide in a condensation reaction. The water released is made by the -OH from a carboxyl group combining with a H from the amine group of a different amino acid. The bond formed between the two different amino acids is called a peptide bond.
Ionic bonds - these are the bonds formed between charged R groups (in aqueous solutions). The negativley charged carboxyl group bonds with the posotivley charged amine group.
Disulphide bonds - this only occurs between the sulphyl group of two cysteine amino acids. There are two types of disulphide bonds: interchain which is between two different polypeptide chains and intrachain between two of the same polypeptide chains.
Hydrogen bonds - Will form between NH groups and O=C groups due to the unequal sharing of electrons, however, can also be between OH groups and O=C groups on the R groups of nearby amino acids.
Finally, the structures of protein:
- Primary structure - Amino acid monomers join together to form polypeptides. The sequence of amino acids in a polypetide chain forms the primary structure of any protein. Proteins can be made of a single polypeptide chain but are mainly made up of a number of polypetide cains. The sequence is specific for each protein.
- Secondary structure - The posotive charge of the -NH and negative charge of the -O=C on either side of the peptide bond slightly attract each other. This causes the polypetide chain to twist forming an alpha helix. Beta sheets can also be formed.
- Tertiary structure - The polypeptide chain folding to form a 3-D shape. This shape can be determined by 1. hydrophyllic amino acids sheilding hydrophobic amino acids in aqueous solution. 2. hydrgen bonds. 3. ionic bonds. 4. disulphide bonds.
- Quaternary structures - A combination of two or more polypeptide chains. The chains are held together by hydrogen bonds, ionic bonds and interchain disulphide bonds.
Hope this is useful and sorry for all of the spelling mistakes!
Christina xx
