Biological Molecules - Proteins Flashcards
What monomers are proteins made from?
Amino acids
What is the general formula of an amino acid?
Where NH2 represents an amine group, COOH represents a carboxyl group and R represents a side chain.
The twenty amino acids that are common in all organisms differ only in their side group.
What bond is formed between two amino acids in a condensation reaction?
Peptide bond
What are two amino acids joined together called? Three or more?
Dipeptide
Polypeptide
What is the primary structure of a protein?
The order and number of amino acids in a protein
The initial sequence of amino acids in a protein
What is the secondary structure of a protein?
The shape that the chain of amino acids chains
Either alpha helix or beta pleated sheet.
The hydrogen in the -NH has a slight positive charge whilst the oxygen in the -C=O has a slight negative charge.
As a result weak hydrogen bonds can form leading to alpha helices or beta pleated sheets.
What is the tertiary structure of a protein?
The 3D shape of the protein and is formed from further twisting and folding.
Disulfide bridges - interactions between the sulfur in the R group of the amino acid cysteine these are strong and not easily broken.
Ionic bonds - form between the carboxyl and amino groups that are not involved in the peptide bond. They are easily broken by pH and are weaker than disulfide bridges.
Hydrogen bonds - numerous and easily broken.
What is the quaternary structure of a protein?
More than one polypeptide chain and the presence of a prosthetic group
Can be globular or fibrous.
Globular proteins such as enzymes are compact
Fibrous proteins such as keratin are long and thus can be used to form fibres
What is the test for proteins?
The Biruet test
Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.
Add a few drops of very dilute (0.05%) copper (II) sulfate soliton and mix gently.
A purple colouration indicates the presence of a peptide bond and hence a protein.
A negative result would mean the solution remains blue.
