Proteins Flashcards
What are amino acids?
The monomers from which proteins are made.
Describe the general structure of amino acids?
Amino acids contain an amino group (NH2), carboxylic acid group (-COOH) and a variable R group which is a carbon-containing chain.
How many types of amino acids of there?
There are 20 different amino acids, each determined by their different R groups.
How are amino acids formed?
Amino acids are joined by peptide bonds formed in condensation reactions. In this reaction a molecule of
water is formed.
What is a dipeptide?
A dipeptide contains two amino acids
What is a polypeptide?
Polypeptides contain three or more amino acids.
Describe the structure of a protein
- determined by the order and number of amino acids, bonding present and the shape of the protein:
• Primary structure of a protein is the order and number of amino acids in a protein. This primary structure contains the initial sequence of amino acids and will
therefore determine the protein’s function in the end.
• The secondary structure is 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.
• Tertiary structure of proteins is the 3D shape of the protein and is formed from further twisting and folding.
A number of different bonds maintain the structure, these are:
- Disulfide bridges - interactions between the sulfur in the R group of the amino acid cysteine 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.
Proteins can be globular or fibrous.
What is a Globular protein?
Globular proteins such as enzymes are compact
What is a fibrous protein?
Long and thus can be used to form fibres. eg keratin
What test is used to find the presence of peptide bonds in a protein?
The Biuret test
How do you carry out the Biuret 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.
What are the four groups surrounding the central carbon atom in an amino acid?
- Amine group
- Carboxyl group
- Hydrogen group
- R group
The two functional groups in amino acids are:
anime group & Carboxyl group
What is the name of the structure of a protein represented by the sequence of the amino acids?
Primary structure
What bonds form between amino acids to hold the secondary structure in place?
Hydrogen bonds
The 4 Structural levels of proteins are:
Primary structure
Secondary structure
Quaternary structure
Tertiary Structure
Primary structure
Sequence of amino acids
Tertiary structure
3D structure of a polypeptide chain
Quaternary structure
The final 3D structure of a protein. This may contain multiple polypeptides
Secondary Structure
Local folding of the polypeptide chain
How many amino acids are common in all organisms
20
A sample is boiled in a test tube with ethanol. The sample is shaken and left to stand. The solution inside is then poured into a tube containing distilled water.
What would be observed if there is a lipid present in the tube
A white, milky layer
Which amino acid does not have carbon in its R group
Glycine
What molecule is released as a byproduct when the amino terminal of one amino acid reacts with the carboxyl terminal or another amino acid?
water
