Proteins Flashcards
What is a protein?
A protein is a polymer made up of the monomer amino acids.
How many levels of structure are there in a protein?
4
What are the 4 levels of structure in a protein?
Primary
Secondary
Tertiary
Quaternary
What is the primary structure?
The order of the amino acids in the polypeptide chain.
What is a polypeptide chain?
A chain of amino acids all joined together by several condensation reactions.
What does the peptide bond do?
Holds each amino acid together in the chain.
What is the secondary structure?
The sequence of amino acids causes parts of a protein molecule to bend into alpha helix shapes or fold into beta pleated shapes.
What are secondary structures held together by?
Hydrogen bonds.
Where do hydrogen bonds form?
Between the C=O groups of the carboxyl group of the amino acid and the H in the amine group of another amino acid.
What is the tertiary structure?
There is a further folding of the secondary structure which forms a unique 3D shape which is held in place by ionic, hydrogen or disulphide bonds.
Where do the ionic and disulphide bonds form between?
The R groups of different amino acids.
Why do disulphide bonds only sometimes occur?
Because there must be sulfur in the R groups for this bond to occur.
What is the quaternary structure?
A protein is made up of more than one polypeptide chain.
What is an example of something made up of 4 polypeptide chains?
Haemoglobin
What happens if a protein is denatured?
The bonds which hold the tertiary and secondary structure in shape will break and thus the unique 3D shape is lost. The enzymes lose their unique active site.
What 2 conditions can lead to the denaturing of proteins?
Too high or low of a pH - too many H+ or OH-.
Too high temp - high kinetic energy.
What causes different 3D structures?
One amino acid being different which causes the ionic/hydrogen/disulphide bonds to form in a different location.
What causes a change in the amino acid?
Changes in DNA.
How are many amino acid monomers joined together?
Through a series of condensation reactions in a process called polymerisation.
Describe disulfide bridges?
Fairly strong and not easily broken.
Describe ionic bonds?
Formed between any carboxyl and amino groups that are not involved in forming peptide bonds. They’re weaker than disulfide bonds and are easily broken by pH changes.
Describe hydrogen bonds?
Numerous but easily broken.
Describe the test for proteins?
1)Place a sample of the solution to be tested in a test tube.
2)Add an equal volume of biuret reagent at room temperature.
3)If it turns purple, there is a presence of peptide bonds and hence a protein. If no proteins are present, the solution remains blue.
What solution is used to test for proteins? What does it detect for?
Biuret test which detects peptide bonds.
