Proteins Flashcards
What elements do proteins contain?
CHO, nitrogen (+ sometimes sulfur)
What are the monomers of proteins?
Amino acids
What do amino acids join together to form?
Polypeptides
What is the generalised structure of an amino acid?
R
|
H2N—C—COOH
|
H
What bonds are amino acids joined together by?
Peptide bonds (-CONH-) formed by condensation reactions
What does the primary structure of a protein represent?
- Refers to the sequence of amino acids in the polypeptide chain
- Determines specific shape of the protein
What does the secondary structure of a protein represent?
- Represents the folding or coiling of the polypeptide chain (as a result of hydrogen bonding between amino acids)
What does the secondary structure include?
Alpha helix OR
Beta-pleated sheet
What does the tertiary structure of a protein represent?
- Formed by further folding and coiling of secondary structure (due to hydrogen bonds, ionic bonds and disulfide bonds)
What is the formation of the bonds in the tertiary structure?
- They form in places determined by the sequence of amino acids in the primary structure
- They form between the R groups of amino acids
What does the NH2 represent?
Amine group
What does the COOH represent?
Carboxyl group
What does R represent?
A side chain
How do the 20 common amino acids differ?
Only by their side group
How are dipeptides formed?
By the condensation of two amino acids
How are polypeptides formed?
By the condensation of many amino acids
What are the characteristics of globular proteins?
- Soluble
- Biochemical functions
- Enzymes, myoglobin
What is the quaternary structure?
When proteins consist of more than one polypeptide chain
In the quaternary structure, what bonds are polypeptide chains held together by?
Ionic, hydrogen and sometimes disulfide bonds
What is denaturation?
- An alteration in the tertiary structure of a protein
Is denaturation reversible?
No, the loss of the 3D shape is often irreversible and makes it no longer functional
What causes denaturation?
- breaking of hydrogen and ionic bonds
- high temps above optimum
- extreme changes in pH
- heavy metals
- disulfide bonds are not broken at temps that break hydrogen and ionic bonds
What is the test for proteins?
Biuret test
How to carry out the biuret test
- Add biuret reagent
- purple/lilac = protein present
- if remains blue = no protein present
