Proteins

You need to know that:•Proteins have a variety of functions within

all living organisms.•The general structure of an amino acid •Condensation reactions form peptide bonds•Amino acids link together to form

polypeptides. •The relationship between primary,

secondary, tertiary and quaternary structure, and protein function.

•The biuret test for proteins.

Proteins

•Enzymes, carrier molecules, hormones, antibodies, cell membrane

•Over 50 % of a cells dry weight is Protein

•Basic Unit Molecule▫Amino acids - 20 amino acids found in living systems

Amino acid structure

•AA-AA Dipeptide

•AA-AA-AA-AA-AA Polypeptide

•Bond between Amino acids - Peptide Bond

Amino acid structure

Levels of Structure

•1. Primary •2. Secondary•3. Tertiary•4. Quaternary

Primary Level of Structure

•The linear sequence of Amino acids

•This is determined by the genetic code built into DNA of a gene

How amino acids combine

↓+ H2O

Linking of amino acids

•This is a hydrolysis reaction

•The bond formed is a peptide bond

Secondary Level of Structure

•When the a chain of polypeptides takes on a specific orientation in space

•2 Main Types▫Alpha Helix▫Beta Pleated Sheet

Tertiary Level of Structure

•Final 3 dimensional configuration

•Held together by many different bonds:▫peptide▫ionic▫hydrogen▫Covalent ▫Disulphide -S – S-

Quaternary Level of Structure

•When 2 or more proteins come together to form a functional unit

Biuret test for protein

•Place test solution in a test tube. Add equal volume of sodium hydroxide, (Biuret A) at room temp.

•Add few drops very dilute (0.05%) copper(II) sulphate solution, (Biuret B) and mix gently.

•Purple colouration = peptide bonds and so a protein.

•If it remains blue = no protein.

Questions• What type of bond links amino acids together? • What type of reaction is involved in linking amino acids

together?

•  What 4 different components make up an amino acid? • Name the 2 bonds involved in holding together the

primary structure of a protein.

 • Name the bonds involved in holding together the

secondary structure of a protein.

Denatured

•Temperature•pH•salt concentrations•heavy metals