How is the amino acid sequence in a protein determined? 3 bases on DNA code for each amino acid. It is the sequence of bases on the DNA which determines the order of amino acids in a protein.

How could similarity between the proteins of different species be used to see how closely related those species are? The more similar the sequence of amino acids for a particular protein in two species is, the more closely related they are.

Read page 32 of your Handbook. Now complete the exercise on page 32 HB. Read page 183 and 184 of the Bill Indge book). What does the data suggest about our closest relatives?

Comparison of amino acid sequences X 2 2 X 3 X 4 6 X 5 X 6 X No of similarities No of differences

Comparison of amino acid sequences No of similarities No of differences

Remember module 1? What is an antigen and where is it found? What is an antibody?

Antigens An antigen is a non-self (foreign) protein to the body that stimulates an immune response. Antigens are most often unusual protein molecules on the outside of a bacterium or a virus or a diseased cell or cancer cell.

Antibodies The presence of a particular antigen in the body, triggers the production of a specific type of antibody protein molecules. The antibody molecules are very specific in shape to bind in a complementary way with the specific antigen molecules, making antigen-antibody complexes (which form a precipitate).

Using Immunology to compare proteins from different species 1)Pure protein molecules (eg albumin protein) are collected from Species A and are then injected into a different Species B. 2)Species B produces specific antibody molecules to the protein antigens from species A. 3)These antibodies produced are now collected. They are mixed in separate tests with protein molecules (in this eg albumin) from a range of other species. 4)If the albumin protein from any species is complementary in shape to the antibodies it is mixed with, some antigen- antibody complexes will be formed. These form a precipitate. 5)The greater the amount of precipitate formed, the more closely the species are related – and the closer in structure are their proteins that were tested.

Immunological comparison of proteins

Key points about this technique: The greater the amount of precipitate made, the closer the evolutionary relationship. Chimp albumin protein only binds in slightly fewer places than human albumin protein to anti-human albumin antibodies. This is due to the amino acid sequences of the chimp and human albumin proteins being slightly different. Fewer places where the chimp albumin protein will bind to the antibodies produces less precipitate.

1.Now read page 210 of Nelson Thornes text book and pg of the Bill Indge text book. Complete page 33 of your booklet. 2.Do the Application Exercise on page 211 – 212 of NT text book 3.Answer the summary questions on pg 210.