DNAs Discovery and Structure Honors Objectives SOL.BIO.6f

Todays Objectives: TSW investigate and understand the common mechanisms of protein synthesis, including the structure of DNA and its discovery.

Our Genetic Code The genetic code is a sequence of nucleotides in the __________ of eukaryotic cells. There are two polymers of nucleic acids, _____ and ______.

Important Scientists that determined DNAs Importance Frederick Griffith – bacterial transformation Oswald Avery – DNA = key to transformation Alfred Hershey & Martha Chase – Bacteriophage transformation experiment Erwin Chargaff – base-pairing rules

Important Scientists in the Race for the Double Helix Maurice Wilkins & Rosalind Franklin – X-ray diffraction – DNA must be a some type of spiral (helix) – DNAs diameter is constant and stable James Watson & Francis Crick – Created the first accurate model of DNA – Won the Nobel Prize

DNAs Structure DNA is a double helix DNA contains four nucleotide bases: – adenine (A) – cytosine (C) – guanine (G) – thymine (T)

Chargaffs Rule The bases form the rungs on the DNA ladder by complementary pairing A == T C == G T == A G == C A == T T == A Sugar- phosphate backbone

DNA Replication Replication = Duplication – Happens in the S phase of Interphase – Must replicate before mitosis or meiosis I Part of the double helix is unwound Replication in small pieces (Okazaki fragments) Enzyme stitches pieces together later

Semi-Conservative Replication One-half of each new molecule of DNA is old (template strand) One-half of new molecule of DNA is new (complementary strand)

What is a Gene? A length of DNA on a chromosome May be in several parts – Exon – the expressed parts of the DNA sequence – Intron – the intervening, junk DNA, not expressed Parts are cut, put together and then used to make RNA and proteins

Odd Types of Genes Multigene families Transposons (Barbara McClintock) Protective Genes Viruses may give us new DNA that can be kept over time to cause new evolutionary changes!