Chapter 12- DNA EQ: How did we discover DNA was the most important in our bodies and what is does?

Page  2 DO NOW  What is DNA?  What does it do for us?  What is the term for the structure of DNA?

Page  3 I. 12.1: Identifying the substance of genes A. Bacterial Transformation 1. Background Information- Griffith a. Wanted to discover a better vaccine for pneumonia b. Found two strains of the bacteria  Type S- caused pneumonia  Type R – was harmless

Page  4 2. Griffith’s Experiments a.Injected mice with type S- mice died b.Injected mice with type R- mice lived c.He thought that type S made a toxin that killed mice Heat-killed type S (killed it) and injected into mice – mice lived

Page  5 d. Injected a mixture of type R and heat-killed type S into mice- mice died! e. Cultured the bacteria found in the dead mice and discovered that they were identical to type S!

Page  6 3. Transformation a.Heat-killed bacteria made the harmless bacteria deadly b.Griffith hypothesized that a particular molecule was transferred from type S to type R and made it deadly c.Transformation – process by which one type of bacteria (harmless) had been changed permanently into another (disease-causing form)

Page  7 4. Molecular Cause of Transformation a. Oswald Avery (1944) led a team to discover the molecule responsible for the transformation b. Extracted various molecules one at a time from the heat-killed bacteria and tested them in mice  Transformation still occurred

Page  8 c. In one experiment, they destroyed the DNA  Transformation did not occur d. Conclusion – DNA was the transforming molecule

Page  9 B. Bacterial Viruses 1. Hershey- Chase experiment (1952) a.Used viruses called bacteriophages to study DNA b.They wanted to find out which part of the virus was entering the bacterial cells c.Used radioactive tags attached to each component

Page  10 d. They used these viruses to infect bacterial cells e. Bacteria received the DNA in their cells but no other component f. Conclusion- this confirms that DNA is the molecule of heredity

Page  11 C. The Role of DNA 1. DNA has 3 major functions a. Storing information  The main job of DNA  The “instructions” that cause a single cell to develop into an oak tree, goldfish, or dog must be written into the DNA

Page  12 b. Copying information  A cell must be able to copy its DNA in order to divide

Page  13 c. Transmitting information  Genes are passed down from parents to offspring  DNA molecules must be carefully stored and passed along  Especially important during meiosis- the loss of any DNA can have dire consequence

Page  14 EXIT TICKET  What are the 3 major functions of DNA?  How many strains of bacteria are there?  What happened when the heated killed strain was mixed with the harmless strain?  How did they determine that DNA was the molecule of heredity? (what did they do to the viruses to figure this out?)

Page  15 DO NOW  What is the molecule of Heredity?  What did Griffith’s experiment do?  What experiment did Avery do?  What experiment did Hershey-Chase complete?

Page  16 II. 12.2: The Structure of DNA A. The Components of DNA 1. Overview a.DNA = Deoxyribonucleic Acid b.Can be copied and passed on from one generation to the next c.Specifies how proteins are made d.Has a special molecular structure

Page  Nucleic acids and nucleotides a. Nucleic acids are long chains of nucleotides b. Found in the nucleus of cells c. Have 3 basic parts -5 carbon sugar (deoxyribose) -Phosphate group -Nitrogenous base

Page  Nitrogenous Bases and Covalent Bonds a. DNA has 4 kinds of nitrogenous bases  Adenine (A)  Guanine (G)  Cytosine (C)  Thymine (T)

Page  19 b. The nucleotides in a strand of DNA are joined by covalent bonds between the sugar of one nucleotide and the phosphate of another

Page  20 B. Solving the Structure of DNA 1. Chargaff’s Rule a. The percentages of A and T bases are almost equal in any sample of DNA b. The percentages of C and G bases are almost equal in any sample of DNA c. A binds to T and C binds to G d. DNA samples of various organisms as different as bacteria and humans obeyed this rule

Page  Franklin’s X-rays (early 1950’s) a. Used X-ray diffraction to get information on the structure of DNA b. Her X-ray pictures showed that strands of DNA are twisted around each other  This shape is known as a double helix c. She also showed that DNA is made up of two strands ( 2 upright supports)

Page  Watson and Crick a.Built theoretical models of DNA using cardboard and wire b.In 1953, Watson saw a copy of Franklin’s x-rays c.Along with Crick, they were able to build a workable model

Page  23 C. The Double-Helix Model 1. DNA is a double helix  Looks like a twisted ladder 2. The shape helped explain the properties of DNA

Page  Anti-parallel strands a.The two strands of DNA run opposite directions b.The nitrogen bases meet in the center c.Each strand carries a sequence of nucleotides Analogy: like letters in a 4-letter alphabet

Page  Hydrogen bonding a. Hydrogen bonds are weak bonds that hold the nitrogen bases together in the middle  Analogy: like rungs on a ladder

Page  Base Pairing a. Defined- the principle that bonds in DNA can form only between adenine and thymine and between guanine and cytosine  A binds to T  C binds to G b. The base pairing explains Chargaff’s rule

Page  27 EXIT TICKET  A must bind to _____  G binds to _____  Why is the % of A and G = to the % of T and C  What did Franklin contribute to discovery of DNA?  Who built the model of DNA?  What is the structure of DNA called?

Page  28 DO NOW  What rule states that the % of A - % of T and % of G = % of C?  What are the 3 building blocks of a nucleotide?  What are the building blocks of DNA?  A,T,C, and G are known as _______________ bases  What does DNA stand for?  Match the letters to the following DNA strand: G C A A C T G G C G A T