How Do We Know DNA is the Genetic Material? §Proteins were thought to carry genetic information §Fred Griffith 1928 §Experimented with pneumonia on mice §Virulent (causes sickness) §Non-Virulent (does not cause sickness)

Griffith Experiment §Proves the genetic material is not Protein §Protein Denatures (breaks down) in heat

Hershey and Chase Experiment b Bacterial cell b Phage b Batch 1: Radioactive sulfur ( 35 S) b Radioactive protein b DNA b Batch 2: Radioactive phosphorus ( 32 P) b Radioactive DNA b Empty protein shell b Phage DNA b Centrifuge b Radioactivity (phage protein) in liquid b Pellet (bacterial cells and contents) b Pellet b Radioactivity (phage DNA) in pellet b EXPERIMENT

Figure 16.7 b 3.4 nm b 1 nm b 0.34 nm b Hydrogen bond b (a) b Key features of DNA structure b Space-filling model b (c) b (b) Partial chemical structure b 3 end b 5 end b 3 end b 5 end bTbT bTbT bAbA bAbA bGbG bGbG bCbC bCbC bCbC bCbC bCbC bCbC bCbC bCbC bCbC bCbC bCbC bGbG bGbG bGbG bGbG bGbG bGbG bGbG bGbG bGbG bTbT bTbT bTbT bTbT bTbT bTbT bAbA bAbA bAbA bAbA bAbA bAbA

STRUCTURE OF DNA - Single units, monomers, called NUCLEOTIDES. - Nucleotide consists of three parts: §five carbon sugar - deoxyribose §phosphate group §nitrogen base - one of four * Sugar & phosphate stay the same but the nitrogen bases can change.

4 NITROGEN BASES : §Adenine §Thymine §Guanine §Cytosine §A & G are double ring (PURINES) §T & C are single ring (PYRIMIDINES) §They all pair specifically A-T, C-G §Combined by a Hydrogen bond.

Base Pairing in the DNA Molecule

§Sugar and phosphate make up the sides §Nitrogen bases make up the middle §Two strands, that twist around each other, are used to make a DNA molecule….

Discovering DNA’s Structure Wilkins & Franklin: Used x-rays to photograph DNA

Chargaff: b Discovered that A=T and G=C

§Proposed the model in 1953 §Earned the 1962 Nobel Prize for Physiology Medicine §Franklin was also named to the Nobel Prize but had died so could not be recognized Watson & Crick: b First model of DNA

The Secret of Life PBS

60 Minutes: Craig Venter Designing Life 60 Minutes: Craig Venter Designing Life

DNA, CHROMOSOMES AND GENES - DNA is found in the nucleus of all cells -Found as strands, known as chromatin, in resting cells -Before cell division, chromatin forms chromosomes. -GENES are short segments of DNA that contain specific information for traits

FUNCTION OF DNA: 1. Control of cells activities 2. Chooses the type of proteins to be made

1. DNA REPLICATION Process of making new copies of DNA 1. DNA untwists 2. An enzyme, DNA Helicase, “unzips” the DNA at the nitrogen bases - breaking their hydrogen bonds.

3. Free nitrogen bases from the nucleoplasm attach to the newly exposed sections of DNA by means of DNA Polymerase.

ANTI-PARALLEL DNA

Leading and Lagging Strands DNA Polymerase only works in 5’  3’direction Polymerase moves along the leading strand Fragments are added in segments of the lagging strand Okazaki Fragments b Replication Animation Replication Animation

Leading and Lagging DNA Strands and Okazaki Fragments

4. The bases are now reattached The result is two DNA strands. 1/2 of the old DNA and 1/2 of the new

DNA helicase DNA polymerase

The Speed of Replication §Replication occurs rapidly because DNA is unzipped at a number of places at a time

§46 Chromosomes/cell §Approximately 3 billion base pairs/cell §Code would fill 1000 biology books/cell §Takes a few hours

Proof Reading §Average of one error per billion nucleotides §Mistakes in replication are check and corrected by specialized “proof-readers” §Consists of 20 or so amino acids §WHAT TYPES OF THINGS COULD CAUSE CHANGES IN OUR CELLS AFTER REPLICATION?

* DNA has the “blueprints” for traits *Too big to pass through the nuclear membrane -Use RNA - ribonucleic acid -sugar -phosphate -nitrogen bases (4) Adenine Uracil Cytosine Guanine -RNA is a single stranded RNA STRUCTURE/REPLICATION

3 Types of RNA 1. Messenger RNA: carries code from DNA 2. Transfer RNA: single folded strand of RNA that carries the amino acids 3. Ribosomal RNA: major component of ribosome’s.

2. TRANSCRIPTION: §Process of transcribing or copying the specific sequence of bases or code from DNA to RNA §DNA is considered to be a TEMPLATE

mRNA Synthesis

1. An enzyme, RNA polymerase, unzips DNA

§2. Free floating RNA nucleotides line up with the appropriate DNA base

3.Continues until the RNA comes to a “stop” sequence and releases the DNA 4. RNA moves out of cell nucleus

Protein Synthesis :

Protein Synthesis Defined as the formation of proteins using information coded on the DNA and carried out by RNA -Proteins may consist of hundred or thousands of amino acids -They are connected by peptide bonds

The Amino Acid Code -20 amino acids are found within our bodies -Proteins are read as CODONS

Amino Acid Code

TRANSLATION:  Process of making proteins from the mRNA § Also referred to as PROTEIN SYNTHESIS § Occurs at the Ribosomes 1. mRNA passes out of the nucleus through the nuclear membrane and moves to a ribosome

2. The mRNA attaches to the ribosome at the start codon, (at the P site) 3. The start codon is always “AUG”

4. The mRNA is read in a series of three (3) nitrogen bases at a time - referred to as CODONS. 5. Ribosome signals the tRNA with the matching ANTICODON to bring in the appropriate Amino Acids

6.The tRNA at the “P-site” is released, but the one at the “A-site” stays 7.The ribosome moves to open up the A site

8. The Amino Acids bond by PEPTIDE bonds to form PROTEINS

Important things to remember… - tRNA carry specific Amino Acids -tRNA are recycled - The arrangement of the Amino Acids determines the type of protein that is made