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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)

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

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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

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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

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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.

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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.

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Base Pairing in the DNA Molecule

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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.

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

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

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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

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The Secret of Life PBS

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

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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

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

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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.

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

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ANTI-PARALLEL DNA

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

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Leading and Lagging DNA Strands and Okazaki Fragments

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

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DNA helicase DNA polymerase

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

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

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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?

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* 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

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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 ribosomes.

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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

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mRNA Synthesis

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1. An enzyme, RNA polymerase, unzips DNA

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

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

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Protein Synthesis :

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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

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

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Amino Acid Code

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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

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

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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

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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

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

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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