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Why do we Study DNA? 1. 2. 3. 4. Disease Better vegetable, fruit, and animals. Crime History of life DNA Karotype • Gene: segment of DNA on your chromosomes that determines your traits. • Trait: characteristics about you. It can be a part or a behavior. You inherited your traits from your parents. • Chromosomes: 23 pairs made up of DNA wind around histones (proteins). • What is the human genome? DNA Facts •One chromosome has 50 - 250 million base pairs. •DNA is found in the mitochondria. •One sequence of DNA is a genome or gene. *DNA molecules are incredibly long. If all of the DNA from all of your cells was stretched out into a single thread, it would extend to the moon and back about one million times! • The human genome is contained in 23 pairs of chromosomes. • The DNA within the human genome makes up 60,000 to 100,000 genes. • . • Humans get one complete set of genes from each parent. • In April 2003, the National Human Genome Research Institute (NHGRI) celebrates • the completion of the human genome sequence and the 50th anniversary of the description of the DNA double helix. • The nucleus, or control centre, of a cell, is where DNA is located. http://genomics.energy.gov/gallery/chromosomes/gallery-01.html Karotype • A display of metaphase chromosomes of a cell arranged by size and centromere positions. • From these pictures, doctors can study to chromosomes to look for disorders. Genetic material of cells… What is the type of organic molecule? • Madeup of DNA • Called NUCLEIC ACIDS • DNA is made up of repeating monomers called NUCLEOTIDES DNA (Deoxyribonucleic Acid) How do we know that all of our genetic information comes from DNA? • What type of experiment would you design to determine that DNA is the source of all genetic information? Fredick Griffith’s Experiment 1. Injected mice with two bacteria - one that made them sick and one that didn’t. 2. He boiled bacteria A and then the mice did not get sick. 3. He injected both bacteria A(boiled) and bacteria B into mice and they got sick. CONCLUDED - Transformation occurred. Bacteria causing bacteria changed the harmless bacteria. Passed on genes somehow. Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation • Frederick Griffiths was a bacteriologist studying pneumonia • He discovered two types of bacteria: – Smooth colonies – Rough colonies Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation CONCLUSION: The smooth colonies must carry the disease! Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation • When heat was applied to the deadly smooth type… • And injected into a mouse… • The mouse lived! Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation • Griffith injected the heat-killed type and the non-deadly rough type of bacteria. • The bacteria “transformed” itself from the heated non-deadly type to the deadly type. Avery, McCarty, and MacLeod Repeated Griffith’s Experiment Oswald Avery Maclyn McCarty Colin MacLeod Avery, McCarty, and MacLeod Repeated Griffith’s Experiment Avery, McCarty, and MacLeod Added the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth Type To the Heat-Killed Smooth Type, added enzymes that destroyed… Carbohydrates Lipids Proteins RNA DNA S-Type S-Type S-Type S-Type S-Type Carbohydrates Lipids Proteins RNA DNA Destroyed Destroyed Destroyed Destroyed Destroyed Conclusion: DNA was the transforming factor! The Hershey-Chase Experiment Alfred Hershey & Martha Chase worked with a bacteriophage: A virus that invades bacteria. It consists of a DNA core and a protein coat Protein coat DNA Protein coats of bacteriophages labeled with Sulfur-35 Phage 1. Hershey and Chase Bacterium mixed the radioactively-labeled viruses with the bacteria Phage Bacterium The viruses infect the bacterial cells. DNA of bacteriophages labeled with Phosphorus-32 Hershey - Chase Injected bacteriophages with radioactive isotopes then placed them with bacteria. The virus injected the bacteria with DNA containing radioactive material. Then tested for the radioactive material. COCNLUDED: Viruses passed on their DNA to the bacteria. The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion: DNA carries the genetic code! However, there were still important details to uncover… A HISTORY OF THE STRUCTURE OF DNA • Discovery of the DNA double helix A. Rosalind Franklin - Used X-ray photo of DNA to discover the shape was a double helix. (1952) B. Watson and Crick - Used Franklin’s work to build the first model of DNA. They figured out the exact structure. (1953) Discovery of DNA Invented X-ray Rosalind diffraction Franklin - photography. Photo used to determine the shape of DNA is spiral. DISCOVERY OF DNA James Watson and Francis Crick used the information from Franklin and other scientists to build a 3-D model of DNA. Won the Nobel Piece Prize in Chemistry in 1961. Watson & Crick proposed… •DNA had specific pairing between the nitrogen bases: ADENINE – THYMINE CYTOSINE - GUANINE •DNA was made of 2 long stands of nucleotides arranged in a specific way called the “Complementary Rule” DNA DNA stands for – Deoxyribonucleic acid Functions of DNA: 1. Carries the codes to make proteins. 2.Carries the genetic material that is passed on from the parents to the offspring. STRUCTURE OF DNA These three parts the basic unit of DNA NUCLEOTIDE(monomer). phosphate Sugar (deoxyribose) Nitrogen base Can be A, T, C or G STRUCTURE OF DNA Side Pieces(The Rope Part) Are alternating units of a 5 carbon sugar and a phosphate group. These go down both sides of the molecule phosphate Sugar (called deoxyribose) STRUCTURE OF DNA Nitrogen Bases (Steps of the ladder) 1.Adenine - A 2.Thymine –T 2 . 3.Cytocine – C 4.Guanine - G The bases are connected to the sugar only !!!!! DNA Nucleotide Phosphate Group O O=P-O O 5 CH2 O N C1 C4 Sugar (deoxyribose) C3 C2 Nitrogenous base (A, G, C, or T) phophate adenine sugar thymine cytocine guanine How are the nucleotides held together? • Nucleotides are held together by covalent bonds between the sugar of one nucleotide and the phosphate of the next. DNA Amount of DNA • Amount of DNA in a sample can be determined by how much UV light is absorbs. DNA absorbs UV light!!! DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone Nitrogenous Bases • PURINES 1. Adenine (A) 2. Guanine (G) A or G • PYRIMIDINES 3. Thymine (T) 4. Cytosine (C) T or C BASE-PAIRINGS H-bonds 3 bonds G C T A 2 Bonds STRUCTURE OF DNA One complete turn of the double helix is 10 base pairs or 10 steps on the ladder DNA is antiparallel The two strand of DNA run opposite of each other. The happens because of the structure of the nitrogen bases. To fit together,they must be upside down. DNA Double Helix 5 O 3 3 O P 5 O C G 1 P 5 3 2 4 4 2 3 1 P T 5 A P 3 O O P 5 O 3 5 P Chargaff’s Rule • Adenine must pair with Thymine • Guanine must pair with Cytosine • Their amounts in a given DNA molecule will be about the same. T A G C Chargaff’s Rule • In his experments on several different organisms, Chargaff discovered that the percentage of A and T were equal. The same for C and G. This observation became Chargaff’s rule. This is always the same no matter what organisms. Video of girl burned!! • United streaming Genetic Diversity… • Different arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms. The Code of Life… • The “code” of the chromosome is the SPECIFIC ORDER that bases occur. A T C G T A T G C G G… See p. 297 DNA is wrapped tightly around histones and coiled tightly to form chromosomes How does DNA copy itself? Purpose: DNA copies itself to ensure that each new cell that is produced in gets the correct number of chromosomes and receives an EXACT copy of the DNA molecule. This is called DNA REPLICATION. The DNA molecule serves as its own pattern or template so as an exact copy can be made. Watson and Crick • The model that Watson and Crick where the nitrogen bases pair suggested a mechanism for DNA to replicate. Messelson and Stahl • They proved that DNA is semiconservative by attaching radioactive material to DNA. As the cell divided, they observed the new DNA in each cell and saw that it contain half of the old. STEPS OF DNA REPLICATION 1. Helicase begin to unzip the double helix at many different places. The hydrogen bonds between the bases are broken. Occurs in two different directions. 2. Free floating in the cytoplasm nucleotides pair with the bases on the template. DNA polyermase bonds together the nucleotides. Small segments are bonded together. 3. Two identical strands of DNA result. The DNA will twist back together. DNA is called SEMICONSERVATIVE because it uses an old strand to make a new one. This results in 2 new identical DNA molecules. DNA Replication 1. DNA helicase breaks the hydrogen bonds between the two strands. 2. Replication occurs at multiple site along DNA called origins of replication. This will cause bubbles. 3. Replication occurs in both directions. This makes it quicker. 4. DNA polymerase bring in new nucleotides to fill match with old strand. 5. One strand is easily replicated, the other is made in pieces because DNA polymerase cannot read the upside down piece. DNA ligase will put the pieces together. 6. DNA polyermase will work it way down DNA strands using old DNA as a template. 7. Once complete DNA polyermase will proofread for mistakes. Go to DNA replication animation www.fed.cuhk.edu.hk/~johnson/teaching/genetics/ animations/dna_replication.htm Okazaki Fragments Small segments of DNA that are used on the 3’ DNA. DNA ligase puts them together. http://video.search.yahoo.com/ search/video;_ylt=Anvp.VTwI60W. BKoUEpJxR. bvZx4?p=dna+replication&toggle= 1&cop=mss&ei=UTF-8&fr=yfp-t-701 DNA Replication Fork Point where DNA is split apart to replicate. Forms a Y! Role of Enzymes • 1. Helicase unzips the two DNA strands. • 2. DNA polymerase is the enzyme that joins individual nucleotides to produce a new strand of DNA. Proofreads DNA when finished! 3. Ligase -links together the 3’ DNA strand DNA Replication in Prokaryotic Cells • 1. Proteins binds to starting point. • 2. Starts at a single point and proceeds in both directions. Eukaryotic Replication • Since eukaryotic cells are so much bigger, the replication will start at dozens to hundreds of different places on the DNA. DNA REPLICATION What if there is a mistake? There is always a chance that the wrong nucleotide bonds to another. HOWEVER, DNA polymerase is responsible for “reading” the bases and recognizing and replacing damaged or wrong nucleotides. This PROOFREADING allows for only one (1) error in ONE BILLION nucleotides. DNA Fingerprinting • When DNA is found at a crime crime, the DNA I replicated many time to make enough to test. Once they have fingerprinted it, they can compare to find suspect. DNA Fingerprinting Speed of DNA Replication • In the human cell, 50 nucleotides can be added every second. It would that several days for replication to occur if the DNA did not start at several spots on the DNA so that it is occurring in many places on the DNA strand. DNA Replication • Replication: coping of DNA • The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C •Each strand of the original DNA serves as a template for the new strand Why is DNA Replication necessary? • DNA must copy itself so that each new cell gets a copy of DNA. Replication must occur before cell division. Semiconservative Model • Replication is called semiconservation because one strand of DNA is used to as a template to make the new DNA. Steps of DNA Replication 1.DNA unzips and the hydrogen bonds between the nitrogen bases pulled apart. The base pairs are separated and are left exposed. This occurs in two different directions. This occurs along hundreds of different places at a time. . DNA Template Parental DNA New DNA Steps of Replication 2. Free-floating nucleotides are paired up to the free nucleotides. DNA polymerase bond the nucleotides together. 3.Two identical strands result. DNA polymerase checks for mistakes when complete. DNA Replication • DNA has 80 million base pairs in a chromosomes. DNA is copied at about 50 base pairs per second. This would take a month if replication did not occur at hundreds of different places at once. Replication Quiz A---? G---? C---? 2. When does replication occur? T---? 3. Describe how replication works. A---? G---? A---? 4. Use the complementary rule to G---? create the complementary C---? strand: A---? G---? T---? 1. Why is replication necessary? Replication Quiz A---T 1. Why is replication necessary? G---C So both new cells will have the correct C---G DNA T---A 2. When does replication occur? A---T During interphase (S phase). G---C 3. Describe how replication works. A---T Enzymes unzip DNA and complementary G---C nucleotides join each original strand. C---G 4. Use the complementary rule to A---T create the complementary strand: G---C T---A (1961) Watson & Crick proposed… • …DNA controlled cell function by serving as a template for PROTEIN structure. • 3 Nucleotides = a triplet or CODON (which code for a specific AMINO ACID) See p.303 • AMINO ACIDS are the building blocks of proteins. DNA Transcription • DNA can “unzip” itself and RNA nucleotides match up to the DNA strand. See p.301 • Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids. DNA Translation • The cell uses information from “messenger” RNA to produce proteins See p.304-305 We will discuss details of this on a later date 1. 2. 3. 4. 5. 6. Transcription/Translation Quiz Why is transcription necessary? Describe transcription. Why is translation necessary? Describe translation. What are the main differences between DNA and RNA. Using the chart on page 303, identify the amino acids coded for by these codons: UGGCAGUGC 1. Why is transcription necessary? Transcription makes messenger RNA (MRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm. 2. Describe transcription. RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble MRNA. 3. Why is translation necessary? Translation assures that the right amino acids are joined together by peptides to form the correct protein. 4. Describe translation. The cell uses information from MRNA to produce proteins. 5. What are the main differences between DNA and RNA. DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil. 6. Using the chart on page 303, identify the amino acids coded for by these codons: UGGCAGUGC tryptophan-glutamine-cysteine AMAZING DNA FACTS… • DNA from a single human cell extends in a single thread for almost 2 meters long!!! • It contains information equal to some 600,000 printed pages of 500 words each!!! (a library of about 1,000 books) LET’S REVIEW DNA… LM p.44 1. List the conclusions Griffith & Avery, Hershey & Chase drew from their experiments. 2. Summarize the relationship between genes & DNA. 3. Describe the overall structure of the DNA molecule. 4. What are the 4 kinds of bases? MUTATIONS Changes in DNA that affect genetic information Gene Mutations • Point Mutations – changes in one or a few nucleotides – Substitution • THE FAT CAT ATE THE RAT • THE FAT HAT ATE THE RAT – Insertion • THE FAT CAT ATE THE RAT • THE FAT CAT XLW ATE THE RAT – Deletion • THE FAT CAT ATE THE RAT • THE FAT ATE THE RAT Gene Mutations • Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function. – Insertion • THE FAT CAT ATE THE RAT • THE FAT HCA TAT ETH ERA T – Deletion H • THE FAT CAT ATE THE RAT • TEF ATC ATA TET GER AT H Sex Chromosome Abnormalities • XYY Syndrome – Normal male traits – Often tall and thin – Associated with antisocial and behavioral problems Chromosome Mutations • Changes in number and structure of entire chromosomes • Original Chromosome ABC * DEF • Deletion AC * DEF • Duplication ABBC * DEF • Inversion AED * CBF • Translocation ABC * JKL GHI * DEF Significance of Mutations • Most are neutral • Eye color • Birth marks • Some are harmful • Sickle Cell Anemia • Down Syndrome • Some are beneficial • Sickle Cell Anemia to Malaria • Immunity to HIV What Causes Mutations? • There are two ways in which DNA can become mutated: – Mutations can be inherited. • Parent to child – Mutations can be acquired. • Environmental damage • Mistakes when DNA is copied Chromosome Mutations • Down Syndrome – Chromosome 21 does not separate correctly. – They have 47 chromosomes in stead of 46. – Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence. Chromosome Mutations • Cri-du-chat – Deletion of material on 5th chromosome – Characterized by the cat-like cry made by cri-du-chat babies – Varied levels of metal handicaps Sex Chromosome Abnormalities • Klinefelter’s Syndrome – – – – – XXY, XXYY, XXXY Male Sterility Small testicles Breast enlargement Sex Chromosome Abnormalities • XYY Syndrome – Normal male traits – Often tall and thin – Associated with antisocial and behavioral problems Sex Chromosome Mutations • Turner’s Syndrome –X – Female – sex organs don't mature at adolescence – sterility – short stature Sex Chromosome Mutations • XXX – Trisomy X – Female – Little or no visible differences – tall stature – learning disabilities – limited fertility