2 Discovery of DNA- Timeline 1865- Gregor Mendel – discovered “Heredity” characteristics are transmitted in units.1869 – DNA molecule isolated from cells by Frederick Miescher.1879 – Mitosis (chromosomes stained & observed during cell division) -described by Walter Flemming.1900- Mendel’s work is “rediscovered” by botanists.1902- Walter Sutton- Chromosome theory. (he observed segregation of chromosomes during meiosis – this matched Mendel’s law of segregation.
3 1911- Thomas Hunt Morgan & students- study fruit flies- show chromosomes carry genes. 1928- Frederick Griffith- “transformation” – hereditary material passed from 1 bacterial cell to another.1944- Oswald Avery- shows hereditary information is transferred on DNA in bacteria.1944- Barbara McClintock- “jumping genes” on corn.1952- Hershey & Chase- DNA- NOT proteins -is the material that hereditary.1953- Watson & Crick- double helix DNA structure.1955- Joe Hin Tjio- humans have 46 chromosomes.1959- Jerome Lejune- trisomy 21 (3 copies rather than 2 of chromosme 21) causes Down’s syndrome.
4 1966- genetic code cracked- figure out which 4 nucleic acids “spell” each amino acid. 1972- recombinant DNA- insert DNA of 1 species into another (usually bacteria)1976- Genetech (1st genetic engineering company) founded. By 1982 markets 1 recombinant drug- insulin.disease gene mapped- Huntington’s- on chromosome 4.1990- launch 15 yr. Human Genome Project. (to sequence all 3.2 billion letters of the human genome)1994- FDA- approves sale of genetically modified food.1997- “Dolly” the sheep is cloned (England-Wilmut)Human Genome Project “completed”.
5 Discussion of Experiments 1. Frederick GriffithHe was working to find a vaccine against “S” smooth virulent (disease causing) strains of bacteria.Steps in experiment220.127.116.11.
6 Griffith Experiment Conclusions: Killed virulent bacteria survived the heating process -& was somehow incorporated into the genetic material of the non-virulent strain -to cause them to become virulent.“Transformation” is transfer of genetic material from one organism to another.2. Since heat denatures protein, he suggested that the genetic material must be made of something else.
7 2. Oswald Avery -proteins or nucleotides? Followed up on Griffith's experiment in 1940’sLike Griffith, he first used heat to kill virulent bacteria.Then extracted RNA, DNA, & proteins from these dead cells (all considered possible carriers of genetic information).Next -added each type of molecule to a culture of live non-virulent bacteria to determine which was responsible for changing them into virulent bacteria as Griffith had observed.Only the non-virulent cells which were given DNA from the dead virulent strain became virulent, so Avery concluded that DNA must be the genetic material.
8 Alfred Hershey – Martha Chase: 1952-Test to see if DNA or protein was hereditary material transferred by virus when infecting a bacterium.Bacteriophages- arethe type of virus thatinfects bacterium.Used Radioactive labels -virus protein coat with (35S)-virus DNA with (32 P)After experiment: only DNA entered bacterial cell.
10 4. Watson & Crick1953 DNA structure discoveredDouble Helix model.(2 chains of DNA)Showed how DNA could replicate.Relied on work of other scientists:Rosalind Franklin & Maurice Wilkins took X-ray photos of DNA structure( Franklin died 1958 before Watson & Crick received Nobel Prize )
11 DNA structureDouble Helix shape is formed by base pairs attached to a sugar-phosphate backbone.-Each full turn of the helix has 10 nucleotide pairs.- count them at right:
12 Parts of Nucleotides 1. 5 carbon sugar in DNA- deoxyribose (in RNA= ribose)2. phosphate group3. nitrogenous bases ( there are 4 different ones)AdenineGuanineCytosineThymine(in RNA- no thymine- Uracil is the base)
13 How Chemical Bonds hold DNA together Covalent bonds- between sugar & phosphates of 2 nucleotidesHydrogen bonds- between complementary nitrogenous bases –
14 Structure & Function of Nitrogenous bases Remember: 10 pairs bases per “turn” in staircaseComplementary base pairinga. Adenine always bonds with Thymine (AT)b. Guanine always bonds with Cytosine (GC)Note 3 hydrogen bonds: GC2 Hydrogen bonds: AT
15 Purines (A, G) double C ring Pyrimidines (T, C) single C ringMust have 1 purine (2 rings) plus 1 pyriomidine (1 ring) in each pair or the would not “fit” inside ladder of DNA
16 DNA ReplicationIs the process by which DNA is copied in a cell before a cell divides by mitosis, meiosis or binary fission.
17 Steps in Replication1. Helicase enzymes -separate hydrogen bonds in strands – create replication fork2. Attach- DNA polymerase enzyme -adds nucleotides3. Release –DNA polymerase enzyme – now have 2 identical DNA strandsoak.cats.ohiou.edu/.../Heredity/Heredity.htm
18 Mutation- a change in the nucleotide sequence of a DNA molecule. ErrorsDNA replication is very accurate.Errors occur ~ 1 in 1 billion paired nucleotides.“Proofreading” enzyme checks for “spelling” errors.*If a mistake does occur- new DNA is different:Mutation- a change in the nucleotide sequence of a DNA molecule.Caused by chemicals, radiation,UV rays.Mutations can be favorable- or harmful. (example- cancer)
19 Genes may only take up about 5% of the DNA in humans Some of The DNA molecule iscalled “junk DNA”- because scientistsdon’t really understand why it is there.Mutations that occur on the green maynot cause any affect at all.Recently in the news -scientiststhink a “mutation” from 5 millionyears ago in our DNA appears to have a role in a rapidtripling of the size of the human brain's crucial cerebralcortex that sets us apart from less intelligentorganisms.
20 Flow of Information (DNA – RNA - Proteins) Protein SynthesisFlow of Information (DNA – RNA - Proteins)Before protein can be synthesized, the instructions in DNA must first be copied to another type of nucleic acid called messenger RNA.Then a group of 3 nucleic acids codes for an amino acid & it is built at the ribosomal RNA with help from the transfer RNA
21 RNA differs from DNA in the following ways: RNA is single stranded while DNA is double stranded.RNA has a sugar called ribose while DNA has a sugar called deoxyribose.RNA has the nitrogenous base uracil while DNA has the base thymine.
22 B. 3 types RNA: 1. messenger RNA(mRNA) 2. transfer RNA (tRNA) 3. ribosomal RNA (rRNA)
23 Messenger RNA, or mRNA. Transfer RNA or tRNA. Ribosomal RNA or rRNA carries the code for building a protein from thenucleus to the ribosomes in the cytoplasm. It actsas a messenger.Transfer RNA or tRNA.picks up specific amino acids in the cytoplasm &brings them into position on ribosome wherethey are joined together in specific order tomake a specific protein.Ribosomal RNA or rRNAplace for protein synthesis
24 Steps in Transcription-making RNA 1. RNA polymerase (enzyme)– binds to promoter area on DNA2. Nucleotides added & joined by the enzyme (RNA polymerase)Termination signal- stop- RNA polymerase releases both DNA & new RNA molecules
26 Proteins Review of protein structure -recall that proteins are made of amino acids joined together with peptide bonds-there are 20 different amino acids, the order they are joined determines the structure & function of the proteins.-proteins can be very large, complicated molecules
27 mRNA codons for specific amino acids Each 3 nucleotide sequence (letters) in mRNA encodes for 1 specific amino acid, or a “start” or “stop” signal.Each 3 nucleotide group is called a codon.The genetic code- means the rules that relate how a particular sequence of nitrogenous bases corresponds to a particular amino acid.
30 Steps in Translation Initiation- tRNA & mRNA join together. (The codon is on the mRNA, the “anticodon” is on tRNA)The tRNA has an amino acid attached to it)Elongation- continued as ribosome moves the distance of 1 codon on mRNAElongation is built with new tRNAs attaching each amino acid as it reads the codons on the mRNA.Termination- ribosome reaches “stop” codon on the mRNADisassembly – each piece is free.
31 The Human Genome Project GOALS: ( )identify all the approximately 20,000-25,000 genes in human DNA,determine the sequences of the 3 billion chemical base pairs that make up human DNA,store this information in databases,improve tools for data analysis,transfer related technologies to the private sector, andaddress the ethical, legal, and social issues (ELSI) that may arise from the project.With a partner- make a list of the ethical, legal, and social issues you think could arise from the project.