DNA: Chapter 12. October 2014

Transcription

1 DNA: Chapter 12 October 2014

2 Goals for the Unit Iden>fy the substance of Genes Explain DNA Structure Sequence and explain the steps of DNA Replica>on

3 Iden>fying Substance of Genes In 1928, Frederick Griffith tried to develop a vaccine against Streptococcus pneumoniae (causes pneumonia) He discovered that S strain (smooth) produced disease and R strain (rough) did not He conducted experiments to determine what hereditary material could be passed on to new cells and cause a safe strain to become harmful

4 Ini>al bacteria: Griffith s Experiment Experiment part 1:

5 Following experiments:

6 Avery s Experiment Oswald Avery (1940s) wanted to determine if Griffith s hereditary material was a protein, carbohydrate, lipid, or nucleic acid Used protease (RNAase & DNAase) Enzymes- breakdown protein, RNA & DNA

7 Avery s Experiment con>nued Found that cells without protein & RNA were s>ll able to transform safe bacteria strain into harmful bacteria Cells without DNA could not do this. DNA was responsible for change

8 Hershey-Chase Experiment Martha Chase & Alfred Hershey (1952) Set out to test Avery s experiment- - whether DNA or protein was the hereditary material viruses transfer when entering bacteria. Concluded that DNA is the hereditary molecule in viruses.

9 Hershey and Chase grew viruses in cultures containing radioac>ve isotopes of phosphorus- 32 (P- 32) sulfur- 35 (S- 35)

10 If they found radioac>vity from S- 35 in the bacteria, it would mean that the virus s protein coat had been injected into the bacteria. If they found P- 32 then the DNA core had been injected.

11 Nearly all the radioac>vity in the bacteria was from phosphorus P- 32, the marker found in DNA. Hershey and Chase concluded that the gene>c material of the bacteriophage was DNA, not protein.

12 Role of DNA Storing gene>c informa>on Copying gene>c informa>on Transmiang gene>c informa>on Same as how you share a book

13 Storing Genes control paberns of development - instruc>ons that cause a single cell to develop into an oak tree, a sea urchin, or a dog must somehow be wriben into the DNA of each of these organisms.

14 Copying Before a cell divides, it must make a complete copy of every one of its genes, similar to the way that a book is copied To many scien>sts, the most puzzling aspect of DNA was how it could be copied Once the structure of the DNA molecule was discovered, a copying mechanism for the gene>c material was soon put forward.

15 The loss of any DNA during meiosis might mean a loss of valuable gene>c informa>on from one genera>on to the next. Transmiang When a cell divides, each daughter cell must receive a complete copy of the gene>c informa>on. Careful sor>ng is especially important during the forma>on of reproduc>ve cells in meiosis.

16 Structure of DNA

17 What is DNA? Deoxyribonucleic acid Located in the nucleus of cells It is a nucleic acid made up of nucleo>des (monomers) Basic components Sugar- Deoxyribose Phosphate Group Nitrogen- containing bases (4) Adenine & Guanine (purines) Thymine & Cytosine (pyrimidines)

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21 DNA Structure 1953: James Watson & Francis Crick described the structure of DNA Watson and Crick relied on work of Rosalind Franklin & Maurice Wilkins: photographs of DNA Double Helix (spiral staircase) Rungs = nitrogenous bases with hydrogen bonds Sides of ladder = sugar and phosphate backbone Each strand is direc>onal (5 and 3 end) Within a double helix, the strands run an>parallel (in opposite direc>ons)

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24 Bonding of DNA Hydrogen bonds hold the nitrogen- containing bases together ( steps ) Complementary base pairing (Chargaff s Rules) Adenine & Thymine bond together Cytosine & Guanine bond together Hydrogen bonds hold the 2 ladder sides together Phosphodiester bonds hold the phosphate groups and the deoxyribose sugars together ( handrails of the ladder )

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26 Chromosomes and DNA Replica>on Length of DNA: The nucleus of a human cell has >1 meter of DNA How does this much fit? Chromosomes- Compacted DNA which is coiled around proteins

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28 Bell Work: 10/16/13 Fill in the Chart Base A C G T % of Total DNA 22

29 DNA Replica>on Copying the Code

30 What is DNA replica>on? Process by which DNA is copied in a cell before a cell divides by mitosis, meiosis or binary fission (bacteria) Semi- conserva<ve replica<on Each new DNA molecule keeps (conserves) one original strand and gains one new strand

31 Steps of DNA Replica>on 1. Separa>on of strands 2. Addi>on of complementary nucleo>des 3. Two iden>cal molecules are a result

32 Step 1 DNA molecule unwinds & unzips Helicase (enzyme) separates DNA strands by breaking the hydrogen bonds Replica>on fork forms Y- shaped region that results when the 2 strands separate

33 Replica>on Fork

34 Step 2 DNA polymerase (enzyme) adds complementary nucleo>des that are already in the nucleus Hydrogen bonds form between the nitrogenous bases Covalent bonds (phosphodiester bonds) bond the sugar and phosphate groups together Replica>on occurs in two different direc>ons

35 DNA polymerase ac>on

36 Step 3 DNA polymerase finishes adding nucleo>des and leaves the DNA molecule Two separate and idenacal DNA molecules are produced that are ready to move to new cells in cell division

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39 Errors in DNA Replica>on Replica>on is usually a very accurate process About 1 error for each 1,000,000,000 base pairs added Repair enzymes that proofread Muta>ons can occur MutaAon: change in the nucleo>de sequence of a DNA molecule

40 Prokaryo>c vs. Eukaryo>c Replica>on Prokaryo>c cells: starts from a single point and proceeds in two direc>ons un>l the en>re chromosome is copied. Eukaryo>c cells: replica>on can begin at hundreds of places on the DNA molecule, proceeding in both direc>ons un>l each chromosome is completely copied.

41 hbp://highered.mcgraw- hill.com/sites/ /student_view0/chapter3/ anima>on dna_replica>on quiz_1_.html