2.  Stores information needed for traits and cell processes  Copying information needed for new cells  Transferring information from generation to generation

5.  Watson and Crick’s discovery of DNA’s structure (double helix) was based on almost fifty years of research by other scientists

6.  Made of nucleotides (3 parts)  Sugar (deoxyribose)  Phosphate group  Base (nitrogenous base) A (adenine) T (thymine) C (cytosine) G (guanine)

7.  Chargaff discovered that the percent of adenine and thymine in DNA were the same.  The percent of guanine and cytosine are also equal.  The observation that [A] = [T] and [G] = [C] became known as one of “Chargaff’s rules.”

8.  Rosalind Franklin (1950) – used X-ray diffraction (aimed X-rays at DNA and looked at the scatter pattern) to find clues about the structure  Showed DNA has 2 strands  The DNA strands are twisted around each other like a spring (helix shaped)  The bases are in the center  Died at age 37 from cancer (x-ray exposure?)

9.  Watson and Crick – built models of DNA  Discovered the double helix structure (2 strands twist around each other like staircases)  Explained Franklin’s and Chargaff’s earlier discoveries  Discovered that hydrogen bonds hold the DNA strands together Weak forces that enable the DNA to come apart

10.  Adenine pairs with Thymine  Guanine pairs with Cytosine

11.  Before a cell divides, it duplicates its DNA in a copying process called replication  This process ensures that each resulting cell has the same complete set of DNA molecules

12.  How does the double helix structure of DNA make replication (copying) possible??????  Each strand of the double helix has all the information needed to reconstruct the other half by the mechanism of base pairing.  Because each strand can be used to make the other strand, the strands are said to be complementary

13.  The DNA molecule separates into two strands and then produces two new complementary strands following the rules of base pairing.  Each strand of the double helix of DNA serves as a template, or model, for the new strand.

14.  The two strands of the double helix separate, or “unzip,” allowing two replication forks to form.  New bases are added following the rules of base pairing (A-T and C-G) to the newly forming strand.

15.  Each DNA molecule has one original strand and one new strand (semi-conservative).  The result of replication is two DNA molecules identical to each other and to the original molecule.

17. Stepped Art Fig. 13-6, p. 208 D DNA ligase seals any gaps that remain between bases of the “new” DNA, so a continuous strand forms. The base sequence of each half-old, half-new DNA molecule is identical to that of the parent DNA molecule. C Each of the two parent strands serves as a template for assembly of a new DNA strand from free nucleotides, according to base-pairing rules (G to C, T to A). Thus, the two new DNA strands are complementary in sequence to the parental strands. B As replication starts, the two strands of DNA are unwound. In cells, the unwinding occurs simul- taneously at many sites along the length of each double helix. A A DNA molecule is double-stranded. The two strands of DNA stay zippered up together because they are complementary: their nucleotides match up according to base-pairing rules (G to C, T to A).

18.  DNA replication is carried out by enzymes.  DNA helicase  Breaks hydrogen bonds between DNA strands  DNA polymerase  Joins free nucleotides into a new strand of DNA  DNA ligase  Joins DNA segments on discontinuous strand 

20.  Computer animation of DNA Replication 2 minutes Computer animation of DNA Replication 2 minutes  4 minute DNA REPLICATION 4 minute DNA REPLICATION  2 minutes detailed DNA replication 2 minutes detailed DNA replication  Bozeman Biology Bozeman Biology

21.  Draw, label and explain DNA replication  Include the following terms  Nucleotide (deoxyribose, base, phosphate)  A, T, C, G  DNA polymerase  DNA ligase  DNA helicase  3’end and 5’end  Continuous replication and discontinuous replication  Old strand and new strand  Okazaki fragments  Semi-conservative replication

22.  Draw, label and explain DNA replication  Include the following terms  Nucleotide (deoxyribose, base, phosphate)  A, T, C, G  DNA polymerase  DNA ligase  DNA helicase  3’end and 5’end  Continuous replication and discontinuous replication  Old strand and new strand  Okazaki fragments  Semi-conservative replication

23.  DNA repair mechanisms  DNA polymerases proofread DNA sequences during DNA replication and repair damaged DNA  When proofreading and repair mechanisms fail, an error becomes a mutation – a permanent change in the DNA sequence

24.  The tips of chromosomes are known as telomeres  Telomeres are hard to copy. DNA may be lost from telomeres each time a chromosome is replicated.  An enzyme (telomerase) adds short, repeated DNA sequences to telomeres, lengthening the chromosomes and making it less likely important gene sequences will be lost during replication.

26.  1997 Dolly News Story 1997 Dolly News Story  GMA Pet Cloning GMA Pet Cloning

27.  Bringing Them Back To Life – Read the article and answer the questions on the next slide. Bringing Them Back To Life

28.  Read the entire article then answer the following in complete sentences. Synthesize information from the entire article to answer the questions completely. Incomplete answers will only receive partial credit.  1) Have we been able to “bring an extinct species back to life”? If so, what was it and what was the result?  2) Do scientists think we will be able to bring a dinosaur back to life? Why or why not?  3) Discuss the benefits of de-extinction. In other words, why would we want to bring extinct species back to life?  4) What are some challenges of bringing a mammoth back to life? What is the procedure researchers would use to bring it back to life?  5) Explain why some people do not think scientists should try to revive extinct species?  6) Do you think that research should be done to recreate extinct species? Support your answer using support from the article.