The Role of dna in Heredity Stores information needed for traits and cell processes Copying information needed for new cells Transferring information from generation to generation Griffiths Experiments ID: 412987
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Slide1
CHAPTER 13 DNASlide2
The Role of
dna in Heredity
Stores information needed for traits and cell processes
Copying information needed for new cells
Transferring information from generation to generationSlide3
Griffith’s ExperimentsSlide4
The Hershey-Chase ExperimentsSlide5
13.2 The Discovery of DNA’s Structure
Watson and Crick’s discovery of DNA’s structure
(double helix) was
based on almost fifty years of research by other scientistsSlide6
Components of DNA
Made of nucleotides (3 parts)
Sugar (deoxyribose)
Phosphate group
Base (nitrogenous base)
A (adenine)T (thymine)C (cytosine)G (guanine)Slide7
Solving the structure of DNA
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.”Slide8
Solving the structure of DNA
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?)Slide9
Solving the structure of DNA
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 apartSlide10
Base pairing
Adenine pairs with Thymine
Guanine pairs with CytosineSlide11
12.3 DNA replication
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 moleculesSlide12
DNA replication
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 complementarySlide13
DNA Replication
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.Slide14
DNA Replication
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.Slide15
Results of DNA
Replication
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.Slide16
Semiconservative Replication of DNASlide17
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).Slide18
DNA Replication and enzymes
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
Slide19
Discontinuous Synthesis of DNASlide20
VIDEOS of DNA Replication
Computer animation of DNA Replication 2 minutes
4 minute DNA REPLICATION
2 minutes detailed DNA replication
Bozeman BiologySlide21
DNA Whiteboarding
Draw, label and explain DNA replication
Include the following terms
Nucleotide (deoxyribose, base, phosphate)
A, T, C, GDNA polymeraseDNA ligase
DNA
helicase
3’end and 5’end
Continuous replication and discontinuous replication
Old strand and new strand
Okazaki fragments
Semi-conservative replication Slide22
DNA Whiteboarding
Draw, label and explain DNA replication
Include the following terms
Nucleotide (deoxyribose, base, phosphate)
A, T, C, GDNA polymeraseDNA ligase
DNA
helicase
3’end and 5’end
Continuous replication and discontinuous replication
Old strand and new strand
Okazaki fragments
Semi-conservative replication Slide23
Checking for Mistakes
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 sequenceSlide24
Telomeres
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.Slide25
We will talk cloning later this year – but here is Somatic
Cell Nuclear Transfer (SCNT)Slide26
Cloning
1997 Dolly News Story
GMA Pet CloningSlide27
National Geographic
Bringing Them Back To Life
– Read the article and answer the questions on the next slide.Slide28
Reviving extinct species
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.