chapter 8: dna and rna section 8-2a: dna structure
TRANSCRIPT
![Page 1: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/1.jpg)
Chapter 8:DNA and RNA
Section 8-2A:
DNA Structure
![Page 2: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/2.jpg)
Animations
http://www.johnkyrk.com/DNAanatomy.html
![Page 3: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/3.jpg)
Introductory Questions
If Hershey and Chase are correct and genes are made of DNA, how is the message of a gene coded in a DNA molecule?
How can a molecule carry information?
![Page 4: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/4.jpg)
DNA Structure
DNA = deoxyribonucleic acid Chain of nucleotides (three parts –
phosphate group, nitrogenous base, 5 carbon sugar)
4 different nucleotides, each with a different nitrogenous base – Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
![Page 5: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/5.jpg)
![Page 6: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/6.jpg)
Purines and Pyrimidines
Adenine and Guanine are purines
Cytosine and Thymine are pyrimidines
![Page 7: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/7.jpg)
Chargaff’s Rule
Erwin Chargaff (USA, 1950) Nucleotides in DNA vary from sample to
sample Amount differ, but a pattern is evident –
amounts of adenine and thymine always the same, amounts of cytosine and guanine always the same (Chargaff’s Rule)
![Page 8: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/8.jpg)
Rosalind Franklin
http://en.wikipedia.org/wiki/Rosalind_Franklin
Britain, 1951 Studying DNA molecule
using X-ray diffraction Powerful X-ray beam
aimed at a sample and scattering pattern recorded on film
Pictures give clues to the actual structure of DNA
![Page 9: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/9.jpg)
X-Ray Diffraction
![Page 10: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/10.jpg)
The Watson-Crick Model
James Watson and Francis Crick (USA, 1952)
Already working on DNA structure, saw Franklin’s X-ray diffraction and everything clicked
Saw that DNA was made of two strands twisted around each other
![Page 11: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/11.jpg)
The Watson-Crick Model
Twisting pattern called a helix Built models or DNA structure – sugar-
phosphate backbone, strands wrap around each other in a double helix
![Page 12: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/12.jpg)
Bonds Between Strands
Nitrogenous bases are close together along the center, held together by hydrogen bonds
Bonds form between purines and pyrimidines – between adenine and thymine, guanine and cytosine
Combinations are called base pairs
![Page 13: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/13.jpg)
Bonds Between Strands
The sequence of bases on one strand matches the sequence of bases on the other strand – Chargaff’s Rule
AATGCC
TTACGG
![Page 14: Chapter 8: DNA and RNA Section 8-2A: DNA Structure](https://reader035.vdocuments.us/reader035/viewer/2022081513/56649ef65503460f94c0a6d4/html5/thumbnails/14.jpg)
Significance of the Double Helix
1962 – Watson, Crick, and Franklin’s assistant Wilkins won Nobel Prize for discovery of DNA double helix (Franklin died in 1958)
Watson and Crick published their model in a scientific paper only one page long
Also suggested method of DNA copying