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The Genetic Code Chapter 8 in your textbook

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1 The Genetic Code Chapter 8 in your textbook
DNA The Genetic Code Chapter 8 in your textbook

2 Discovery of DNA Experiments that identified DNA as the genetic material & determined its structure: Griffith Avery Hershey – Chase Chargaff Franklin & Wilkins Watson & Crick

3 Griffith’s Experiment
Used mice and pneumonia bacteria One strain, “S”, was harmful (pathogenic) Other strain, “R”, was not harmful (non-pathogenic) Discovered transformation – one bacteria was genetically changed by another bacteria

4 Griffith, cont’d Animation
The harmless strain (R) mixed with the heat-killed pathogenic strain (S) killed the mice.

5 Griffith, cont’d Some “factor” was transferred from the S to the R bacteria, turning the harmless R into something deadly At this point, scientists weren’t sure whether the transforming factor was DNA or protein

6 Avery’s Experiment Piggy-backed off of Griffith’s experiment to figure out what the “transforming factor” was Used enzymes to isolate various components of the bacteria: DNA, proteins, lipids, and carbohydrates Transformation only took place when the harmless bacteria was treated with DNA from the harmful bacteria

7 Avery, cont’d Discovered that DNA stores and transmits genetic information

8 Hershey & Chase’s Experiment
Used viruses that infect bacteria (bacteriophages) Used radioactive phosphorus to mark the DNA Used radioactive sulfur to mark the proteins This allowed them to trace where these molecules went during the viral infection process Demonstrated that DNA was the genetic material -- video (2:05)

9 Hershey / Chase, cont’d

10 Chargaff Chargaff determined that the amount of adenine is the same as the amount of thymine in all the organisms he studied (and that C = G)

11 Franklin & Wilkins Franklin & Wilkins did X-ray crystallography pictures of the DNA molecule that showed it to be a helical structure with at least 2 helices

12 Watson & Crick Using Chargaff’s rules, they knew that A=T and C=G
Using the X-ray pictures from Franklin & Wilkins, they knew it was a helical shape They knew the structure had to provide a way to replicate very accurately Video (4:04)

13 Watson & Crick, cont’d Determined the structure of DNA in 1953
Double helix with bases on the inside and sugar and phosphate alternating on the outside

14 DNA Basics Deoxyribonucleic Acid Double helix (twisted ladder)
Located in the nucleus of eukaryotic cells Prokaryotes lack a nucleus, but still have DNA in their cells; prokaryotic (bacteria) DNA hangs out in the nucleoid region

15 DNA is a Nucleic Acid Organic compound made up of carbon, hydrogen, nitrogen, oxygen, and phosphorus. Made of repeating subunits (monomers) called nucleotides

16 The Nucleotide Made of a sugar (deoxyribose), a phosphate group and one of 4 nitrogen bases

17 Types of Nitrogen Bases
Pyrimidines (1 ring) Cytosine Thymine Purines (2 rings) Adenine Guanine

18 DNA Structure Sides of the ladder are the sugar and phosphate group
The rungs (part you’d step on) are 2 of the nitrogen bases Each rung is one purine paired with one pyrimidine – always C-G and A-T

19 DNA Structure

20 DNA Structure

21 DNA Replication The process of making identical copies of DNA
It is semiconservative – in each molecule, there is one old and one new strand Occurs during the S phase of the cell cycle It is necessary for cell division

22 Steps of DNA Replication
Step 1: DNA helicase (an enzyme) unwinds the molecule Step 2: DNA polymerase binds free-floating nucleotides to the exposed bases on the original strands Step 3: The 2 new molecules wind up again Animation

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