390 likes | 391 Vues
DNA video project SOME BACKGROUND INFO…. WHAT IS THE “STUFF” OF HEREDITY? WHAT IS ITS STRUCTURE?. The following scientists helped to answer these questions. Griffith Avery Hershey-Chase Watson, Crick Wilkins and Franklin Chargaff. I. GRIFFITH’S EXPERIMENT 1928.
E N D
WHAT IS THE “STUFF” OF HEREDITY?WHAT IS ITS STRUCTURE? The following scientists helped to answer these questions. • Griffith • Avery • Hershey-Chase • Watson, Crick • Wilkins and Franklin • Chargaff
I. GRIFFITH’S EXPERIMENT 1928 A. - make a vaccine against harmful S. pneumoniae bacteria 1. virulent S strain (S. pneumoniae) a. virulent means disease causing b. capsule around the bacteria provides protection from body defenses 2. non virulent Rstrain (no capsule) a. destroyed by body(can not cause disease)
1. mouse injected with R cells 2. mouse injected with S cells 3. mouse injected with heat killed S cells 4. mouse injected with killed S cells mixed with live R cells mouse lives mouse dies mouse lives mouse dies B. PROCEDURE and RESULTS
C. C - Heat-killed S bacteria release hereditary material that makes R strain bacteria virulent HOW??? 1.Principle of Transformation a. transfer of genetic material (DNA) from one organism to another b. DNA for making a capsule was transferred from the S strain to the R strain making it virulent
II. AVERY’S EXPERIMENTS (early 1940’s) A – Is the transforming agent protein, RNA or DNA? B. PROCEDURE– (Three Experiments) 1. destroy 3 different molecules in the heat-killed S strain bacteria and mix with R strain bacteria a. destroy protein (protease enzyme) b. destroy RNA (RNase enzyme) c. destroy DNA (DNase enzyme)
C. Results 1. Missing protein a. transforms R cells to S cells (mouse dies) 2. Missing RNA a. transforms R cells to S cells) (mouse dies) 3. Missing DNA a. did not transform R cells to S cells (mouse lives)
Oswald Avery • D. Conclusion – DNA is responsible for the transforming principle
III. HERSHEY-CHASE EXPERIMENT1952 (Martha Chase and Alfred Hershey) – Is the hereditary material in viruses protein or DNA? B. PROCEDURE 1. Label protein and DNA in a phage with radioactive isotopes (S-35 and P-32) a. a phage is a virus that attacks bacteria b. S-35 labels protein and P-32 labels DNA
B. Procedure 2. Allow protein-labeled and DNA- labeled phage (virus) to infect E. coli bacteria 3. remove and separate phage (virus) from the bacteria (E. coli)
Hershey-Chase Experiment • all viral DNA and a small amount of protein entered the bacteria D.CONCLUSION - DNA is the hereditary molecule in viruses
IV. Watson and Crick (1953) /Wilkins and Franklin A. Watson and Crick 1. double helix model of DNA based on the work of other scientists B. Maurice Wilkins and Rosalind Franklin 1. x-ray diffraction photographs of DNA helped Watson and Crick develop their model 2. Watson, Crick and Wilkins received Nobel Prize in l962 (Franklin died in 1958 and could not be named for the award)
X-ray Diffraction Photo Rosalind Franklinof DNA) and Maurice Wilkens
V. Erwin Chargaff - 1949 A. Percent of nitrogen bases that pair with each other (complementary bases) is the same 1. percentadenine equals percentthymine percent guanine equals percent cytosine 2. implied base pairing rules
IV. DNA (Structure / Function)
Questions you should be able to answer… • Where is DNA located in the cell? • How is it arranged? • What is the purpose of DNA? What does it do???? • How many strands does it have and what does it generally look like? • What is the basic building block of DNA called and what three components make it up? • What are the complimentary base pairs of DNA?
Where is it located in the cell? NUCLEUS! How is it arranged? Chromosome - DNAChromosome-Chromatid Purpose? To code for everything in your body...genetic blueprint!
DNA Structure 1. Deoxyribonucleic acid is shaped like a twisted ladder (double helix)
DNA Structure • DNA is a polymer made up of monomers called nucleotides Each nucleotide consists of: a. a sugar called deoxyribose b. a phosphate c. 1 of 4 nitrogen bases (A, G, T, C)
DNA Structure • Purine and pyrimidine • adenine nitrogen bases (purine)= thymine nitrogen bases (pyrimidine) • guanine nitrogen bases (purine)= the cytosine nitrogen bases (pyrimidine)
DNA Structure • Erwin Chargaff: discovered complementary base pair rules • the # of adenine nitrogen bases = the # of thymine nitrogen bases • the # of guanine nitrogen bases = the # of cytosine nitrogen bases
G= C A = T • DNA carries the genetic code in its sequence of bases
What is the complementary sequence of the bases listed below? A T T G C A A G C T C T G C
DNA Structure • The sides of the DNA helix are held up by phosphates and sugars (deoxyribose) Hydrogen bonds: hold complimentary bases together; very weak and can be easily broken
DNA Replication • Build a DNA molecule • http://learn.genetics.utah.edu/content/begin/dna/builddna/
WE ALSO HAVE RNA in our bodies A. RNA contains 1. sugar molecule -ribose 2. phosphate 3. nitrogen bases a. adenine and guanine b. cytosine and uracil B. The three types of RNA are: a) messenger RNA (m-RNA) b) transfer RNA (t-RNA) c) ribosomal RNA (r-RNA)
Differences between DNA -RNA • DNA RNA • Deoxyribose Ribose • Double strand Single strand • ThyamineUracil
G= C A = T • But it’s the DNA that carries the genetic code in its sequence of bases • GENES are segments of DNA that code for characteristics!
GENES ARE SEGMENTS OF DNA THAT CODE FOR A CHARACTERISTIC, LIKE DIMPLES. REALLY ITS THE ORDER OF THE BASES IN THE DNA DETERMINE THE CHARACTERISTIC. BUT SOMETIMES PROBLEMS ARISE….
Mutations A. Location of Mutations 1. somatic cell (body cell) 2. germ cell (cells that form sperm and egg cells) B. Causes 1. radiation a. x-rays, alpha, beta, gamma radiation, u.v. light 2. chemicals (mutagens) 3. DNA sequence changes in replication
C. Effects of Mutations 1. lethal (deadly) 2. may be beneficial 3. no effect
Point Mutation change in one nucleotide …or change in a base (A,T,C,G) in the DNA molecule Types of mutations – a. substitution– one base is substituted for another b. addition or insertion – an extra base is added c. removal or deletion of a base