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Lecture 14

01:119:115 Lecture Notes - Lecture 14: Frederick Griffith, Embryology, Genetic Recombination

6 Pages
35 Views
Fall 2018

Department
Biological Science
Course Code
01:119:115
Professor
Stern Cardinale
Lecture
14

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Biology 10/19
All about DNA
1. DNA is the genetic material
SEQ, CC DNA experiments
2. DNA structure
CC, HD DNA structure
3. DNA Replication
SEQ, HD DNA replication
Last time’s stuff:
Determining linkage:
Can tell from dihybrid test cross results.
If the parental genotype is expressed by 100% of the offspring, there is linkage.
If the parental genotype is expressed by 50% of the offspring, there is no linkage.
If the parental genotype is expressed by between 50 and 100% of the offspring,
there is incomplete linkage.
Genetic recombination: 2 mechanisms
Unlinked genes: Independent assortment
Linked genes: Crossing over (unless they are completely linked)
Today’s lecture
1. DNA is the genetic material
Chromosomes= DNA+prteins
DNA= deoxyribonucleic acid
4 monomers- nucleotides
Protein- 20 amino acids
General consensus- genes-proteins
A. Frederick Griffith
Bacteriologist and embryologist
Working on pneumonia vaccine
1st to show evidence against protein hypothesis.
His model organism: Streptococcus pneumoniae
Bacteria causes pneumonia in humans
Lethal to mice
2 strains:
- Smooth (has capsule-pathogenic)
- Rough (no capsule-nonpathogenic)
Griffith’s experiment
- Live smooth bacteria recovered from dead mice
- Demonstrated transformation: Change in genotype and
phenotype due to some factors.
What transformed the cells?
2
What happens to proteins when heated?
Do proteins simultaneously go back to correct
shape?
Conclusion: DNA most likely carries the genes.
B. Avery, McLeod and McCarty
Lysed S cells
Separated components
Tested for transformation
C. Hershey and Chase
Used Bacteriophage T2
Bacteriophage: Virus that affects bacteria
Viruses are less complex than cells
2 main components: DNA/RNA and a protein coat.
Virus life cycle
Virus attaches to host cells
Something enters the cells
New viruses made
Cell lyses, viruses released
Experimental design:
Label 1 virus population with radioactive sulfur
Label second with radioactive phosphorus
Allow each to infect bacteria
Separate viruses from bacteria
Determine location of radioactive isotopes.
Hershey and chase: Results:
Radioactive Sulphur in separated virus
Radioactive phosphorus present in infected cells.
Conclusion: Viruses transmit DNA; DNA carries genes
II. DNA structure
A. Nucleotides: monomers of nucleic acids. (FIG. 16.5)
Nitrogenous bases:
1. Purines: 2 rings
- Adenine
- Guanine
2. Pyrimidines: 1 ring
- Cytosine
- Thymine
DNA strand (16.5)
B. Determining DNA structure:
o Published in 1953 by James Watson and Francis Crick
o Much work done by others
Erwin Chargaff

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Description
Biology 10/19 All about DNA 1. DNA is the genetic material SEQ, CC DNA experiments 2. DNA structure CC, HD DNA structure 3. DNA Replication SEQ, HD DNA replication Last times stuff: Determining linkage: Can tell from dihybrid test cross results. If the parental genotype is expressed by 100% of the offspring, there is linkage. If the parental genotype is expressed by 50% of the offspring, there is no linkage. If the parental genotype is expressed by between 50 and 100% of the offspring, there is incomplete linkage. Genetic recombination: 2 mechanisms Unlinked genes: Independent assortment Linked genes: Crossing over (unless they are completely linked) Todays lecture 1. DNA is the genetic material Chromosomes= DNA+prteins DNA= deoxyribonucleic acid 4 monomers- nucleotides Protein- 20 amino acids General consensus- genes-proteins A. Frederick Griffith Bacteriologist and embryologist Working on pneumonia vaccine 1 to show evidence against protein hypothesis. His model organism: Streptococcus pneumoniae Bacteria causes pneumonia in humans Lethal to mice 2 strains: - Smooth (has capsule-pathogenic) - Rough (no capsule-nonpathogenic) Griffiths experiment - Live smooth bacteria recovered from dead mice - Demonstrated transformation: Change in genotype and phenotype due to some factors. What transformed the cells? What happens to proteins when heated? Do proteins simultaneously go back to correct shape? Conclusion: DNA most likely carries the genes. B. Avery, McLeod and McCarty Lysed S cells Separated components Tested for transformation C. Hershey and Chase Used Bacteriophage T2 Bacteriophage: Virus that affects bacteria Viruses are less complex than cells 2 main components: DNA/RNA and a protein coat. Virus life cycle Virus attaches to host cells Something enters the cells New viruses made
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