Module 5 Flashcards
1930 R.A. Fisher
- quantitative geneticist
Two view points about genes
- hypothetical entity
- chemical compound
Chemical composition of the chromosome
- Lipids
- Proteins
- histones or protamines (basic proteins)
- non-histone chromosomal proteins (acidic proteins) - Nucleic acids
- DNA and RNA
Characteristics of genetic material according to
( H.J. Muller)
- Can duplicate itself with extra fidelity.
- 1/1 M copies
- Stable molecular structure
- very low frequency of mutation
- Mutation is duplicated faithfully.
- inheritance of mutation
- genetic source of variation
- Can carry all necessary biological
information. - Can transmit the information from
generation to generation. - Stored information must be decoded
and translated into action.
Events leading to the discovery of DNA
*1830s Proteins were thought to be the
most important molecule.
➢ proteios (Greek)
➢ “of first importance”
(1866) Ernst Haeckel
➢discovered that the most
obvious cellular component of
the cell is the nucleus
(1895) Edmund Wilson
*using staining technique to study
karyokinesis of ovum
*important nuclear element handed
from cell to cell: DNA
(1928)
Frederick Griffith
(US Medical Officer)
*transformation experiment using
Streptococcus pneumoniae
*avirulent (R) strain was
transformed to virulent (S)
*declared the presence of
transforming principle
(1944)
Oswald Avery,
Colin MacLeod,
Maclyn McCarty
*Physician-Scientists (Canadian & American)
*identified the transforming principle (TP)
as DNA
- when TP was treated with proteinases and
Rnases
➢ transforming ability is retained
➢ therefore, TP is neither protein nor RNA
- when TP was treated to remove protein
and RNA
➢ the composition of the substance
left matched the composition of
DNA
(1952) Alfred Hershey and Martha Chase
*proved that DNA is the genetic material
of the bacterial viruses (phages)
*DNA is labeled with P32
*protein coat is labeled with 35S
*famous blender experiment
*separates phages from bacteria after
infection
*this proved: DNA is injected into the cell
while the protein coat remained outside
(1860) Friedrich Miescher
- while characterizing
proteins from pus cells - isolated a molecule from the nucleus and
called it “nuclein” (DNA in the 1930s)
(1952) Norton Zinder, Joshua and Esther Lederberg
*Nobel Prize for genetic research in 1958
(Joshua)
*performed transduction experiment in
Salmonella typhimurium
(1953) Elucidation of the structure of the DNA
*Francis Crick
- involved in the development of
radar and magnetic mines
-did his Ph.D. on X-ray
studies on proteins
*James D. Watson
- child prodigy from Chicago
- did labeling of phage DNA at Denmark
*Maurice Wilkins
➢ Worked on X-ray diffraction of DNA
➢ Manhattan project (1939-46)
*Rosalind Franklin
- expert on X-ray diffraction technique
- joined King’s College in 1951
- worked on X-ray diffraction of DNA
(1951-53) Rosalind Franklin, Gosling and
Maurice Wilkins (King’s College)
➢ helical DNA structure
➢ sugar and phosphate outside
➢ nucleotides inside
James Watson and Francis Crick
- triple helix
- phosphate in the center
1950s Linus Pauling
- Chemist, California
Institute of Technology - triple helix DNA
*John Griffith
- nucleotides are flat, one on top of another
- possibility of A=T, C=G pairing
- Crick saw the importance of specific pairing
in replication.
*Erwin Chargaff
- purine-pyrimidine ratio 1:1
(Chargaff’s rule)
*Jerry Donohue
- H in the bases can change its position
- possibility for H bonding
Publications of Watson and Crick
*Molecular Structure of Nucleic Acid. April
1953. Nature. 171:737-738.
*Genetic Implications of the Structure of
Deoxyribonucleic Acid. May 1953.
Nature.171:964-967.
Nobel Prize Winners in 1962 for configuration
of DNA
Watson, Crick
and Wilkins
Features of DNA
- It is composed of two polynucleotide strands.
- The two strands are anti-parallel.
- Specific pairing A = T, C = G
- It forms a helical coil.
- Sugar is 2-deoxy-D-ribose.
Evidences to show that DNA is the genetic material
- Relative constancy of DNA in all diploid tissues.
- in starvation, DNA unchanged
- Haploid cell has half the amount of DNA in
diploid cell. - Doubling of DNA content at S phase.
- Cells with extra sets of chromosomes have a
proportional increase in DNA content.
- polyploidy, polyteny
- Parallelism of UV absorption with mutation
rates - Transformation and transduction in bacteria
- Production of new viral particles in
bacterial cells. - RNA content of TMV caused infection and
not the protein coat.
RNA Structure
- composed of one polynucleotide strand
- sugar is D-ribose
- no Thymine but instead Uracil;
Adenine Cytosine Guanine
1958, Matthew Meselson and
Franklin Stahl
- semi-conservative mode
- grew E. coli in 15N and 14N
- isolated the DNA
- centrifugation in cesium chloride
1958, Matthew Meselson and
Franklin Stahl
- semi-conservative mode
- grew E. coli in 15N and 14N
- isolated the DNA
- centrifugation in cesium chloride
replisome
- DNA Polymerase III with two catalytic cores
- Primosome (helicase + primase)
Mechanisms of high precision replication
- specificity of base pairing
- proof reading ability of DNA Polymerases
88
- Excision repair mechanisms
a. repair of thymine dimer
➢ endonuclease (excision and filling)
b. N glycosidase activity
➢ hydrolyzes bond between damaged
base and sugar
Prokaryotic chromosome
Escherichia coli with single chromosome
- double stranded
- approximately 11,000 μm long
- 1.1 mm (1mm = 1000 μm)
- 4 x 106 bp (1 kb = 1000 bp); amount of DNA
approximately 1,000x the length of E. coli
Prokaryotic chromosome organization
- nucleoid
- organized into about 10 independent domains
- each domain consists of loops
- each loop is about 40,000 bp (40kb) of
supercoiled DNA - each domain is held by a protein
- DNA binding protein Hu and H
Eukaryotic Chromosome
- with large amount of DNA
- diploid human cell
- length of DNA is 6 ft. long (end to end)
- 6 ft. X 12 in./ft. x 2.54 cm/inch =183 cm
- 5.5 x 109 bp (or 5.5 billion bp
- 5 x 10-4 cm. (or 5 μm) diameter of nucleus
