Module 5 Flashcards
(32 cards)
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.
