DNA as genetic material #3-4 Flashcards
name the 4 scientists that contributed to the discovery of DNA as genetic material
~Johann Friedrich Miescher
~Fredrick Griffith
~Avery, Macleod, McCarty
~Hershey and chase
what was Johann Friedrich Mieschers’ discovery?
in 1871 he isolated DNA from pus
Fredrick Griffith
in 1928, he discovered that dead streptococcus pneumonia pathogenic cells can transfer their virulence to living non-pathogenic S. pneumonia cells
Avery, Macleod, McCarty
in 1944, identified DNA as genetic material
Hershey and Chase
in 1952, the studies on bacteriophages confirmed that DNA is the genetic material
who used the term ‘nuclein’
johann friedrich meischer. He identified it as the cause of fertilization
explain the Griffith Experiment? (1928)
- Rough colony R is benign (lacks protective capsule=destroyed)
- Smooth colony S is virulent(polysaccharide capsule prevents detection by immune system)
- Dead S and live R kill the mouse
- lead to definition of ‘Transformation’ of genetic material
what are the 2 characteristics of transformation?
permanence, inheritability
Phoebus Aaron Theodore Levene
discovered the polynucleotide structure but not that it existed in long polymers
what are the 3 steps for the avery, Macleod, McCarty experiment
~remove lipids and carbohydrates from a sol’n of heat killed S. – Proteins, RNA and DNA remain
~subject the solution to treatment of enzymes that destroy either the proteins, RNA or DNA
~add a small amount of each sol’n to a culture containing R cells. Observe weather transformation has occurred by testing for presence of virulent S cells.
NO S CELLS REAPPEAR IN THE SOL’N WITH NO DNA–NO TRANSFORMATION HAS OCCURED
Hershey Chase Experiment
showed that only DNA enters the bacterial cells and thus it must contain all necessary information to produce new progeny
S35 -present in Cys + Met but not in DNA
P35 - present only in DNA
Lytic cycle of a Bacteriophage
~Adsorption/injection ~expression of viral early proteins ~replication of viral DNA/Expression of viral late proteins ~assembly ~lysis/release
Lysogenic cycle of a Bacteriophage
~Adsorption/injection
~phage DNA circulises
~Phage DNA integrates with the bacterial chromosome by recombination becoming a prophage
~lysogenic bacterium reproduces normally
~sometimes the prophage might detach from bacterial chromosome by another recombination event
what is a nucleoside triphosphate
a nucleotide
Pyrimidines are
cytosine
uracil
thymine
purines are
adenine
guanine
rare bases in DNA
5- methyl cytosine
6- methyl adenine
2- dimethyl guanine
5-hydroxy methyl guanine
Watson and Crick unified the following works
chargaffs rules
the correct tautomeric forms of the bases JERRY DONAHUE
the information that DNA is a helical molecule ROSALIND FRANKLIN
Erwin Chargaff 1950
A+T, G+T amount is constant in a species but different between 2 different species
A=T, G=C
‘Pitch of a helix’
is the width of one complete helix turn
‘Tautomers’
are constitutional isomers of organic compounds that readily interconvert
‘Tautomerism’
frequently involves a H changing places with a double bond. EG: keto-enol thymine, imino-amino cytosine, amino-imino adenine, keto-enol guanine
how is X-ray diffraction analysis performed
using an X-ray source shone through a lead screen onto a crystal sample through a detector which forms a diffraction pattern
by scattering and interference
how wide if the major period
3.4 nm
