DNA as genetic material #3-4

Question 1

name the 4 scientists that contributed to the discovery of DNA as genetic material

Answer 1

~Johann Friedrich Miescher
~Fredrick Griffith
~Avery, Macleod, McCarty
~Hershey and chase

Question 2

what was Johann Friedrich Mieschers’ discovery?

Answer 2

in 1871 he isolated DNA from pus

Question 3

Fredrick Griffith

Answer 3

in 1928, he discovered that dead streptococcus pneumonia pathogenic cells can transfer their virulence to living non-pathogenic S. pneumonia cells

Question 4

Avery, Macleod, McCarty

Answer 4

in 1944, identified DNA as genetic material

Question 5

Hershey and Chase

Answer 5

in 1952, the studies on bacteriophages confirmed that DNA is the genetic material

Question 6

who used the term ‘nuclein’

Answer 6

johann friedrich meischer. He identified it as the cause of fertilization

Question 7

explain the Griffith Experiment? (1928)

Answer 7

• 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

Question 8

what are the 2 characteristics of transformation?

Answer 8

permanence, inheritability

Question 9

Phoebus Aaron Theodore Levene

Answer 9

discovered the polynucleotide structure but not that it existed in long polymers

Question 10

what are the 3 steps for the avery, Macleod, McCarty experiment

Answer 10

~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

Question 11

Hershey Chase Experiment

Answer 11

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

Question 12

Lytic cycle of a Bacteriophage

Answer 12

~Adsorption/injection
~expression of viral early proteins
~replication of viral DNA/Expression of viral late proteins
~assembly
~lysis/release

Question 13

Lysogenic cycle of a Bacteriophage

Answer 13

~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

Question 14

what is a nucleoside triphosphate

Answer 14

a nucleotide

Question 15

Pyrimidines are

Answer 15

cytosine
uracil
thymine

Question 16

purines are

Answer 16

adenine

guanine

Question 17

rare bases in DNA

Answer 17

5- methyl cytosine
6- methyl adenine
2- dimethyl guanine
5-hydroxy methyl guanine

Question 18

Watson and Crick unified the following works

Answer 18

chargaffs rules
the correct tautomeric forms of the bases JERRY DONAHUE
the information that DNA is a helical molecule ROSALIND FRANKLIN

Question 19

Erwin Chargaff 1950

Answer 19

A+T, G+T amount is constant in a species but different between 2 different species
A=T, G=C

Question 20

‘Pitch of a helix’

Answer 20

is the width of one complete helix turn

Question 21

‘Tautomers’

Answer 21

are constitutional isomers of organic compounds that readily interconvert

Question 22

‘Tautomerism’

Answer 22

frequently involves a H changing places with a double bond. EG: keto-enol thymine, imino-amino cytosine, amino-imino adenine, keto-enol guanine

Question 23

how is X-ray diffraction analysis performed

Answer 23

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

Question 24

how wide if the major period

Answer 24

3.4 nm

Question 25

how wide is the minor period

Answer 25

0.34 nm

Question 26

what is the diamenter of the diffraction pattern

Answer 26

2nm

Question 27

DNA is which sided spiral?

Answer 27

right handed