Lecture 6. DNA Is The Genetic Material

Question 1

When was the concept of ‘the inborn errors of metabolism presented and who presented the concept?

Answer 1

1902, Sir Archibald Garrod

Question 2

Albinism

Answer 2

Lack of pigment

Question 3

Alkaptonuria

Answer 3

Individuals secrete homogenistic acid into their urine, which goes black following exposure to air

Question 4

What did the concept of ‘inborn errors of metabolism’ state?

Answer 4

In each case an inheritable factor for a metabolic step (production of pigment; conversion of homogenistic acid to tyrosine) was defective

Question 5

Who suggested the ‘one gene-one enzyme’ and when was it suggested?

Answer 5

Beagle and Tatum, 1941

Question 6

What organism was used a the model organism in the ‘one gene-one enzyme’ theory and why was it used?

Answer 6

Neurospora crassa (red bread mould), grows rapidly on simple medium containing only salts, carbon, nitrogen sources and biotin (vitamin H)

Question 7

What is Neurospora crassa, haploid or diploid?

Answer 7

Haploid

Question 8

Auxotroph

Answer 8

A mutant that requires a particular additional nutrient

Question 9

Protoroph

Answer 9

The normal strain which does not require that nutritional supplement

Question 10

What do Neurospora crassa contain?

Answer 10

Two different types of nuclei, vegetative mycelium (A) and vegetative mycelium (a)

Question 11

What were the steps in B&T’s experiment on Neurospora crassa

Answer 11

1. Mutagenesis
2. Grow all survivors
3. Identify mutants
4. Identify nutritional requirement
5. Identify arginine auxotroph

Question 12

What did the arginine biosynthesis experiments show?

Answer 12

If there was only one gene for the whole of arginine biosynthesis, the same result would be expected for every arg- cross, since every nucleus would be defective in the same gene

Question 13

How many mutants defective arginine biosynthesis were detected and what test was used to detect them?

Answer 13

3 classes, the Complementation test

Question 14

Home message of B&T experiment

Answer 14

They demonstrated multiple genes for a pathway

Question 15

When was nucleic acid discovered and who discovered it?

Answer 15

Friedrich Miescher, 1869

Question 16

How was ‘nuclein’ discovered?

Answer 16

Found in the nuclei of leukocytes found in pus from bandages

Question 17

Who discovered bacterial transformation and when was it discovered?

Answer 17

Frederick Griffith, 1928

Question 18

R Streptococcus pneunomiae

Answer 18

Rough colonies, non-pathogenic

Question 19

S Streptococcus pneunomiae

Answer 19

Smooth colonies, pathogenic, secrete a gelatinous polysaccharide capsule

Question 20

Did the mouse injected with R cells die?

Answer 20

No

Question 21

Did the mouse injected with S cells die?

Answer 21

Yes

Question 22

Did the mouse injected with heat-killed S cells die?

Answer 22

No

Question 23

Did the mouse injected with heat-killed S cells and R cells die?

Answer 23

Yes

Question 24

Why did the mouse die when injected with both heat-killed S cells and R cells?

Answer 24

An S cell is a transforming principle that survives heat treatment has altered (transformed) some of the R cells

Question 25

Who discovered that DNA is the transforming principle and when?

Answer 25

Avery - MacLeod and McCarty, 1944

Question 26

What does DNase do to the transforming principle?

Answer 26

Destroy it

Question 27

What do the results of the Avery - MacLeod _ McCarty experiments tell us?

Answer 27

DNA is the hereditary material

Question 28

Who discovered that protein is not the hereditary material and when did they discover it?

Answer 28

Alfred D Hershey and Martha Chase

Question 29

Structure of ‘phage T2

Answer 29

DNA is tightly packed inside an icosahedral head attached to a core that is surrounded by a sheath that is terminated with a base plate from which tail fibres emerge

Question 30

How T2 ‘phage infects E. Coli

Answer 30

Attaches to E. coli via mediation from the base plate and fibres
After infection, phage remains attached with empty head, forming a ‘ghost’
Lysis of E. Coli and release of new virions

Question 31

What radioactive elements were used to label the ‘phage?

Answer 31

³²P and ³⁵S

Question 32

How were the ‘phages labelled?

Answer 32

E. Coli should be grown in medium containing the radioactive element and then centrifuged to collect the DNA-labelled ‘phage

Question 33

How was DNA confirmed as the genetic material?

Answer 33

Some of the viral progeny and bacteria were ³²P-labelled