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BIOL 207 > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What were the key experiments that led to the conclusion that DNA is the carrier of genetic information?

A

Griffiths
Avery, MacLeod, & McCarty
Hershey & Chase
Watson & Crick

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2
Q

When was the griffiths experiment

A

1928

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3
Q

What did the griffiths experiment do?

A

Discover the Transforming Principle

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4
Q

Describe the bacteria Streptococcus pneumonia used in the Griffiths experiment

A

Has 2 forms: rough and smooth
Smooth has a protective polysaccharide layer called glycocalyx, is virulent
Rough doesn’t have glycocalyx, isn’t virulent

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5
Q

Why is the smooth form of Streptococcus virulent?

A

The glycocalyx protects the bacteria from the mouse’s immune system

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6
Q

What happened when the smooth form of Streptococcus was heat treated?

A

The heat killed the s strain, and was no longer virulent

No s strain could be obtained from mice after injection

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7
Q

What happened when heat treated s-strain of Streptococcus was injected along with the r strain?

A

The mouse died

Live R and S-strains could be obtained from the mice after injection

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8
Q

What was the conclusion of the griffiths experiment

A 
living cells (“R”) could be “transformed” by dead (“S”) cells
Something in the S-cell debris could convert (transform) R cells into S cells
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9
Q

T/F certain bacteria can take up fragments of DNA

A

True

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10
Q

What do bacteria need to be in order to take up dna?

A

Need to be competent

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11
Q

What is bacteria competency caused by?

A

Competency factors

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12
Q

What are competency factors?

A

Single stranded binding proteins, which help incorporating the ingested DNA into the bacterial genome

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13
Q

When was the Avery, MacLeod & McCarty experiment

A

1944

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14
Q

What did Avery, MacLeod & McCarty do?

A

Treated S-strain with compounds that would destroy different elements of the bacteria

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15
Q

What were the elements that were destroyed in the Avery, MacLeod & McCarty experiment?

A 
Glycocalyx
Lipids
RNA
Protein
DNA
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16
Q

What happened after each element was destroyed?

A

When glycocalyx, lipids, RNA, and protein were destroyed, the activity stayed
But when DNA was destroyed, activity was lost

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17
Q

What was the conclusion of the Avery, MacLeod & McCarty experiment

A

DNA is the transforming substance

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18
Q

T/F Avery, MacLeod & McCarty’s results were widely accepted

A

False

People were reluctant to accept DNA was the genetic material

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19
Q

why were people reluctant to accept dna as the genetic material?

A

DNA seemed not complex enough (compared to proteins) to be the base for genetic material (4 different nucleotides vs. 20 amino acids).

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20
Q

When was the Hershey & Chase experiment?

A

1952

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21
Q

Describe the bacteriophage T2 used in the Hershey & Chase experiment

A

It is composed of only DNA and protein, therefore the genetic material had to be either protein or DNA

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22
Q

What did Hershey & Chase do with the bacteriophages?

A

Labelled some with 32P to follow DNA

and some with 35S to follow Protein

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23
Q

What were the results of Hershey & Chase experiment when they labelled bacteriophage with 35S?

A

35S labels proteins

Most of the radioactivity was recovered in phage ghosts

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24
Q

What were the results of Hershey & Chase experiment when they labelled bacteriophage with 32P?

A

32P labels DNA

Most of radioactivity was recovered inside the bacteria

25
Q

Explain the results of the Hershey & Chase experiment, in terms of what was going on with the bacteriophage

A

Upon injection, only the dna enters the bacterium, the empty phage “ghosts” remain outside the bacterium

26
Q

What was the conclusion of the Hershey & Chase experiment

A

DNA is the hereditary material (NOT protein). At least for bacteriophage T2…

27
Q

What realizations did we have after the Hershey & Chase experiment

A 
Cells must be able to replicate DNA.
Carries hereditary information 
Transfer information to control a cell's activity 
Must be able to change (mutate). 
How does this all happen?
28
Q

Describe nucleotide structure

A

Phosphate group
Pentose sugar
Nitrogenous base

29
Q

How do we name nucleotides?

A

Base + sugar + phosphate

30
Q

How do we name nucleosides

A

Base + sugar

31
Q

How are nucleotides linked?

A

Phosphodiester linkage

Phosphate group at 5’ of the sugar of one nucleotide covalently bonds to the 3’ of the sugar on the next nucleotide

32
Q

T/F the phosphate backbone of DNA is positively charged

A

False

Negative charged

33
Q

What did Chargaff do in the 1940’s

A

He looked at the nucleotide distribution across species

34
Q

What did chargaff find?

A

The chemical composition of dna across species is the same
That each species has a specific quantity of dna
Dna found in different species have the same ratio of bases

35
Q

What are chargaff’s rules?

A

A = T
C = G
In rna, A = U

36
Q

What did rosalind franklin do

A

Produce an X-ray diffraction image of DNA

37
Q

How are nitrogenous bases connected to each other?

A

Hydrogen bonds

38
Q

Minor groove

A

The backbones are close together

39
Q

Major groove

A

The backbones are further apart

40
Q

Describe dna structure

A 
2nm wide
Helical
2 strands run antiparallel
Sugar and phosphate face out, bases face in
10.5 bases per helical turn
41
Q

Purine

A

Double ring

A and G

42
Q

Pyrimidine

A

Single ring

T and C and U

43
Q

How did we conclude that pyrimidine pairs with purine?

A

Spacing, pyra + pyra = too narrow, pur + pur = too wide

Pyra + pur = consistent with xray data

44
Q

Complementary base pairing

A

A always pairs with T (or U)

C always pairs with G

45
Q

What are the three models of DNA replication models?

A

Conservative
Semiconservative
Dispersive

46
Q

Describe the conservative model of dna replication

A

Parent strands separate
Each parental strand is replicated, creating a two DNA duplexes, each with one parental and one daughter strand
These new strands separate
The parental strands reanneal and the daughter strands anneal

47
Q

If the conservative model of dna replication is true, how much new vs. old DNA is present in first round of replication and in second round of replication?

A

First: one duplex is 100% old, one duplex is 100% new
Second: one duplex is 100% old, three duplexes are 100% new

48
Q

If the conservative model of dna replication is true, what is the ratio of old vs. new DNA in first round of replication and in second round of replication?

A

First: 1:1
Second: 1:3

49
Q

Describe the semiconservative model of dna replication

A

Parent strands separate

Each parental strand is replicated, creating a two DNA duplexes, each with one parental and one daughter strand

50
Q

If the semiconservative model of dna replication is true, how much new vs. old DNA is present in first round of replication and in second round of replication?

A

First: both duplexes are 50% old and 50% new
Second: two duplexes are 50% old and 50% new, two duplexes are 100% new

51
Q

If the semiconservative model of dna replication is true, what is the ratio of old vs. new DNA in first round of replication and in second round of replication?

A

First: 1:1
Second: 1:3

52
Q

Describe the dispersive model of dna replication

A

Segments of parental DNA and newly synthesized daughter DNA are interspersed amongst both strands of the DNA molecules

53
Q

If the dispersive model of dna replication is true, how much new vs. old DNA is present in first round of replication and in second round of replication?

A

It would vary, but there would be around 50% new dna after each round of replication

54
Q

Which replication model is correct

A

Semiconservative

55
Q

How did we figure out which model of dna replication was correct?

A

Through the Meselson-stahl pulse-chase experiment

56
Q

What happened in the first part of the Meselson-stahl pulse-chase experiment

A

Grew bacteria in a medium with heavy 14N, which would be incorporated in the dna
After enough time that the isotope has been incorporated, but before dna is replicated, the bacteria is transferred to fresh medium without the isotope, so new dna would not have the isotope

57
Q

What happened in the second part of the Meselson-stahl pulse-chase experiment

A

The dna was put in CsCl solution and spun really fast to make a gradient where heavier dna was at the end

58
Q

T/F for the Meselson-stahl pulse-chase experiment, they ran it for 3 rep cycles

A

False

Two rep cycles

59
Q

In the Meselson-stahl pulse-chase experiment, why did they run it for 2 cycles?

A

Because after one rep cycle, semiconservative and dispersive both have 50% of parent dna, they’re both in the middle of the solution

BIOL 207 (6 decks)

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