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Microbiology > Bacterial Genetics II > Flashcards

Bacterial Genetics II Flashcards

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1
Q

what is the difference between sense codons and nonsense codons, of the 64 how many are there of each

A

61 are sense codons, codons that code for Amino Acids

3 are nonsense/stop codons (UAA, UAG, UGA)1

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2
Q

What are the two major types of mutations

A
  1. Base substitution mutations

2. Addition/Deletion (Frameshift mutations)

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3
Q

What happens to the length of the molecule based on the two major types of mutations

A
  1. BS: overall length stays the same

2. FS: changes the entire length of the DNA molecule

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4
Q

What is a base substitution mutation

A

Incorrect nucleotide/s incorporated during DNA synthesis

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5
Q

What is a point mutation

A

Change of a single base pair

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6
Q

What are the three possible outcomes from a base substitution

A
  1. Silent mutation: same AA coded
  2. Missense mutation: Different AA coded
  3. Nonsense mutation: inserts early stop codon
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7
Q

T/F base mutations are always point mutations

A

False, they may involve changing more than one base in the DNA sequence

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8
Q

Silent mutation

A

codes for the wild-type amino acid

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9
Q

Missense mutation

A
  1. different amino acid

2. effect on protein depends on role played by changing amino acid

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10
Q

Nonsense mutation

A
  1. Specifies stop codon or nonsense codon

2. Yields a shorter protein

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11
Q

What is a mutation that inactivates genes

A

a null or a knockout mutation

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12
Q

Which environment are base substitutions more common, why?

A

aerobic

  • Reactive Oxygen species are produced from O2 and some of these radicals are more responsible for mutations
  • can oxidize nucleobase guanine which DNA polymerase often mispairs with adenine
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13
Q

Can protein still be functional with a three codon addition or deletion

A

most likely, will only be the addition or loss of a single amino acid
-impact will depend on location within the protein

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14
Q

T/F one or two nucleotide pairs yields and frameshift mutation

A

True

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15
Q

What type of mutation is a transposon mutation

A

an addition mutation

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16
Q

why are transposons called “jumping genes”, and what is this process called

A

can move from one location to another and can insert themselves randomly at any point in the chromosomal DNA
-process is called transposition

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17
Q

how do transposons enter the cell

A

by being carried by a plasmid

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18
Q

What is the difference between a transposon and a plasmid

A
  • A transposon can not replicate independently

- A transposon can not exist independently in the cytoplasm and will always exist as part of another DNA molecule

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19
Q

T/F A transposon generally does not inactivate the gene into which it inserts

A

False, gene insertionally inactivated

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20
Q

How does a transposon move around the host genome

A
  • it can move from one site to another on the host genome
  • replicates and leaves a copy in the original position
  • can jump from plasmid to chromosome or chromosome to plasmid
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21
Q

Who was the first person to study transposons

A

Barbara McClintock observed color variation in corn kernels

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22
Q

T/F transposons are only present in prokaryotic cells

A

False, present in eukaryotic as well

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23
Q

How often do spontaneous mutations occur

A
  • occur randomly and infrequently,

- the mutation rate is between 10^-4 and 10^-12 for a given gene

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24
Q

What is the mutation rate

A

the probability of mutation each cell division

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25
Q

T/F mutations are passed to progeny

A

True

26
Q

what is a spontaneous mutation

A

a natural mutation, mistake made by DNA polymerase in replication

27
Q

Describe the process of reversion

A

Mutations that are changed back to their original state

28
Q

T/F Environment selects cells that grow under its conditions

A

True, ex: antibiotics select for resistant bacteria if present

29
Q

What are Induced mutations?

A
  • AKA artificial mutations

- result from the outside influence

30
Q

what is an agent that induces change?

A

A mutagen

31
Q

Do mutagens increase or decrease mutation rate?

A

Increase

32
Q

What are the two general types of induced mutations

A
  1. Chemical

2. Radiation

33
Q

What are the four groups of chemical agent mutagens

A
  1. Chemicals that modify nucleobases
  2. Base analogs
  3. Intercalating agents (chemicals that insert themselves into the DNA)
  4. Transposons
34
Q

What are the two types of radiation mutagens

A
  1. UV light

2. X-rays

35
Q

What types of mutations can chemical mutagens cause

A
  1. Base substitutions

2. Frameshift mutations

36
Q

Chemical Mutagen: Chemicals that modify nucleobases (2)

A
  1. Alkylating agents

2. Nitrous acid

37
Q

What is the role of an alkylating agent and what is an example and what mutation does it cause

A
  1. Alkylating agents add alkyl groups onto nucleobases
    - ex: nitrosoguanidine: adds methyl group to guanine
    - base pairs with thymine
38
Q

What is the role of nitrous acid (HNO2) and what mutation does it cause

A

Converts C to U

-base pairs with adenine instead of Guanine

39
Q

Chemical Mutagen: Base analogs

A

Resemble nucleobases but have different hydrogen-bonding properties
-can be mistakenly incorporated by DNA polymerase

40
Q

what is the example of a base analog

A

5-bromouracil, resembles thymine and will often base-pair with cytosine

41
Q

What types of mutations do intercalating agents cause

A

Frameshift mutations

42
Q

What is the role of an intercalating agent

A

They are flat molecules that insert between adjacent base pairs in DNA

  • pushes nucleotides apart, produces space causing an addition mutation on the opposite strand
  • causes errors during replication
43
Q

What are two examples of an intercalating agent

A

Ethidium Bromide
- a likely carcinogen
Chloroequine: used to be used to treat Malaria

44
Q

Radiation: Ultraviolet irradation, what kind of mutation does it cause

A

Forms thymine dimers

  • covalent bonds between adjacent thymines
  • will always bind wit the adjacent thymine on the same strand
45
Q

What is the effect of thymine dimers because of UV irridation

A
  • cannot fit into double helix, distorts molecules
  • replication and transcription stall at distortion
  • cell will die if damage is not repaired
46
Q

Is UV radiation considered a ionizing or non-ionizing radiation

A

non-ionizing radiation, does not kill endospores

47
Q

Radiation: X-ray, what kind of mutations does it cause

A

causes single- and double-strand breaks in DNA

  • causes deletions
  • double-strand breaks often produce lethal deletions
  • can alter nucleobases
48
Q

True/False: X-rays can penetrate very deep

A

False

49
Q

Is x-ray radiation considered a ionizing or non-ionizing radiation

A

ionizing reagent, can kill endospores

50
Q

True/False: X-rays will cause breaks in DNA and fragment it

A

True

51
Q

Where are plasmids typically found

A

in most Bacteria and Archaea, sometimes in a few Eucarya

52
Q

what is the typical structure of plasmids

A
  • dsDNA with an origin of replication

- few to thousands of years

53
Q

T/F plasmids are an autonomously independent replicating unit

A

True

54
Q

How essential is a plasmid?

A

generally nonessential, only dispensable genes are located in the plasmid and only under certain circumstances are these genes required

55
Q

T/F cell will spontaneously delete the plasmid when not needed to conserve their energy

A

True, for ex: Antibiotic resistance made by R-plasmids are only required when taking antibiotics

56
Q

What are some traits that are encoded by plasmids

A

antibiotic resistance, pilus synthesis, nitrogen fixation, oil degradation, etc.

57
Q

What are low-copy-number plasmids

A

F-plasmid

one of a few per cell

58
Q

What are high-copy-number plasmids

A

R-plasmid
Many perhaps 500
-very powerfully resistant to drugs since has so many copies and resistant to multiple drugs

59
Q

What is the difference of narrow host range vs. broad host range

A

narrow: single species; most common

broad range: includes both gram positive and gram negative

60
Q

What are two similar properties between all plasmids

A
  • the presence of non-essential genes

- the ability for the plasmid to replicate

61
Q

T/F broad host range plasmids can be transferred to other bacterias

A

True

Microbiology (7 decks)

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