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

1. Specifies stop codon or nonsense codon 2. Yields a shorter protein

Bacterial Genetics II Flashcards by ashley portale

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

61 are sense codons, codons that code for Amino Acids

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

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What are the two major types of mutations

Base substitution mutations

2. Addition/Deletion (Frameshift mutations)

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

BS: overall length stays the same

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

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What is a base substitution mutation

Incorrect nucleotide/s incorporated during DNA synthesis

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What is a point mutation

Change of a single base pair

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What are the three possible outcomes from a base substitution

Silent mutation: same AA coded
Missense mutation: Different AA coded
Nonsense mutation: inserts early stop codon

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T/F base mutations are always point mutations

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

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Silent mutation

codes for the wild-type amino acid

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Missense mutation

different amino acid

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

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Nonsense mutation

Specifies stop codon or nonsense codon

2. Yields a shorter protein

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What is a mutation that inactivates genes

a null or a knockout mutation

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Which environment are base substitutions more common, why?

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

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

True

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What type of mutation is a transposon mutation

an addition mutation

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

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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how do transposons enter the cell

by being carried by a plasmid

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What is the difference between a transposon and a plasmid

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

False, gene insertionally inactivated

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How does a transposon move around the host genome

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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Who was the first person to study transposons

Barbara McClintock observed color variation in corn kernels

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T/F transposons are only present in prokaryotic cells

False, present in eukaryotic as well

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How often do spontaneous mutations occur

occur randomly and infrequently,

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

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What is the mutation rate

the probability of mutation each cell division

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T/F mutations are passed to progeny

True

what is a spontaneous mutation

a natural mutation, mistake made by DNA polymerase in replication

Describe the process of reversion

Mutations that are changed back to their original state

T/F Environment selects cells that grow under its conditions

True, ex: antibiotics select for resistant bacteria if present

What are Induced mutations?

- AKA artificial mutations | - result from the outside influence

what is an agent that induces change?

A mutagen

Do mutagens increase or decrease mutation rate?

Increase

What are the two general types of induced mutations

1. Chemical | 2. Radiation

What are the four groups of chemical agent mutagens

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

What are the two types of radiation mutagens

1. UV light | 2. X-rays

What types of mutations can chemical mutagens cause

1. Base substitutions | 2. Frameshift mutations

Chemical Mutagen: Chemicals that modify nucleobases (2)

1. Alkylating agents | 2. Nitrous acid

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

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

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

Converts C to U | -base pairs with adenine instead of Guanine

Chemical Mutagen: Base analogs

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

what is the example of a base analog

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

What types of mutations do intercalating agents cause

Frameshift mutations

What is the role of an intercalating agent

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

What are two examples of an intercalating agent

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

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

Forms thymine dimers - covalent bonds between adjacent thymines - will always bind wit the adjacent thymine on the same strand

What is the effect of thymine dimers because of UV irridation

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

Is UV radiation considered a ionizing or non-ionizing radiation

non-ionizing radiation, does not kill endospores

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

causes single- and double-strand breaks in DNA - causes deletions - double-strand breaks often produce lethal deletions - can alter nucleobases

True/False: X-rays can penetrate very deep

False

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

ionizing reagent, can kill endospores

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

True

Where are plasmids typically found

in most Bacteria and Archaea, sometimes in a few Eucarya

what is the typical structure of plasmids

- dsDNA with an origin of replication | - few to thousands of years

T/F plasmids are an autonomously independent replicating unit

True

How essential is a plasmid?

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

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

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

What are some traits that are encoded by plasmids

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

What are low-copy-number plasmids

F-plasmid | one of a few per cell

What are high-copy-number plasmids

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

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

narrow: single species; most common | broad range: includes both gram positive and gram negative

What are two similar properties between all plasmids

- the presence of non-essential genes | - the ability for the plasmid to replicate

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

True