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Microbiology > Chapter 16 Part A > Flashcards

Chapter 16 Part A Flashcards

Genetic Variation, Exam 3

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Biology 101 flashcards
1
Q

How do eukaryotes undergo genetic variation?

A

Sexual reproduction (vertical gene transfer)

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2
Q

How does sexual reproduction cause genetic variation?

A

Gametes form to make a zygote, mixing and matching chromosomes from parents
-Parents come together to make a child with different genetics

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3
Q

How do bacteria (prokaryotes) undergo genetic variation?

A
  • Horizontal gene transfer (HGT)

- Mutations

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4
Q

What is horizontal gene transfer?

A

The movement of genetic information between organisms

-Can be used to create antibiotic resistance

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5
Q

What are the different types of horizontal gene transfer?

A
  • Transformation
  • Conjugation
  • Transduction
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6
Q

What is transformation?

A

The uptake of free/naked DNA from the environment

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7
Q

What is conjugation?

A

The transfer of genetic information that involves direct cell to cell contact
-Initiated by sex pilus from the original cell binding to the receiving cell

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8
Q

What is transduction?

A

Genes from the host cell (bacterium) are incorporated into the genome of a bacterial virus (bacteriophage)

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9
Q

What are the 2 different types of mutation?

A
  • Spontaneous mutation

- Induced mutation

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10
Q

What is a spontaneous mutation?

A

Mistakes made during replication or DNA repair

-Wrong letter/an extra letter/missing a letter

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11
Q

What is an induced mutation?

A

Mutation that is caused by a mutagen agent, causing distortion or damage to the DNA
-Causes errors in replication

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12
Q

What are the different types of mutagen agents?

A
  • From the environment that distorts DNA
    • Chemicals, radiation, etc.
  • Intercalating agents
  • Base analogs
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13
Q

What is an intercalating agent?

A

It makes its way into the double helix ladder, making replication very difficult causing mistakes)

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14
Q

What is a base analog?

A

A chemical which resembles a purine or pyrimidine base, which differs slightly in structure from the normal bases found in nucleic acids

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15
Q

Why is it that a mutation may not cause a different amino acid to be produced?

A

Redundancy in the genetic code

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16
Q

What are the different types of spontaneous mutations?

A
  • Silent mutation
  • Missense mutation
  • Nonsense mutation
  • Frameshift mutation
  • Point mutation
  • Transition mutation
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17
Q

What is a silent mutation?

A

A mutation in the DNA that does not result in a difference in the amino acid sequence within the organism

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18
Q

What is a missense mutation?

A

A single base substitution that changes a codon for one amino acid to a codon for a different amino acid
-Causes the production of a different protein

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19
Q

What is a nonsense mutation?

A

When a codon that codes for an amino acid is converted into a nonsense codon (stop codon)
-It does not produce a protein and it shortens the polypeptide

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20
Q

What is a frameshift mutation?

A

Addition of an extra base or removal of a base within the DNA
-Since the DNA is read in groups of 3, the change in the number of bases changes the way the DNA is read

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21
Q

What is a point mutation?

A

When one base in the DNA is changed to another base

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22
Q

What is the difference between a point mutation and a missense mutation?

A

Point mutation changes only a base, a missense mutation occurs when the point mutation causes a different amino acid to be produced from that codon

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23
Q

What is a transition mutation?

A

A type of point mutation that changes a purine nucleotide to a pyrimidine, or vice versa

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24
Q

What are the purine nucleotides?

A
  • Guanine (G)

- Adenine (A)

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25
Q

What are the pyrimidine nucleotides?

A
  • Cytosine (C)

- Thymine (T)

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26
Q

What is tautomerization?

A

The spontaneous isomerization of a nitrogen base to an alternative form
-Bonding gets modified/ incorrect bonding

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27
Q

What are the forms that nucleotides can be in?

A
  • Imino

- Enol

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28
Q

How many H’s are available for covalent bonds in imino form?

A

2 H’s available for covalent bonds

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29
Q

How many H’s are available for covalent bonds in enol form?

A

3 H’s available for covalent bonds

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30
Q

What kind of mutation does tautomerization cause?

A

Point mutation

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31
Q

What causes specific mispairings?

A

A mutagen changing the base’s structure which alters its base-pairing character
-Its modified base causes it to mispair

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32
Q

What is Thymine Dimer Distortion of DNA?

A

Distortion of the DNA structure, causing a gap when replicating

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33
Q

What causes a thymine dimer distortion of DNA?

A

UV light from the environment being absorbed in the DNA

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34
Q

Why is a thymine dimer distortion so dangerous?

A

A bump is formed when the DNA is distorted from the UV light

  • Bond is broken between complementary bases, so the T’s bind to each other in an attempt to stabilize
  • The strand cannot be read perfectly, causing a gap that can be lethal
35
Q

How can a thymine dimer distortion be repaired?

A

Novel DNA sequences can be introduced

  • A patch is found that is different nucleotide sequence
    • Causes dramatic change, but done in order to avoid death
36
Q

What are the different repair mechanisms?

A
  • Proofreading
  • Mismatch repair
  • Nucleotide excision repair
  • Photoreactivation
  • Recombinational repair
  • SOS response
37
Q

What is proofreading?

A

The process of detecting errors made during DNA replication

-The error is removed and replaced

38
Q

When does proofreading occur?

A

As the cell is going through DNA replication

39
Q

What is involved in proofreading?

A
  • DNA polymerase III
  • Exonuclease
  • DNA polymerase
40
Q

What does DNA polymerase III do during proofreading?

A

It is the enzyme that is proofreading to detect the error

41
Q

What does exonuclease do during proofreading?

A

It takes out the error after it has been detected

42
Q

What does DNA polymerase do during proofreading?

A

It adds the correct nucleotide where the error previously was

43
Q

What is mismatch repair?

A

The process of detecting mismatched bases after DNA replication
-The mismatched base is removed and replaced

44
Q

When does mismatch repair occur?

A

Right after DNA replication

-When DNA polymerase III did not catch the mistake the first time

45
Q

What is involved in mismatch repair?

A
  • MutHLSProteins
  • Endonuclease
  • Exonuclease
  • DNA polymerase I
  • DNA ligase
46
Q

What does MutHLSProteins due during mismatch repair?

A

It scans and detects mismatches within the DNA

47
Q

What does endonuclease do during mismatch repair?

A

It cuts error in the nucleic acid DNA sequence

48
Q

What does exonuclease do during mismatch repair?

A

It removes the error that was found within the DNA

49
Q

What does DNA polymerase I do during mismatch repair?

A

It synthesizes short strands of DNA to replace the error that was detected

50
Q

What does DNA ligase do during mismatch repair?

A

It links newly synthesized section of DNA to the rest

51
Q

What is excision repair?

A

The process of detecting anomalies in DNA & removing it, replacing it with existing DNA

52
Q

What is are anomalies in DNA?

A

Abnormalities or damage within the DNA

53
Q

What is involved in excision repair?

A
  • UvrABCD proteins
  • Endonuclease
  • Helicase
  • DNA polymerase I
  • DNA ligase
54
Q

What do UvrABCD proteins do during excision repair?

A

It detects the anomaly within the DNA

55
Q

What does endonuclease do during excision repair?

A

It cuts the anomaly within the DNA

56
Q

What does helicase do during excision repair?

A

It removes the anomaly within the DNA

57
Q

What does DNA polymerase I do during excision repair?

A

It synthesizes short strands of DNA to replace the anomaly that was detected in the DNA

58
Q

What does DNA ligase do during excision repair?

A

It links newly synthesized section of DNA to the rest

59
Q

What organism does methyl-directed mismatch repair occur in?

A

E.coli

60
Q

What strand is methylated for methyl-directed mismatch repair: The old strand or the new strand?

A

The old strand is methylated

61
Q

What are the steps for methyl-directed mismatch repair?

A
  1. ) MutS scans the new unmethylated DNA for mismatches
  2. ) MutL binds to MutS and a MutS/MutL complex is formed
  3. ) MutH binds to MutS/MutL, detects and nicks the new nonmethylated strand using endonuclease, and uses the exonuclease activity to digest the new DNA including the mismatch
  4. ) DNA polymerase I synthesizes the complementary strand to fill in the gap
  5. ) DNA ligase joins the newly synthesized DNA to the rest of the molecule
62
Q

What are the steps for nucleotide excision repair?

A
  1. ) Endonuclease (UvrAB) detects distortions (T-T dimer) by feeling if the strands are parallel
  2. ) Endonuclease (UvrC) cuts damaged DNA strand
  3. ) Helicase (UvrD) removes the damaged DNA strand by lifting the section
  4. ) DNA polymerase I synthesizes the complementary strand of DNA to fill in the gap
  5. ) DNA ligase joins newly synthesized DNA to the rest of the molecule
63
Q

How does photoreactivation work?

A

It repairs the thymine dimers by breaking the incorrect nucleotide bonds and permitting appropriate bonds to reform

64
Q

What does photoreactivation require?

A

Visible light, it cannot be done in the dark

65
Q

What is unique about photoreactivation?

A

No nucleotides get removed, only bonds break causing the mechanism to be 100% error free

66
Q

What is recombinational repair?

A

Repair of the DNA where the is no template due to combining 2 different DNA sources to create a hybrid molecule
-Hole/gap in DNA

67
Q

What is involved in recombinational repair?

A
  • Endonuclease (RecA)
  • DNA ligase
  • DNA polymerase I
68
Q

What does endonuclease (RecA) do during recombinational repair?

A

It obtains a patch from a sister molecule

69
Q

What does DNA ligase do during recombinational repair?

A

It attaches the patch from the sister molecule to the rest of the DNA

70
Q

What does DNA polymerase I do during recombinational repair?

A

It synthesizes the patch from the sister molecule

71
Q

What is a recombinant DNA molecule?

A

A hybrid molecule that results from recombination

72
Q

Why is recombinational repair not ideal?

A

It is very error prone, but the cell is willing to take the risk of error since having a gap is worse

73
Q

When would recombinational repair be used?

A

When excision repair and/or photoreactivation did not fix the problem

74
Q

What is SOS response?

A

A last resort by the cell tot fix extensive DNA damage

75
Q

Why is SOS response a last resort?

A

The damaged DNA induces unregulated expression of genes involved in excision repair and recombination repair
-This causes it to be highly error prone (both excision repair and recombination are error prone)

76
Q

Which repair mechanism(s) can be used to repair thymine dimers?

A

Photoreactivation and excision repair

77
Q

Which of the repair mechanism(s) involves the action of an exonuclease?

A

Proofreading

78
Q

What is the difference between exonuclease and endonuclease?

A
  • Exonucleases cut nucleotides at the end of the DNA strand

- Endonucleases cut nucleotides in the middle of the DNA strand

79
Q

What repair mechanism involves the MutS, MutL, and MutH proteins?

A

Mismatch repair (M goes with M)

80
Q

Which repair mechanism involves the RecA protein?

A

Recombinational repair (rec goes with rec)

81
Q

What repair mechanism can be used when there are games in the DNA (no template for the repair enzymes?)

A

Recombinational repair since it uses a sister molecule to create a patch

82
Q

SOS repair involves enhancing levels of which repair mechanism(s)?

A
  • Excision repair

- Recombinational repair

83
Q

What is the least error prone repair mechanism?

A

Photoreactivation

84
Q

What repair mechanism is most error-prone?

A

SOS repair

Microbiology (9 decks)

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