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Chapter 16 Part A Flashcards

Genetic Variation, Exam 3

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
What are the pyrimidine nucleotides?
- Cytosine (C) | - Thymine (T)
26
What is tautomerization?
The spontaneous isomerization of a nitrogen base to an alternative form -Bonding gets modified/ incorrect bonding
27
What are the forms that nucleotides can be in?
- Imino | - Enol
28
How many H's are available for covalent bonds in imino form?
2 H's available for covalent bonds
29
How many H's are available for covalent bonds in enol form?
3 H's available for covalent bonds
30
What kind of mutation does tautomerization cause?
Point mutation
31
What causes specific mispairings?
A mutagen changing the base's structure which alters its base-pairing character -Its modified base causes it to mispair
32
What is Thymine Dimer Distortion of DNA?
Distortion of the DNA structure, causing a gap when replicating
33
What causes a thymine dimer distortion of DNA?
UV light from the environment being absorbed in the DNA
34
Why is a thymine dimer distortion so dangerous?
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
How can a thymine dimer distortion be repaired?
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
What are the different repair mechanisms?
- Proofreading - Mismatch repair - Nucleotide excision repair - Photoreactivation - Recombinational repair - SOS response
37
What is proofreading?
The process of detecting errors made during DNA replication | -The error is removed and replaced
38
When does proofreading occur?
As the cell is going through DNA replication
39
What is involved in proofreading?
- DNA polymerase III - Exonuclease - DNA polymerase
40
What does DNA polymerase III do during proofreading?
It is the enzyme that is proofreading to detect the error
41
What does exonuclease do during proofreading?
It takes out the error after it has been detected
42
What does DNA polymerase do during proofreading?
It adds the correct nucleotide where the error previously was
43
What is mismatch repair?
The process of detecting mismatched bases after DNA replication -The mismatched base is removed and replaced
44
When does mismatch repair occur?
Right after DNA replication | -When DNA polymerase III did not catch the mistake the first time
45
What is involved in mismatch repair?
- MutHLSProteins - Endonuclease - Exonuclease - DNA polymerase I - DNA ligase
46
What does MutHLSProteins due during mismatch repair?
It scans and detects mismatches within the DNA
47
What does endonuclease do during mismatch repair?
It cuts error in the nucleic acid DNA sequence
48
What does exonuclease do during mismatch repair?
It removes the error that was found within the DNA
49
What does DNA polymerase I do during mismatch repair?
It synthesizes short strands of DNA to replace the error that was detected
50
What does DNA ligase do during mismatch repair?
It links newly synthesized section of DNA to the rest
51
What is excision repair?
The process of detecting anomalies in DNA & removing it, replacing it with existing DNA
52
What is are anomalies in DNA?
Abnormalities or damage within the DNA
53
What is involved in excision repair?
- UvrABCD proteins - Endonuclease - Helicase - DNA polymerase I - DNA ligase
54
What do UvrABCD proteins do during excision repair?
It detects the anomaly within the DNA
55
What does endonuclease do during excision repair?
It cuts the anomaly within the DNA
56
What does helicase do during excision repair?
It removes the anomaly within the DNA
57
What does DNA polymerase I do during excision repair?
It synthesizes short strands of DNA to replace the anomaly that was detected in the DNA
58
What does DNA ligase do during excision repair?
It links newly synthesized section of DNA to the rest
59
What organism does methyl-directed mismatch repair occur in?
E.coli
60
What strand is methylated for methyl-directed mismatch repair: The old strand or the new strand?
The old strand is methylated
61
What are the steps for methyl-directed mismatch repair?
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
What are the steps for nucleotide excision repair?
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
How does photoreactivation work?
It repairs the thymine dimers by breaking the incorrect nucleotide bonds and permitting appropriate bonds to reform
64
What does photoreactivation require?
Visible light, it cannot be done in the dark
65
What is unique about photoreactivation?
No nucleotides get removed, only bonds break causing the mechanism to be 100% error free
66
What is recombinational repair?
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
What is involved in recombinational repair?
- Endonuclease (RecA) - DNA ligase - DNA polymerase I
68
What does endonuclease (RecA) do during recombinational repair?
It obtains a patch from a sister molecule
69
What does DNA ligase do during recombinational repair?
It attaches the patch from the sister molecule to the rest of the DNA
70
What does DNA polymerase I do during recombinational repair?
It synthesizes the patch from the sister molecule
71
What is a recombinant DNA molecule?
A hybrid molecule that results from recombination
72
Why is recombinational repair not ideal?
It is very error prone, but the cell is willing to take the risk of error since having a gap is worse
73
When would recombinational repair be used?
When excision repair and/or photoreactivation did not fix the problem
74
What is SOS response?
A last resort by the cell tot fix extensive DNA damage
75
Why is SOS response a last resort?
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
Which repair mechanism(s) can be used to repair thymine dimers?
Photoreactivation and excision repair
77
Which of the repair mechanism(s) involves the action of an exonuclease?
Proofreading
78
What is the difference between exonuclease and endonuclease?
- Exonucleases cut nucleotides at the end of the DNA strand | - Endonucleases cut nucleotides in the middle of the DNA strand
79
What repair mechanism involves the MutS, MutL, and MutH proteins?
Mismatch repair (M goes with M)
80
Which repair mechanism involves the RecA protein?
Recombinational repair (rec goes with rec)
81
What repair mechanism can be used when there are games in the DNA (no template for the repair enzymes?)
Recombinational repair since it uses a sister molecule to create a patch
82
SOS repair involves enhancing levels of which repair mechanism(s)?
- Excision repair | - Recombinational repair
83
What is the least error prone repair mechanism?
Photoreactivation
84
What repair mechanism is most error-prone?
SOS repair

Microbiology (9 decks)

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