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My Packs: (WIZEPREP) (BIO 2581) > Chapter 10: 10.1 Repair and Recombination > Flashcards

Chapter 10: 10.1 Repair and Recombination Flashcards

1
Q

Mutations in DNA occur when…

A

There is a change in the normal DNA sequence

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2
Q

What are spontaneous mutations known as?

A

Point mutations

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3
Q

What can point mutations be caused by?

A
  • Errors in DNA replication
  • Environmental exposure to damaging agents (UV light, radiation etc.)
  • Harmful chemicals/toxins
  • Byproducts of normal cell metabolism (e.g. lipid oxidation)
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4
Q

What are the types of point mutations?

A
  1. Nonsense mutations
  2. Missense mutations
  3. Silent mutations
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5
Q

Nonsense mutations

A

A premature stop codon is introduced into a sequence

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6
Q

Missense mutation

A

A change to the amino acid sequence

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7
Q

Silent mutation

A

No change to the amino acid sequence

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8
Q

Can mutations be beneficial?

A

Mutations can be:
* Beneficial
* Benign
* Harmful

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9
Q

Beneficial mutations

A

Improves the fitness of an organism

Examples
* Resistance to a virus
* Lactose tolerance

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10
Q

Benign mutations

A

Does not change the overall fitness of an organism

Examples
* Change in eye color or silent mutations

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11
Q

Harmful mutations

A

Negatively impacts the fitness of an organism

Examples
* Development of diseases (cancer, birth defects)

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12
Q

DNA polymerases make a mistake approximately every…

A

1 in 10,000 bases

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13
Q

What is the actual number of mistakes that researchers found in DNA?

A

1 in 1,000,000,000 bases

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14
Q

Processes:

DNA Replication Proofreading

A
  1. The DNA polymerase(s) pause
  2. 3’-5’ exonuclease removes the incorrect base pair
  3. DNA polymerase(s) adds the correct one
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15
Q

What is Base Excision Repair used to repair?

A
  • Spontaneous natural deamination (C becomes U, resulting in a G-U mismatch)
  • Depurination (loss of A or G) lesions
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16
Q

Processes:

Base Excision Repair (BER)

A
  1. DNA glycosylase identifies + removes U from sugar-phosphate backbone
  2. APE1 endonuclease removes deoxyribose phosphate that is abasic
  3. Specialized DNA polymerase adds a C
17
Q

How does DNA glycosylase remove the base?

A

Flips the base out of the helix and removes it

18
Q

When are Base Excision Repairs done?

A

BEFORE replication to prevent the mutation becoming permanent

19
Q

What does Mismatch Excision Repair do?

A

Fixes mutations that include:
* Base pair mismatches
* Small insertions/deletions of a few nucleotides

20
Q

When does Mismatch Excision Repair occur?

A

Made AFTER replication

21
Q

What is thought to be the mechanism behind Mismatch Excision Repair?

A
  1. Specialized proteins determine which strand is the template and which is the mutated daughter strand
  2. An endonuclease removes the mismatch/insertion/deletion
  3. The daughter strand is repaired to produce an exact copy of the template strand
22
Q

What does Nucleotide Excision Repair fix?

A

A mutation that causes a distortion in the double helix structure of DNA
* E.x. Thymine dimers

23
Q

What is the process of Nucleotide Excision Repair?

A
  1. Distortion is identified by a complex of XP-C and 23B proteins
  2. TFIIH helicase, RPA, and XP-Gunwinds the DNA at this site
  3. XP-G and XP-F work as endonucleases to cut out the distorted segment of DNA
  4. DNA polymerase fills in the gap
24
Q

What are the two main systems for repairing double stranded DNA breaks?

A
  • Non-homolgous end joining
  • Homologous recombination
25
Q

How does NHEJ work?

A

Joins 2 non-homologous ends of DNA together
* The two strands are usually still close enough together that they will be ligated back together

26
Q

What are some issues with NHEJ?

A
  • Causes minor deletions
  • N-terminus of one gene can fuse to the C-terminus of a different gene
27
Q

True or False:

Small deletions from either ends in NHEJ is a major issue

A

Not necessarily
* Majority of DNA is noncoding/intronic DNA

28
Q

Why is the fusing of the N-terminus of one end and the C-terminus of the other end problematic?

A

Results in chimeric genes
* Can result in changes to cell function
* Can result in cancer

29
Q

How does Homologous Recombination?

A

Damaged DNA sequence is copied from an undamaged or highly similar (homologous) copy of DNA
* Repaired by an exchange of two different DNA strands (recombination)

30
Q

True or False:

Homologous Recombination is error-free

A

True

My Packs: (WIZEPREP) (BIO 2581) (50 decks)

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