Gene Mutations and DNA Repair

Question 1

Mutation

Answer 1

Alteration in DNA sequence; source of genetic change

Question 2

Gene mutation

Answer 2

Mutation in coding sequence of a gene or in an intron/regular toy sequence of a gene

Ex: base pair substitution, deletion or insertion

Question 3

How point mutations affect codons:

Answer 3

Missense mutation, nonsense mutation, silent mutation, neutral mutation

Question 4

Other terms that describe a point mutation (base substituon)

Answer 4

Transition (purine to purine, pyrimidine to pyrimidine) and transversion (purine to pyrimidine and pyrimidine to purine)

Question 5

Frameshift mutation

Answer 5

Changes reading frame due to insertion or deletion of one or more base pairs not divisible by three

Question 6

How gene mutations affect function

Answer 6

Loss of function mutation (and even null mutation), gain of function mutation, and neutral mutation

Question 7

Location of gene mutations

Answer 7

Somatic mutations occur in all cells in the body that aren’t germ cells (autosomal occur on chromosomes 1 through 22, X-linked occur on X) and germline mutations (sperm and egg; only kind carried to offspring)

Question 8

Spontaneous vs. induced mutations

Answer 8

Spontaneous hallen naturally and randomly due to normal biological processes; induced start as a result of influence of external factor (natural or artificial)

Question 9

Sources of spontaneous mutations

Answer 9

DNA replication (DNA polymerase occasionally “slips” and deletes or inserts), depurination (loss of nitrogenoud base, usually a purine), deamination (modifications to nitrogenous bases), and oxidative damages (by-products of normal cellular processes from mitochondria and peroxisomes)

Question 10

Sources of induced mutations

Answer 10

Natural mutagens (fungal toxins, cosmic rays, UV light) and human made mutagens (industrial pollutants, chemicals, medical rays), alkylating agents (alter base pairing affinity) and base analogs (mutagenic chemicals that mimic purine or pyrimidine)

Question 11

Purpose of DNA repair

Answer 11

Process of repairing DNA; prote td cells and organisms form mutations that could lead to disease

Question 12

Each type of DNA repair mechanism is specific for:

Answer 12

Certain types of DNA damage

Question 13

Mismatch repair

Answer 13

Corrects error that remains after proofreading by DNA polymerase, causing cells to be more susceptible to cancer

Question 14

Post-replication repair

Answer 14

When DNA replication skills over a lesion and requires homologous reconfirmation mediated by RecA protein

Question 15

Photoreactive repair

Answer 15

Removes thymine dimers caused by UV light; depends on enzyme PRE that uses blue light

Question 16

DNA excision repair

Answer 16

Acts on mutations present in one of the two strands by removing mutation with a nuclear, filling the gap with DNA polymerase, and sealing of the nick with ligase

Question 17

Base excision repair (BER)

Answer 17

Activated by simple lesions that are caused by endogenous sources; glycosylase detect and removes the error and AP endonuclease cuts the sugar-phosphate backbone, then polymerase and ligase fill gap

Question 18

Nucleotide excision repair

Answer 18

Repairs bulky lesions by detecting lesion, removing piece of strand, and filling the gap using the undamaged strand as a template

Question 19

Double-stranded break

Answer 19

When both DNA strands are cut in the same location; DSB repair must reannel through two ways:

Homologous recombination and nonhomologous end joining

Question 20

Homologous recombination repair

Answer 20

Digests the 5 ends, then uses the 3 end to join with an undamaged sister chromatin (template) and copy the sequence onto the damaged strand

Occurs in late G2 or early S phase because sister strands are available

Question 21

Nonhomologous end joining

Answer 21

Repairs DSB by using rejoining ends; however, they are trimmed so genetic material is lost–preferred mechanism due to simplicity

Question 22

Alkylating agents

Answer 22

Induced mutation; found in toxins and tabocco smoke and alters base pairing affinity by adding an alkyl group to the amino or keto groups on nucleotides

Used in chemotherapy

Question 23

Apurinic site

Answer 23

Result of depurination; loss of a nitroigenous base that creates an apurinic site where there is only the sugar-phosphate backbone

Question 24

Deamination

Answer 24

Spontaneous mutation that modified niteogenous bases, changing the base pairing ability; C changes to U (which pairs with A instead of G) and A changes to hypoxanthine (which pairs with C instead of T)

Question 25

Pyrimidine dimers

Answer 25

Source of induced mutation by UV light which distorts the DNA conformation in such a way that errors tend to be introduced during replication

Question 26

Ionizing irradiation

Answer 26

Can produce double stranded breaks

Question 27

Base analogs

Answer 27

Mutagenic chemical that mimics purine or pyrimidine, added by DNA polymerase