Module 10

Question 1

Point Mutations

Answer 1

Can be in the form of a missense, nonsense, silent, or frameshift mutation

Question 2

Gene mutations outside coding regions:

Answer 2

• Promoter
• Regulatory element
• 5’/3’-UTR
• Splice recognition sequence

Question 3

Position Effect

Answer 3

An alteration in the expression of a gene after it is transposed (changes position), it may either assume the expressivity of another gene under which promoter it lands under, or it may not be expressed if moved to heterochromatin/inactive sequence

Question 4

Germ Line Mutations

Answer 4

Can occur directly on an egg or sperm cell, affects the entire zygote

Question 5

Somatic Cell Mutations

Answer 5

Can occur within a single embryonic cell, as that cell proliferates a patch develops with the mutation

Question 6

Lederberg & Lederberg Experiments

Answer 6

Studied resistance of E. coli to bacteriophage T1, discovered ton^r gene conferring resistance only from specific colonies repeatedly, which supported their random mutation hypothesis

Question 7

Spontaneous Mutations

Answer 7

Mutations with intracellular causes (ex. DNA replication errors)

Question 8

Induced Mutations

Answer 8

Mutations caused by environmental agents (ex. chemical or physical mutagens)

Question 9

Examples of Spontaneous Mutations:

Answer 9

• Depurination (removes purines, forming apurinic sites)
• Deamination (removes amino group from cytosine, which becomes uracil or thymine)
• Tautomeric Shift (T and G can convert to enol, A and C can convert to imino)

Question 10

Trinucleotide Repeat Expasion (TNRE)

Answer 10

Causes some human genetic disease above a length limit for carriers, contain C and G and form hairpin during replication which lengthen the DNA strand

Question 11

Mutagen

Answer 11

Agents altering DNA structure and causing mutations

Can be physical (ex. ionizing and non-ionizing radiation) or chemical (ex. base modifiers, intercalating agents, and base analogues)

Question 12

Base Modifiers

Answer 12

Covalently modify nucleotide structure (C to U, A to H)

Ex. Nitrogenous mustards

Question 13

Intercalating Agents

Answer 13

Contain flat, planar structure which form double helix that distorts helical structure of DNA to result in frameshifts

Ex. Proflavin

Question 14

Base Analogues

Answer 14

Become incorporated into daughter strand during replication

Ex. 5-bromouracil is a T analogue

Question 15

Ionizing radiation can cause ____

Answer 15

damage to DNA backbone and double stranded breaks

Question 16

Non-ionizing radiation such as UV light exposure can result in the formation of ____, which then do not base pair properly

Answer 16

thymine dimers

Question 17

Ames Test

Answer 17

For determining if a substance is a mutagen, monitors the rate of a second mutation restoring the function of histidine synthesis to S. typhimurium, uses rat liver extract to induce mutations

Question 18

____ can repair thymine dimers using visible light energy

Answer 18

Photolyse

Question 19

Alkyltransferase

Answer 19

Repairs alkylated bases (methylated), transfers methyl/ethyl group to itself to inactivate

Question 20

Base Excision Repair (BER)

Answer 20

Removes damaged bases, abnormal bases

Question 21

Nucleotide Excision Repair (NER)

Answer 21

Removes damaged DNA segments, can fix T dimers, modified or missing bases, and is found in all eukaryotes and prokaryotes

Question 22

NER in E. coli requires 4 key proteins: ____, which are involved in UV light repair and recognize and remove short DNA strands

Answer 22

UvrA, UvrB, UvrC, and UvrD

Question 23

Homologous Recombination

Answer 23

Involves crossing over between identical/homologous chromosomal regions, occurs during meiosis I, involves pairing of homologs, breaking at analogous locations, and exchange of corresponding segments

Question 24

Sister chromatid exchange (SCE) produces new ____

Answer 24

allelic combinations

Question 25

Holliday Recombination Model

Answer 25

When two ds DNA strands interact, can result in either non-recombinant or recombinant chromosomes gaining a heteroduplex region

Question 26

Double Strand Break Model

Answer 26

Similar to Holliday model, however it proposes a double strand break on one of the chromatids, requiring DNA gap repair synthesis

Question 27

E. coli contains many proteins playing a role in recombination, such as:

Answer 27

• RecBCD
• SSBPs
• RecA
• RuvABC
• RecG

Question 28

Two mechanisms accounting for gene conversion:

Answer 28

1. DNA mismatch repair
2. DNA gap repair synthesis