Module 10 Flashcards
Point Mutations
Can be in the form of a missense, nonsense, silent, or frameshift mutation
Gene mutations outside coding regions:
- Promoter
- Regulatory element
- 5’/3’-UTR
- Splice recognition sequence
Position Effect
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
Germ Line Mutations
Can occur directly on an egg or sperm cell, affects the entire zygote
Somatic Cell Mutations
Can occur within a single embryonic cell, as that cell proliferates a patch develops with the mutation
Lederberg & Lederberg Experiments
Studied resistance of E. coli to bacteriophage T1, discovered tonr gene conferring resistance only from specific colonies repeatedly, which supported their random mutation hypothesis
Spontaneous Mutations
Mutations with intracellular causes (ex. DNA replication errors)
Induced Mutations
Mutations caused by environmental agents (ex. chemical or physical mutagens)
Examples of Spontaneous Mutations:
- 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)
Trinucleotide Repeat Expasion (TNRE)
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
Mutagen
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)
Base Modifiers
Covalently modify nucleotide structure (C to U, A to H)
Ex. Nitrogenous mustards
Intercalating Agents
Contain flat, planar structure which form double helix that distorts helical structure of DNA to result in frameshifts
Ex. Proflavin
Base Analogues
Become incorporated into daughter strand during replication
Ex. 5-bromouracil is a T analogue
Ionizing radiation can cause ____
damage to DNA backbone and double stranded breaks
Non-ionizing radiation such as UV light exposure can result in the formation of ____, which then do not base pair properly
thymine dimers
Ames Test
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
____ can repair thymine dimers using visible light energy
Photolyse
Alkyltransferase
Repairs alkylated bases (methylated), transfers methyl/ethyl group to itself to inactivate
Base Excision Repair (BER)
Removes damaged bases, abnormal bases
Nucleotide Excision Repair (NER)
Removes damaged DNA segments, can fix T dimers, modified or missing bases, and is found in all eukaryotes and prokaryotes
NER in E. coli requires 4 key proteins: ____, which are involved in UV light repair and recognize and remove short DNA strands
UvrA, UvrB, UvrC, and UvrD
Homologous Recombination
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
Sister chromatid exchange (SCE) produces new ____
allelic combinations
Holliday Recombination Model
When two ds DNA strands interact, can result in either non-recombinant or recombinant chromosomes gaining a heteroduplex region
Double Strand Break Model
Similar to Holliday model, however it proposes a double strand break on one of the chromatids, requiring DNA gap repair synthesis
E. coli contains many proteins playing a role in recombination, such as:
- RecBCD
- SSBPs
- RecA
- RuvABC
- RecG
Two mechanisms accounting for gene conversion:
- DNA mismatch repair
- DNA gap repair synthesis
