汪世华分子生物学 4

the encoded protein.
Missense mutation is a point mutation in which
a single nucleotide change results in a codon
that codes for a different amino acid.
(2)Induced mutation
① Physical: UV, x-rays and γ-rays; ② Chemical: Base analogs, Intercalating,
Nitrous acid, Alkylating agents,
Oxidative agents.
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UV
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4.2.4 Mismatch Repair
(3) DNA polymerase III, with help from SSB, fills in the
gap left by the exonuclease,
and DNA ligase seals the remaining nick.
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4.1.1 Types of Mutations
(4)Nonsense, stop codon & suppressor mutation
Nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product.
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4.2.3 Nucleotide Excision Repair
(4) DNA helicase UvrD releases the single-strand fragment from the duplex, and DNA Pol I and ligase repair and seal the gap.
4.2.5 Recombination Repair
(1) During replication, the replication machinery skips over the region with the dimer, leaving a gap; the
UV light can induce adjacent pyrimidine
bases in a DNA strand to become
covalently joined as a pyrimidine dimer.
UV radiation, in particular longer-wave
by the absence of methyl
and introduce a nick into that new strand, across from a methylated GATC
groups on GATC sequences,
and upstream of the
incorrect nucleotide.
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Frameshift mutation
A type of gene mutation wherein the insertion or deletion of nucleotide(s) causes a shift in the reading frame of the codons in the mRNA, thus, may eventually lead to the alteration in the amino acid sequence at protein translation.
(2) UvrA leaves the complex, and the remaining UvrB dimer melts DNA locally around the distortion.
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4.2.3 Nucleotide Excision Repair
(3) UvrC forms a complex with UvrB and creates nicks 3’ to the lesion and 5’ to the lesion.
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4.1.1 Types of Mutations
(1) Induced mutation & spontaneous mutation
Mutations which are artificially induced with the help of mutagenic agents are called induced mutations. A mutation that arises naturally and not as a result of exposure to mutagens are called spontaneous mutations.
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4.2.4 Mismatch Repair
(2) Exonuclease I, along with MutL, MutS, DNA helicase, and ATP, removes DNA downstream of the nick, including the incorrect nucleotide.
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Notes
Base excision repair is more prevalent and
usually works on common, relatively subtle changes to DNA bases, such as chemical modifications caused by cellular agents.
(low dose radiation, temperature, etc.)
② Harmful metabolites； （hydrogen peroxide, etc.) ③ DNA replication error.
(Tautomerism, etc.)
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4.1.2 Mechanism of mutagenesis
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4.1.1 Types of Mutations
(2) Single-point & multi-point mutation
Single-point is a type of mutation that causes a single nucleotide base change, insertion, or deletion of the genetic material, 4.1.1 Types of Mutations
(3) Synonymous &missense mutation
Synonymous mutations change the sequence of
a gene without directly altering the sequence of
between the planar bases of DNA.
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Nitrous acid
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Alkylating agents
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Ames test
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4.2 DNA repair
4.2.1 Photoreactivation
4.2.2 Base Excision Repair
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4.2.3 Nucleotide Excision Repair
(1) ATP hydrolysis forms UvrA/UvrB. UvrA/UvrB scans DNA to identify a distortion.
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4.2.3 Nucleotide Excision Repair
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Transition & Transversion mutation
Transition is a point mutation that changes a purine nucleotide to another purine (A↔G) or a pyrimidine nucleotide to another pyrimidine (C↔T). Transversion refers to the substitution of a (two ring) purine for a (one ring) pyrimidine or conversely in DNA.
Chapter 4
Gene mutation and exchange
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Contents
4.1 Gene mutation
4.2 DNA repair 4.3 DNA recombination 4.4 Transposition
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4.1 Gene mutation
Mutations are permanent, heritable alterations in the base sequence of the DNA. It is the main factor in biological evolution.
Nucleotide excision repair generally deals with
more drastic changes to bases, many of which distort the DNA double helix.
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4.2.4 Mismatch Repair
(1) mutH, L, and S genes along with ATP, recognize a base mismatch, identify the newly synthesized strand