CHMI-2227EL Lecture Notes - Lecture 20: Reverse Transcriptase, Francis Crick, Sos Response
27 Jun 2018
School
Course
Professor
Biochemistry - Day 20 2018.04.04.
DNA Repair Mechanisms (Continued)
-2- Nucleotide excision repair removes large lesions like thymine
dimers and bases with bulky side groups from DNA
-In this type of repair:
-A unique excision nuclease activity cuts on either side of the
damaged nucleotide(s)
-Excises an oligonucleotide containing the damaged base(s)
-The nuclease is called excinuclease
-Defective DNA repair mechanisms can lead to severe pathological
conditions
-Xeroderma pigmentosum (XP; Greek: xeros, dry + derma, skin)
-A rarely hereditary disease in humans
-Believed to be due to a deficiency of the endonuclease that
introduce nicks into damaged sections of DNA
-Patients exhibit abnormal sensitivity to sunlight
-Thymine dimers, produced by UV light are not repair
-Continuous skin cell death
-Skin cancer development often fatal
-Cockayne syndrome (CS)
-An inherited disease associated with defective nucleotide excision
repair
-Patients are hypersensitive to UV light
-Exhibit stunted growth
-Neurological dysfunction (neuron demyelination)
-Normal incidence of skin cancer
-3) Mismatch DNA Repair
-This system corrects error introduced during DNA replication by
identifying mismatched nucleotides
-The mechanism is based on the occurrence of methylated bases of
DNA
-During replication, parental DNA is fully methylated
-Daughter DNA strands remain unmethylated for a brief period of time
-Because DNA methylation lags behind DNA synthesis
-The mismatch repair system has the capacity to recognize
-Unmethylated sequences
-Mismatched base pairs in the newly synthesized daughter strand
-Recognition of unmethylated sequences serves to target that strand
-The mechanism of repair involves excising a segment of the daughter strand
(adjacent to the unmethylated sequence) and includes the mismatched
-The excised segment is then replaced by a new segment containing the correct
base
-4) SOS repair
-Emergency repair
find more resources at oneclass.com
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Document Summary
2- nucleotide excision repair removes large lesions like thymine dimers and bases with bulky side groups from dna. A unique excision nuclease activity cuts on either side of the damaged nucleotide(s) Excises an oligonucleotide containing the damaged base(s) Defective dna repair mechanisms can lead to severe pathological conditions. Xeroderma pigmentosum (xp; greek: xeros, dry + derma, skin) Believed to be due to a de ciency of the endonuclease that introduce nicks into damaged sections of dna. Thymine dimers, produced by uv light are not repair. An inherited disease associated with defective nucleotide excision repair. This system corrects error introduced during dna replication by identifying mismatched nucleotides. The mechanism is based on the occurrence of methylated bases of. During replication, parental dna is fully methylated. Daughter dna strands remain unmethylated for a brief period of time. Because dna methylation lags behind dna synthesis. The mismatch repair system has the capacity to recognize. Mismatched base pairs in the newly synthesized daughter strand.
