BIOL 141 Lecture Notes - Lecture 18: Signal Transduction, Angiogenesis, Cell Type
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Wednesday, November 8, 2017
BIOL141
•Mutation = change in DNA sequence (error/mistake in DNA or something different
from template)#
•Causes of mutations:#
•Spontaneous - e.g.: polymerase error during replication#
•Replication errors: prevention by proofreading, or repair of replication errors by
mismatch repair#
•Mismatch repair:#
•1- recognize mistake#
•2-cut it out#
•3- try again#
•Induced - e.g.: UV radiation (environment / lifestyle)#
•UV radiation - repair by photoreactivation or nucleotide excision repair (NER)#
•Causes a pyrimidine dimer#
•Kink in DNA, blocks transcription and replication#
•Xeroderma pigmentosum (XP) - lack of repair leads to cancer#
•Nucleotide excision repair:#
•1- enzymes detect an irregularity in DNA structure and cut the damaged
strand#
•2- an enzyme excises nucleotides on the damaged strand#
•3- DNA polymerase fills in the gap#
•4- DNA ligase links the new and old nucleotides#
•Reversal (photoreactivation) - not in placental mammals#
•HNPCC - defect in MMR genes, so no repair, errors remain, leads to cancer#
•BRCA1 and BRCA2 - tumor suppressor genes involved in DNA repair, defects lead
to cancers#
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