Flashcards in Topic 3 - Origins Of Mutation Deck (15):
In terms of heritability and evolutionary change, what is the essential difference between germ-line and somatic cells?
The germ-line cells contribute to the next generation via the production of gametes, while the somatic cells do not. Thus mutations in germ-line cells are inherited by the offspring, while mutations in somatic cells are not.
recall the enzyme that is essential to DNA replication.
What are pseudogenes?
Non-functional copies of a gene, which, if transcribed, produce an inactive protein.
Why are pseudogenes useful for studying the rate at which DNA sequences acquire mutations?
Unlike expressed and functional genes, pseudogenes do not express a product. There is therefore no selection against sequence changes in a pseudogene.
Explain misincorporation in DNA replication.
Occasionally an incorrect nucleotide is incorporated in the nascent (growing) DNA strand. This may occur purely by chance, or as a result of a chemically damaged nucleotide residue in the template strand permitting an inappropriate base pairing with the incoming nucleotide.
Why might errors in DNA replication have a more severe effect on an organism than errors in transcription or translation?
Errors in DNA replication are perpetuated through subsequent cell divisions (and indeed, where they occur in the germ line, are carried on to the next generation), whereas transcription and translation errors are not.
What might you expect the consequences to be of replacing a cytosine base with a uracil base?
Uracil (like thymine, its counterpart in DNA) pairs with adenine, and uncorrected deamination of cytosine to uracil will lead to a change from a C:G base pair to a U:A base pair in the first round of replication.
What is an apurinic site?
Where a purine base has been lost from a DNA strand.
What effect would a single base pair deletion in an open reading frame have on the gene?
A single base pair deletion would cause a frameshift.
Explain base excision repair (BER)
The process of scanning and removal of single damaged bases or nucleotides, particularly depurinated or deaminated bases.
Explain nucleotide excision repair (NER)
A DNA repair mechanism that recognises damaged or modified bases (such as thymidine) and excises the damaged nucleotide prior to repair of the DNA molecule.
Explain mismatch repair (MMR)
A form of DNA repair that identifies mismatched bases in a DNA molecule and replaces the mismatched base with the correct base.
Explain non-homologous end-joining (NHEJ) in DNA repair
A mechanism of double-strand break repair that does not make use of sequence homology between the DNA termini that are joined.
Explain homologous end-joining in DNA repair
A mechanism of double-strand break repair that uses the double helix of a homologous chromosome to guide accurate repair.