Mutations Flashcards
(25 cards)
What is a mutation?
A permanent change in the DNA sequence.
What are the two main categories of mutations based on location in the body?
Somatic mutations and germ-line mutations
How are somatic mutations different from germ-line mutations?
Somatic mutations occur in body cells and are not inherited; germ-line mutations occur in gametes and can be passed to offspring.
What are the three types of DNA polymerase errors?
1) Base substitutions, 2) Insertions and deletions (indels), 3) Expanding nucleotide repeats.
What is a base substitution?
When one base is incorrectly replaced by another during DNA replication.
What is the difference between a transition and a transversion?
Transition = purine ↔ purine or pyrimidine ↔ pyrimidine;
Transversion = purine ↔ pyrimidine.
Which type of base substitution is more common—transition or transversion?
Transition.
Name 3 possible effects of base substitutions on proteins.
Neutral mutation, loss-of-function mutation, gain-of-function mutation.
What causes sickle cell disease at the molecular level?
A base substitution mutation changing glutamic acid to valine in hemoglobin.
What is a frameshift mutation?
A shift in the reading frame caused by insertion or deletion of a nucleotide not in multiples of 3.
What is a nonsense mutation?
A mutation that introduces a premature stop codon, leading to truncated, usually non-functional proteins.
What is cystic fibrosis caused by?
A nonsense mutation in the CFTR gene.
What are in-frame insertions or deletions?
Indels that occur in multiples of 3 bases, maintaining the reading frame.
What is an expanding nucleotide repeat?
A mutation where the number of repeated DNA sequences increases during replication.
Give 3 diseases caused by expanding nucleotide repeats.
Fragile X syndrome, Huntington’s disease, ALS (C9orf72 mutation).
What enzyme repairs thymine dimers caused by UV radiation?
Photolyase.
Name two types of physical mutagens.
Ionising radiation (e.g., X-rays), non-ionising radiation (e.g., UV light).
How does ionising radiation cause mutations?
It creates ions that break DNA strands, causing translocations and point mutations.
What damage does UV radiation cause to DNA?
Forms thymine dimers, leading to replication errors and mutations.
What are base analogues?
Chemicals that resemble normal DNA bases but pair incorrectly, causing mutations.
What is EMS (ethyl methanesulfonate)?
A chemical mutagen that modifies guanine to 6-ethylguanine, which pairs with thymine.
List advantages of EMS over nitrous acid.
Non-volatile, water-soluble, inactivates overnight for safe disposal.
What do base-modifying agents like nitrous acid do?
They chemically alter bases, changing their pairing behavior (e.g., C → U, A → hypoxanthine).
What are intercalating agents?
Chemicals that insert between DNA bases, distorting the helix and causing frameshift mutations.
