Mutations Flashcards
(40 cards)
What is a gene mutation?
A gene mutation is a change in the nucleotide sequence of DNA that can affect how genes function.
What causes most gene mutations?
Mistakes made by DNA polymerase during DNA replication.
What are the two main types of mutations based on where they occur?
Somatic mutations and germline mutations.
What is a somatic mutation?
A mutation that occurs in somatic (non-reproductive) cells and is not passed to offspring.
What is a germline mutation?
A mutation that occurs in gametes (sperm or egg) and can be inherited by offspring.
Are most mutations harmful?
No, most mutations have no obvious effect and may even contribute to natural variation.
What can somatic mutations lead to if they affect certain genes and replicate rapidly?
Cancer.
What are proto-oncogenes?
Genes that normally regulate normal cell growth and division. When mutated, they can become oncogenes and lead to cancer.
What are tumor suppressor genes?
Genes that slow down cell division or trigger cell death; when mutated, they may allow uncontrolled cell growth.
Are mutations in oncogenes usually dominant or recessive?
Dominant – one mutated copy is enough to affect cell function.
Are mutations in tumor suppressor genes usually dominant or recessive?
Recessive – both copies must be mutated to affect cell control.
What are the two main types of base substitutions?
Transitions (purine↔purine or pyrimidine↔pyrimidine) and transversions (purine↔pyrimidine).
Which type of substitution is more common and often silent?
Transitions; due to similar chemical structures and often leading to synonymous codons.
What are the outcomes of base substitutions?
Silent Mutation – No change in amino acid
Missense Mutation – Change in amino acid
Nonsense Mutation – Introduces premature stop codon
What are the types of missense mutations?
Neutral – Changes amino acid with little/no effect on function
Loss-of-function – Disrupts protein function
Gain-of-function – Enhances or alters protein activity (often dominant)
What is the molecular cause of sickle cell anemia?
A missense mutation in the hemoglobin gene changes glutamate to valine, causing red blood cells to sickle.
What are indels and how do they affect proteins?
: Insertions or deletions of bases; can cause frameshifts that drastically alter protein function.
What is a frameshift mutation?
A shift in the reading frame caused by insertion/deletion not in multiples of 3, altering downstream amino acid sequence.
What is the effect of insertions/deletions in multiples of 3?
No frameshift occurs, but the protein may gain/lose one amino acid, which can still affect function.
What is cystic fibrosis caused by at the molecular level?
A premature stop codon or deletion causing a truncated, non-functional CFTR protein.
What are trinucleotide repeat expansions?
Repeats of 3-base sequences (e.g., CAG) that expand abnormally during replication, causing disorders.
What is the molecular basis of Fragile X syndrome?
Expansion of CGG repeats on the X chromosome leading to hypermethylation and transcriptional silencing.
What is the molecular basis of Huntington’s disease?
CAG repeat expansion encoding polyglutamine stretches that form toxic protein aggregates in neurons
How do repeat expansions cause disease?
By producing toxic proteins or silencing gene expression through methylation and chromatin compaction.
