Gene Mutations

What is a synonymous mutation?

A nucleotide substitution that changes a codon but still specifies the same amino acid.

What is a missense mutation?

A nucleotide substitution that changes a codon so it specifies a different amino acid.

What is a nonsense mutation?

A nucleotide substitution that converts an amino-acid codon into a stop codon, causing premature translation termination.

What is a frameshift mutation?

An insertion or deletion that changes the reading frame, usually altering many downstream amino acids.

What is the difference between synonymous and missense mutations?

Synonymous mutations do not change the amino acid, while missense mutations change one amino acid.

What is the difference between missense and nonsense mutations?

Missense mutations substitute one amino acid for another, while nonsense mutations create a premature stop codon.

What is a transition mutation?

A base substitution between bases of the same category

What is a transversion mutation?

A base substitution between different categories

What are the purines?

Adenine (A) and guanine (G).

What are the pyrimidines?

Cytosine (C) and thymine (T) in DNA; uracil (U) replaces thymine in RNA.

What is the difference between transitions and transversions?

Transitions exchange bases within the same category, while transversions exchange bases between different categories.

What is a promoter mutation?

A mutation affecting a promoter that changes transcription initiation or the amount of RNA produced.

What is a splicing mutation?

A mutation affecting RNA processing that can cause improper intron removal or exon exclusion.

What is a polyadenylation mutation?

A mutation affecting the 3′ processing signal that can interfere with proper mRNA processing and poly-A tail addition.

What is the difference between coding and regulatory mutations?

Coding mutations affect the protein-coding sequence, while regulatory mutations affect gene expression or RNA processing.

What is a spontaneous mutation?

A mutation that occurs naturally without exposure to an external mutagen, often due to replication errors or chemical changes in DNA.

What is an induced mutation?

A mutation caused by exposure to mutagenic agents, such as certain chemicals or radiation.

What is the difference between spontaneous and induced mutations?

Spontaneous mutations occur naturally, while induced mutations result from exposure to mutagens.

What is a base analog?

A chemical that resembles a normal nucleotide and can be incorporated into DNA, potentially causing incorrect base pairing.

What are examples of base analogs?

5-bromouracil (5-BU) and 2-aminopurine (2-AP).

What is a deaminating agent?

A chemical that removes amino groups from DNA bases, potentially changing their base-pairing properties.

What is an example of a deaminating agent?

Nitrous acid.

What is an alkylating agent?

A chemical that adds alkyl groups, such as methyl or ethyl groups, to DNA bases and can interfere with normal base pairing.

What is an example of an alkylating agent?

Ethyl methanesulfonate (EMS).

What is an oxidizing agent?

A chemical or reactive molecule that oxidizes DNA bases, potentially causing incorrect base pairing or DNA damage.

What is an example of an oxidizing agent?

Oxygen radicals.

What is a hydroxylating agent?

A chemical that adds hydroxyl groups to DNA bases, potentially changing their pairing properties.

What is an example of a hydroxylating agent?

Hydroxylamine.

What is an intercalating agent?

A chemical that inserts between DNA base pairs, distorting the DNA structure and potentially causing insertions or deletions during replication.

What are examples of intercalating agents?

Acridine orange and proflavin.

What is photoreactivation repair?

A repair mechanism in which photolyase uses visible light energy to reverse UV-induced DNA photoproducts.

What does photoreactivation repair fix?

UV-induced DNA damage, especially pyrimidine dimers.

What is base excision repair (BER)?

A DNA repair pathway that removes an individual damaged or incorrect base and replaces it.

What is nucleotide excision repair (NER)?

A DNA repair pathway that removes a stretch of nucleotides containing bulky DNA damage and replaces the removed section.

What is mismatch repair?

A repair pathway that corrects incorrectly paired nucleotides left behind after DNA replication.

What is the main difference between BER and NER?

BER removes an individual damaged base, while NER removes a larger section of DNA containing the damage.

What is the first step of base excision repair?

DNA glycosylase recognizes and removes the damaged base, leaving an AP site.

What is an AP site?

An apurinic or apyrimidinic site where a DNA base is missing but the sugar-phosphate backbone remains.

What happens after an AP site forms?

AP endonuclease cuts the DNA backbone near the AP site.

What happens after AP endonuclease cuts the DNA?

DNA polymerase fills the gap with the correct nucleotide.

What is the final step of base excision repair?

DNA ligase seals the sugar-phosphate backbone.

What is the first step of nucleotide excision repair?

Proteins recognize a damaged or distorted region of DNA.

What happens after the damaged region is recognized?

Nucleases cut the DNA strand on both sides of the damaged section.

What happens after the damaged DNA section is removed?

DNA polymerase fills the gap using the undamaged strand as a template.

What is the final step of nucleotide excision repair?

DNA ligase seals the DNA backbone.

What enzyme begins base excision repair?

DNA glycosylase.

What enzyme cuts near the AP site during base excision repair?

AP endonuclease.

What enzymes fill and seal the gap during base excision repair?

DNA polymerase fills the gap, and DNA ligase seals the backbone.

What is the main difference in the damage removed by BER and NER?

BER removes one damaged base, while NER removes a stretch of nucleotides.

What did the Luria and Delbrück experiment demonstrate?

Bacterial resistance mutations occur randomly before exposure to a selective agent rather than being produced because bacteria need resistance.

What is a germ-line mutation?

A mutation occurring in reproductive cells or their precursors that can be passed to offspring.

What is a somatic mutation?

A mutation occurring in nonreproductive body cells that is generally not inherited by offspring.

What is the difference between germ-line and somatic mutations?

Germ-line mutations can be inherited by offspring, while somatic mutations generally affect only the individual.

What is a forward mutation?

A mutation that changes a normal or wild-type allele into a mutant allele.

What is a true reversion?

A second mutation that restores the original DNA sequence and usually restores the original phenotype.

What is an intragenic reversion?

A second mutation within the same gene that compensates for the original mutation and restores the phenotype without necessarily restoring the original DNA sequence.

What is a second-site suppressor mutation?

A mutation at a different location that compensates for the effects of the original mutation and restores some or all of the normal phenotype.

What is strand slippage?

A replication error in which DNA strands misalign, potentially producing insertions or deletions.

What is depurination?

The spontaneous removal of a purine base (adenine or guanine) from DNA.

What is deamination?

The removal of an amino group from a DNA base, potentially changing its base-pairing properties.

What is incorrect base pairing?

A situation in which DNA bases pair incorrectly, potentially producing a mutation during replication.

What is trinucleotide repeat expansion?

An increase in the number of repeated three-nucleotide DNA sequences, which can cause genetic disorders.

What are thymine dimers?

UV-induced covalent bonds between adjacent thymine bases that distort DNA and interfere with replication and transcription.

What are 6-4 photoproducts?

UV-induced DNA lesions formed between adjacent pyrimidines that distort DNA structure and interfere with DNA replication and transcription.

What activates p53 after DNA damage?

ATM kinase can activate p53 through phosphorylation and related signaling pathways.

What is the role of p53?

A tumor suppressor protein that responds to DNA damage by regulating cell-cycle arrest, DNA repair, and apoptosis.

How does p53 respond to DNA damage?

It can pause the cell cycle to allow DNA repair to occur.

Why does p53 cause cell-cycle arrest?

It prevents damaged DNA from being replicated or passed to daughter cells before repair can occur.

What happens if DNA damage cannot be repaired?

p53 can trigger apoptosis, or programmed cell death, to prevent severely damaged cells from surviving and potentially becoming cancerous.