Genetics Flashcards
What are mutations?
Changes in the base sequences in DNA
Can be harmful, beneficial or have no effect
What are the 3 main types of mutation in terms of changes to the DNA?
Insertion, deletion and substition
What are 3 main types of mutation in terms of effects of the mutation?
Silent, nonsense, missense
What is insertion and deletion and give an example of a disease caused by each
Insertion is the addition of an extra nucleotide into the DNA sequence (Huntington’s disease)
Deletion is the removal of a nucleotide (or more than one) from a DNA base sequence (cystic fibrosis)
What is substitution? name a disease caused by this type of mutation
When one nucleotide is exchanged for another (sickle cell anaemia)
What is frameshift?
When insertion and deletion mutations change many codons along the DNA sequence due to them all shifting one or more places left or right - more harmful than substitution mutations
What is a silent mutation?
A mutation in a non-coding region or that produces a different codon for the same amino acid (due to the degenerate code) that has no effect.
What is a nonsense mutation?
A mutation that changes a codon into a stop codon, leading to a shorter polypeptide, which can be very harmful
What is a missense mutation?
A mutation that introduces at least one new amino acid into a protein’s primary structure, which is usually harmful but potentially beneficial or neutral
What are mutagens?
Factors which increase the rate of mutations. Can be biological (e.g. viruses), chemical or physical (e.g. radiation)
What is gene expression?
When a sequence of codons is transcribed and translated into a polypeptide
How can gene expression be controlled at the transcription stage?
- Altering the structure of chromatin (heterochromatin- no
transcription occurs, euchromatin - transcription can
occur) - Transcription factors (molecules that bind to DNA to
either promote or prevent transcription - Epigenetics - acetylation of histones increases
transcription rates, methylation of DNA prevents
transcription - Operons - genes switched off when repressor binds to
operator region, which blocks a promoter region,
preventing RNA polymerase binding and stopping the
transcription of structural genes - genes are switched on
when the repressor is removed
When does heterochromatin form and how is the DNA wound around the histones?
During cell division - DNA wound tightly around histones - no transcription occurs
When does euchromatin form and how is the DNA wound around the histones?
During interphase - DNA wound loosely around histones - transcription can occur
How can gene expression be controlled at the post transcription stage?
mRNA processing - splicing - introns (non-coding DNA) are removed from mRNA. Different polypeptides can be formed by retaining some introns and rearranging exons
mRNA editing - mRNA can be edited by adding, deleting, or substituting nucleotides
