mutations topic 8 Flashcards
What is a gene mutation?
A change in the base sequence of DNA.
What can mutations affect?
The amino acid sequence of a polypeptide → may change protein structure/function → possible loss or gain of function.
Why don’t all mutations affect the amino acid sequence?
Due to the degenerate nature of the genetic code — more than one codon can code for the same amino acid.
What is substitution?
A base is swapped for another — may or may not change the amino acid.
What is insertion?
An extra base is added — usually causes a frameshift.
What is deletion?
A base is removed — often results in a frameshift.
What is duplication?
A section of DNA is copied and inserted.
What is inversion?
A sequence of bases is reversed.
What is translocation?
A section of DNA moves to another location in the genome — can disrupt multiple genes.
What causes a frameshift mutation?
Insertions, deletions, or duplications not in multiples of 3 — shifts the reading frame of codons, altering downstream amino acids.
What are mutagenic agents?
Environmental factors that increase the rate of mutation.
Examples of mutagenic agents?
UV radiation, ionising radiation, chemicals (e.g. base analogs), some viruses.
How do mutagenic agents increase mutation rate?
Act as base analogs – mimic bases and are inserted into DNA; alter or delete bases; disrupt DNA structure (e.g. UV causes thymine dimers).
What are transcription factors?
Proteins that control the transcription of specific genes by binding to DNA.
Where do transcription factors bind?
To specific DNA sequences near the target gene (often the promoter region).
Types of transcription factors?
Activators: increase transcription by helping RNA polymerase bind; Repressors: decrease transcription by blocking RNA polymerase binding.
How does oestrogen affect gene expression?
Binds to oestrogen receptor (a transcription factor); forms an oestrogen–receptor complex; moves into the nucleus and binds to DNA → acts as an activator of transcription.
How is oestrogen linked to cancer?
Can stimulate breast cell division, increasing mutation risk; may promote tumour growth by supporting rapid replication of existing cancer cells; possibly induces mutations directly in DNA of breast cells.
What is a stem cell?
An undifferentiated cell that can develop into specialised cell types.
What is cell differentiation?
The process by which a stem cell becomes specialised, involving changes in gene expression.
What are totipotent stem cells?
Can become any cell type, including placenta — only present in early embryo (first few divisions).
What are pluripotent stem cells?
Can become any body cell type, but not placenta cells — found later in embryo.
What are multipotent stem cells?
Can develop into a limited range of cells (e.g. adult bone marrow stem cells → RBCs, WBCs).
What are unipotent stem cells?
Can only differentiate into one specific cell type.
What are cardiomyocytes?
Heart muscle cells responsible for heart contraction.
Can cardiomyocytes regenerate?
They have limited ability to regenerate — thought to be slow and incomplete, with some cells never replaced.
How does gene expression control stem cell specialisation?
Only specific genes are expressed in a given cell type; these genes are transcribed and translated into proteins; proteins modify the structure/function of the cell → determines cell type.
What are iPS cells?
Specialised adult body cells reprogrammed to become pluripotent, similar to embryonic stem cells.
How are iPS cells made?
Introduce genes for transcription factors into adult cells; often done using viral vectors to insert transcription factor genes into the adult cell’s DNA.
Why are iPS cells useful?
They avoid ethical issues of using embryos and offer potential for regenerative medicine.
How are stem cells used to treat disease?
Bone marrow transplants for conditions like SCID or sickle cell anaemia; research into treating spinal cord injuries, heart disease, type 1 diabetes, etc.
Ethical issues with stem cell use?
Use of embryos raises debates around the moral status of the embryo.
