✅20 - Gene Expression Flashcards
What is a mutation?
Any change to the quantity or the structure of the DNA of an organism
What is a gene mutation?
Any change to one or more nucleotide bases or any rearrangement of the bases in DNA
What is substitution?
A nucleotide in a section of DNA is replaced by another nucleotide that has a different base
What are the three possible consequences for substitutions?
- The formation of a stop codon which leads to the end of the polypeptide chain
- The formation of a codon for a different amino acid, meaning that the structure of the polypeptide produced would differ and potentially be non functional
- The formation of a codon that produced the same amino acid, no change
What is deletion?
The loss of a nucleotide from the DNA sequence
What can deletion cause?
Frame shift to the left
What is addition?
An extra base becomes inserted into the sequence
What does addition cause?
Frame shift to the right
In what case will frame shift not occur with an addition mutation?
If three bases are added consecutively, to form a new codon
What is duplication?
One or more bases are repeated
What does duplication produce?
Frame shift to the right
What is inversion of bases?
A group of bases becomes separated from the DNA sequence and rejoin at the same position but the the inverse order
What is translocation?
A group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome
What effect can translocations have?
Significant effects on gene expression leading to an abnormal phenotype effecting the development of some types of cancer and reduced fertility
What can cause gene mutations?
They can be random, or caused by mutagenic agents
Typically how many mutations occur per generation in most species?
1 or 2 in every 100,000 genes
What are some mutagenic agents?
High energy ionising radiation
Chemicals
How can high energy ionising radiation act as a mutagenic agent?
They can disrupt the structure of DNA
How can chemicals act as mutagenic agents?
Chemicals such as nitrogen dioxide may directly alter the structure of DNA or interfere with transcription. Some chemicals in cigarette smoke can inactivate tumour suppressor genes
What are totipotent cells?
Ones which can differentiate into any type of body cell
In what ways can gene be ‘switched off’ in a cell?
By preventing transcription and so preventing the production of mRNA
By preventing translation
What are stem cells?
Undifferentiated dividing cells that occur in adult animal tissues and need to be constantly replaced
What are the sources of stem cells in mammals?
Embryonic stem cells
Umbilical cord blood stem cells
Placental stem cells
Adult stem cells
What are adult stem cells?
Found in the body tissues of the fetus through to the adult. Specific to a particular tissue or organ in which they produce the cells to maintain and repair tissues throughout the organisms life
What are the types of stem cells?
Totipotent stem cells
Pluripotent stem cells
Multipotent stem cells
Unipotent stem cells
What are totipotent stem cells?
Ones which can differentiate into any type of cell, including placental cells
What are pluripotent stem cells?
Ones which can differentiate into any type of body cell
What are multipotent stem cells?
Can differentiate into a limited number of specialised cells
What are unipotent cells?
Can only differentiate into a single type of cell
What are induced pluripotent stem (iPS) cells?
A type of pluripotent cell produced from unipotent stem cells
How are iPS cells created?
They are genetically altered to make them acquire the characteristics of an embryonic stem cell. Genes and transcriptional factors are induced to make this happen.