Gene Expression Flashcards
What is a mutation?
An alteration to the DNA base sequence. Often arise during DNA replication
What are addition and deletion mutations?
Where one or more nucleotides are either inserted or deleted from the DNA sequence
What is a substitution mutation?
Where one nucleotide in the DNA sequence is replaced by another
What is a duplication mutation?
Where one or more nucleotides duplicate and repeat
What is an inversion mutation?
Where a group of nucleotides become separated from the DNA sequence then rejoin in the reverse order i.e they have flipped
What is a translocation mutation?
Where a group of nucleotides become separated from the DNA sequence and are then inserted into the DNA of a different chromosome
Which mutations are most likely to have a significant impact and why?
Insertion, deletion, duplication and translocation because they produce a frameshift meaning the entire amino acid sequence produced will be different
Which mutations are less likely to have a significant impact and why?
Substitution and inversion because they only alter one or very few triplets, the amino acid sequence might not be affected due to the degenerate nature of the genetic code
Is a mutation resulting in a change to the amino acid sequence always harmful?
No; may be neutral if the resulting change in protein has no effect on the organism
Also may be beneficial which is the basis for evolution and natural selection
What is a mutagenic agent?
Factors that increase the rate of gene mutation. Chemical mutagens such as alcohol and ionising radiation such as UV and X ray
What is a stem cell?
Undifferentiated cells that can divide indefinitely and turn into other specific cell types
Name and define the three types of stem cell
Totipotent = can develop into any cell type including the placenta and embryo
Pluripotent = can develop into any cell type excluding the placenta and embryo
Multipotent = can only develop into a few different types of cell
What happens to totipotent cells during embryonic development?
Certain parts of the DNA are selectively translated so that only some genes are switched on in order to differentiate the cell into a specific type and form the tissues that make up the foetus
Give a unique feature of pluripotent cells and the use of this feature
They can divide in unlimited numbers and can therefore be used to repair or replace damaged tissue
What is a unipotent cell, give an example
A cell that can only develop into one type of cell. This happens at the end of specialisation when the cell can only propagate its own type. An example is cardiomyocytes (heart cells)
Which type of stem cells are found in embryos?
Totipotent and pluripotent
Multipotent and unipotent are only found in mature mammals
Give some uses of stem cells
Medical therapies e.g bone marrow transplants
Drug testing on artificially grown tissues
Research e.g on embryos
How are induced pluripotent stem cells produced?
From mature, fully specialised cells. The cell regains capacity to differentiate through the use of proteins, in particular transcription factors
What is a transcription factor?
A protein that controls the transcription of genes so that only certain parts of the DNA are expressed
How do transcription factors work?
- Move from the cytoplasm into nucleus
- Bind to promoter region upstream of target gene
- Makes it easier or more difficult for RNA polymerase to bind to the gene. This increases or decreases rate of transcription
Give an example of a hormone that affects transcription and explain how it works
- Steroid hormone oestrogen diffuses through cell membrane
- Forms hormone receptor complex with ER a receptor in the cytoplasm
- Complex enters the nucleus and acts as transcription factor to facilitate binding of RNA polymerase
What is meant by epigenetics?
A heritable change in gene function without change to the base sequence of DNA
How does increased methylation of DNA affect gene transcription?
Involves addition of CH3 group to cytosine bases which are next to guanine. Prevents transcription factors from binding. Therefore gene transcription is suppressed
How does decreased acetylation of histones affect gene transcription?
Positively - charged histones are positively charged bind to negatively charged DNA. Decreasing acetylation increases positive charge of histones.
Binding becomes too tight and prevents transcription factors from accessing the DNA. Therefore gene transcription is suppressed
