Topic 8 - Mutations and Gene Expression Flashcards
when does mutation occur
dna replication
what is a duplication mutation
one or more bases are repeated
always causes a frame shift
what is an inversion mutation
a sequence of bases is reversed
what is translocation mutation
- a sequence of bases is moved from one location in the genome to another
- could be within a same chromosome or a different one
how can mutagenic agents increase the rate of mutations
- acting as a base - chemicals callled base analogs can substitute for a base during dna replication, changing the sequence
- altering bases - some chemicals can delete or alter bases
- changing th structure of DNA - Some types of radiation can change the structure of DNA which causes problems during replication
what are stem cells
undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism
where are stem cells found in humans
embryo
stem cells
what are totipotent stem cells
- stem cells that can differentiate into any type of body cell including the placenta
- they are only present in the first few cell divisions of an embryo
what are pluripotent stem cells
- stem cells that can specialise into any cell in the body but cannot make up the placenta
what are unipotent stem cells
- stem cells that can only differentiate into one type of cell
what are multipotent stem cells
- stem cells that can differentiate into a few different types of cells
how do stem cells become specialised
- mRNA is only transcribed for specific genes
- the mRNA is then translated into proteins
- These proteins modify the cell - they determine the cell structure and control cell processes
- changes to the cell produced by the proteins cause the cell to become specialised
- these changes are difficult to reverse
what is an example of a unipotent stem cells
cardiomyocytes
what are cardiomyocytes
- heart muscle cells that make up the tissue in our hearts
- some scientists think that old or damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart
how are stem cells used to treat disease
- bone marrow transplant
- stem cells divide and specialise into healthy cells
what type of stem cells are in bone marrow
multipotent
how are embryonic stem cells extracted
- embryos created in a lab using IVF - egg cell is fertilised outside thw womb
- once the embryos are 4-5 days old stem cells are removed from them and the rest of the embryo is destroyed
- embryonic stem cells can divide an unlimited number of times and develop into all types of body cells - pluripotent
what are induced pluripotent stem cells
- reprogramming specialised adult body cells so they become pluripotent
- the adult cells are made to express a series of transcription factors that are associated with pluripotent stem cells
- one of the ways that these can be introduced is by infecting them with a modified virus
why do organisms carry the same genes but the structure and function of cells varies
- different genes are expressed
- different proteins are made
- these proteins modify the cell
- they determine cell processes and structure
what is transcription controlled by
transcription factors
how do activator transcription factors work
- in eukaryotes, transcription factors move from the cytoplasm to the nucleus
- in the nucelus they bind to specific DNA sites near the start of their target genes - the genes they control the expression of
- some transcription factors called activators stimulate or increase the transcription, e.g. help RNA polymerase bind to the start of the target genes
how do repressor transcription factors work
- decrease the rate of transription
- they bind to the start of the target gene
- preventing RNA polymerase from binding, stopping transcription
how does oestrogen initiate transcription of a target cell
- oestrogen is a steroid hormone that binds to a oestrogen receptor forming an oestrogen-oestrogen receptor complex
- the complex moves from the cytoplasm into the nucleus where it binds to specific DNA sites near the start of the target gene
- the complex can act as an activator of transcription
what is RNA interference
inhibits the translation of mRNA
how does RNA interference work in plants
- once mRNA has been transcribed, it leaves the nucleus for the cytoplasm
- in the cytoplasm, double stranded siRNA associated with several proteins and unwinds
- a single strand then binds to the target mRNA
- the base sequence of the siRNA is complimentary to the base sequence in sections of the target mRNA
- the protein associates with the siRNA cut the mRNA into fragments so it can no longer be translated.
- the fragmets move into a processing body which containes tools to degrade them
how does miRNA work in mammals
- the miRNA isnt usually fully complimentary to the target mRNA
- this makes it less specific than siRNA and so it may target more than one mRNA molecule
- it associates with proteins and binds to target mRNA in the cytoplasm
- mRNA protein complex blocks the translation of the target mRNA
- the mRNA is then moved into a processing body where it can either be stored or degraded
- when its stored it can be returned and translated at another time
