Studied by 1 personwhat does gene expression do?
control how different tissues and organs are produced
what must happen for a gene to be expressed?
production of mRNA translation of mRNA polypeptide protein production
which methods of controlling gene expression are epigenetic modification?
destruction of mRNA DNA methylation histone acetylation
how do DNA regulatory sequences and transcription factors control gene expression?
typically turn a gene on by allowing RNA polymerase to attach to transcription factors attached to regulatory sequences
what do promoters do?
enable RNA polymerase to bind to the gene
what do enhancers do?
stimulate promoters causing an increase in the rate of transcription
why do both types of regulatory sequences lie upstream of the gene they regulate?
ensure the correct gene is read and transcribed
what does alternative splicing produce?
isoforms
what are isoforms?
different arrangements of exons in mature mRNA transcribed from a single gene, which results in different polypeptides
how does alternative splicing control gene expression?
alternative splicing turns genes off if done incorrectly and on if done correctly
what is post-transcriptional modification of mRNA?
alternative splicing results in different arrangements of exons in mature mRNA, which creates different polypeptides and these turn genes on or off if done correctly or incorrectly
how is mRNA destroyed?
small non-coding sections of RNA ensure that mRNA can be destroyed so it never gets translated
what is the complex that destroys mRNA?
RISC - RNA induced silencing complex
what does miRNA (microRNA) do?
causes mRNA to be hydrolysed and causes disruption of mRNA so it can't be translated and results in no gene expression
what happens after mRNA binds to RISC?
mRNA is degraded if bases extensively match mRNA is disrupted by forming bulges if bases do not extensively match
what happens if mRNA is hydrolysed or bulged?
cannot be translated, so the gene is not expressed
how is siRNA (small inhibitory RNA) formed?
a dicer (type of RNA hydrolyse) hydrolysed the dsRNA (double stranded RNA) and forms lengths of 20 bases - these small pieces are siRNA
how does siRNA hydrolyse mRNA?
siRNA binds to protein and forms a RISC, which unwinds the siRNA - one strand is lost and the other remains bound in the RISC siRNA strand binds to target mRNA strand and mRNA is hydrolysed
how is histone acetylated?
histone are grouped into nucleosomes and have tails containing leucine leucine can be acetylated by CoA
how does acetylation change gene expression?
acetylation causes nucleosomes to become more loosely packed, which frees/exposes the gene and allows transcription factors and RNA polymerase to access it
what happens if there is no histone acetylation?
nucleosomes are tightly packed and transcription factors and RNA polymerase cannot access the gene
how does DNA methylation change gene expression?
prevents base sequence from being transcribed when cytosine is methylated in vertebrates
where does methylation normally happen?
in a base sequence where C is next to G (CpG)
where is CpG commonly located and what effect does this have?
near promoter regions, which prevents activation of RNA polymerase and target gene is silenced
what do restriction enzymes do?
hydrolyse phosphodiester bonds to form double stranded fragmemts of DNA
what do restriction enzymes do in bacteria?
protect against bacteriophages by restriction multiplication of phage viruses
why are sticky ends needed?
because they bind to other DNA molecules, whereas blunt ends don't
what must happen before a DNA fragment can be cloned?
it must be added to a vector
why are plasmids used as a vector?
more numerous, easier to isolate, and easier to reintroduce when the plasmid replicates, any copies will be passed on to daughter cells during binary fission
why is the same restriction endonuclease used to cut the plasmid and the DNA fragment?
ensures the sticky ends created are complimentary and the plasmid and DNA fragment can join together
which enzyme joins the plasmid and the DNA fragment and what is this process called?
DNA ligaments joins the two fragments together in a process called annealing
what is annealing?
formation of phosphodiester bonds between plasmid and DNA fragments following alignment of the complimentary base pairs
how is the transfer of recombinant DNA encouraged?
soaking in ice cold sodium chloride followed by heat shock at 42oC for two minutes
promoters
regulatory sequence which lie close to target genes start transcription by enabling RNA polymerase to bind to the gene
enhancers
regulatory sequence that lie at a distance from target genes stimulate promoters causing an increase in the rate of transcription
why do regulatory sequences lie upstream of the gene they regulate?
so that the correct gene is read and transcribed
alternative splicing
different arrangements of exons in mature mRNA transcribed from a single gene, which results in different polypeptides
sticky ends and blunt ends
sticky ends bind more readily to other DNA molecules blunt ends are made into sticky ends during in vivo methods of DNA amplification
why are plasmids used as a vector?
more numerous, easier to isolate, easier to reintroduce replicates and any copies will be passed on to daughter cells during binary fission
how can the transfer of recombinant DNA be encouraged?
soaking in ice cold sodium chloride followed by heat shock at 42oC for 2 minutes - discovered by trial and error
transformation
once a plasmid has been taken up by bacteria
DNA ligase
an enzyme which catalyses the formation of phosphodiester bonds between DNA fragments which is used to join okazaki fragments in the lagging strand during replication DNA ligase can be used to join fragments cut by restriction endonucleases during genetic engineering
gene gun
a method of injecting DNA combined with metals into a cell (typically a plant cell) using propulsion
knockout mice
laboratory mice which have had gene(s) removed or inactivated and are used in studies to identify the function of the knockout genes and the effect of harmful mutations in those genes
marker genes
specific detectable genes which are inserted along with other genes during the creation of a transgenic organism so that the organisms which successfully took up the other genes can be identified
recombinant DNA
artificially modified DNA which is made by the combination of genes from different sources
restriction endonucleases
enzymes which break double stranded DNA at specific sequences which are used in genetic engineering
transgenic organism
an organism which has had foreign genetic material inserted into its genome
vector (gene technology)
a carrier such as a virus or gene gun which is used for insertion of foreign DNA into an organism
induced pluripotent stem cells (iPS cells)
pluripotent stem cells produced artificially by the reprogramming of somatic cells through the introduction of genes
multipotent stem cell
a type of stem cell which has the ability to differentiate into any cell type within a certain tissue in the body
pluripotent stem cell
a type of stem cell which has the ability to differentiate into any cell type in the body
totipotent stem cell
a type of stem cell which has the ability to differentiate into any type of cell in the body or in the placenta
stem cell
an undifferentiated cell that can divide indefinitely to produce a given range of specialised cells+
DNA methylation
the addition of methyl groups to DNA molecules as a method of epigenetic modification
epigenetic modification
heritable changes to gene expression brought about without changing the original sequence of bases that compose the DNA molecules
gene expression
the transcription (and often subsequent translation) of genes
histone acetylation
the addition of negative acetyl groups to histones which loosens their binding to DNA, allowing for transcription
histone deacetylation
the removal of negative acetyl groups from histones which means the histone proteins can bind more tightly to DNA which restricts transcription
histone modification
changes made to histone proteins through the addition or removal of chemical groups which affect gene expression
histone proteins
positively charged proteins which bind to and package DNA and can be a target of epigenetic modification
non-coding RNA
RNA molecules which have been transcribed but are not translated to produce proteins
post-transcriptional modification
the production of mature mRNA from pre-mRNA through splicing
transcription factors
proteins which bind to regulatory regions of DNA and control DNA transcription
DNA amplification
the production of many copies of DNA from a small starting amount
DNA profiling
a method of comparing DNA sequences by splitting DNA sections into fragments and comparing the fragments with each other for genetic identification or determining genetic relationships
gene sequencing
the process of determining the specific order of nucleotides in a sequence of DNA
genome
all the genetic information within an organism
genomics
the study of structure and function of the genome
polymerase chain reaction (PCR)
a laboratory technique used to amplify DNA using Taq polymerase, primers, free nucleotides and a buffer
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