7.2 Factors affecting gene expression Flashcards
why does cell differentiation take place
to form different tissues and organs, and so different cells can go on to produce proteins specific to their cell types
how do scientists measure different degrees of cell differentiation
gel electrophoresis
how would a scientists find a known gene out of all the genes present in the DNA of a cell
- they use gene probes, which allow a specific section of DNA and mRNA in a cell to be identified
- the gene probe finds the unique sequence of nucleotides in DNA that make up the gene by using RNA with a complimentary sequence
describe the process of using gene probes to find a specific sequence of DNA or mRNA
- DNA from the cells under investigation is heated to break hydrogen bonds
- fluorescently labelled mRNA for the required gene is added (the probe)
what determines the type of cell and its function in the body
- the proteins present in a cell and the quantities of different proteins
what is transcription
the process by which the genetic code of DNA is copies into a complimentary strand of RNA before protein synthesis takes place
why is mRNA transcription an effective point to control gene expression
- because a single mRNA strand results in the production of many protein molecules
what is a transcription factor
proteins that bind to the DNA in the nucleus and affect the process of transcribing genetic material
what is a promoter sequence and where are they found
- the part of the DNA that the transcription factor binds to
- usually found just above the point of transcription
- some of them stimulate DNA transcription, by binding to the promoter sequence, by making transcription start from that point
what is an enhancer sequence, what happens when it is bound to
- a region on the DNA sequence that the transcription factor binds to
- when they bind here, they regulate the activity of DNA by changing the structure of the chromatin and deciding how open it is to RNA polymerase
- when its very open, the gene is active and whet it’s closed, it’s not active
- they can stimulate or prevent the transcription of a gene
what is pre-mRNA, and what are the modifications made to it
- the RNA that’s produced in the nucleus from transcription usually gets modified before it lines up on the ribosomes
- the introns are removed and sometimes some exons are removed, then they’re rejoined together by spliceosomes
what is RNA splicing
when spliceosomes join together the same exons in a variety of ways, so a single gene can produce different versions of functional mRNA that code for different amino acids which in turn produce different polypeptide chains
how is a protein modified
- protein modification can take place after they have been synthesised by being shortened or lengthened by enzymes to give a variety of other proteins
what is epigenetics
- a new area of research in biology
- studied genetic control by factors other than base sequences on DNA
what are the three intracellular systems that interact to control genes
- DNA methylation
- histone modification
- non-coding RNA
what’s a histone
a protein that provides structural support for chromatin
what is DNA methylation
- widely used mechanism in epigenetics
- addition of a methyl (CH3) group to cytosine, SILENCES a gene/ sequence
- methyl group is added by methyltransferase
- it can also modify the structure of histones
- methyl group changes structure of DNA molecule so transcription can’t occur
what is DNA demethylation
- the removal of a methyl group
- enables the gene to become active so they can be transcribed
what’s the problem with DNA methylation / demethylation
- researchers are finding that its associated with diseases, including a number of human cancers
describe a histone
- positively charged proteins
- DNA helices wind around histones to form chromatin, which makes up chromosomes
- the histones determine the structure of chromatin
what is histone acetylation
- an acetyl group (COCH3) is added to one of the lysines in a histone
- this opens up the structure and activates chromatin, allowing the genes to be transcribed
what is histone methylation
- a methyl group is added to lysine in a histone
- depending on the position of the lysine, methylation can cause activation or inactivation of the DNA
- however it is often linked to the silencing of a gene/ chromosome