E6 Transcription and gene expression Flashcards
what do micro-RNAs do?
make normal RNA more or less stable
why are humans diploid?
it is a safety net to produce the correct proteins we need - we have evolved to be that way
what are the 3 steps of protein production in all of which regulation of gene expression occurs? explain how gene expression is regulated in each of these
regulation of transcription
- control of which genes are expressed
regulation of mRNA processing and decay
- some RNA can last for years and others just for minutes
regulation of translation
- control of how the ribosome binds to the RNA and how much it translates it
what structures can RNA fold into and how?
- eg. hairpins, stem-loops
- happens by internal base pairing by hydrogen bonds
constrast RNA and DNA
- DNA has 2’ deoxyribose sugar and RNA has ribose
- RNA has uridine instead of thymidine phosphate residues like DNA
- RNA is usually single-stranded while DNA is usually a double-helix
describe polymerase 1, 2 and 3
- polymerase 2 is most important
- polymerase 3 makes tRNA
- polymerase 1 makes ribosomal RNAs
what is RNA transcribed from and how?
- from the complementary DNA strand
- no RNA primer needed for transcription as the RNA is its own primer
- polymerases track along DNA template and add onto 3’ end with nucleotides
how does RNA polymerase know where and when to start?
- RNA polymerase doesn’t need a primer
- a DNA sequence called a promoter directs the RNA polymerase to the right spot
- the binding of RNA polymerase to the promoter is mediated by transcription factors and also requires chromatin modification
what is a promoter region?
- where basic transcription factors and RNA polymerase come in
- polymerase can then use template DNA strand to copy the DNA into RNA
describe chromatin rearrangement in terms of transcriptional regulation
- open conformation and low nucleosome density permit RNA polymerase access and can prevent polymerase access
how is RNA polymerase recruitment regulated?
RNA polymerase has to be positioned at the transcription start site of the gene
what are transcription factors? describe genes in terms of transcription factors
- DNA binding proteins that recognise specific DNA sequences in the genes they control
- every gene has a unique combination of transcription factor binding sites that regulates its expression
- every genes has the potential to be expressed if the correct transcription factors are present
how can transcription factors work in terms of modifying chromatin?
- recruit co-activator proteins that modify chromatin
- may modify histones to change their interaction with DNA (allows FNA to open up to allows RNA polymerase to come in and transcribe)
- unblocks promoter regions
describe modifications on nucleosomes / chromatin
- often long-lasting
- can be copied over in DNA replication
- inherit a memory of gene expression when we replicate DNA in our epigenetics long after the stimulus
- chromatin modifications can be passed on to offspring
describe basal and gene-specific transcription factors
- basal transcription factors bind to nearly all genes
- they don’t distinguish between different genes and don’t cause gene specific regulation
- gene-specific transcription factors bind to DNA sequences found in a subset of genes and therefore contribute to gene regulation
