Gene Expression Flashcards
prokaryotic gene expression
genes coding for proteins with similar functions are group together and under control of an operon; the genes in an operon are transcribed into polycistronic mRNA w/ start and stop codons for each structural gene
- proteins are in same biosynthetic pathway
- RNAP binds to promoter upstream of coding regions and controls transcription of all genes
repressor
regulatory proteins that prevent the polymerase from binding and initiating transcription (negative control)
inducers
small molecules, usually nutrients, that bind to repressors and change its conformation to make it unable to bind to the operator (once the inducer inactivates the repressor, RNAP can bind to allow transcription)
lac operon
a gene system whose operator gene and three structural genes control lactose metabolism in E. coli
- lactose as an energy source instead of glucose
- metabolite of glucose acts as the inducer, releases the repressor and allows transcription of genes
what are the levels of eukaryotic gene regulation?
chromatin remodelling and gene rearrangement, transcription factors affecting RNAP binding, processing of transcripts, DNA methylation, and translation, inittion and mRNA stability
chromatin remodelling
reducing the +ve charge on histones, allowing DNA unwinding for transcription
- HAT or acetylases add acetyl groups while HDACs remove them
methyltransferase
used to silence genes promoting uncontrolled cell growth by adding methyl donors
gene rearrangement
immunoglobulins recognize a great variety of antigens as when B cells are forming, they have different combinations; the mature one that is able to bind to an antigen will multiply
transcriptional control
control of gene expression by the use of transcription factors, and other proteins, that regulate either the initiation of transcription or the rate at which it occurs
- lipid-soluble steroid hormones diffuse through the membrane and can bind to receptors forming dimers in the cytosol
- enter the nucl. to bind to DNA and activate transcription
thyroid hormone receptors
able to form a complex that is always on DNA and represses transcription of downstream genes
- when THs bind, repressor complex is replaced with an activator complex; allowing the release of DNA from histones and transcription to take place
DNA binding proteins
proteins bind to specific sequences on DNA and have a conformation that fits into the grooves of DNA
- a.a. side chains in alpha helices fitting into grooves can form H bonds w/ specific DNA sequences for transcriptional regulation
what are other controls of expression?
alternative splice sites on a gene, so that different proteins may be made from the same gene in diff. tissues; proteins that bind to the poly A tail of mRNA for stabilization allowing to exist for longer periods in cytosol, mRNAs having their lifepan coded into DNA in the 3’ region (less protein is made from shorter-lived transcripts)
globin synthesis
iron is needed to complete the heme molecule in RBCs (no nuclei so globin synth. regulated at level of translation); heme not being available due to low iron causes heme kinase phosphorylation and inactivation of initation factors so globin mRNA can’t be translated
- presence of heme = kinase activation = translation
what can occur with gene expression that should not be happening?
for example, mutation of a proto-oncogene to an oncogene resulting in uncontrolled cell growth causes CANCER
what can occur when there is no signal for gene expression received?
for example, a tumour suppressor gene is turned OFF due to a mutation in the gene, causing CANCER
