Lecture 7 - Genes & Their Expression Flashcards
gene expression:
“the information encoded by a gene is used in a functional manner”
what percentage of genes are coding in the human genome?
only 1%
what is the most common RNA found in our cells?
tRNA and rRNA (ribosomal)
gene:
“DNA sequence that is the template that encodes information for a functional product made of RNA or protein”
gene products contain:
both RNA and protein - but not all RNA becomes protein
RNA is critical player in gene expression:
being a key information molecule, an important regulator of gene expression, and being critical for the synthesis of protein
first step gene expression can be controlled:
transcription
what controls initial gene expression specifically?
segments of DNA around a gene control its expression by regulating the activity of RNA polymerase II, which is responsible for generating the RNA molecule
structure of a bacterial gene:
relatively simple structure:
- promoter region
- transcriptional terminator site
- transcriptional start site
(terminator and start site is NOT the same as stop and start codons)
promoters:
the promoter is a sequence of the DNA where RNA polymerase binds to the DNA to synthesise the RNA transcript
comes before the gene itself, important in directing RNA polymerase to which strand of DNA they should bind and transcribe
what can help the promoter region and where is it found?
sometimes, there is an UP element further upstream of the gene that is rich in thymine that helps to strengthen the promoter region
what can deviations in the ‘UP Element’ cause?
deviations from these sequences impairs the binding of RNA polymerase to the promoter and affects gene expression
operators:
- structural feature specific to prokaryotes
- either within the promoter or between the promoter and the target gene
- they are a binding sequence in which a repressor protein can bind which can physically stop RNA polymerase binding
termimation sequence:
- signal that tells RNA polymerase to stop transcribing
- these are a sequence which creates a hairpin that matches which causes the stalling of the RNA polymerase
do genes overlap in prokaryotes/bacteria?
genes rarely overlap in bacterium
Most of the time, there is ___ _____ between the promoter and termination site
one gene
monocistronic gene:
gene between the promoter and termination site - producing one mRNA transcript that makes one protein
polycistronic genes:
where there are multiple genes between one promoter and a termination site - still making only one mRNA transcript, but one that can produce multiple proteins
what do polycistronic genes allow for in bacteria?
polycistronic genes allows for a coordinated expression of multiple genes in the same pathway and often occurs with enzymatic pathways
how is the structure in bacterial gene expression?
genes in bacteria have a simple but effective structure to control gene expression
Both the promoter and terminator sites have _________ _________which are common and are important for the initiation and termination of transcription
consensus sequences
how are eukaryotic genes similar to bacterial genes but also different?
they both have things such as promoter regions but there are greater levels of complexity in eukaryotic genes which adds additional levels of regulation
how do we transcribe type II genes?
using RNA polymerase II
function of the TATA Box:
involved in positioning the RNA polymerase correctly at the promoter and is similar to pribnow boxes in bacteria
what actually is a TAT Box?
a sequence about 25 upstream of the transcription start site that has the sequence TATAAAA
what can be found in the space beyond the TATA box?
there are a range of upstream control elements with common sequences:
–CAAT box with the sequence GGCCAATCT
–GC box with GGGCGG
Most eukaryotic genes have one of these and act as sites in which general transcription factors can bind
general transcription factors:
general transcription factors are proteins that help with the recruitment and positioning of RNA polymerase II
two effects regulators can have on gene expression:
–Enhancers can promote gene expression
–Silencers can inhibit gene expression
•Both of these play crucial roles in regulating gene expression and ensuring the right genes are expressed when needed in the right cells
•Sometimes, there are enhancers and silencers sequences occupying the same space that compete with each other to regulated gene expression
what is meant when regulators are referred to as being ‘trans-acting’?
their regulatory sequences operate hundreds to thousands of nucleotides away from the gene itself
why are bacterial regulators referred to as being ‘cis-acting’?
in bacteria they are cis-acting as they are right next to the promoter
the upstream control elements binds general transcription factors which:
recruits the mediator complex which can then interact with the proteins binding to the regulators significantly further upstream along the DNA
how can specialised proteins increase the association of a gene with a regulator?
specialized proteins can also hold eukaryotic chromosomal DNA in loops, which increases the association of a gene with a regulator like an enhancer or repressor
why are there very little genes found in the telomeres and centromeres, where lists of chromatin is found?
there are very little genes because it is not efficient to keep unwinding to allow for gene expression, and could compromise chromosome integrity
insulators:
Insulators are cis-acting elements that essentially act as ensuring that genes that other genes and/or chromosomal structure do not interfere with gene expression
•Insulators can block enhancers from working from neighbouring genes from interacting with promoters
•They can also act as a barrier against heterochromatin from encroaching into the euchromatin and repressing gene expression.
eukaryotic genes have two non-coding regions in their coding regions:
– Exons are the part of the gene that code for the amino acid sequence for proteins
– Intros are the part of the gene that do not code for proteins and are between introns, but can play important regulatory roles
bacteria + introns & exons?
Bacteria do not have introns and exons – the coding region of bacterial genes are generally uninterrupted
Genes often controlled by many regulators – ensure genes are expressed:
–at the right level
–in the right cell
–in response to the right conditions
–at the right time.
