Unit 2: Gene Regulation Flashcards
gene regulation
- various ways in which cells control gene expression
what are the characteristics of gene expression (3)
- where (in which cells) are genes turned on
- when (during development or in response to changes in the environment) are they turned on
- how much gene product is made
positive regulation
- process where a regulatory molecule (usually a protein) must bind to the DNA at a site near the gene in order for transcription to take place
negative regulation
- process where regulatory molecule (usually a protein) must bind to DNA site near the gene to prevent transcription
What sequence do eukaryote promoters contain and where are they located? (2)
- 5’-TATAAA-3’
- about 25-35 base pairs upstream from the transcription start site
Where are prokaryote promoters located and what are they called? (2)
- about 10 and 35 base pairs upstream of the transcription start site
- -10 and -35 sequence motifs
transcriptional activator
- regulatory protein/compound that increases activity of an enzyme
What are the 2 binding sites that DNA contains?
- an activator protein binding site and the RNA polymerase complex binding site
In positive regulation, what occurs when the activator is successfully recruited to a site near the RNA polymerase promoter?
- RNA polymerase can bind to the promoter
In positive regulation, what occurs when the activator is unsuccessfully recruited to a site near the RNA polymerase promoter?
- RNA polymerase cannot bind and transcription does not occur
Where can the binding site for the activator be in positive regulation?
- upstream of the promoter, downstream of the promoter, or even overlap the promoter
allosteric effect
- change in the activity or affinity of a protein as the result of binding of a molecule to a site other than the active site
Why do activators change shape in different situations? (2)
- small molecules can bind to activators to change their shape so that they can bind to DNA
- small molecules can bind to activators to change their shape so they can no longer bind to DNA
repressor
- a protein that, when bound with a sequence in DNA, can inhibit transcription
In negative regulation, what occurs when there is no repressor bonded to the repressor bonding site?
- this allows RNA polymerase complex to be recruited and transcription takes place
In negative regulation, what occurs when there is a repressor bonded to the repressor bonding site?
- the repressor inhibits the recruitment of RNA polymerase and transcription does not occur
Where can the binding site for a repressor be located relative to a promoter?
- upstream, downstream, or overlapping with the promoter
inducer
- small molecule that elicits gene expression by changing the shape of repressors so they cannot inhibit transcription
what is the relationship between a strong promoter, a weak promoter, and a consensus sequence?
- strong promoters are closer to consensus while weak promoters are further from consensus
What is transcriptional control?
- controlling the amount of transcription via promoter strength and regulatory proteins
What is translational control?
- controlling the amount of translation by altering how fast a mRNA survives in the cell (for example by changing the length of the poly-A tail)
What is post-translational control?
- modifying enzymes directly by changing their shape or blocking active sites
constitutive gene expression
- when genes are expressed all the time (genes that code for RNA polymerases, ribosomes, tRNA, etc)
- this does not mean that there are high levels of expression
Although two different genes are constitutively expressed, how can their level of transcription and translation differ?
- promoter strengths may be different resulting in different amounts expressed
- the RNA made may have different half lives which would results in different amounts of translation
environmentally regulated gene expression
- expression of a gene is linked to a condition in the environment (either inside or outside of the cell)
- environmental conditions changes cause the expression of the gene to change as well
operon (2)
- set of related coding sequences (that make related proteins) that all share the same promoter and terminator
- single mRNA is made from an operon, and from that single mRNA multiple different proteins are produced
polycistronic mRNA
- mRNA molecule that contains more than one ORF and encodes for more than one protein
- typically products of operon transcription
basal transcription
- minimal amount of (but not zero) transcription that occurs even when gene expression is turned off
How can a cell achieve zero transcription?
- removing or destroying a promoter so that no RNA Polymerase (or more accurately, the transcription factors) can bind
regulatory protein
- protein that regulates (controls) expression of a gene or operon in some fashion
operator (2)
- DNA region where a regulatory protein binds
- sometimes the operator is the promoter itself but often they are different sequences or only have partial overlap
Can genes that code for regulatory proteins be apart of the operons they control?
- no
positive regulation (Jarod) (3)
- regulatory protein binds to a region near the promoter (the operator region) and INCREASES transcription
- regulatory protein is called an ACTIVATOR protein
- example is MalT
negative regulation (3)
- regulatory protein binds to a region near the promoter (the operator region) and DECREASES transcription
- regulatory protein is called a REPRESSOR protein
- example is LacI
