Ch 8: Control of Gene Expression Flashcards
What is true/not true of liver cells and kidney cells in the same organism?
True: They contain different proteins
True: They express different genes
True: They contain the entire set of instructions needed to form the whole organism
False: They contain different genes
What would be the best method for determining which genes are bring transcribed in a particular cell type?
RNA sequencing
In eukaryotes, where do transcription regulators bind?
Upstream, downstream, or within the genes they control. Gene activation can occur at a distance in eukaryotes
What is an operon?
A set of genes transcribed as a single mRNA from a single promoter
Which does not affect gene expression at the post-transactional level? (small interfering RNAs, microRNAs, nucleotide sequences in the untranslated regions of an mRNA, DNA methylation)?
DNA methylation
When is gene expression controlled?
It can be controlled at any of the steps between a gene and its ultimate functional product. However, most of the control happens with initiation of transcription
How and where is the transcription of individual genes switched on and off, and how is this different between eukaryotes and bacteria?
Transcription of individual genes is switched on and off by transcription regulators, which are proteins that bind to short stretches of DNA called regulatory DNA sequences.
In bacteria, the regulatory DNA sequences are usually close to where the RNA polymerase could bind. In Eukaryotes, regulatory DNA sequences are often separated from the promoter by many thousands of nucleotide pairs
Transcription regulators in eukaryotes
They usually act in one of two main ways:
1) they direct the assembly process that requires RNA polymerase and the general transcription factors at the promoter
2) The locally modify the chromatin structure of promoter regions.
The expression of the gene is usually controlled by a combination of different transcription regulators.
How does cellular memory work?
- One prominent mechanism in multicellular organisms is positive feedback: transcription regulators that perpetuate transcription of their own gene.
- Patterns of DNA methylation and chromatin structure can be transmitted from one cell generation to the next
DNA methylation
the enzymatic addition of methyl groups to cytosine bases in DNA. This covalent modification generally tuns off genes by attracting proteins that block gene expression
Epigenetic inheritance
the transmission of a heritable patters of gene expression from one cell to its progeny that does not involve altering the nucleotide sequence of the DNA
long noncoding RNA
class of RNA molecules more than 200 nucleotides in length that does not encode proteins. Often used to regulate gene expression
microRNA
miRNA, small noncoding RNA that controls gene expression by base-pariing with a specific mRNA to regulate its stability and translation
post-transcriptional control
regulation of gene expression that occurs after transcription has already begun. Examples include RNA splicing and translational control
promoter
DNA sequence that initiates gene transcription. Includes sequences recognized by RNA polymerase and its accessory proteins
regulatory DNA sequence
DNA sequence to which a transcription regulator binds to determine where, when, and in what quantities a gene is to be transcribed into RNA
reporter gene
gene encoding a protein whose activity is easy to monitor experimentally; used to study the expression patters of a target gene or the localization of its protein product
RNAi
RNA interference; cellular mechanism that results in the destruction of RNAs containing a similar nucleotide sequence. It is widely exploited as an experimental tool for preventing the expression of selected genes (gene silencing)
What are the steps at which gene expression can be regulated?
1) transcriptional control
2) RNA processing control
3) RNA transport and localization control
4) mRNA degradation control
5) translational control
6) protein degradation control
7) protein activity control
Explain the control of the Lac operon
When there is glucose, the CAP activator is in its inactive form. When there is no glucose, cAMP binds to the CAP activator, causing it to be able to bind to the DNA, stabilizing and promoting the DNA polymerase.
When there is no lactose, LacI binds to the operator site, blocking transcription. There there is lactose, the lactose binds to the LacI, inactivating it an allowing transcription to happen.
So the gene should only be transcribed where there is no glucose, and there is lactose.
Insulator
DNA sequences what pervent eukaryotic gene regulatory proteins from influencing distant genes (they block transcription from happening beyond a certain point)
positive feedback
a transient signal turns on a gene, which then produces activators for itself.
One common way that cell memory happens
Transcription circuits
they allow the cell to carry out logic operations (measure duration of a signal).
Both A and B are needed to turn on output. A produces B. So when the input to turn on A is only there briefly, A is not around long enough to turn on B, so there is no output. When the signal for A is on long enough, A has time to produce B, so the end output is produced as well.
Examples of translational regulation
