Lecture 8: Regulation of gene expression Flashcards
How many genes are expressed in a cell generally and what causes them to turn off or on
Cells only express a small percentage of the possible proteins they could make. They turn genes on and off in response to the presence of signals from internal and external environment (eg. things can use)
What causes differentiation in cell types in eukaryotes even when all cells have all the genes
The only express unique subsets of their genes, enabling them to become one particular type
How is eukaryotic gene expression regulated at chromatin modification and what causes this modification
In Heterochromatin, chromatin is packed densely so DNA is not able to be transcribed. This is caused by methylation of histone tails. But in Euchromatin DNA is less condensed allowing RNA polymerase access for transcription. This is caused by acetylation of histone tails.
What is epigenetic inheritance
The inheritance of traits transmitted by mechanisms not involving the nucleotide sequence itself.
How is methylation of DNA an example of epigenetic inheritance
Chromatin can stay methylated before and after cell division so subsequent cell can have those genes silenced as well
How is eukaryotic gene expression regulated at INITIATION OF TRANSCRIPTION
The availability of transcription factors can repress or stimulate the transcriptionof a gene because it binds to promoter region of DNA facilitating the binding of RNA polymerase and initiation of transcription
How is eukaryotic gene expression regulated at RNA PROCESSING
Proteins specific to cell type determine Alternative RNA splicing where different mRNA molecules are produce from the same premRNA. They determine which mRNA is made
How is eukaryotic gene expression regulated at TRANSLATION
The initiation of translation can be blocked by regulatory proteins binding to the UTRs so this stops the mRNA binding to the ribosome to be translated
How is eukaryotic gene expression regulated at DEGRADATION OF mRNA
Prokaryotic mRNA lasts only minutes but Eukaryotic mRNA can last hours to weeks. How long it can live determines how long it has to be translated
How is eukaryotic gene expression regulated at PROTEIN PROCESSING (3 ways)
Protein modification (glycosylation or phosphorylation) is required to produce functional protein so when protein not needed, this isn't done. Even if this is done it can be stopped by not allowing it to be trafficked to the right organelle. The lifespan of a protein can be shortened by tagging it with ubiquitin for proteosomes to destroy.
How do noncoding RNAs can regulate gene expression
They can regulate chromatin packing, translation, mRNA degradation
How do Prokaryotes adjust their gene expression based on the available nutrients
They either 1. adjust the catalytic activities of enzymes already made (feedback inhibition)(quickly) or
2. Adjust the production of enzyme molecules, by regulating expression of the genes encoding enzymes (long term)
What is the most frequent way prokaryotes regulate metabolic processes
Transcriptional control
What are the 3 structural genes for enzymes that enable cell to process lactose are grouped in the lac operon
- lacZ gene for B-galactosidase (enzyme that helps to use lactose most important)
- lacY gene for permease
- lacA gene for transacetylase
Why is there a lag phase in the growth curve of bacteria on lactose alone
Bacteria start to transcribe B-galactosidase mRNA which is translated into B galactosidase.
Why can enzymes conc increase exponentially in bacteria
Bacterial mRNA only lasts a few minutes so change in protein synthesis can be rapid
What is an operon made of. Is regulation gene part of it
A group of genes coding for proteins with related functions. Expression of these genes is under control of a single promoter and operator included. Regulatory not included
Compare negative and positive regulation
Negative is repressor protein is bound to operator to prevent gene being expressed. Positive is where Transcription factors or activator binds to promoter to enable transcription.
Which gene codes for the repressor protein in the lac operon and when are repressor protein active
lacI gene and the repressor can be transcribed anytime. Its active when lactose is absent
How is repressor protein inactivated
Lactose binds to repressor inducing allosteric shape change in repressor so it can’t bind to operator
When bacteria is grown on glucose and lactose it prefers glucose. When will it use lactose
When the glucose conc is low cAMP accumulates and this binds to CRP, activating it. This CRP binds to the promoter and increases the efficiency of binding of RNA polymerase binding to promoter.
Compare mutations in structural genes vs mutations in repressor proteins
Structural genes make a non functional protein, but in repressor lacI/ operator/ promoter region may either abolish transcription (mutation in the binding site for RNA polymerase or permanently turn it on (inactivate repressor) - constitutive mutants
