Module 6 : Control of gene expression Flashcards
Gene expression can be controlled at the ….
4 levels
transcriptional , post transcriptional , pre translational and post translational levels
What is an example of transcriptional control?
What is an operon?
Are they more common in prokaryotes or eukaryotes?
the lac operon
a group of genes under control of the same regulatory mechanism and expressed at same time
more common in prokaryotes
Describe why operons are a very efficient way of saving resources?
because if certain gene products are not needed , all the genes involved in their production can be switched off
Make 4 points about the lac operon
-its a group of 3 structural genes
-they are called lac Z , lac Y and lac A
-they are involved in the metabolism of lactose
-they are transcribed onto a single long molecule of mRNA
On the mRNA strand containing the lac operon , what is present near the operon and what is the role of this structure?
a regulatory gene , it codes for a repressor protein that prevents transcription of the structural genes in the absence of lactose
The repressor protein is constantly produced by the regulatory gene , what does the repressor protein bind to?
What happens as a result of this binding?
binds to the operator
binding prevents RNA polymerase binding to DNA and beginning transcription
What is the name of the section of DNA that is the binding site for RNA polymerase?
the promoter
What happens to transcription of the lac operon when lactose is present?
4 points
1)lactose binds to the repressor protein causing it to change shape
2)the protein can no longer bind to the operator
3)as a result RNA polymerase can bind to the promoter
4)the structural genes can be transcribed , therefore producing the 3 enzymes required to metabolise lactose
What is the product of transcription?
What happens to this molecule? 1 point
pre-mRNA
-it is modified to form mature mRNA so it can bind to a ribosome
Post transcriptional/Pre-translational level-RNA processing:
What is meant by the term splicing?
Where within the cell does splicing occur?
when RNA is cut at specific points , the introns are removed and exons are joined together
-this occurs in the nucleus
Make 3 points about RNA editing
(this is also part of control at the post-transcriptional and pre-translational level)
-nucleotide sequence of some mRNA molecules can be changed through base addition , deletion or substitution
-this results in synthesis of different proteins which may have different functions
-this increases range of proteins that can be produced by a single mRNA molecule/gene
Protein kinases:
What type of molecules are they and what do they do?
they are enzymes that catalyse the addition of phosphate groups to proteins
Protein kinases:
What does the addition of a phosphate group do to a protein?
What molecule are protein kinases often activated by?
it changes the tertiary structure and therefore the function of a protein
the second messenger molecule cAMP
Post translational control involves modifying the proteins that have been synthesised … name and explain 4 processes that occur
1)addition of non protein groups (carb chains , lipids , phosphates etc)
2)modifying amino acids and formation of bonds
3)folding or shortening of proteins
4)modification by cAMP
Make 3 points about the role of cyclic AMP in the lac operon
-binding of RNA polymerase still results in slow rate of transcription so this needs to be increased to produce the required quantity of enzymes
-this is achieved by the binding of a cAMP receptor protein
-this is only possible when the receptor protein is bound to cAMP
