Translational Regulation. Flashcards
Define an oocyte?
An unfertilised egg.
Define oogenesis?
The generation of an oocyte.
What does the abbreviation UTR stand for?
An abbreviation for an untranslated region of DNA.
How many main mechanisms are involved in the regulation of gene expression in eukaryotes?
At least 6.
At what stage does the majority of the regulation of gene expression occur in eukaryotes?
At the transcriptional level.
Other than during transcription, at what other times can the regulation of gene expression occur in eukaryotes?
During RNA processing.
At multiple points between the transport of mRNA to the cytoplasm and post-transcriptional modification.
What is translational regulation occur in eukaryotes?
It is the various methods that the cell can control the formation of a protein from mRNA.
What section of mRNA is used for recognition by the ribosomes?
The 5 prime cap.
What are the poly-A tails used for on an mRNA molecule?
To prevent degradation by an endonuclease.
Are the 5 prime cap and poly-A tails examples of post-translational regulation?
Yes.
Why are the 5 prime cap and poly-A tails examples of post-translational regulation?
Because their presence will determine whether transcription occurs.
What post transcriptional method can determine the type of protein that is made from an mRNA strand?
RNA splicing.
What are the global effects of translational regulation?
When almost every mRNA in the body is affected.
What factor usually causes the global effects of translational regulation?
The rate limiting factors that are involved in translation or the availability of a substrate.
What are the specific effects of translational regulation?
They affect a particular mRNA via different mechanisms.
What 3 factors can cause specific effects of translational regulation?
Different responses to nutrients.
Different developmental cues.
A physical change within the cell such as cell polarity.
What factors about mRNA will lead to translational modification?
Intrinsic factors that are within the mRNA or have arisen due to modifications to the molecule.
Give an example of an intrinsic factor within mRNA that can lead to translational modification?
Hairpin loops which can interact with and be modified by various proteins.
The different forms of hairpin loops on an mRNA molecule will determine what?
It will determine the different proteins that can bind to it and this will control how translation occurs.
What 4 things is the translation of mature mRNA is regulated by?
Sequence elements within the mRNA.
Which version of an mRNA transcript is translated.
Modifications to the mRNA.
mRNA stability.
Do oocytes contain any mRNA?
Yes.
They contain mRNA transcripts so that proteins can be made immediately after fertilisation occurs.
How are the mRNA transcripts in the oocyte kept silent until fertilisation occurs?
By masked messages which are small ribonucleoproteins called maskin proteins.
How do maskin proteins keep the oocyte silent until fertilisation occur?
By preventing the mRNA transcripts from attaching to the ribosomes until after fertilisation has occurred.
How are the maskin proteins removed from the oocyte once fertilisation has occured?
Fertilisation induces intracellular ionic changes which leads to the release of the maskin proteins.
What will the stored mRNA’s in the oocyte do once the maskin proteins have been released?
They can bind to the ribosome.
What mRNA’s will be immediately translated during oogenesis?
The mRNA’s that are responsible for the growth and maturation of the oocyte.
How are the mRNA’s that are responsible for the growth and maturation of the oocyte differentiated from other mRNAs during oogenesis?
They have long poly-A tails.
How are the mRNA’s that are stored in the oocyte differnetiated from the mRNA’s that are used during oogenesis?
They have their poly-A tails cut off and will have their translation blocked.
The mRNA’s that are used during oogenesis have long poly-A tails.
What happens to the poly-A tails of the mRNAs that code for oocyte growth when the oocyte has matured and been fertilised?
The poly-A tails will be removed.
What happens to the stored mRNA’s once the oocyte is mature and fertilisation has occurred?
They will receive a long poly-A tails allowing these mRNAs to be translated.
What is the process of selective poly-adenylation?
The method of cleaving poly-A tails on specific mRNA’s which will inhibit translation.
What intrinsic factor in the mRNA will signal for poly-adenylation to occur?
A cytoplasmic poly-adenylation element (CPE) in the 3-trailer marks mRNAs to be poly-adenylated at fertilisation.
What will bind to the short poly-A tails on the stored mRNA’s in the oocyte?
They are bound to maskin proteins and to CPE binding proteins (CPEB).
What will activate the the CPE binding proteins on the short poly-A tails of mRNA in the fertilised oocyte?
Progesterone.
Progesterone levels are high after fertilisation.
How does progesterone activate the CPE binding proteins in the fertilised oocyte?
It will activate a kinase enzyme that phosphorylates and activates CPEB.
What happens to the CPE binding proteins once they have been activated by the presece of progesterone?
The maskin proteins are released and mRNA is poly-adenylated until translation can occur.
Where will the PUF proteins bind to on an mRNA transcript?
To specific nucleotides in the 3-UTR.
What will the presence of the PUF proteins in the 3-UTR of an mRNA molecule prevent?
They will prevent poly-adenylation.
How can the PUF proteins affect translation?
They prevent ribosomal binding by interacting with a sequence on the 5-UTR or with the 7-methylguanosine cap.
Will PUF proteins enhance or repress the translation of mRNA?
They will repress the translation of mRNA.
What area of an mRNA transcript will bind to the ribosome?
The 7-methylguanosine cap on the 5-prime end.
How is the methyl guanosine cap changed on mRNA’s in the oocyte?
Oocyte mRNAs contain an un-methylated guanosine cap.
When is the methyl group added to the guanosine cap in the oocyte?
After fertilisation has occurred.
What enzyme adds the methy group to the guanosine cap of the mRNA’s in the oocyte?
7-methyl guanosine transferase.
What are the 2 proteins used in fruit fly development that will determine the anterior and posterior regions of the developing fruit fly?
BICOID and CAUDAL.
What end of the developing fruit fly is determined by the presence of the BICOID protein?
The anterior end.
What end of the developing fruit fly is determined by the presence of the CAUDAL protein?
The posterior end.
How do the BICOID proteins prevent CAUDAL mRNA from being translated in the anterior region of the developing fruit fly?
The proteins will bind to the CAUDAL mRNA and preventing translation to CAUDAL proteins.
Why will BICOID proteins not be translated in the posterior region of the developing fruit fly?
The BICOID proteins form a gradient and are in high concentrations in the anterior region.
The BICOID concentration gets lower as it proceeds to the posterior region of the embryo.
Is CAUDAL mRNA expressed in a gradient in the developing fruit fly?
No.
It is expressed in equal quantities throughout the embryo.
Where will BICOID proteins inhibit the translation of CADUAL mRNA?
In regions where the BICOID protein is expressed.
What region of the developing fruit fly embryo will the translation of CAUDAL mRNA be inhibited in?
In the anterior region of the embryo.
Where will the CAUDAL proteins be expressed in the fruit fly embryo?
In the posterior region.
How do BICOID protiens inhibit the translation of CAUDAL mRNA in the fruit fly embryo?
They will inhibit the poly-A binding proteins meaning that poly-adenylation will not occur.
Where do the BICOID proteins bind to on the CAUDAL mRNA?
To specfic sequences in the 3-UTR.
Why does the cell not want high concentrations of iron within the cell?
As they can act as free radicals.
What protein is responsible for stroing iron in the cytosol of the cell?
Ferritin.
How does ferritin store iron?
When free iron is in the cytoplasm ferritin will bind to it and store it.
When will the translation of the mRNA that makes the ferritin protein be blocked?
Under low iron conditions.
Why is the translation of ferritin mRNA blocked under low iron condition?
To allow free iron to accumulate in the cell which can then be used for cellular processes.
When will the translation of the mRNA that makes the ferritin protein occur?
When free iron levels within the cell get too high.
Why is ferritin mRNA translated when free iron levels within the cell are high?
The ferritin protein can bind to the iron and remove it from the cell.
What protein will bring iron into the cell when intracellular iron concentrations are low?
Transferrin.
When is transferrin mRNA translated?
When intracellular iron concentrations are low.
Will the mRNA of transferrin ever be blocked?
It will be degraded when intracellular iron concentrations are high so that no more iron enters the cell.
What are internal ribosomal entry sites (IRES)?
They placed on the 5 prime end of viral mRNA instead of a 5 prime cap.
Are ribosomes able to translate mRNA that does not have a 5 prime cap?
No.
How does viral mRNA with an IRES manage to get translated if it does not have a 5 prime cap?
The IRES mimics the 5 prime cap and fools the ribosomes into producing viral proteins.
Do any human mRNA’s contain an IRES?
Some mRNA’s that code for proteins involved in apoptosis will also contain an IRES.
Will an IRES enhnace or repress the translation of mRNA?
It will enhance translation.
Whe does the process of differential proteolytic cleavage occur?
It is part of the the post translational processing of proteins and occurs after translation has occurred.
Differential proteolytic cleavage commonly occurs in which gland of the body?
In the pituitary gland, where different proteins will be expressed in different lobes of the pituitary.
What protein often undergoes differential proteolytic cleavage in the pituatary gland?
The melanocyte stimulating hormone (MSH).
What 2 proteins will MSH be cleaved to form via differential proteolytic cleavage in the anterior domain of the pituitary gland?
The N-terminal fragment.
The B-lipoprotien.
How is MSH cleaved via differential proteolytic cleavage in the intermediate lobe of the pituitary gland?
MSH is cleaved to form the N-terminal fragment and the B-lipoprotien.
How is the N terminal fragment cleaved by differential proteolytic cleavage after cleavage of the MSH in the intermediate lobe of the pituitary gland?
The N-terminal fragment is cleaved to form the adrenocorticotropic hormone.
The adrenocorticotropic hormone can be cleaved again to produce a polypeptide sequence and the a-MSH protein.
How is the B-lipoprotein cleaved by differential proteolytic cleavage after cleavage of the MSH in the intermediate lobe of the pituitary gland?
It can be cleaved to form the B endorphin.
