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Molecular Biology > Translation Regulation > Flashcards

Translation Regulation Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

How many steps are there in regulation of gene expression in eukaryotes?

A

There are at least 6 main mechanism involved in the regulation of gene expression in eukaryotes

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2
Q

What is RNA Processing?

A

Differential splicing of primary transcripts can lead to the production of mRNAs which encode for completely different proteins

-7-methylguanosine cap added to 5’ end and poly A tail added to 3’ end

Primary transcript, hnRNA= (heteronuclear RNA also known as primary RNA)

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3
Q

What is differential splicing?

A

Differential splicing yields alternate mRNA transcripts

What influences differential splicing?

Proteins expressed differently in different cells can influence splicing

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4
Q

What happens to mRNA during translation initiation?

A

Circulization

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5
Q

Describe global mechanisms of translation regulation

A

Global
-affects most mRNAs

-Due to rate limiting activities of translation initiation factors

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6
Q

Describe specific mechanisms of translation regulation

A

Affects particular mRNAs

Different mechanisms

Response to

  • Nutrients
  • Development cues
  • Cell polarity/location
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7
Q

What are the types of mechanisms of translational regulation?

A

Global and specific

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8
Q

Elements within the mRNA and modifications of the molecule are…

A

Involved in regulating translation

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9
Q

What happens when mRNAs are uncapped?

A

Efficient translation requires presence of a complete 7-methyl-guanosine “cap” at the 5’ end of mRNA
Ex. Tobacco hornworm with:

Unfertilized oocyte:
5’ guanosine on oocyte mRNAs are not methylated therefore they can’t attach to ribosomes

After fertilization:
7-methyl added to 5’ guanosine on mRNAs-association with ribosome

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10
Q

Describe differential mRNA polyadenylation for mRNAs encoding for oocyte growth

A

During oogenesis: mRNAs with long poly-A tails leads to immediate translation

After oocyte maturation/fertilization: poly-A tails are removed leads to translation stops

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11
Q

Describe differential mRNA polyadenylation for mRNAs encoding proteins needed for: cleavage

A

During oogenesis: mRNAs have most of their poly-A clipped off (15-90 A’s retained) leads to blocked translation

After oocyte maturation/ fertilization: Stored maternal mRNAs acquire long poly-A tails (150-600 A’s)-translation begins

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12
Q

What marks mRNAs to be selectively polyadenylated at fertilization?

A

Specific nucleotide sequence (cytoplasmic polyadenylation element; CPE) in the 3’ trailer (3 UTR) of the message marks the mRNAs to be selectively polyadenylated at fertilization (UUUAU)

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13
Q

Explain the functioning of interfering proteins

A

Ex1. Interfering proteins: Maskin proteins prevent mRNA polyadenylation and translation

  1. Stored mRNAs in early embryos contain short poly-A tails
  2. CPE Binding protein (CPEB) recruits Maskin.
  3. Progesterone (production resulting from fertilization) activates protein kinases that phosohorylates CPEB
  4. Maskin is released
  5. mRNA is poly-adenylated
  6. PABP binding initiates translation
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14
Q

Describe the PUF family of proteins

A

-pumilo proteins in drosophila

PUF proteins bind to element in the 3’ UTR of the mRNA and prevent polyadenylation of the mRNA

They may also inhibit translation of the mRNA by interacting with the 5’ UTR or 7mG cap

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15
Q

Describe interacting proteins “masked messages”

A

Unfertilized egg-mRNAs are packaged in ribonucleoprotein (RNP) particles —> no translation of mRNAs- mRNAs can’t attach to ribosomes due to RNPs

At fertilization- ionic changes ( increase in calcium ions, sodium ions, pH) increase ca7se release of “masking proteins”—> Translation of mRNA- mRNAs are free to attach to ribosome

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16
Q

What are the functions of internal Ribosomal entry sites (IRES) ?

A

allow for cap independent translation

Viral mRNAs often contain IRES so that their mRNAs can still be translated while disrupting translation of host cell mRNA

Some human mRNAs that encode proteins involved in inhibiting apoptosis (cell death) contain (IRES)

17
Q

Briefly describe the functioning of Bicoid mRNA

A

Bicoid mRNA is produced and assoc8ates with microtubules at the anterior end of the fruit fly egg

Bicoid protein affects translation of caudal mRNA

Bicoid protein binds Caudal mRNA and inhibits translation

18
Q

Explain determination of posterior axis of the fruitfly

A

BCD protein forms a gradient with highest amounts in anterior

Bcd is a transcription factor that activates genes at different concentrations as well as preventing the translation of specific mRNA

Bicoid protein is made at anterior end only and will begin go diffuse across the cell toward the posterior

19
Q

Describe Bicoid and caudal concentration gradient

A

Bicoid protein represses caudal mRNA translation

Bicoid protein protein in high concentration where caudal protein concentration in low concentration and vice versa

20
Q

Explain Bicoid being an interfering protein

A

Bicoid is an interfering protein: interaction of translation initiation complex with 3’ UTR bound proteins

Proteins like Bicoid (Bcd) can bind to elements in the 3’ UTR that recruit proteins that bind to the m7G cap and prevent binding of the translation initiation complex

21
Q

What is the role of ferritin in regulation of iron storage?

A

Ferritin is an iron storage protein
-in low iron: Ferritin mRNA translation is blocked allowing free iron

-in high Iron: ferritin protein is made & excess iron is stored

Without this storage free iron can facilitate the formation of Reactive oxygen species

When you have too much Fe

22
Q

What is the role of transferrin in iron regulation?

A
  • in low iron: transferrin mRNA is stabilized to allow translation of more transferrin
  • in high iron: transferrin mRNA is degraded to reduce protein levels

When you have too little Fe

23
Q

Explain how interplay between mRNA motifs and binding proteins regulate mRNA

A

The iron-responsive element (IRE) is a particular hairpin structure located in the 5’ untranslated region (5’-UTR) or in the 3’-untranslated region (3’-UTR) of various mRNAs coding for proteins involved in cellular iron metabolism

The IREs are recognized by trans-acting proteins known as Iron Regulatory Proteins (IRPs) that control mRNA translation rate and stability

24
Q

Describe binding of competitive inhibitors to iron responsive elements (IRE)(e.g. ferritin-iron storage molecule)

A

Binding of IRPs sterically hinder the binding of the 40S ribosome

There is competition between iron regulatory proteins (IRP’s) and 40S ribosome for binding to mRNA

Binding of IRP-1 or IRP-2 to IRE prevents binding of ribosome

Therefore no protein is produced and iron is not stored and is free for use in the cell

High iron, iron will bind to IRP so it will no longer bind to IRE and the ribosome will bind .

Protein is produced and iron is stored safely in the cell

25
Q

Briefly describe regulation of transferrin receptor & ferritin mRNA

A

The IRP proteins can bind to different location on different genes to elicit a different response

Low iron requires increase in free iron

  • transferrin receptor expression ON
  • ferritin expression OFF

High iron requires the prevention of accumulation of toxic levels of free iron

  • transferrin receptor expression OFF
  • ferritin expression ON
26
Q

Explain the functioning of transferrin receptor mRNA regulation

A

Low iron: IRP bind, mRNA stabilized transferrin receptor protein is made

High iron: Iron blocks IRP binding transferrin mRNA degraded. No protein made

27
Q

Explain ferritin mRNA regulation

A

Low iron: IRP binds; ferritin synthesis blocked. No protein made

High iron: Iron blocks IRP binding. Ferritin is synthesized

28
Q

What is the function of Proprotein Convertase Proteolytically?

A

Proprotein Convertase Proteolytically activates precursor proteins

Molecular Biology (24 decks)

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