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Eukaryotic Post-transcriptional Gene Regulation

 

Page by: OpenStax College

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Biology

Book by: OpenStax College

RNA is transcribed, but must be processed into a mature form before translation can begin. This processing after an RNA molecule has been transcribed, but before it is translated into a protein, is called post-transcriptional modification. As with the epigenetic and transcriptional stages of processing, this post-transcriptional step can also be regulated to control gene expression in the cell. If the RNA is not processed, shuttled, or translated, then no protein will be synthesized.

Before the mRNA leaves the nucleus, it is given two protective "caps" that prevent the end of the strand from degrading during its journey. The 5' cap, which is placed on the 5' end of the mRNA, is usually composed of a methylated guanosine triphosphate molecule (GTP). The poly-A tail, which is attached to the 3' end, is usually composed of a series of adenine nucleotides. Once the RNA is transported to the cytoplasm, the length of time that the RNA resides there can be controlled. Each RNA molecule has a defined lifespan and decays at a specific rate. This rate of decay can influence how much protein is in the cell. If the decay rate is increased, the RNA will not exist in the cytoplasm as long, shortening the time for translation to occur. Conversely, if the rate of decay is decreased, the RNA molecule will reside in the cytoplasm longer and more protein can be translated. This rate of decay is referred to as the RNA stability. If the RNA is stable, it will be detected for longer periods of time in the cytoplasm.

Binding of proteins to the RNA can influence its stability. Proteins, called RNA-binding proteins, or RBPs, can bind to the regions of the RNA just upstream or downstream of the protein-coding region. These regions in the RNA that are not translated into protein are called the untranslated regions, or UTRs. They are not introns (those have been removed in the nucleus). Rather, these are regions that regulate mRNA localization, stability, and protein translation. The region just before the protein-coding region is called the 5' UTR, whereas the region after the coding region is called the 3' UTR (Figure). The binding of RBPs to these regions can increase or decrease the stability of an RNA molecule, depending on the specific RBP that binds.

RNA splicing, the first stage of post-transcriptional control

In eukaryotic cells, the RNA transcript often contains regions, called introns, that are removed prior to translation. The regions of RNA that code for protein are called exons (Figure). After an RNA molecule has been transcribed, but prior to its departure from the nucleus to be translated, the RNA is processed and the introns are removed by splicing.

Figure 1. Pre-mRNA can be alternatively spliced to create different proteins.

Control of RNA Stability

Figure 3. The protein-coding region of mRNA is flanked by 5' and 3' untranslated regions (UTRs). The presence of RNA-binding proteins at the 5' or 3' UTR influences the stability of the RNA molecule.

RNA Stability and microRNAs

Post-transcriptional control can occur at any stage after transcription, including RNA splicing, nuclear shuttling, and RNA stability. Once RNA is transcribed, it must be processed to create a mature RNA that is ready to be translated. This involves the removal of introns that do not code for protein. Spliceosomes bind to the signals that mark the exon/intron border to remove the introns and ligate the exons together. Once this occurs, the RNA is mature and can be translated. RNA is created and spliced in the nucleus, but needs to be transported to the cytoplasm to be translated. RNA is transported to the cytoplasm through the nuclear pore complex. Once the RNA is in the cytoplasm, the length of time it resides there before being degraded, called RNA stability, can also be altered to control the overall amount of protein that is synthesized. The RNA stability can be increased, leading to longer residency time in the cytoplasm, or decreased, leading to shortened time and less protein synthesis. RNA stability is controlled by RNA-binding proteins (RPBs) and microRNAs (miRNAs). These RPBs and miRNAs bind to the 5' UTR or the 3' UTR of the RNA to increase or decrease RNA stability. Depending on the RBP, the stability can be increased or decreased significantly; however, miRNAs always decrease stability and promote decay.

Section Summary

In addition to RBPs that bind to and control (increase or decrease) RNA stability, other elements called microRNAs can bind to the RNA molecule. These microRNAs, or miRNAs, are short RNA molecules that are only 21–24 nucleotides in length. The miRNAs are made in the nucleus as longer pre-miRNAs. These pre-miRNAs are chopped into mature miRNAs by a protein called dicer. Like transcription factors and RBPs, mature miRNAs recognize a specific sequence and bind to the RNA; however, miRNAs also associate with a ribonucleoprotein complex called the RNA-induced silencing complex (RISC). RISC binds along with the miRNA to degrade the target mRNA. Together, miRNAs and the RISC complex rapidly destroy the RNA molecule.

Question 1

1. What will result from the binding of a transcription factor to an enhancer region?

1. What will result from the binding of a transcription factor to an enhancer region?

Answer

What will result from the binding of a transcription factor to an enhancer region?

1

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b

Increased transcription of a distant gene

a

Decreased transcription of an adjacent gene

c

Alteration of the translation of an adjacent gene

d

Initiation of the recruitment of RNA polymerase

What will result from the binding of a transcription factor to an enhancer region?

1

w

Label

b

Increased transcription of a distant gene

c

Alteration of the translation of an adjacent gene

d

Initiation of the recuitment of RNA polymerase

Decreased transcription of an adjacent gene

What will result from the binding of a transcription factor to an enhancer region?

1

Next Question

Binding of a transcription factor to an enhancer region increases the transcription of a distant gene.

Label

a

Increased transcription of a distant gene

c

Alteration of the translation of an adjacent gene

d

Initiation of the recuitment of RNA polymerase

Decreased transcription of an adjacent gene

What will result from the binding of a transcription factor to an enhancer region?

1

Next Question

Enhancers are the DNA sequences that influence the rate of transcription by up-regulating the gene expression.

Label

a

Increased transcription of a distant gene

b

Alteration of the translation of an adjacent gene

d

Initiation of the recruitment of RNA polymerase

Decreased transcription of an adjacent gene

Genes are not translated directly -- only mRNA is translated.

What will result from the binding of a transcription factor to an enhancer region?

1

Next Question

Label

b

Increased transcription of a distant gene

c

Alteration of the translation of an adjacent gene

Initiation of the recruitment of RNA polymerase

a

Decreased transcription of an adjacent gene

What will result from the binding of a transcription factor to an enhancer region?

1

Next Question

Enhancers do not generally affect the recruitment of RNA polymerase.

Question 2

2. The diagram shows different regions (1-5) of a pre-mRNA molecule....

2. The diagram shows different regions (1-5) of a pre-mRNA molecule....

Answer

The diagram shows different regions (1-5) of a pre-mRNA molecule, a mature-mRNA molecule, and the protein corresponding to the mRNA.A mutation in region ___ is most likely to be damaging to the cell.

2

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b

1

a

2

c

3

d

5

The diagram shows different regions (1-5) of a pre-mRNA molecule, a mature-mRNA molecule, and the protein corresponding to the mRNA.A mutation in region ___ is most likely to be damaging to the cell.

2

Label

b

1

c

3

d

5

2

Region 2 seems to be encoding a gene.  Any mutation in this region would likely produce a non-functional protein, damaging the cell. 

Next Question

The diagram shows different regions (1-5) of a pre-mRNA molecule, a mature-mRNA molecule, and the protein corresponding to the mRNA.A mutation in region ___ is most likely to be damaging to the cell.

2

Label

a

1

c

3

d

5

2

Next Question

The diagram shows different regions (1-5) of a pre-mRNA molecule, a mature-mRNA molecule, and the protein corresponding to the mRNA.A mutation in region ___ is most likely to be damaging to the cell.

2

A mutation in region 1 will not damage the cell.

Label

a

1

b

3

d

5

2

Next Question

The diagram shows different regions (1-5) of a pre-mRNA molecule, a mature-mRNA molecule, and the protein corresponding to the mRNA.A mutation in region ___ is most likely to be damaging to the cell.

2

Region 3 is present between exons 2 and 4. It is an intron, the non-coding sequence.

Label

b

1

c

3

5

a

2

Next Question

The diagram shows different regions (1-5) of a pre-mRNA molecule, a mature-mRNA molecule, and the protein corresponding to the mRNA.A mutation in region ___ is most likely to be damaging to the cell.

2

UTR is important for the process of translation and region 5 does not encode a gene.

Question 3

3. Label regions 1-5 in the diagram as introns or exons.

3. Label regions 1-5 in the diagram as introns or exons.

Answer

Label regions 1-5 in the diagram as introns or exons.

3

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b

2 and 4 are introns; 1,3, and 5 are exons

a

1, 3, and 5 are introns; 2 and 4 are exons

c

1 and 5 are introns; 2, 3, and 4 are exons

d

2, 3, and 4 are introns; 1 and 5 are exons

Label regions 1-5 in the diagram as introns or exons.

3

Label

b

2 and 4 are introns; 1,3, and 5 are exons

c

1 and 5 are introns; 2, 3, and 4 are exons

d

2, 3, and 4 are introns; 1 and 5 are exons

Regions 1, 3 and 5 are the introns. These are the DNA regions that do not encode any part of the protein. Regions 2 and 4 encode the resulting protein, so these regions are exons.

Done

Label regions 1-5 in the diagram as introns or exons.

3

1, 3, and 5 are introns; 2 and 4 are exons

Label

2 and 4 are introns; 1,3, and 5 are exons

c

1 and 5 are introns; 2, 3, and 4 are exons

d

2, 3, and 4 are introns; 1 and 5 are exons

1, 3, and 5 are introns; 2 and 4 are exons

Introns do not code for a protein. Therefore, regions 2 and 4 cannot be introns.

Done

Label regions 1-5 in the diagram as introns or exons.

3

a

Label

2 and 4 are introns; 1,3, and 5 are exons

b

d

2, 3, and 4 are introns; 1 and 5 are exons

1, 3, and 5 are introns; 2 and 4 are exons

Only exons code for a protein. Therefore, regions 3 is not an exon.

Done

Label regions 1-5 in the diagram as introns or exons.

3

a

1 and 5 are introns; 2, 3, and 4 are exons

Label

b

2 and 4 are introns; 1,3, and 5 are exons

c

1 and 5 are introns; 2, 3, and 4 are exons

a

2, 3, and 4 are introns; 1 and 5 are exons

1, 3, and 5 are introns; 2 and 4 are exons

Introns do not code for a protein. Therefore, regions 2 and 4 cannot be introns. Also, exons always code for proteins. Therefore, regions 1 and 5 cannot be exons.

Done

Label regions 1-5 in the diagram as introns or exons.

3

CONCEPT COACH

My Progress

My Progress

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The Study of Life

The Science of Biology

Themes and Concepts of Biology

 

1

1.1

1.2

 

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The Chemical Foundation of Life

Atoms, Isotopes, Ions, and Molecules: The Building Blocks

Water

Carbon

 

2

2.1

2.2

2.3

 

Biological Macromolecules

Synthesis of Biological Macromolecules

Carbohydrates

Lipids

Proteins

Nucleic Acids

3

3.1

3.2

3.3

3.4

3.5

Cell Structure

Studying Cells

Prokaryotic Cells

Eukaryotic Cells

The Endomembrane System and Proteins

The Cytoskeleton

Connections between Cells and Cellular Activities

 

4

4.1

4.2

4.3

4.4

4.5

4.6

 

Structure and Function of Plasma Membranes

Components and Structure

Passive Transport

Active Transport

Bulk Transport

5

5.1

5.2

5.3

5.4

Metabolism

Energy and Metabolism

Potential, Kinetic, Free, and Activation Energy

The Laws of Thermodynamics

ATP: Adenosine Triphosphate

Enzymes

6

6.1

6.2

6.3

6.4

6.5

Cellular Respiration

Energy in Living Systems

Glycolysis

Oxidation of Pyruvate and the Citric Acid Cycle

Oxidative Phosphorylation

Metabolism without Oxygen

Connections of Carbohydrate, Protein, and Lipid Metabollic Pathways

Regulation of Cellular Respiration

7

7.1

7.2

7.3

7.4

7.5

7.6

7.7

Photosynthesis

Overview of Photosynthesis

The Light-Dependent Reactions of Photosynthesis

Using Light Energy to Make Organic Molecules

8

8.1

8.2

8.3

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Cell Communication

Signaling Molecules and Cellular Receptors

Propagation of the Signal

Response to the Signal

Signaling in Single-Celled Organisms

9

9.1

9.2

9.3

9.4

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Cell Reproduction

Cell Division

The Cell Cycle

Control of the Cell Cycle

Cancer of the Cell Cycle

Prokaryotic Cell Division

10

10.1

10.2

10.3

10.4

10.5

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Meiosis and Sexual Reproduction

The Process of Meiosis

Sexual Reproduction

Control of the Cell Cycle

Cancer of the Cell Cycle

Prokaryotic Cell Division

11

11.1

11.211.3

11.4

11.5

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Mendel's Experiments and Heredity

Mendel's Experiements and the Laws of Probability

Characteristics and Traits

Laws of Inheritance

12

12.1

12.2

12.3

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Modern Understandings of Inheritance

Chromosomal Theory and Genetic Linkage

Chromosomal Basis of Inherited Disorders

1313.1

13.2

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DNA Structure and Function

Historical Basis of Modern Understanding

DNA Structure and Sequencing

Basics of DNA Replication

DNA Replication in Prokaryotes

DNA Replication in Eukaryotes

DNA Repair

14

14.1

14.2

14.3

14.4

14.5

14.6

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Genes and Proteins

The Genetic Code

Prokaryotic Transcription

Eukaryotic Transcription

RNA Processing in Eukaryotes

Ribosomes and Protein Synthesis

15

15.1

15.2

15.3

15.4

15.5

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Gene Expression

Regulation of Gene Expression

Prokaryotic Gene Regulation

Eukaryotic Epigenetic Gene Regulation

16

16.1

16.2

16.3

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