16. Regulation of Expression

Eukaryotic Post-Transcriptional Regulation

What is alternative splicing?
a. phosphorylation that leads to different types of post-translational regulation
b. mRNA processing that leads to different combinations of exons being spliced together
c. folding that leads to proteins with alternative conformations
d. the outcome of regulatory proteins that leads to changes in the life span of an mRNA

Small RNA molecules interfere with translation by targeting ribosomes for degradation.

Small DNA molecules interfere with mRNA molecules by blocking their ability to bind to a ribosome.

Small RNA molecules interfere with translation by targeting specific tRNA molecules

Small RNA molecules interfere with translation by blocking a target mRNA’s ability to bind to a ribosome.

Which of the following statements best describes the function of RNAi?

Post-Transcriptional Modification of Pre-mRNA

Post-Transcriptional Modification (2016) IB Biology

 Inhibit RNA splicing and bind to complementary DNA sequences to prevent transcription 

 No. These RNAs do not affect RNA splicing or bind to DNA. 

 Cut up mRNAs using the Dicer enzyme and bind to complementary mRNA sequences to prevent translation 

 No. The Dicer enzyme is involved in forming miRNAs and siRNAs but not in degrading mRNAs. 

 Cut up mRNAs using the Dicer enzyme and bind to complementary DNA sequences to prevent transcription 

 No. The Dicer enzyme is involved in forming miRNAs and siRNAs but not in degrading mRNAs. Also, these RNAs bind to other RNA molecules, not to DNA. 

 Promote the degradation of mRNA and inhibit RNA splicing 

 Promote the degradation of mRNA and bind to complementary mRNA sequences to prevent translation 

They both act at the post-transcriptional stage.

MicroRNAs and small interfering RNAs both function similarly in "silencing" genes. What are two ways in which they may act?

A short double-stranded RNA with one strand that can complimentarily bind to and inactivate an mRNA.

A single-stranded RNA with internal complementary base pairs that allow it to fold into a cloverleaf pattern.

A portion of rRNA which is a component of the large and small ribosomal subunits.

A molecule, known as Dicer, that can degrade or cut RNA sequences.

Which of the following best describes siRNA?

Which of the following is an example of post-transcriptional control of gene expression?
a. the addition of methyl groups to cytosine bases of DNA
b. the binding of transcription factors to a promoter
c. the removal of introns and alternative splicing of exons
d. gene amplification contributing to cancer

 The number of introns removed during processing 

 No. Introns do not leave the nucleus, so they do not play a role in the breakdown process that occurs in the cytoplasm. 

 The number of exons removed during processing 

 No. The exons present or absent are not the determining factor. The ends of the molecule are more important. 

 No. Enzymes that break down RNAs generally start at the 3&prime; end. 

 The presence of proteasomes in the cytoplasm 

 No. Proteasomes break down proteins, not RNAs. 

 Nucleotide sequences in the 3&prime; untranslated region of the mRNA 

Remember that there are enzymes in the cytoplasm that break down mRNAs.

What determines how long a particular mRNA molecule will persist in a eukaryotic cell?

Post-Transcriptional Regulation

3) RNA Interference

 Most of the genome does not contain meaningful genetic information and is not transcribed. 

 No. This sums up our earlier understanding of the human genome makeup. 

 Most of the genome consists of protein-coding DNA. 

 No. Only about 1.5% of the human genome consists of protein-coding DNA. 

 A large proportion of DNA consists of genes for ribosomal RNA and transfer RNA, whose transcripts are not translated. 

 No. Only a small percentage of the genome made is up of genes for rRNA and tRNA.  

 None of the listed responses is correct. 

 No. One of the listed responses is correct. 

 Genes for noncoding RNA make up the majority of meaningful genetic information in the human genome. 

Consider how our understanding of the human genome in terms of the amount of "functional" DNA sequence it contains has radically changed in recent years.

Which of the following best describes the current understanding of the makeup of the human genome?

1) Alternative RNA Splicing

 No. This statement is true, but there is a better response. 

 may involve changes to the rate at which an mRNA is translated 

 may involve regulation of mRNA splicing 

 All of the listed responses are correct. 

Consider the events that occur after transcription in eukaryote gene expression.

Post-transcriptional controls of gene expression __________.

Alternative RNA splicing increases diversity without increasing genome size.

Different protein variants can be expressed by the same gene in different tissues.

Alternative RNA splicing creates shorter mRNA transcripts.

Different protein variants can be expressed by the same gene during different stages of development.

Alternative RNA splicing has been estimated to occur in more than 95% of multi-exon genes. Which of the following is not an evolutionary advantage of alternative RNA splicing?

 It can silence genes, giving cells another way of controlling gene expression. 

 No. RNA splicing does not appear to silence genes. 

 Because it is not specific to a cell type, alternative RNA splicing can make sweeping changes in gene expression, allowing an organism to adapt quickly to new situations. 

 No. Splicing of RNA is closely controlled by the particular cell in which it is occurring. It is one way cells regulate gene expression, ensuring that a cell expresses appropriate genes. 

 It acts as a defense against viral RNA, helping organisms avoid infection, particularly by cancer-causing viruses. 

 No. Alternative RNA splicing does not appear to have any connection to viral RNA. 

 The introns that are spliced out can become miRNAs and can recognize and degrade mRNA transcripts. 

 No. miRNAs are coded for by specific sequences of DNA. 

 It expands the number of proteins that can be coded for by one gene, increasing an organism's ability to produce novel proteins. 

What is the evolutionary advantage of having untapped resources in the genome?

What is the evolutionary significance of alternative RNA splicing?

Types of Small Noncoding RNAs

A2 Biology - Post-transcriptional control of gene expression (OCR A Chapter 19.2)

 ncRNAs can fine-tune translation by binding with mRNA via complementary base pairing and promote the degradation of the mRNA strand or block its translation. 

 No. Although some microRNAs (miRNAs) and small interfering RNAs (siRNAs) are thought to function in this way, there is a better answer. 

 ncRNAs can re-establish proper patterns of DNA methylation in the genome during gamete formation. 

 No. Although some piwi-associated RNAs (piRNAs) are thought to function in this way, there is a better answer. 

 Some ncRNA can promote the formation of heterochromatin, thereby blocking the expression of genes in the tightly coiled region.  

 No. Although some siRNAs and piRNAs are thought to function in this way, there is a better answer. 

 Whereas some ncRNA block the transcription and translation of some genes, others have been observed to activate gene expression. 

 No. Although some miRNAs and piRNAs are thought to function in this way, there is a better answer. 

Consider the multiple levels of gene regulation in eukaryotic cells.

It is hypothesized that an increase in the number and diversity of noncoding RNA (ncRNA) in the genomes of species has driven the evolution of morphological complexity by way of their influence on gene regulation. Which of the following accurately represents our current understanding of the role that ncRNA is thought to play in gene regulation?

Eukaryotic Transcription Regulation

2) mRNA Protection in the Cytoplasm

 No. This statement is true, but there is a better answer. 

 there are only three types of RNA&#151;tRNA, rRNA, and mRNA 

 the vast majority of the human genome consists of "junk" DNA 

 only DNA that codes for protein, tRNA, and rRNA is transcribed 

The term "junk" DNA has been discarded.

The discovery of many noncoding RNAs is causing scientists to revise the long-held view that __________.

 each gene being activated by a unique combination of control elements and activator molecules 

 No. This is true, but it does not contribute to a greater number of gene products from a fixed number of genes.  

 coordinate control of genes on different chromosomes 

 No. Although coordinate control of genes helps explain the high complexity found in the human organism, it does not contribute to a greater number of gene products from a fixed number of genes. 

 the congregation in specific sites in the nucleus of genes involved in related metabolic processes but on different chromosomes 

 No. This contributes to the coordinate control of gene expression in humans but does not contribute to a greater number of gene products from a fixed number of genes. 

 differential activation of genes in different cell types 

 No. This can account for the cell specialization necessary for the complexity of form and function in humans, but it is not a means to generate a greater number of gene products from a fixed number of genes. 

 alternate arrangements of exons from a primary transcript 

Consider that different functional proteins can be formed by different linear combinations of shared domains.

Although the number of genes in the human genome is surprisingly low compared to less complex organisms, the number of possible products from those genes is greatly amplified by __________.

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