BIOL207-Chapter 14 Sapling Homework

In eukaryotic gene regulation, RNA interference occurs through A-the action of small interfering RNAs that mediate the degradation of complementary mRNA molecules. B-the action of RNA-protein complexes that degrade the regulatory proteins responsible for initiating transcription. C-the accumulation of mRNA that blocks transcription of the target gene by feedback inhibition. D-the accumulation of mRNA that blocks transcription of nearby genes.

A

Identify the true statements about RNA interference. Select all the true statements. A-Duplex RNA is cleaved by the Dicer enzyme complex. B-siRNAs suppress gene expression by interfering with transcription. C-RNA interference can temporarily suppress the expression of a target gene. D-siRNAs are short, single-stranded RNA segments about 45 nucleotides long. E-Duplex RNA can be intentionally inserted into an organism to suppress a gene.

A, C, E

Suppose that a scientist deletes the AAUAAA consensus sequence, the poly(A) tail, or the 5' cap from pre-mRNAs in an mRNA. She then observes the effects on RNA regulation. Assign each RNA regulation consequence to the type of deletion most likely to result in the consequence. A-introns are not removed from the pre-mRNA B-the pre-mRNA is not cleaved at the cleavage site C-the mRNA is not transported to the cytoplasm

AAUAA deletion: B Poly(A) tail deletion: C 5' cap deletion: A

Each type of pre-mRNA processing has one or more important functions. Match the function with the appropriate type of processing. Types of processing: Addition of 5' cap, Addition of poly (A) tail, RNA splicing, RNA editing Options: A-alters nucleotide sequence in exons B-assists mRNA in binding to the large ribosomal subunit C-removes non-coding regions from pre-mRNA D-stabilizes mRNA at the end adjacent to the start codon E-assists in RNA splicing F-constructs multiple products from a single gene G-enables movement of mRNA out of the nucleus

Addition of 5' cap: D and E Addition of poly(A) tail: B RNA splicing: C, F, and G RNA editing: A

Eukaryotic messenger RNA can undergo post synthetic processing after transcription and before translation. One of the processing steps is splicing, where portions of the RNA are removed and the remaining RNA joined together. Sort the following statements regarding mRNA splicing as true or false. A-splicing occurs while the mRNA is attached to the nucleosome B-in splicing, intron sequences are removed from the mRNA in the form of lariats (loops), and are degraded C-one mRNA can sometimes code for more than one protein by splicing at alternative sites D-splicing of mRNA does not involve any proteins E-splicing occurs while the mRNA is still in the nucleus

True: B, E, C False: D and A

Cleavage and polyadenylation of the 3' end of pre-mRNA is a posttranscriptional modification common to most protein-coding mRNA. It facilitates binding to ribosomes for translation, stabilizes the mRNA molecule, and prevents its degradation by exonucleases. Using recombinant DNA techniques, any gene that has a promoter for RNA polymerase II can instead be connected to a promoter for RNA polymerase I. This hybrid gene is transcribed by RNA polymerase I, but the transcript does not undergo 3\' cleavage and polyadenylation. Explain why the hybrid gene mRNA transcript does not undergo 3\' cleavage and polyadenylation. A-RNA polymerase II binds to the 3' end and prevents processing by RNA polymerase I. B-Recombinant DNA techniques cause premature stop codons that prevent 3'-end transcription and processing. C-Regulatory factors must first associate with RNA polymerase II before 3' cleavage and polyadenylation. D-Regulatory factors for RNA polymerase I prevent 3' cleavage and polyadenylation. E-Protein-coding genes have a consensus sequence that interferes with RNA polymerase I and proteins involved in polyadenylation.

C

How do the nucleus and ribosomes work together to generate a protein? A-Ribosomes produce mRNA that migrates into the nucleus and uses a gene in the DNA as instructions to synthesize a specific protein. B-The segment of DNA that contains a gene leaves the nucleus and is used by the ribosomes as instructions to synthesize a protein. C-In the nucleus, DNA is transcribed to mRNA, which the ribosomes use as instructions to synthesize a specific protein. D-Ribosomes migrate into the nucleus, attach to a gene in the DNA, and use the gene as a transcript to synthesize a specific protein.

C

RNA interference may be triggered when inverted repeats in an RNA molecule fold to form double-stranded RNA. Which of the following RNA sequences can potentially fold to form double-stranded RNA via a hairpin loop? A-5'-.....AGUCC..........AGUCC.....-3' B- 5'-.....CCAUG..........AUGCC.....-3' C- 5'-.....AGUCC..........GGACU.....-3' D- 5'-.....UACAG..........CAUAG.....-3'

C

Where would the 3' untranslated region be located on the DNA and RNA molecule? A-exon 2 B-exon 1 C-exon 8 D-intron 1 E-intron 7

C

Why is a cap added to mRNA, but not to tRNA or rRNA? A-Transfer RNA and rRNA exhibit complex structures with double stranded regions. The three-dimensional shapes of these molecules keep the 5\' end of the RNA away from the enzymes that process the cap. B-Transcription and processing of mRNA occur in the nucleus, where cap binding proteins are found. These proteins, which add and modify the cap, are not found in the cytoplasm, where tRNA and rRNA are transcribed and processed. C-Each of the three types of RNA are transcribed by different RNA polymerases. Only RNA polymerase II, involved in mRNA synthesis, contains a domain capable of interacting with enzymes that form the cap. D-Only mRNA contains introns. Capping occurs simultaneously with intron removal because the same enzymes and proteins involved in both of these processes must bind to RNA at the same time.

C

RNA interference (RNAi) is a mechanism of gene silencing that is mediated by the presence of double-stranded RNA. Arrange the steps involved in gene silencing by RNAi. A-Target RNA is degraded B-RNA-induced silencing complex (RISC) binds to short dsRNA C-Long dsRNA is cleaved into short dsRNA D-the sense strand is separated from the antisense strand and degraded. E-antisense RNA pairs with the target RNA

C, B, D, E, A

Suppose that RNA polymerase was transcribing a eukaryotic gene with several introns. In what order would the RNA polymerase encounter the following elements in the DNA sequence of the gene? A-stop codon B-translation initiation codon C-TATA box element D-3' UTR E-5' UTR F-splice acceptor site

C, E, B, F, A, D

Classify each description as true of introns only, exons only, or both. A-present in eukaryotic genomes B-generally absent from bacterial genomes C-part of the final mRNA strand D-code for an amino acid sequence E-removed from initial mRNA strand prior to translation F-present in the DNA used as the template for transcription

Introns only: B and E Exons only: D and C Both introns and exons: F and A

Suppose a geneticist mutates the gene for the poly(A) tail-binding protein (PABP) in an eukaryotic cell line. The resulting mutant protein cannot bind to poly(A) tails. What is the effect of the PABP mutation in the cultured cells? A-Transcription will not occur in the cultured cells, because PABP is an essential transcription factor. B-Translation will not occur in the cultured cells, because mRNAs will be degraded at a greater rate than normal. C-Transcription will occur in the cultured cells, but the resulting transcript will be longer than normal. D-Translation will occur in the cultured cells, but the resulting polypeptide will be longer than normal. E-Replication will not occur in the cultured cells, because PABP determines the location of the origin of replication.

B

Use the diagram provided to select the correct statement regarding RNA splicing. A-a protective cap is put on the 5' end B-only coding exons are spliced together to make finished mRNA C-the 3' end receives a string of adenines D-only coding introns are spliced together to make finished mRNA

B

What is the function of the spliceosome? A-The spliceosome transcribes mitochondrial and chloroplast genes. B-The spliceosome removes the introns and joins the exons to form the mature transcript. C-The spliceosome removes the Shine-Delgarno sequence from the 5' end of the mRNA. D-The spliceosome adds a stretch of about 170 adenine nucleotides to the 3' end of the mRNA. E-The spliceosome adds a 7-methylguanosine residue to the 5' end of the mRNA.

B

Why can alternative splicing of messenger RNAs (mRNAs) be advantageous for eukaryotic organisms? A-allows exons from two different genes to be spliced into a new mRNA B-increases the variety of proteins that can be produced C-decreases the average gene length in eukaryotes D-allows for smaller genomes than prokaryotes E-removes exons instead of introns from newly transcribed mRNA

B

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disease caused by mutations in the gene that encodes dystrophin, a large protein that plays an important role in the development of normal muscle fibers. The dystrophin gene is immense, spanning 2.5 million base pairs, and includes 79 exons and 78 introns. Many of the mutations that cause DMD produce premature stop codons, which bring protein synthesis to a halt, resulting in a greatly shortened and nonfunctional form of dystrophin. Some geneticists have proposed treating DMD patients by introducing small RNA molecules that cause the spliceosome to skip the exon containing the stop codon. The introduction of the small RNAs will produce a protein that is somewhat shortened because an exon is skipped and some amino acids are missing, but it may still result in a protein that has some function. The small RNAs, antisense RNAs, used for exon skipping are complementary to bases in the pre-mRNA, which will prevent proper associating of spliceosome for intron removal. (A. Goyenvalle et al., 2004. Science 306:1796-1799). In order to skip the mutated exon and potentially treat DMD, select the best antisense RNA targets. A- a 5' splice site of the intron upstream of the exon to be skipped B- a branch point of the intron upstream of the exon to be skipped C-a 5' splice site of the intron downstream of the exon to be skipped D-a 3' splice site of the intron upstream of the exon to be skipped E-a 3' splice site of the intron downstream of the exon to be skipped

B, C, D

For the full-length ovalbumin gene shown below, where is the most likely location of the 5\' untranslated region on the DNA and RNA molecule? A-exon 2 B-exon 8 C-intron 1 D-intron 7 E-exon 1

E

How would the deletion of the Shine-Dalgarno sequence affect a bacterial mRNA? A-DNA replication would not occur. B-Translation would occur at a slower rate. C-Transcription would not occur. D-Transcription would occur at a slower rate. E-Translation would not occur.

E

Which description applies to alternative mRNA splicing? A-protein modifications such as addition of a functional group, or structural changes such as folding B-heritable changes in gene expression that occur without altering the DNA sequence C-a gene cluster controlled by a single promoter that transcribes to a single mRNA strand D-mRNA modifications such as additions of a 5'-cap and 3' poly-A tail and removal of introns E-processing of exons in mRNA that results in a single gene coding for multiple proteins

E

Identify which statements apply to the ribosome, RNA polymerase II, or both in eukaryotic cells. A-has protein components B-is can attach to the endoplasmic reticulum C-is used in translation D-found in nucleus E-made of two RNA-protein subunits F-is used in transcription

Ribosome: C, E, B RNA polymerase II: D and F Both: A