Sapling Ch. 13 & 14 Homework

Intron

region of a gene or transcript that is spliced out during RNA maturation

Exon

region of a gene or transcript that remains in the mature RNA transcript

Spliceosome

protein complex that removes regions of pre-messenger RNA

Scientists have engineered bacteria to produce human proteins such as insulin to help treat diabetes. Suppose the unmodified eukaryotic gene coding for insulin is inserted directly into a bacterial chromosome. Select the reasons why no expression would be seen in the bacterial cell for the insulin gene.

Bacteria cannot remove intronic sequence from a gene, so if the gene for insulin were transcribed, it would translate to a nonfunctional protein. The bacterial RNA polymerase will not bind to the eukaryotic promoter sequence.

Order the steps that would be used in a laboratory to engineer a bacterium that could express the human gene coding for insulin. Not all steps will be placed.

1. Isolate the mRNA of the insulin gene. 2. Generate cDNA of the insulin gene using reverse transcriptase. 3. Insert the insulin cDNA into a bacterial vector near a promoter site. 4. Transform the vector into an E. coli bacterium.

DNA encodes the cell’s genetic instructions for making proteins. The process of making proteins from DNA is divided into two stages called transcription and translation. Transcription is further divided into three steps called initiation, elongation, and termination. Classify the statements about transcription according to the step in which each occurs.

Initiation: The RNA polymerase binds to the group of transcription factors at the promoter. The DNA double helix unwinds, and RNA synthesis begins. Elongation: The RNA polymerase traverses the DNA template, adding complementary base pairs in the 5′ to 3′ direction. The newly transcribed RNA transcript is read for errors. Termination: The RNA polymerase detaches from the DNA. The RNA polymerase stops adding base pairs when it reaches a certain DNA sequence that signals the end of the gene. The RNA transcript is released.

Gene transcription occurs from right to left for gene A and gene B, whereas transcription occurs from left to right for gene C. Select the answer below that has the correct template strand for each gene.

Gene A: top, gene B: top, gene C: bottom

Transcription

Acts on only one strand Catalyzed by RNA polymerase

Replication

Catalyzed by DNA polymerase RNA primase is required

Both transcription & replication

localized in the cytoplasm in prokaryotic cells

Order the steps that pre-mRNA undergoes after eukaryotic transcription is initiated.

1. 5′ capping of transcript 2. Cleavage of 5′ donor site 3. 3′ acceptor site connects two exons 4. 3′ end processing

Complete the transcription of the RNA sequence using the DNA template.
DNA template: ATCGAC

RNA sequence: UAGCUG

The pre-mRNA strand below is a gene that is transcribed into mRNA. Label the mRNA so that it codes for the correct protein.

Blue exon, green exon, purple exon, beige exon

At least three types of RNA are required for protein synthesis. Compare and contrast mRNA, rRNA, and tRNA by moving the descriptions of their structure and function to the appropriate categories. Some phrases may describe all three types of RNA.

mRNA: moves genetic information out of the nucleus and into the cytoplasm, contains nucleotide triplets that code for specific amino acids rRNA: acts as an enzyme for peptide synthesis tRNA: moves amino acids to the site where they are added to a growing peptide, has a convoluted structure with a three-base sequence called an anticodon All: in eukaryotes, can exist outside the nucleus, composed of ribonucleic acid

Do the following phrases describe prokaryotic promoters, eukaryotic promoters, or both?

Prokaryotic: recognized by the sigma factor of RNA polymerase, includes two conserved sequences at -35 and -10 Eukaryotic: requires multiple proteins called general transcription factors, may include a TATA box (not the Pribnow box) upstream of the transcription start site Both: may include sequences downstream from the transcription start site, contains highly conserved DNA sequences

Place the steps of eukaryotic transcription in order of occurrence.

1. DNA is unzipped by RNA polymerase. 2. Ribonucleotides align with complementary DNA nucleotides. 3. RNA polymerase links triphosphate ribonucleotides together. 4. Guanylyl transferase adds a guanine cap to the 5′ end of the mRNA. 5. RNA polymerase is released from DNA. 6. The mRNA is polyadenylated and spliced.

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.

True: The spliceosome consists of five small RNA molecules and many associated proteins. Splicing occurs while the mRNA is still in the nucleus. One mRNA can sometimes code for more than one protein by splicing at alternative sites. False: Proteins in the spliceosome recognize the 5′ and 3′ splice site sequences. Splicing occurs while the mRNA is attached to the nucleosome.

The following descriptions pertain to either prokaryotic or eukaryotic transcription. Match each description to the appropriate category.

Prokaryotic: can be terminated by rho helicase, promoter includes -35 consensus sequence Eukaryotic: includes spliceosome processing, requires TFIIH, promoter includes a TATA box