ch. 13 transcription

Which statements are true? Select all that apply. -Intrinsic termination in prokaryotes occurs when the rho termination factor interacts with the growing RNA transcript. - Since prokaryotes lack a nucleus, translation can begin before the transcript is fully transcribed. -Three different RNA polymerases in eukaryotes transcribe different classes of genes. -Eukaryotic RNA polymerase II requires general transcription factors for initiation of transcription.

-Since prokaryotes lack a nucleus, translation can begin before the transcript is fully transcribed. -Three different RNA polymerases in eukaryotes transcribe different classes of genes. -Eukaryotic RNA polymerase II requires general transcription factors for initiation of transcription. One of the fundamental differences between prokaryotes and eukaryotes is that prokaryotes lack a nucleus that separates transcription from translation. Additionally, prokaryotes have only one RNA polymerase that transcribes all of the genes, whereas eukaryotes have three different RNA polymerases that recognize different promoters, transcribe different genes, and produce different RNAs. In prokaryotes, RNA polymerase/sigma factor can initiate transcription alone, but in eukaryotes, RNA polymerases require many protein-protein interactions with several general transcription factors for initiation of transcription to occur.

During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. Which of the following initially determines which DNA strand is the template strand, and therefore in which direction RNA polymerase II moves along the DNA? -the position of the gene's promoter on the chromosome -the location of specific proteins (transcription factors) that bind to the DNA -which of the two strands of DNA carries the RNA primer -the location along the chromosome where the double-stranded DNA unwinds -the specific sequence of bases along the DNA strands

-the specific sequence of bases along the DNA strands In eukaryotes, binding of RNA polymerase II to DNA involves several other proteins known as transcription factors. Many of these transcription factors bind to the DNA in the promoter region (shown below in green), located at the 3' end of the sequence on the template strand. Although some transcription factors bind to both strands of the DNA, others bind specifically to only one of the strands. Transcription factors do not bind randomly to the DNA. Information about where each transcription factor binds originates in the base sequence to which each transcription factor binds. The positioning of the transcription factors in the promoter region determines how the RNA polymerase II binds to the DNA and in which direction transcription will occur.

After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus? 1. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. 2. Coding sequences called exons are spliced out by ribosomes. 3. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. 4. A translation stop codon is added at the 3' end of the pre-mRNA. 5. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA.

1. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. 3. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. 5. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. Once RNA polymerase II is bound to the promoter region of a gene, transcription of the template strand begins. As transcription proceeds, three key steps occur on the RNA transcript: Early in transcription, when the growing transcript is about 20 to 40 nucleotides long, a modified guanine nucleotide is added to the 5' end of the transcript, creating a 5' cap. Introns are spliced out of the RNA transcript by spliceosomes, and the exons are joined together, producing a continuous coding region. A poly-A tail (between 50 and 250 adenine nucleotides) is added to the 3' end of the RNA transcript. Only after all these steps have taken place is the mRNA complete and capable of exiting the nucleus. Once in the cytoplasm, the mRNA can participate in translation.

Below is a partial DNA sequence used to answer the following questions. (4-9) 5' - TATGCAGCACATT - 3' 3' - ATACGTCGTGTAA - 5' If transcription occurred from left to right, which strand is the template strand? 3' - TATGCAGCACATT - 5' 5' - TATGCAGCACATT - 3' 5' - ATACGTCGTGTAA - 3' 3' - ATACGTCGTGTAA - 5'

3' - ATACGTCGTGTAA - 5' RNA polymerase travels along the template strand in the 3' to 5' direction, synthesizing an RNA molecule from 5' to 3'. If the polymerase is moving from left to right, the strand that is oriented from 3' to 5' left to right is the bottom strand. This is the template strand. The top strand is called the coding strand (or sometimes the non-template) strand. The template strand is complementary to the mRNA sequence; the coding strand is the same sequence with uracil (U) instead of thymine (T).

If transcription occurred from right to left, what RNA sequence would be produced? 3' - ATACGTCGTGTAA - 5' 5' - TATGCAGCACATT - 3' 5' - UAUGCAGCACAUU - 3' 3' - AUACGUCGUGUAA - 5' 5' - AUGCAGCACAUU - 3'

3' - AUACGUCGUGUAA - 5' The RNA sequence is synthesized 5' to 3' by base complementarity with the template strand. If the top strand is the template, then the RNA sequence should be identical to the bottom strand except with uracil (U) instead of thymine (T).

If transcription occurred from right to left, which strand is the template strand? 3' - ATACGTCGTGTAA - 5' 5' - ATACGTCGTGTAA - 3' 3' - TATGCAGCACATT - 5' 5' - TATGCAGCACATT - 3'

5' - TATGCAGCACATT - 3' Regardless of whether transcription is being carried out from left to right, or right to left, the RNA polymerase moves in the 3' to 5' direction along the template strand. If transcription is proceeding from right to left, the top strand is the template strand as it is oriented from 3' to 5' going from right to left.

If transcription occurred from left to right, what the RNA sequence would be produced? 5' - UAUGCAGCACAUU - 3' 5' - TATGCAGCACATT - 3' 3' - AUACGUCGUGUAA - 5' 3' - ATACGTCGTGTAA - 5' 5' - AUGCAGCACAUU - 3'

5' - UAUGCAGCACAUU - 3' The RNA sequence is produced 5' to 3' by base complementarity with the template strand. This produces an RNA sequence identical to the coding strand of DNA (top strand in this example) except with uracil (U) instead of thymine (T).

Enter the sequence of bases as capital letters with no spaces and no punctuation. Begin with the first base added to the growing RNA strand, and end with the last base added. 5' GGCTCA 3' template strand

5' UGAGCC 3' There are three principles to keep in mind when predicting the sequence of the mRNA produced by transcription of a particular DNA sequence. -The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand. -The RNA polymerase reads the code from the template strand in the 3' to 5' direction and thus produces the mRNA strand in the 5' to 3' direction. -In RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the base-pairing rules in transcription are A→U, T→A, C→G, and G→C, where the first base is the coding base in the template strand of the DNA and the second base is the base that is added to the growing mRNA strand.

Based on the results of the copolymer experiment, what triplet code can definitely be assigned to valine? GUU UGU GUG GGU UGG

GUG Both copolymers have the GUG codon and only have Valine in common.

Use the following copolymers to decipher the genetic code: UG and UGG. Which codons are present in the UG copolymer? Select all that apply. TGT GUG GUA UGU UGG

GUG and UGU The possible codons are determined by repeating the copolymer. Within a UGUGUGUGUG sequence of RNA, it is possible to have a UGU codon and a GUG codon. It is not possible to have a UGG codon, because the copolymer is repeated UG, and there are never two G's together.

Which amino acids are encoded by the UGG copolymer? Select all that apply. Glycine Tryptophan Arginine Valine

Glycine Tryptophan Valine The three codons present in the UGG copolymer are UGG which codes for tryptophan, GGU which codes for glycine and GUG which codes for valine.

Identify the components involved in the initiation of transcription. Sort each term into the appropriate bin. (explination in answer) prokaryotic initiation of transcription eukaryotic initiation of transcription neither word bank: -35 consensus pribnow box enahncers sigma subunit -30 TATA box rho DNA polymerase RNA polymerase II

Prokaryotic: -35 consensus, pribnow box, sigma subunit eukaryotic: -30 TATA box, enhancers, RNA polymerase II neither: rho, DNA polymerase While the basics of transcriptional initiation in prokaryotes and eukaryotes are similar, they differ in complexity. Prokaryotic RNA polymerase, with the addition of the sigma subunit, recognizes the Pribnow box and the -35 consensus. Eukaryotic promoters and consensus sequences are considerably more diverse, and the three different RNA polymerases recognize different promoters, transcribe different genes, and produce different RNAs. Most eukaryotic promoters have a -30 TATA box. In addition to the core promoter, enhancer sequences around the eukaryotic gene bind activator proteins that interact with initiation complex to dramatically increase the efficiency of transcription. Many protein-protein interactions are necessary to initiate transcription in eukaryotes.

Which codons are present in the UGG copolymer? Select all that apply. GGT UGG UGA UGU GGU GUG

UGG GGU GUG The possible codons are determined by repeating the copolymer. Within a UGGUGGUGG sequence of RNA, it is possible to have a UGG codon, a GGU codon and a GUG codon. It is not possible to have a UGU codon, because the copolymer is repeated UGG.

Which one of the following amino acids is encoded by both copolymers? Glycine Valine Arginine Tryptophan

Valine The UG copolymer has UGU and GUG codons. The UGG copolymer has UGG, GGU and GUG codons. Both copolymers have the GUG codon in them, which encodes valine.

Which amino acids are encoded by the UG copolymer? Select all that apply. Valine Tryptophan Cysteine Arginine

Valine Cysteine The two codons present in the UG copolymer are UGU which codes for cysteine and GUG which codes for valine.

If transcription occurred from right to left, what is the second amino acid in the growing polypeptide chain? cys gln val ala

cys The RNA sequence is synthesized 5' to 3' by base complementarity with the template strand. If the top strand is the template, then the RNA sequence should be identical to the bottom strand except with uracil (U) instead of thymine (T).Translation then starts at the first AUG from the 5' end of the RNA. RNA nucleotide are not grouped into codons until the AUG. If the first codon is AUG/Methonine, then the second codon is UGC which encodes cysteine.

If transcription occurred from left to right, what is the second amino acid in the growing polypeptide chain? ala gln cys val

gln Grouping RNA nucleotides into codons does not start until the AUG start codon. The AUG in this sequence begins with the second nucleotide from the 5' end of the coding strand (top strand). If AUG/Methionine is the first codon, then the second codon is CAG which encodes glutamine (gln).

In prokaryotes, which component must disassociate to allow for elongation of the transcriptional complex? RNA polymerase sigma subunit rho none of the above

sigma subunit The sigma subunit helps RNA polymerase bind the promoter. This interaction is so strong that the RNA polymerase cannot leave the promoter. When the sigma subunit disassociates, this interaction is weakened, which allows the RNA polymerase to leave the promoter for elongation to begin.