Mastering Biology- Biotech and Gene Expression

In the diagram below, the gray unit represents _____.

RNA polymerase: RNA polymerase untwists a portion of the DNA double helix.

In the diagram below, the green unit represents _____.

the promoter: The promoter is the region of DNA at which the process of transcription begins.

In the diagram below, the two blue strands represent _____.

DNA: DNA is a double helix.

Which of these correctly illustrates the pairing of DNA and RNA nucleotides?

GTTACG CAAUGC: In RNA, uracil takes the place of thymine.

The direction of synthesis of an RNA transcript is _____.

5′ -> 3′: Nucleotides are added to the 3′ end of RNA.

Which of the following is true for both prokaryotic and eukaryotic gene expression?

RNA polymerase binds to the promoter region to begin transcription.

In which of the following actions does RNA polymerase differ from DNA polymerase?

RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis.

During RNA processing a(n) _____ is added to the 5′ end of the RNA.

modified guanine nucleotide: The 5′ cap consists of a modified guanine nucleotide.

During RNA processing a(n) _____ is added to the 3′ end of the RNA.

a long string of adenine nucleotides: A poly-A tail is added to the 3′ end of the RNA.

Spliceosomes are composed of _____.

snRNPs and other proteins: These are the component of spliceosomes.

The RNA segments joined to one another by spliceosomes are _____.

exons: Exons are expressed regions.

Translation occurs in the _____.

cytoplasm: Ribosomes, the sites of translation, are found in the cytoplasm.

What are the coding segments of a stretch of eukaryotic DNA called?

exons

A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that

many noncoding stretches of nucleotides are present in mRNA.

Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes

excision of introns

Introns are significant to biological evolution because

their presence allows exons to be shuffled.

Alternative RNA splicing

can allow the production of proteins of different sizes from a single mRNA.

Suppose that a portion of double-stranded DNA in the middle of a large gene is being transcribed by an RNA polymerase. As the polymerase moves through the sequence of six bases shown in the diagram below, what is the corresponding sequence of bases in the RNA that is produced? 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.

* UGAGCC Why? 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.

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.
For any given gene, what ultimately determines which DNA strand serves as the template strand?

* the base sequence of the gene’s promoter Why? 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?

* A cap consisting of a modified guanine nucleotide is added to the 5′ end of the pre-mRNA. * Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. * A poly-A tail (50-250 adenine nucleotides) is added to the 3′ end of the pre-mRNA. Why? 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.

Which of these is a tRNA?

B

What enzyme catalyzes the attachment of an amino acid to tRNA?

aminoacyl-tRNA synthetase: This enzyme matches a particular tRNA with a particular amino acid.

The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____.

CUG: In RNA uracil replaces thymine.

What is the name of the process shown in the diagram?

initiation (of translation): The diagram illustrates the initiation of translation.

The initiator tRNA attaches at the ribosome’s _____ site.

P: The initiator tRNA attaches to the ribosome’s P site.

A part of an mRNA molecule with the following sequence is being read by a ribosome: 5′ CCG-ACG 3′ (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3′ to 5′ direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form.

proline-threonine.