Chapter 17

Where does RNA polymerase begin transcribing a gene into mRNA?

It starts after a certain nucleotide sequence called a promoter. In both eukaryotes and prokaryotes, RNA polymerase binds to the gene's promoter and begins transcription at a nucleotide known as the start point, although in eukaryotes the binding of RNA polymerase to the promoter requires transcription factors.

The direction of synthesis of an RNA transcript is _____.

5' —> 3' Nucleotides are added to the 3' end of RNA.

Which of these is currently considered the best definition of a gene?

A gene codes for either a polypeptide or an RNA molecule.

Which of the following statements about mutations is false?

A knock-out mutation results in a total absence of the mutated protein. A knock-out mutation refers to the loss of a protein's function but not necessarily to its complete absence.

At which site do new aminoacyl tRNAs enter the ribosome during elongation?

A-site This is the site at which new aminoacyl tRNAs that are complementary to the mRNA codon enter the ribosome.

If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred?

An addition mutation and a deletion mutation. If the mutations occur within the same codon, only that codon (amino acid) will be altered. One addition mutation would alter all subsequent codons (and amino acids) in the sequence.

What is the function of RNA polymerase?

It unwinds the double helix and adds nucleotides to a growing strand of RNA. RNA polymerase has several functions in transcription, including unwinding the DNA double helix and adding RNA nucleotides.

Translation occurs in the _____.

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

Which one of the following is true of tRNAs?

Each tRNA binds a particular amino acid. Aminoacyl-tRNA synthetase joins a specific amino acid to a tRNA, a single strand of RNA about 80 nucleotides long.

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

Exons

True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.

FALSE There are no tRNAs complementary to the three stop codons; termination occurs when release factors recognize the stop codon in the A-site and catalyze the release of the polypeptide from the tRNA in the P-site.

True or false? A codon is a group of three bases that can specify more than one amino acid.

False A codon is a group of three bases that can specify only one amino acid.

Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)?

One addition and one deletion mutation. This combination results in no net change in the number of bases, so the reading frame would eventually be restored.

Transcription begins at a promoter. What is a promoter?

This is the site where the RNA polymerase must bind to initiate transcription. (The promoter is the region of DNA at which the process of transcription begins.)

A codon consists of _____ bases and specifies which _____ will be inserted into the polypeptide chain.

Three ... amino acid Three nucleotide bases make up a codon and specify which amino acid comes next in the sequence.

What is the process called that converts the genetic information stored in DNA to an RNA copy?

Transcription DNA is transcribed to give an RNA copy.

Transcription

Transcription is the process by which a DNA template is used for the manufacture of several different types of RNA.

translation

Translation is the process by which information encoded in RNA is used to manufacture a polypeptide.

What is a ribozyme?

a biological catalyst made of RNA A number of examples of biological catalysts containing RNA have been discovered, including ribozymes, snRNAs, and ribosomes themselves.

What does a mutagen cause?

a change in the sequence of DNA

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.

Polypeptides are assembled from _____.

amino acids

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 flow of information in a cell proceeds in what sequence?

from DNA to RNA to protein

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

P The initiator tRNA attaches to the ribosome's P site.

Which of the following processes is an example of a post-translational modification?

Phosphorylation Enzymes can phosphorylate proteins to alter their activity.

What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing RNA processing edits the RNA transcript that has been assembled along a DNA template.

Which of the following steps occurs last in the initiation phase of translation?

The large ribosomal subunit joins the complex. This step occurs after the 5' mRNA is bound by the ribosome and the start codon is bound by an aminoacyl tRNA.

Which of the following statements best describes the promoter of a protein-coding gene?

The promoter is a nontranscribed region of a gene. The promoter is the regulatory region of a protein-coding gene at which RNA polymerase must bind to initiate transcription—it is not transcribed into the RNA.

Spliceosomes are composed of _____.

snRNPs and other proteins``

After an RNA molecule is transcribed from a eukaryotic gene, what are removed and what are spliced together to produce an mRNA molecule with a continuous coding sequence?

introns ... exons Introns, intervening sequences, are removed and the exons, expressed sequences, are spliced together.

RNA processing converts the RNA transcript into _____.

mRNA The editing of the RNA transcript produces mRNA.

Which nucleic acid is translated to make a protein?

mRNA mRNA is the message that is translated to make a protein.

What determines which base is to be added to an RNA strand during transcription?

Base pairing between the DNA template strand and the RNA nucleotides. Transcription involves the formation of an RNA strand that is complementary to the DNA template strand.

Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?

Complementary Because the template strand determines the nucleotides to be added to the RNA strand, using the same complementarity rules of the DNA, they will be complementary to each other.

What happens to RNA polymerase II after it has completed transcription of a gene?

It is free to bind to another promoter and begin transcription. The enzyme is free to transcribe other genes in the cell.

What is meant by translocation?

The ribosome slides one codon down the mRNA. Translocation is the process by which the ribosome slides down the mRNA so a new cycle of elongation can begin.

How is translation initiated?

The small ribosomal subunit binds to the mRNA. The tRNA bearing methionine binds to the start codon. The large ribosomal subunit binds to the small one. The start codon signals the start of translation.

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.