Cellular Physiology Test 2

The sigma subunit of bacterial RNA polymerase: (a) contains the catalytic activity of the polymerase. (b) remains part of the polymerase throughout transcription. (c) recognizes promoter sites in the DNA. (d) recognizes transcription termination sites in the DNA.

(c) recognizes promoter sites in the DNA.

Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5′-TTTTTTTTTTTTTTTTTTTTTTTTT-3′ has been covalently attached. After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following will be most abundant? (a) DNA (b) tRNA (c) rRNA (d) mRNA (e) Primary transcript RNA

(d) mRNA

According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a (a) molecule that could provide a template for the production of a complementary molecule. (b) double-stranded DNA helix. (c) molecule that could direct protein synthesis. (d) molecule that could catalyze its own replication.

(d) molecule that could catalyze its own replication.

Transcription is similar to DNA replication in that: (a) it requires a molecule of DNA helicase to unwind the DNA. (b) it uses the same enzyme as that used to synthesize RNA primers during DNA replication. (c) the newly synthesized RNA remains paired to the template DNA. (d) nucleotide polymerization occurs only in the 5′-to-3′ direction. (e) an RNA transcript is synthesized discontinuously and the pieces then joined together.

(d) nucleotide polymerization occurs only in the 5′-to-3′ direction.

Name three modifications that can be made to an RNA molecule in eucaryotic cells before the RNA molecule becomes a mature mRNA.

1) poly(A) tail must be added 2) A 5' guanosine cap must be added 3) Introns must be spliced out

You are studying a disease that is caused by a virus, but when you purify the virus particles and analyze them you find they contain no trace of DNA. Which of the following molecules are likely to contain the genetic information of the virus? (a) Protein (b) RNA (c) Lipids (d) Carbohydrates

(b) RNA

A tRNA for the amino acid lysine is mutated such that the sequence of the anticodon is 5′-UAU-3′ (instead of 5′-UUU-3′). Which of the following aberrations in protein synthesis might this tRNA cause? (a) Read through of stop codons (b) Substitution of lysine for isoleucine (c) Substitution of lysine for tyrosine (d) Substitution of lysine for phenylalanine (e) Substitution of lysine for the amino-terminal methionine

(b) Substitution of lysine for isoleucine

A strain of yeast translates mRNA into protein with a high level of inaccuracy. Individual molecules of a particular protein isolated from this yeast have the following variations in the first 11 amino acids compared with the sequence of the same protein isolated from normal yeast cells. What is the most likely cause of this variation in protein sequence? Explain your answer. (a) A mutation in the DNA coding for the protein (b) A mutation in the anticodon of the isoleucine tRNA (tRNAIle) (c) A mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different amino acids (d) A mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different tRNA molecules (e) A mutation in a component of the ribosome that allows binding of incorrect tRNA molecules to the A-site

(c) A mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different amino acids

Which of the following pairs of codons might you expect to be read by the same tRNA as a result of wobble? (a) CUU and UUU (b) GAU and GAA (c) CAC and CAU (d) AAU and AGU (e) CCU and GCU

(c) CAC and CAU

A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5′-AUGAAAAAAAAAAAAUAA-3′ has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis? (a) It inhibits binding of the small subunit of the ribosome to mRNA. (b) It inhibits peptidyl transferase activity. (c) It inhibits movement of the small subunit relative to the large subunit. (d) It inhibits release factor. (e) It mimics release factor.

(c) It inhibits movement of the small subunit relative to the large subunit.

Which of the following reactions are known to be carried out by a ribozyme? (a) DNA synthesis (b) Transcription (c) RNA splicing (d) Protein hydrolysis (e) Polysaccharide hydrolysis

(c) RNA splicing

The concentration of a particular protein X in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results? (a) The introduction of a stop codon that truncates protein X at the fourth amino acid. (b) A change of the first ATG codon to CCA. (c) The deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein. (d) A change at a splice site that prevents splicing of the RNA.

(c) The deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein.

RNA in cells differs from DNA in that: (a) it contains the base uracil, which pairs with cytosine. (b) it is single-stranded and cannot form base pairs. (c) it is single-stranded and can fold up into a variety of structures. (d) the nucleotides are linked together in a different way. (e) the sugar ribose contains fewer oxygen atoms than does deoxyribose.

(c) it is single-stranded and can fold up into a variety of structures.

Which of the following statements is TRUE? (a) Ribosomes are large RNA structures composed solely of rRNA. (b) Ribosomes are synthesized entirely in the cytoplasm. (c) rRNA contains the catalytic activity that joins amino acids together. (d) A ribosome consists of two equally sized subunits. (e) A ribosome binds one tRNA at a time.

(c) rRNA contains the catalytic activity that joins amino acids together.

Is this statement TRUE or FALSE? Explain your answer. "Since introns do not contain protein coding information, they do not have to be removed precisely (meaning, a nucleotide here and there should not matter) from the primary transcript during RNA splicing."

False, an error of 1 or 2 nucleotides would cause a frame shift in the mRNA, which would change the protein it encodes

Below is a segment of RNA from the middle of an mRNA. If you were told that this segment of RNA was part of the coding region of an mRNA for a large protein, give the amino acid sequence for the protein that is encoded by this segment of mRNA. 5′- UAGUCUAGGCACUGA -3′

S-L-G-T

Give a reason why DNA makes a better material than RNA for storage of genetic information and explain your answer.

The deoxyribose in DNA makes the molecule less susceptible to breakage compared to RNA, due to the lack of hydroxyl groups on carbon 2 of the ribose sugar

The length of a particular gene in human DNA, measured from the start site for transcription to the end of the protein-coding region, is 10,000 nucleotides, whereas the length of the mRNA produced from this gene is 4000 nucleotides. What is the most likely reason for this discrepancy?

The gene contained introns that were spliced out from the RNA

Where does Polyadenylation take place in the cell?

nucleus

Where does RNA capping take place in the cell?

nucleus

Where does RNA splicing take place in the cell?

nucleus

Where does Transcription take place in the cell?

nucleus

Where does Translation take place in the cell?

ribosomes

Once an mRNA is produced, its message can be decoded on ribosomes. The ribosome is composed of two subunits: the (1)__________________ subunit, which catalyzes the formation of the peptide bonds that link the amino acids together into a polypeptide chain, and the (2)__________________ subunit, which matches the tRNAs to the codons of the mRNA. During the chain elongation process of translating an mRNA into protein, the growing polypeptide chain attached to a tRNA is bound to the (3)__________________ -site of the ribosome. An incoming aminoacyltRNA carrying the next amino acid in the chain will bind to the (4)__________________ -site by forming base pairs with the exposed codon in the mRNA. The (5)__________________ enzyme catalyzes the formation of a new peptide bond between the growing polypeptide chain and the newly arriving amino acid. The end of a protein-coding message is signaled by the presence of a stop codon, which binds the (6)__________________ called release factor. Eventually, most proteins will be degraded by a large complex of proteolytic enzymes called the (7)__________________.

(1) large (2) small (3) P (4) A (5) peptidyl transferase (6) protein (7) proteosome

In order for a cell's genetic material to be utilized, the information is first copied from the DNA into the nucleotide sequence of RNA in a process called (1)__________________. Various kinds of RNAs are produced, each with different functions. (2)__________________ molecules code for proteins, (3)__________________ molecules act as adaptors for protein synthesis, (4)__________________ molecules are integral components of the ribosome, while (5)__________________ molecules are important for splicing of RNA transcripts.

(1) transcription (2) mRNA (3) tRNA (4) rRNA (5) snRNA

Which amino acid would you expect a tRNA with the anticodon 5′-CUU-3′ to carry? (a) Lysine (b) Glutamate (c) Glutamine (d) Leucine (e) Phenylalanine

(a) Lysine

From the list below, pick THREE reasons why the primase that is used to make the RNA primer for DNA replication would not be suitable for gene transcription? (a) Primase initiates RNA synthesis on a single-stranded DNA template. (b) Primase can initiate RNA synthesis without the need for a base-paired primer. (c) Primase synthesizes only RNAs of around 5 to 20 nucleotides in length. (d) The RNA synthesized by primase remains base-paired to the DNA template. (e) Primase uses nucleotide triphosphates.

(a) Primase initiates RNA synthesis on a single-stranded DNA template. (c) Primase synthesizes only RNAs of around 5 to 20 nucleotides in length. (d) The RNA synthesized by primase remains base-paired to the DNA template.

Which of the following statements about the genetic code are correct? (a) All codons specify more than one amino acid. (b) The genetic code is redundant. (c) All amino acids are specified by more than one codon. (d) The genetic code is different in procaryotes and eucaryotes. (e) All codons specify an amino acid.

(b) The genetic code is redundant.

In eucaryotes, but not procaryotes, ribosomes find the start site of translation by (a) binding directly to a ribosome-binding site preceding the initiation codon. (b) scanning along the mRNA from the 5′ end. (c) recognizing an AUG codon as the start of translation. (d) binding an initiator tRNA.

(b) scanning along the mRNA from the 5′ end.

Which of the following might decrease the transcription of only one specific gene in a bacterial cell? (a) A decrease in the amount of sigma factor (b) A decrease in the amount of RNA polymerase (c) A mutation that introduced a stop codon into the DNA preceding the coding sequence of the gene (d) A mutation that introduced extensive sequence changes into the DNA preceding the transcription start site of the gene (e) A mutation that moved the transcription termination signal of the gene farther away from the transcription start site

(d) A mutation that introduced extensive sequence changes into the DNA preceding the transcription start site of the gene

The following DNA sequence includes the beginning of a sequence coding for a protein. What would be the result of a mutation that changed the C marked by an asterisk to an A? 5′- AGGCTATGAATGGACACTGCGAGCCC....

A stop codon. A complete protein would not be made

One strand of a section of DNA isolated from the bacterium E. coli reads: 5′- GTAGCCTACCCATAGG -3′ A. Suppose that an mRNA is transcribed from this DNA using the complementary strand as a template. What will be the sequence of the mRNA in this region (make sure you label the 5′ and 3′ ends of the mRNA)? B. How many different peptides could potentially be made from this sequence of RNA, assuming translation initiates upstream of this sequence? C. What are these peptides? (Give your answer using the one letter amino acid code.

A. 5' GUAGCCUACCCAUUGG 3' B. 2 different peptides C. VAYP and SLPIG

Imagine that an RNA polymerase is transcribing a segment of DNA that contains the sequence: 5′- AGTCTAGGCACTGA -3′ 3′- TCAGATCCGTGACT -5′ A. If the polymerase is transcribing from this segment of DNA from left to right, which strand (top or bottom) is the template? B. What will be the sequence of that RNA (be sure to label the 5′ and 3′ ends of your RNA molecule)?

A. bottom B. 5' AGUCUAGGCACUGA 3'

Why is the old dogma "one gene—one protein" not always true for eucaryotic genes?

Splicing can give mRNAs containing different sequences, which encode different proteins. One gene can encode many proteins