Exam 3 Practice Questions
Which of the following statements is true? (a) Ribosomes are large structures composed of both of rRNA and proteins. (b) A ribosome binds one tRNA at a time. (c) Eukaryotes and prokaryotes have identical ribosomes. (d) Ribosomes have three subunits: two small subunits and one large subunit.
(a) Ribosomes are large structures composed of both of rRNA and proteins.
Which type of lipids are the most abundant in the plasma membrane? (a) phospholipids (b) glycolipids (c) sterols (d) triacylglycerides
(a) phospholipids
Peripheral membrane proteins can be removed from the membrane without disruption of the membrane.
t
Unlike DNA polymerase, RNA polymerase only has one active site and so "backtracks" to proofread the newly synthesized transcript.
t
Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus? (a) The ribosome binds to the mRNA. (b) The mRNA is polyadenylated at its 3′ end. (c) 7-methylguanosine is added in a 5′-to-5′ linkage to the mRNA. (d) RNA polymerase dissociates.
(a) The ribosome binds to the mRNA.
Which of the following might decrease the transcription of only one specific gene in a bacterial cell? (a) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site (b) a decrease in the amount of sigma factor (c) a decrease in the amount of RNA polymerase (d) a mutation that introduced a stop codon into the DNA that precedes the gene's coding sequence
(a) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site
Below is the sequence from the 3′ end of an mRNA 5′CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-3′ If you were told that this sequence contains the stop codon for the protein encoded by this mRNA, what is the anticodon on the tRNA in the P site of the ribosome when release factor binds to the A site? (a) 5′-CCG-3′ (b) 5′-CCA-3′ (c) 5′-UGG-3′ (d) 5′-UUA-3′
(b) 5′-CCA-3'
A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity? (a) Produce lipids with hydrocarbon tails that are longer and have fewer double bonds. (b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds. (c) Decrease the amount of cholesterol in the membrane. (d) Decrease the amount of glycolipids in the membrane.
(b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds.
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) proteins (b) RNA (c) lipids (d) carbohydrates
(b) RNA
You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd gene. Which of the following statements describes the most likely effect of this mutation on Abd transcription? (a) The Abd RNA will not be produced in the mutant strain. (b) The Abd RNA from the mutant strain will be longer than normal. (c) Sigma factor will not dissociate from RNA polymerase when the Abd operon is being transcribed in the mutant strain. (d) RNA polymerase will move in a backward fashion at the Abd operon in the mutant strain.
(b) The Abd RNA from the mutant strain will be longer than normal.
Flippases differ from scramblases in that (a) scramblases catalyze transfer of specific phospholipids to cytosolic monolayer. (b) flippases catalyze transfer of specific phospholipids to cytosolic monolayer. (c) flippases are bound the cytosolic side of the membrane, but scramblases are not. (d) scamblases are bound the cytosolic side of the membrane, but flippases are not.
(b) flippases catalyze transfer of specific phospholipids to cytosolic monolayer.
In eukaryotes, but not in prokaryotes, 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.
The plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins? (a) intercellular communication (b) selective permeability (c) cellular movement (d) import/export of molecules
(b) selective permeability
A mutation in the tRNA for the amino acid lysine results in the anticodon sequence 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
(b) substitution of lysine for isoleucine
Ubiquitination, the posttranslational modification of a protein which attaches a ubiquitin tag ( a) targets that protein to be transferred into the nucleus. (b) targets that protein to the proteasome to be degraded. (c) targets that protein to the Golgi for additional posttranslational modifications. (d) targets that protein to the spliceosome for further processing.
(b) targets that protein to the proteasome to be degraded.
Which of the following statements about the carbohydrate coating of the cell surface is false? (a)It is usually found on the extracelluar side of the membrane. (b) It can play a role in cell-cell adhesion and recognition. (c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain (d) It absorbs water, which creates a slimy surface.
(c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain
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 difference? (a) A mutation in the DNA (b) RNA polymerase is malfunctioning (c) The gene contains one or more introns (d) The poly-A tail has not been added yet.
(c) The gene contains one or more introns
Different mRNA molecules can have poly(A) tails of different lengths and this affects the lifetime of the mRNA molecule in the cell. Longer poly(A) tails, means the mRNA is present for a greater time in the cell. Why do you think this is? (a) The poly(A) tail is the binding site for mRNA export factors. (b) The poly(A) tail helps with translation initiation. (c) The poly(A) tail protects the mRNA from being degraded. (d) The poly(A) tail has a role in mRNA splicing.
(c) The poly(A) tail protects the mRNA from being degraded.
Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. Which of the following is not true of glycoproteins? (a) They can be secreted into the extracellular environment. (b) They have only one transmembrane domain. (c) They have long carbohydrate chains. (d) They are recognized by lectins.
(c) They have long carbohydrate chains.
New membrane phospholipids are synthesized by enzymes bound to the _____________ side of the _________________ membrane. (a) cytosolic, mitochondrial (b) luminal, Golgi (c) cytosolic, endoplasmic reticulum (d) extracellular, plasma
(c) cytosolic, endoplasmic reticulum
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.
The plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins? (a) import/export of molecules (b) intercellular communication (c) selective permeability (d) cellular movement
(c) selective permeability
Which of the following statements about the carbohydrate coating of the cell surface is false? (a) It is not usually found on the cytosolic side of the membrane. (b) It can play a role in cell-cell adhesion. (c) the arrangement of the ogliosaccharide side chains is highly ordered much like the peptide bonds of a polypeptide chain. (d) Specific oligosaccharides can be involved in cell-cell recognition.
(c) the arrangement of the ogliosaccharide side chains is highly ordered much like the peptide bonds of a polypeptide chain. The sugars in an oligosaccharide side chain attached to the cell surface can be joined together in many different ways and in varied sequence
For eukaryotic transcription to begin, the initiation complex must assemble. What is the function of TFIID? (a) TFIID polyadenylates the tail of RNA polymerase. (b) TFIID phosphorylates the tail of RNA polymerase. (c) TFIID contains the subunit TBP that recognizes the -10 and -35 promoter site. (d) TFIID contains the subunit TBP that recognizes the TATA box promoter site.
(d) TFIID contains the subunit TBP that recognizes the TATA box promoter site.
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 that precedes the gene's coding sequence (d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start
(d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start
Which of the following statements is false? (e) A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule's synthesis is completed. (f) If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies. (g) RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides. (h) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.
(h) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.
Give three reasons why DNA makes a better material than RNA for the storage of genetic information, and explain your answer.
-The deoxyribose sugar of DNA makes the molecule much less susceptible than RNA to breakage, because of the lack of the hydroxyl group on carbon 2 of the ribose sugar. • DNA is double-stranded and therefore the complementary strand provides a template from which damage can be repaired accurately. -The use of "T" in DNA instead of "U" (as in RNA) protects against the effect of deamination, a common form of damage. Deamination of T produces an aberrant base (methyl C), whereas deamination of U generates C, a normal base. The presence of an abnormal base eases the cell's job of recognizing the damaged strand.
Match the following types of RNA with the main polymerase that transcribes them. a.) most rRNA genes b.) tRNA genes c.) 5S rRNA genes d.) protein coding genes e.) miRNA genes
A-1 B-3 C-3 D-2 E-2
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 that translation initiates upstream of this sequence? C. What are these peptides? (Use a codon table and give your answer using the one-letter amino acid code.)
A. 5′-GUAGCCUACCCAUAGG-3′ B. Two. (There are three potential reading frames for each RNA. In this case, they are GUA GCC UAC CCA UAG ... UAG CCU ACC CAU AGG ... AGC CUA CCC AUA GG? ... The center one cannot be used in this case, because UAG is a stop codon.) VAYP SLPIG Note: PTHR will not be a peptide because it is preceded by a stop codon.
Glycolipids are found on the surface of healthy cells, and contribute to the cell's defense against chemical damage and infectious agents. A. In which organelle are sugar groups added to membrane lipids? B. By what mechanism are glycolipids transported to the plasma membrane and presented to the extracellular environment? Draw a diagram to support your answer to part B.
A. The Golgi apparatus. B. Membranes that contain newly synthesized glycolipids bud from the Golgi apparatus to form vesicles. These vesicles then fuse with the plasma membrane. The glycolipids that were facing the lumen of the Golgi will now face the extracellular environment (Figure A)
Cell membranes are fluid, and thus proteins can diffuse laterally within the lipid bilayer. However, sometimes the cell needs to localize proteins to a particular membrane domain. Name three mechanisms that a cell can use to restrict a protein to a particular place in the cell membrane.
Any combination of the following four answers is acceptable. 1. The protein can be attached to the cell cortex inside the cell. 2. The protein can be attached to the extracellular matrix outside the cell. 3. The protein can be attached to other proteins on the surface of a different cell. 4. The protein can be restricted by a diffusion barrier, such as that set up by specialized junctional proteins at a tight junction.
List three ways in which the process of eukaryotic transcription differs from the process of bacterial transcription.
Any three of the following are acceptable. 1. Bacterial cells contain a single RNA polymerase, whereas eukaryotic cells have three. 2. Bacterial RNA polymerase can initiate transcription without the help of additional proteins, whereas eukaryotic RNA polymerases need general transcription factors. 3. In eukaryotic cells, transcription regulators can influence transcriptional initiation thousands of nucleotides away from the promoter, whereas bacterial regulatory sequences are very close to the promoter. 4. Eukaryotic transcription is affected by chromatin structure and nucleosomes, whereas bacteria lack nucleosomes.
While many prokaryotic cells have a single membrane bilayer, all eukaryotic cells have a complex system of internal membrane-bound compartments. How might it be advantageous for the cell to have these additional compartments?
Compartmentalization using intracellular membranes allows eukaryotic cells to separate a variety of cell processes. Although this requires a higher degree of coordination, the cell also gains a more stringent degree of control over these processes (examples include: the separation of transcription and translation; the separation of enzymes involved in protein modifications for secreted versus cytosolic substrates; the separation of proteolytic events in the lysosomes versus the cytosol etc.).
Below is the sequence from the 3′ end of an mRNA. 5′-CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-3′ mRNA, what is the anticodon on the tRNA in the P site of the ribosome when release factor binds to the A site? a) 5′-CCA-3′ b) 5′-CCG-3′ c) 5′-UGG-3′ d) 5′-UUA-3′
a) 5′-CCA-3′
Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes? (a) switching between lipid layers (b) lateral movement (c) rotation (d) flexing of hydrocarbon chains
a) switching between lipid layers
Which of the following statements about the proteasome is false? a. Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome. b. Proteases reside in the central cylinder of a proteasome. c. Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold. d. The protein stoppers that surround the central cylinder of the proteasome use the energy from ATP hydrolysis to move proteins into the proteasome inner chamber.
c. Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold.
Which of the following molecules is thought to have arisen first during evolution? a. protein b. DNA c. RNA d. all came to be at the same time
c. RNA
A mutation in the tRNA for the amino acid phenylalanine results in the anticodon sequence 5′-AUA-3′ (instead of 5′-AAA-3′). Which of the following aberrations in protein synthesis might this tRNA cause? a. read-through of stop codons b. substitution of phenylalanine for isoleucine c. substitution of phenylalanine for tyrosine d. substitution of phenylalanine for lysine
c. substitution of phenylalanine for tyrosine
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 that precedes the gene's coding sequence (d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site
d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site
Eukaryotic RNA polymerase can substitute for bacterial RNA polymerase in bacterial transcription.
f
Membrane lipids frequently flip-flop between one monolayer and the other.
f
One reason DNA is better storage molecule than RNA is that the use of "T" in DNA instead of "U" (as in RNA) protects against the effect of depurination, a common form of damage.
f
