cell bio test 3
You isolate DNA from a particular organism and analyze it. The amount of adenine was 6 µmoles and the A+T/G+C ratio is 4.0. How much guanine should be in the sample?
1.5 µmoles
In addition to their key role in vesicle targeting by recruiting specific cytosolic tethering proteins to specific membrane surfaces, Rabs also play a key role in ________: 1) regulating the activities of numerous proteins involved in other aspects of membrane trafficking; 2) regulating the aspects of motor proteins that move membranous vesicles through the cytoplasm; 3) regulating metabolic processes
1/2
How many mitochondrial subcompartments exist into which proteins can be delivered?
2
How many subcompartments do peroxisomes have into which an imported protein can be placed?
2
You are working on a project in which you block autophagy in a particular portion of the brain of a laboratory animal. What happens to these animals?; 1) Nothing happens since nerve cells are so long-lived.; 2) That region of the nervous system experiences a massive loss of nerve cells.; 3) There is slight, but not dangerous damage, to the organelles and proteins of the nerve cells.; 4) There is continuous damage to the proteins and organelles of these long-lived cells.
2/4
Which of the following is a mechanism that is thought to be responsible for maintaining proteins in a particular organelle, like the ER or the Golgi complex? 1) retention of molecules resident in an organelle that are excluded from transport vesicles; 2) destruction of proteins that find their way mistakenly into transport vesicles; 3) retrieval of molecules that have left the compartment in which they normally reside; 4) solubilization in the cytoplasm and refolding by chaperonins
3
In what direction is a polypeptide produced
5 to 3
In what direction is mRNA translated by a ribosome?
5' to 3' direction
Which two genes above are likely to have the most crossing over between them?
A/b
What GTP-binding protein is associated with the formation of the COPI coat on COPI-coated vesicles?
ARF1 (adenosylation ribose factor)
What circumstantial evidence supports the proposed role of the Rabs in recruiting cytosolic tethering proteins to specific membrane surfaces?
All of these are correct statements that support the proposed role of the Rabs
The coat of vesicles that transport materials around the cell interior ___________.
All of these are correct.
Which of the following is a function associated with the smooth endoplasmic reticulum in at least some cells?
All of these are correct.
Which of the following is a specific way in which miRNAs may carry out translational-level control?
All of these are correct.
_______ mRNAs are preferentially localized at the anterior end of a fruit fly larva; ______ mRNAs are preferentially localized at the opposite or posterior end of the larva.
Bicoid, oskar
What is the effect on a yeast cell of the presence of a mutant gene involved in vesicle fusion?
Cells amassed an excess number of unfused vesicles.
ow does the histone content associated with centromeric DNA differ from those associated with the rest of the chromosome?
Centromeric DNA contains a unique H3 histone variant CENP-A, which replaces H3 in many of the nucleosomes.
You are studying two chromosomes, one (chromosome 10), which carries no genes that are active in the cells being studied, and the other (chromosome 13), which is rich in protein-coding sequences, most of which are transcribed in the cells you are studying. Where would these chromosomes be likely to be located within the interphase nucleus?
Chromosome 10 would be in the heterochromatin; chromosome 13 would be in the euchromatin.
Which enzyme, also responsible for siRNA formation, carves miRNAs from their double-stranded, fold-back RNA precursor (pre-miRNA)?
Dicer ribonuclease
Why does the isoleucyl-tRNA synthetase use two types of proofreading mechanisms to ensure its accurate aminoacylation?
Isoleucine is very hard to distinguish from valine, since they differ only by a single methylene group.
In what way does the bound IRP (iron regulatory protein) prevent translation?
It interferes physically with the binding of a ribosome to the 5' end of the ferritin mRNA
Why is RNAi now used as a strategy for investigating the effect of a missing protein more often than generating an organism that possesses a mutant gene?
It is easier to synthesize a small RNA than to generate an organism that possesses a mutant gene.
It is important that the two strands of DNA near the front end of a gene are able to separate easily so that the gene can be expressed at the appropriate time. What should the base composition in this part of the gene therefore be and why?
It should be AT-rich since the smaller number of H bonds in that region of the gene will allow the strands to separate more easily.
Given that an a-helix goes through one turn every 3.5 residues, why do the leucines of the leucine zipper all face in the same direction?
Leucines in a leucine zipper appear every 7 residues, two full turns of the helix.
What evidence supports the Ohno suggestion about vertebrate evolution from ancestral invertebrates by whole-genome duplication?
Modern vertebrates have four times the number of certain groups of genes compared to their homologues in Amphioxus.
If you treated a macrophage with colchicine (a microtubular inhibitor), what would be likely to happen to the rate of phagocytosis? What would be likely to happen to the rate of phagocytosis if you treated the macrophage with an inhibitor of microfilament contractile activities?
Nothing would happen after colchicine exposure. The rate would drop after cytochalasin B exposure.
________ is one of the more abundant nuclear proteins in amphibian oocytes and it has a stretch of amino acids at its ____-terminus that serves as a signal directing this protein to the nucleus.
Nucleoplasmin, C
Cells are infected with a vesicular stomatitis virus (VSV) strain in which a viral gene (VSVG) is fused to the green fluorescent protein gene. When the chimeric protein is synthesized, what pathway does it follow from synthesis until it leaves the cell?
RER, Golgi complex, plasma membrane, viral envelopes
What is responsible for synthesizing hnRNAs
RNA polymerase II
Exonic splicing sequences (ESEs) serve as binding sites for which RNA-binding proteins below?
SR proteins
The _______ binds integral proteins of the inner mitochondrial membrane and inserts them into lipid bilayer and the ______ binds matrix proteins and translocates them completely through the inner mitochondrial membrane into the aqueous matrix compartment.
TIM22 complex, TIM23 complex
The outer mitochondrial membrane contains a protein import complex, the _________ that includes ________ and protein-lined ________ through which unfolded polypeptides are translocated across the outer mitochondrial membrane.
TOM complex, receptors that recognize and bind mitochondrial proteins, channels
When the RNA primer is removed from the 5' end of a newly made DNA strand, what effect does this have on the structure of the double helical DNA molecule?
The 3' end of the template strand overhangs the 5' end of the newly made strand.
If chromatin from which histone H1 has been selectively removed has the H1 histone added back to it, what happens?
The 30-nm fibers reform.
How are integral membrane proteins thought to enter the lipid bilayer?
The aqueous translocon channel seems to have a gate that continuously opens and closes, giving each nascent polypeptide segment a chance to partition itself into the lipid bilayer's hydrophobic core.
What may happen if a protein that is supposed to have a short survival time and that is involved in the initiation of cell division is not destroyed when it is supposed to be destroyed?
The cells may become malignant.
If cells cannot replicate the ends of their DNA, what should happen with each round of cell division?
The chromosomes should get shorter
Susumu Ohno proposed that the evolution of vertebrates from a much simpler invertebrate ancestor was made possible by two separate rounds of whole-genome duplication during an early evolutionary period. How was it proposed that the whole-gene duplication led to the encoding of the more complex vertebrate body?
The many extra genes generated by genetic duplication can be molded over time into new genes needed to encode the complex vertebrate body.
Which of the following is a difference between the coats of COPII- and clathrin-coated vesicles?
The outer scaffold subunits of the clathrin lattice of coated vesicles overlap extensively, while those of the COPII lattice of coated vesicles do not overlap.
Why are satellite DNAs separated from the bulk of the genome during density gradient centrifugation?
Their base composition is significantly different from that of the bulk of the genome.
What happened to COPI-coated vesicles within the cell when the cell was treated with GTP analogues that could not be hydrolyzed?
They accumulated in the cytoplasm
Which of the following is not a normal property of eukaryotic mRNAs?
They are found in the cytoplasm and inside the Golgi complex.
If it were demonstrated that translocation can occur in vitro in the absence of the elongation factor (either EF-G in prokaryotes or eEF2 in eukaryotes) and GTP, what would be suggested about the process of translocation with all of its complex conformational changes?
Translocation is an intrinsic property of the ribosome and not a property of the elongation factors and GTP.
Cells are infected with a virus carrying a temperature-sensitive mutant VSVG gene that encodes a protein that cannot leave the ER of infected cells grown at restrictive temperatures. Thus, at higher temperatures, ______________.
VSVG protein cannot leave the ER.
Which explanation below would explain the initial inability to demonstrate RNAi in mammalian cells?
When exposed to mammals or their cells, dsRNAs usually initiate a global response that inhibits protein synthesis in general that would obscure the inhibition of a specific protein.
What happens to a newly synthesized glycoprotein after the binding of calnexin or calreticulin to help the protein correctly complete its folding?
When the glycoprotein's folding is correctly completed, the remaining glucose on its oligosaccharide chain is eventually removed enzymatically and the glycoprotein is released from the chaperone.
Based on what is known about the involvement of calcium ions in exocytosis, what should happen if Ca2+ ions are injected into a cell?
Wholesale exocytosis of secretory product occurs.
Several methods have been developed that allow investigators to synthesize proteins that contain unnatural amino acids (amino acids other than the 20 normally incorporated by the translation machinery). The addition of these unnatural amino acids is encoded in the mRNA. This "expansion" of the genetic code generally involves the use of an experimentally modified tRNA and cognate amino acyl-tRNA synthetase that specifically recognizes the unnatural amino acid. When it is encountered, what codon codes for the incorporation of this unnatural amino acid?
a particular stop codon
What do studies suggest governs the "decision" to destroy a defective protein that has been unable to fold correctly and has been in the ER for an extended period of time?
a slow-acting ER enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
The following recombination frequencies were found for four genes (A, B, C and D) on the same chromosome: between genes A and B - 45%, between genes C and D - 10%, between A and D - 7%, between genes C and B - 18%, between genes C and A - 17%, and between genes B and D - 28%. Which two genes above are likely to have the least crossing over between them?
a/d
What is the rate at which bacterial RNA polymerase synthesizes RNA?
about 20 50 nucleotides/sec
The final steps in translation involve the release of the deacylated tRNA from the P site, dissociation of the mRNA from the ribosome, and disassembly of the ribosome into its large and small subunits in preparation for another round of translation. In bacterial cells, which protein below is involved in these processes?
all
What components below are selected for transport by vesicles originating in the Golgi complex
all of the other answers
A control cell that is synthesizing a GFP-labeled version of mannosidase II has fluorescence localized in the numerous Golgi complexes of the cell. Normally, this enzyme is synthesized in the endoplasmic reticulum and moves via transport vesicles to the Golgi complex, where it takes up residence. If an experimental cell contains an siRNA that leads to the fluorescence being restricted to the endoplasmic reticulum, with what would the siRNA be likely to interfere?
an mRNA that codes for a protein involved in the transport of the enzyme from the ER to the Golgi complex
Which of the following is not required for protein synthesis
anions
The global shutdown of protein synthesis exhibited by RNA interference in mammalian cells appears to have evolved for what reason?
as a means to protect cells from infection by viruses
Proteins carrying the helix-loop-helix motif with the positively charged amino acids preceding it are said to have a ______ motif and almost always occur as ______.
bHLH, heterodimers
The drugs that lower LDL concentration in the blood function by ________.
blocking a key cholesterol synthesis enzyme, HMG CoA reductase
What subunit(s) of the COPII coat bind(s) to the vesicle membrane to form the outer structural cage of the protein coat?
both Sec31and Sec13
Which endosome serves as a sorting station that directs different types of receptors and ligands along different pathways?
carbohydrate chains attached to integral membrane proteins
What appears to be responsible for the formation of the 30 nm chromatin fiber from the 10 nm nucleosomal filament?
coiling of the 10 nm nucleosomal filament
How would you describe the half-lives of rRNAs and tRNAs?
days or weeks long
What powers the movement of proteins into the mitochondrial matrix?
electric potential across the inner mitochondrial membrane acting on the positively-charged targeting signal
The process of membrane fusion and subsequent content discharge is called ______ and is usually triggered by a release of ______.
exocytosis, Ca2+ ions
What sugar is usually removed from the N-linked core oligosaccharide chains on proteins in the Golgi complex as opposed to the glucose residues trimmed off in the ER?
fucose
There are genes on the X chromosome that manage to escape inactivation by an as yet unknown mechanism. What particular genes are included in this group and what might be the reason that they remain activated?
genes that are also present on the Y chromosome; they will be expressed equally in both sexes
Which of the following carbohydrates is not synthesized in the Golgi complex?
glycogen
Once the s factor leaves the core enzyme, what happens?
he core enzyme continues synthesis.
If the internal promoter of the 5S rRNA gene is placed in a gene elsewhere in the genome and transcription is then monitored, what happens?
he gene into which the promoter was inserted is transcribed by polymerase III.
You attach the regulatory region for the renalin gene, a gene normally only active in kidney tissue, to the bacterial b-galactosidase gene. The renalin gene is normally activated by a bHLH-containing transcription factor. You introduce the engineered gene into a transgenic mouse embryo. As the embryo develops, where can b-galactosidase be seen?
in the cells and tissues that will give rise to the kidney
SNAREs vary in structure quite a bit, but all of them contain a common domain. Where is this domain located, of what is it composed and what is it called?
in the cytosol, 60 70 amino acids that form a complex with another SNARE motif
The greatest similarities among codons that specify the same amino acid occur _________.
in the first two nucleotides of the triplet
The greatest variability among codons that specify the same amino acid occurs _________.
in the third nucleotide of the triplet
Where are v-SNAREs and t-SNARES found, respectively
incorporated into transport vesicle membranes during budding, in target compartment membranes
During the formation of mitotic chromosomes, the CENP-A-containing nucleosomes become situated on the outer surface of the centromere where they serve as the platform for the assembly of the ________, which serves as the attachment site of the __________ that separate the chromosomes during cell division.
kinetochore, microtubules
What cells are known to have escaped normal growth control and thus keep dividing indefinitely
malignant cancer cells
The N-terminal targeting sequence of mitochondrial-matrix proteins is ultimately removed by _______ following import into the matrix.
mitochondrial processing peptidase
Which type of DNA sequence in the genome is interspersed throughout the genome, arose predominantly by transposition of mobile genetic elements and constitutes a significant portion of the eukaryotic genomes?
moderately repeated DNA sequences
What appears to determine the modifications that appear on newly synthesized histones in daughter chromatin?
modifications present on the histone tails in parental chromatin
The ER reportedly contains sensors that monitor the concentration of unfolded or misfolded proteins in the lumen. One proposal suggests that the sensors are normally kept in an inactive state by ______, particularly ______.
molecular chaperones, BiP
What is thought to cause or at least be linked to dyskeratosis?
mutations in the enzyme that converts uridine to pseudouridine
In addition to binding RNA, SR proteins may bind to RNA polymerase. To what portion of RNA polymerase might they bind?
negatively-charged phosphate groups that are added to the polymerase's CTD as transcription begins
You are interpreting data on a DNA chip or microarray. You expose the chip to a mixture of two cDNA populations: one from cells that were not treated with a glucocorticoid hormone (untreated controls; labeled with a red fluorescent dye) and a population from cells that were treated with glucocorticoid hormones (glucocorticoid-treated; labeled with green fluorescent dye). You look at a spot on the chip representing the gene for esterase, a gene that is expressed in neither the untreated controls nor the glucocorticoid-treated cells. What color should the spot representing the esterase gene be?
no color, the spot is not labeled
The naked regions seen on the DNA fiber between transcriptional units are called ________.
nontranscribed spacers
What enzyme is required for the movement of transposable elements that involve an RNA intermediate?
peptidyltransferase
Which of the proteins below is(are) not made on the membrane-bound ribosomes of the RER?
peripheral proteins of the inner surface of the plasma membrane
The length of a particular minisatellite DNA locus is highly variable in the population and may even vary among members of the same family. Such minisatellites are said to be ________ and are often used to identify individuals in criminal or paternity cases through the technique of DNA fingerprinting.
polygenic
The effect of _________ on embryonic development is ___________.
polyspermy, disruptive cell divisions and the early death of the embryo
What is the name of the structure that is composed of RNA polymerase II bound to a gene's promoter with the cooperation of a number of general transcription factors (GTFs)?
preinitiation complex and PIC
What provides the energy that drives the polymerization of RNA from a DNA template
ribonucleoside triphosphate precursors
Which of the following is guanosine?
ribose + guanine
The consensus sequence of the -35 element is recognized by the _____ and has the sequence ______.
s factor associated with an RNA polymerase, TTGACA
The inactive mRNAs that are stored in an egg prior to fertilization typically have ________.
shortened poly(A) tails
What specific cellular responses are known to be triggered by the regulated release of Ca2+ ions from the SER?
skeletal muscle cell contraction
The behavior of what cell constituent correlated perfectly with that of Mendel's genetic factors?
the homologous pairs of chromosomes
What removes the ubiquitin chain from a protein targeted for destruction and what supplies the energy that helps to unfold the target protein?
the proteasome cap, ATP hydrolysis
What determines the sequence of sugar addition to glycoproteins traveling through the Golgi complex?
the spatial arrangement of specific glycosyltransferases that contact proteins as they pass through the Golgi complex
What allows smooth and rough vesicles (microsomes) to be readily separated by density gradient centrifugation?
their differences in density
What reaction is catalyzed by reverse transcriptase?
transcription of RNA to DNA
The genetic rearrangement that Barbara McClintock discovered was called _________ and the mobile genetic elements she discovered were called ________.
transposition, transposable elements
