cell bio exam 3

14. Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. a. the cytosol. b. the mitochondria. c. the interior of the nucleus. d. the nuclear membrane.

a

16. What is the role of the nuclear localization sequence in a nuclear protein? a. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. b. It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. c. It aids in protein unfolding so that the protein can thread through nuclear pores. d. It prevents the protein from diffusing out of the nucleus through nuclear pores.

a

19. Which of the following statements about vesicle budding from the Golgi is false? a. Clathrin molecules are important for binding to and selecting cargoes for transport. b. Dynamin is required for vesicle formation. c. Once vesicle budding occurs, clathrin molecules are released from the vesicle. d. Clathrin molecules act at the cytosolic surface of the Golgi membrane.

a

A molecule moves up its concentration gradient _______ transport. a. active b. passive c. hydrophobic d. hydrophilic

a

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________. a. active transport. b. free diffusion. c. facilitated diffusion. d. passive transport.

a

The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions? a. Acetylcholine b. Glutamate c. GABA d. Glycine

a

Transporters, in contrast to channels, work by ________________. a. specific binding to solutes. b. a gating mechanism. c. filtering solutes by charge. d. filtering solutes by size.

a

Which of the following channels would NOT be expected to generate a change in voltage by movement of its substrate across the membrane where it is found? a. an aquaporin b. a sodium channel c. a calcium channel d. a proton channel

a

Which of the following statements about the Lac operon is FALSE? a. The Lac repressor binds when lactose is present in the cell. b. Even when the CAP activator is bound to DNA, if lactose is not present, the Lac operon will not be transcribed. c. The CAP activator can only bind DNA when it is bound to cAMP. d. The Lac operon only produces RNA when lactose is present and glucose is absent.

a

You are studying a set of mouse genes whose expression increases when cells are exposed to the hormone cortisol, and you believe that the same cortisol-responsive transcriptional activator regulates all of these genes. Which of the following statements below should be true if your hypothesis is correct? a. The cortisol-responsive genes share a DNA sequence in their regulatory regions that binds the cortisol-responsive transcriptional activator. b. The cortisol-responsive genes must all be in an operon. c. The transcriptional regulators that bind to the regulatory regions of the cortisol-responsive genes must all be the same. d. The cortisol-responsive genes must not be transcribed in response to other hormones.

a

_________ ion channels respond to changes in membrane potential.. a. Voltage-gated b. Ligand-gated c. Mechanically-gated

a

miRNAs, tRNAs, and rRNAs all _____________. a. do not code for proteins. b. act in the nucleus. c. are packaged with other proteins to form RISC. d. form base pairs with mRNA molecules.

a

The CAP activator protein and the Lac repressor both control the Lac operon. You create cells that are mutant in the gene coding for the Lac repressor so that these cells lack the Lac repressor under all conditions. For these mutant cells, state whether the Lac operon will be switched on or off in the following situations, and explain why. a. in the presence of glucose and lactose b. in the presence of glucose and absence of lactose c. in the absence of glucose and lactose d. absence of glucose and presence of lactose

a. off. no CAP binding to actovate b. off. no CAP binding c. on. CAP will bind to activate but no lac repressor to prevent transcription d. on. CAP will activate. no lac repressor so default state of no prevention of transcription

Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for _____________. a. maintaining osmotic balance. b. maintain low intracellular Ca2+ concentration. c. providing enzymes in the endoplasmic reticulum with Ca2+ ions that are necessary for their catalytic activity. d. maintaining a negative membrane potential.

b

Many receptors for neurotransmitters are _________ ion channels. a. voltage-gated b. ligand-gated c. mechanically-gated

b

The acetylcholine receptor in skeletal muscle cells is a(n) _________ ion channel. a. voltage-gated b. ligand-gated c. mechanically-gated

b

The distinct characteristics of different cell types in a multicellular organism result mainly from the differential regulation of the _________________. a. replication of specific genes. b. transcription of genes transcribed by RNA polymerase II. c. transcription of housekeeping genes (genes required for basic cellular function). d. proteins that directly bind the TATA box of eukaryotic genes.

b

The figure illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow? (bottom line) a. effect of a depolarizing stimulus b. resting membrane potential c. threshold potential d. action potential

b

Which of the following statements about prokaryotic mRNA is false a. a single prokaryotic mRNA molecule can be translated into several proteins b. ribosomes must bind to the 5' cap before initiating translation c. mRNAs are not polyadenylated d. ribosomes can start translating an mRNA molecule before transcription is complete

b

Some cells have aquaporins—channels that facilitate the flow of water molecules through the plasma membrane. For these cells, what regulates the rate and direction of water diffusion across the membrane? a. aquaporin conformation b. resting membrane potential c. solute concentrations on either side of the membrane d. availability of ATP

c

The tryptophan repressor _________________. a. is a microRNA. b. binds to the tryptophan operon when the repressor is bound to tryptophan. c. is required for production of the mRNA encoded by the tryptophan operon. d. is important for the production of the tryptophan repressor.

c

When the net charge on either side of the plasma membrane is zero, what else is true? a. There is an equal number of K+ ions on each side of the plasma membrane. b. The K+ leak channels are open. c. The electrochemical potential across the membrane is zero. d. The resting membrane potential is between -20 mV and -200 mV.

c

Which of the following gated ion channels are involved in inhibitory synaptic signaling? a. voltage-gated Na+ channels b. voltage-gated Ca2+ channels c. glycine-gated Cl- channels d. voltage-gated K+ channels

c

Which of the following is NOT involved in post-transcriptional control? a. the spliceosome b. Dicer c. Mediator d. RISC

c

Which of the following statements about resting membrane potential is TRUE? a. The resting membrane potential for most animal cells is 0 mV, because the positive and negative ions are in balance. b. The resting membrane potential for most animal cells is positive, because Na+ ions are so plentiful inside cells. c. The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell. d. At the resting membrane potential, no ions enter or exit the cell.

c

_________ ion channels in the mimosa plant propagate the leaf-closing response. a. Voltage-gated b. Ligand-gated c. Mechanically-gated

c

Which of the following is NOT a general mechanism that cells use to maintain stable patterns of gene expression as cells divide? a. a positive feedback loop, mediated by a transcriptional regulator that activates transcription of its own gene in addition to other cell-type-specific genes b. faithful propagation of condensed chromatin structures as cells divide c. inheritance of DNA methylation patterns when cells divide d. a "memory" cell that instructs new cells to express the correct pattern of genes

d

Which of the following is required for the secretion of neurotransmitters in response to an action potential at the nerve terminal? a. neurotransmitter receptors b. Na+-K+ pumps c. voltage-gated K+ channels d. voltage-gated Ca2+ channels

d

Which of the following methods is NOT used by cells to regulate the amount of a protein in the cell? a. Genes can be transcribed into mRNA with different efficiencies. b. Many ribosomes can bind to a single mRNA molecule. c. Proteins can be tagged with ubiquitin, marking them for degradation. d. Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.

d

Which of the following protein families are NOT involved in neurotransmitter vesicles fusing to the presynaptic membrane? a. v-SNAREs b. t-SNAREs c. synaptotagmins d. aquaporins

d

Which of the following statements does not accurately describe the events involved in the propagation of an action potential? a. An initial influx of Na+ through a small cluster of channels causes local depolarization of the membrane. b. Local depolarization causes nearby Na+ channels to open. c. Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished. d. The opening of ligand-gated K+ channels helps to repolarize the membrane.

d

Describe the process by which gut epithelial cells use transporters to take up ingested glucose (against the concentration gradient) and to distribute glucose to other tissues by moving it back out of the cell (down the concentration gradient).

uses Na+ electrochemical gradient to use Na+ influx to bring in glucose (against conc gradient.) This is a symporter

20. Starting from mRNA translation, trace the path of a secreted protein (protein trafficking/transport). Describe where/how translation occurs for this protein. Make sure to describe (not just mention), if appropriate, the mechanism of import, the mechanism of vesicle formation, protein modifications, vesicle targeting, vesicle fusion, and protein targeting. Or in other words, describe this particular protein targeting including all the steps discusses in lecture.

went over in class

A molecule moves down its concentration gradient by ______ transport. a. active b. passive c. hydrophobic d. hydrophilic

b

Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is NOT one of the common ways to perform active transport? a. Na+-coupled b. K+-coupled c. ATP-driven d. light-driven

b

microRNAs and small interfering RNAs (siRNAs) share some of the same proteins, enzymes, and have similar mechanisms. a. (3 pts) Name or state 3 things (can be proteins, enzymes, mechanisms) that they share. In other words, what are 3 things that are similar or the same? b. name 1 thing that is different

a. DICER process RNA RISC complex association targets mRNA for destruction via complementary base pairing b. source of RNA- miRNA is genomic, siRNA is viral

1. You are testing the rate of glucose transport into vesicles using the Na+-glucose pump. a. In experiment 1, you employ liposomes that have the pump in the same orientation as that found in the plasma membrane in epithelial cells. These liposomes contain glucose but no Na+ ions. You then transfer the liposomes to a series of tubes with solutions containing the same glucose concentration as that inside the vesicle and 0, 1, 2, 3, or 10 mM Na+. You measure the initial rates of glucose transport and plot your results (figure below). Why do the initial rates of glucose transport into the liposome reach a plateau as the concentration of Na+ increases? b. In experiment 2, there is one new variable: you have included leaky Na+ channels in the liposomal membrane. The figure shows your results. Explain the reason for obtaining such different results in experiment 2 from those in experiment 1.

a.Saturation of Na+-glucose transporter b. Na+ influx through leak channels + NOT symporter

1. Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell? a. Na+ b. K+ c. Ca2+ d. Au (gold)

b

17. Which of the following statements about transport into mitochondria and chloroplasts is false? a. The signal sequence on proteins destined for these organelles is recognized by a receptor protein in the outer membrane of these organelles. b. After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane. c. Proteins that are transported into these organelles are unfolded as they are being transported. d. Signal peptidase will remove the signal sequence once the protein has been imported into these organelles.

b

. _________ ion channels are found in the hair cells of the mammalian cochlea (inner ear). a. Voltage-gated b. Ligand-gated c. Mechanically-gated

c

15. Signal sequences that direct proteins to the correct compartment are _________. a. added to proteins through post-translational modification. b. added to a protein by a protein translocator. c. encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination. d. always removed once a protein is at the correct destination.

c

If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected? a. The membrane potential is not affected by Na+. b. It becomes more negative. c. It becomes more positive. d. It is permanently reset.

c

MicroRNAs ____________________. a. are produced from a precursor miRNA transcript. b. are found only in bacteria. c. control gene expression by base-pairing with DNA sequences. d. can degrade RNAs by using their intrinsic catalytic activity

c

Operons _______. a. are commonly found in eukaryotic cells. b. are transcribed by eukaryotic RNA polymerase II. c. contain a cluster of genes transcribed as a single mRNA. d. can only be regulated by transcriptional activator proteins, not transcriptional repressors.

c

18. After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? a. soluble secreted proteins b. ER membrane proteins c. plasma membrane proteins d. all of the above

d

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell? a. They set the K+ concentration gradient to zero. b. They set the membrane potential to zero. c. They disrupt the resting membrane potential. d. They keep the electrochemical gradient for K+ at zero.

d

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use? a. voltage-gated b. extracellular ligand-gated c. intracellular ligand-gated d. mechanically-gated

d

Voltage-gated channels contain special protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes these "voltage-sensor" domains? a. These domains are full of negatively charged amino acids such that they move inwards in response to membrane depolarization. b. These domains are full of negatively charged amino acids such that they move outwards in response to membrane depolarization. c. These domains are full of positively charged amino acids such that they move inwards in response to membrane depolarization. d. These domains are full of positively charged amino acids such that they move outwards in response to membrane depolarization.

d

It is thought that the glucose transporter switches between two conformational states in a completely random fashion. How is it possible for such a system to move glucose across the membrane efficiently in a single direction?

glucose concentration gradient