Cell Bio "most missed questions"
Motor proteins use the energy in ATP to transport organelles, rearrange elements of the cytoskeleton during cell migration, and move chromosomes during cell division. Which of the following mechanisms is sufficient to ensure the unidirectional movement of a motor protein along its substrate?
A conformational change is linked to ATP hydrolysis
Despite the differences between eukaryotic and prokaryotic cells, prokaryotes have proteins that are distantly related to eukaryotic actin filaments and microtubules. What is likely to be the most ancient function of the cytoskeleton?
Cell Division
Which of the following drives the movement of glucose through the glucose transporter?
Concentration gradient
T/F: GTP binding proteins required an extramolecular enzyme to hydrolyze GTP to GDP to switch the protein to the off conformation
False, GTP binding proteins have intrinsic GTPase activity and hydrolyze GTP to GDP to switch the protein to the off conformation
Cholera toxin causes diarrhea ah and dehydration by affecting which of the following pathways?
GPCR/Adenylate Cyclase
Active transport required the input of energy into a system to move solutes against their electrochemical and concentration gradients. Which of the following is NOT one of the common ways to preform active transport?
K+-coupled
The Ras protein is a GTPase that functions in many growth-factor signaling pathways. In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations is the gene for Ras are are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells?
a change that decreases the rate of hydrolysis of GTP by Ras
the concentration of H+ ions inside the mitochondrial matrix is lower than it is in the cytosol or the mitochondrial intermembrane space. What would be the IMMEDIATE effect of a membrane-permeable compound that carries and releases protons into the mitochondrial matrix?
inhibition of ATP synthesis
A protein kinase can act as an integrating device in signaling it if...
is activated by two or more proteins in different signaling pathways
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?
it inhibits movement of the small subunit relative to the large subunit
What is the energy source for the glucose uniport
none, it is passive transport
Pyruvate kinase catalyzes phosphoenolpyruvate to pyruvate by removing phosphate from phosphoenolpyruvate and adding a phosphate to ADP. This is known as...
substrate level phosphorylation
The length of time a G protein will signal is determined by...
the GTPase activity of GA
You have a segment of DNA that contains the following sequence: 5'-GGACTAGACAATAGGGACCTAGAGATTCCGAAA-3' 3'-CCTGATCTGTTATCCCTGGATCTCTAAGGCTTT-5' You know that the RNA transcribed from this segment contains the following sequence: 5'-GGACUAGACAAUAGGGACCUAGAGAUUCCGAAA-3' Which of the following choices best describes how transcription occurs?
the bottom strand is the template strand; RNA polymerase moves along this strand from 3' to 5'
Which of the following represents a situation in which your cell can use ATP synthase in reverse?
when prokaryotic cells are in anaerobic conditions but the cell still needs to maintain the H+ concentration to fuel the movement of other metabolites
Which of the following statements about prokaryotic mRNA molecules is FALSE?
ribosomes must bind to the 5' cap before initiating translation
Which of the following would yield the most highly mobile phospholipid (listed as a number of carbons and number or double bonds, respectively)?
15 carbon bonds with two double bonds
which of the following molecules is an allosteric inhibitor of this phosphofructokinase?
ATP
Cystolic IMP-GMP specific 5' nucleotide (cN-11) is a hydrolytic enzyme that catalyzes the hydrolysis of GMP or IMP (or both). The affinity for GMP or IMP increases with the attachment of GTP. This is an example of which of the following (THINK)
Allostery
You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is...
MtA binds to GTP-bound tubulin on microtubules
The correct folding of proteins is necessary to maintain healthy cells and tissues. Unfolded proteins are responsible for such neurodegenerative disorders as Alzheimer's disease, Huntington's disease, and Creutzfeldt-Jakob disease (the specific faulty protein is different for each disease). What is the ultimate fate of these disease-causing, unfolding proteins?
They form protein aggregates
Protein structures have several different levels of organization. The primary structure of a protein is its amino acid sequence. The secondary and tertiary structures are more complicated. Consider the definitions below and select the one that best fits the term "protein domain"
a protein segment that folds independently
Compared to the normal situation, in which actin monomers carry ATP, which do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments?
actin filaments would grow longer
which of the following statements about the unfolded protein response (UPR) is false?
activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins
The figure below shows how normal signaling works with Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line?
addition of a drug that blocks protein Y form interacting with its target
Which of the situations below will enhance microtubule shrinkage?
addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers
You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of the nuclear lamina from its individual subunits in vitro. Which of the following additions do you predict would most likely to enhance the assembly of the nuclear lamina?
addition of protein kinase inhibitors
Which of the following is NOT a component of the cell theory?
all organisms are composed of more than one cell
Which of the following pathways are utilized to breakdown an obsolete organelle in a cell?
autophagy
Which of the following mechanisms best describes the manner in which lysozyme lowers the energy required for its substrate to reach its transition state conformation?
by altering the shape of substrate to mimic the conformation of the transition state
which of the following is not a function of chaperone proteins inside the mitochondria
capture misfolded proteins before exportation
Cyanide(a poison) will bind to which of the following to prevent ATP production?
cytochrome C oxidase
For both actin and microtubule polymerization, nucleotide hydrolysis is important for
decreasing the binding strength between subunits on filaments
The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that...
energy can be extracted in usable amounts
which of the following occur without coupling transport of the solute to the movement of a second solute?
export of CA2+ from the cytosol
During gluconeogenesis, which enzyme catalyzes the formation of fructose 6-phosphate from fructose 1,6- bisphosphate?
fructose 1,6 bisphosphatase
The formation and degradation of glycogen is allosterically regulated by
glucose 6-phosphate
Which of the following components of the electron transport chain have the highest affinity for electrons
oxygen
Which of the following describes how Mycobacterium tuberculosis prevents phagocytosis macrophage?
prevents phagosome fusion with lysosome
Your friend has just joined a lab that studies vesicle budding from the golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but was not listening carefully when he was told about the molecular defect of this cell line. He is too embarrassed to ask and comes to you for help. He does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen. Which of the following proteins might be lacking in this cell line?
prevents phagosome fusion with lysosome
Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PCK. The figure on the right shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKV is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty?
the expression of a constitutively active phospholipase C
To produce the correct mRNA sequence to produce the correct protein in a cell, the cell must determine which strand of the DNA double Helix to use as the template strand. Which of the following help determine which strand is the template strand?
the promoter region has a specific polarity that positions the RNA polymerase in the correct orientation on the correct template strand
Which of the following does NOT occur before a eukaryotic mRNA is exported from the nucleus?
the ribosome binds to the mRNA
To study how proteins fold, scientists must be able to purify the protein of interest, use solvents to denature the folded protein, and observe the process of refolding at successful time points. What is the effect of the solvents used in the denaturation process?
the solvents break all noncovalent interactions
In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of high-energy thioester bond. The energy of the thioester bond is harnessed in step 5. What is the energy used for?
to generate a molecule of GTP
