NPB110A Quizzes for MT2 (Quiz 3 and 4)

Which of the following statements is FALSE? A. Mitochondria play a major role in triggering apoptosis. B. One hallmark of apoptosis is a change in the symmetry of plasma membrane lipids. C. DNA fragmentation is random in necrosis and ladder-like in apoptosis. D. Apoptosis only occurs in mammals. E. Necrosis and apoptosis are two distinct mechanisms of cell death.

Answer. D.

Which of the following statements is true? A. Normal somatic cells can grow indefinitely in culture B Telomerase activity is the same in normal somatic cells and cancer cells. C. Telomere length is unrelated to cell senescence. D. The enzyme telomerase maintains the length of telomeres. E. Telomere length in normal somatic cells is not affected by cell division.

Answer. D. Normal somatic cells have a Hayflick limit. Telomerase is the molecular basis for cell senescence (i.e. at each cell division, the telomeres shrink. if it shrinks too much it cannot divide. Telomere length is not affected in cancer cells and ES. Note that certain cells like neurons and cardiomyoctyes are terminally differentiated, thus they maintain telomere length.

Which of the following statements is TRUE? A. The covalent addition of protein ubiquitin to cyclins allows for their binding to CDKs. B. The rate of degradation of cyclins is relatively constant throughout the cell cycle. C. Ubiquitin ligase activity is relatively constant throughout the cell cycle. D. Whether cyclins are present or absent is governed by cyclin gene expression E. Proteasomes are large structures in which proteins enter and get degraded.

Answer. E. Ubiquitin is a tag for protein degradation. This is a way to degrade cyclin to maintain its levels. Ubiquitin ligase (for example, APC and SCF) are what puts ubiquitin onto certain cyclins. Cyclin levels are determined by its degradation.

Which of the following statements is FALSE? A. p53 protein levels are normally low in cells due to its ubiquitin-dependent degradation. B. DNA damage leads to increased activity of p53 protein. C. DNA damage leads to increased levels of p53 protein. D. p53 is a transcription factor. E. The only impact of p53 activation is cell cycle arrest.

Answer. E. p53 can also lead to apoptosis.

Which of the following statements about quorum sensing is FALSE? A. It has no medical relevance. B. It can be targeted with abx that have many advantage over those in current use C. It is a mechanism to sense population density D. It can lead to changes in bacterial phenotype. E. It has some aspects that are similar to signaling in mammalian cells.

Answer: A. Changes in bacterial phenotype include pathogenicity and biofilm formation.

Which of the following statements is FALSE? A. Synaptic signaling cannot be pharamcologically modulated. B. Synaptic signaling can be enhanced by increasing neurotransmitter release. C. Synaptic signaling can be enhanced by decreasing the re-uptake of released neuotransmitter D. Synaptic signaling can activate both ionotropic and metabotropic receptors. E. Synaptic signaling can be enhanced by decreasing the degradation of released neurotransmitter.

Answer: A.Synaptic signaling can be modulated by SSRIs.

Which of the following statements is FALSE? A. Receptors in the plasma membrane can go through lateral diffusion. B. Diacylglycerol can diffuse through the cytosol. C. G protein subunits attached to the membrane through fatty acid chains can undergo lateral diffusion. D. cAMP can diffuse through the cytosol. E. IP3 can diffuse throughout the cytosol.

Answer: B. cAMP can diffuse through the cytosol to activate Protein Kinase A. IP3 can diffuse through the cytosol to open up calcium channels in the ER.

Which of the following statements about the eukaryotic cell cycle is TRUE? A. DNA replication occurs gradually over the entire cell cycle. B. The cell cycle is the same length in all dividing cell types. C. Certain cell types can exit the cell cycle and remain alive for many years/ decades. D. The terms "M phase" and "mitosis" mean the same thing in the cell cycle. E. There are checkpoints between every phase.

Answer: C. DNA replication occurs during S phase. G1 phase is most variable. M phase means mitosis and cytokinesis. There are three checkpoints; G1/S, G2/M, and anaphase.

Which of the following statements is FALSE? A. Most signals cannot cross the lipid bilayer and therefore must bind to cell surface receptors. B. Ca2+ is relatively low in the cytosol compared to extracellular fluids. C. Phospholipids are important in membrane structure but not as cell signaling molecules. D. Ca2+ is relatively low in the cytosol compared to the lumen of the ER. E. Most cell surface receptors are transmembrane proteins.

Answer: C. Phospholipids used in cell signaling like PLC that cleaves PIP3 into DAG and IP3.

Which of the following statements is TRUE? A. Paracrine signaling is used to integrate physiology across the entire organism. B. Endocrine signaling only impacts cells near the endocrine gland. C. Cells are impacted by signals whether they express receptors for that signal or not D. In autocrine signaling the same cell must produce the signal and the receptor. E. Contact- dependent signaling is the most common form of signaling in mammals.

Answer: D Explanation: endocrine (not paracrine) used to inegrate physiology over entire organism. Paracrine is local. Cells that are impacted must express the receptors (see TNF), contact dependent isn't as common but an example is Fas ligand for apoptosis.

Which of the following statements is TRUE? A. Cyclins are the only proteins that regulate the activity of CDKs. B. Phosphorylation of CDKs is always stimulatory. C. The CAK kinase phosphorylates CDKs independent of whether cyclin is bound or not. D. Cyclins are necessary but not sufficient for full CDK activity. E. Phosphorylation can occur only at one site at any individual CDK molecule.

Answer: D. Cyclins, other proteins like P21 and P27, inhibitory and activating phosphorylation regulate CDK activity. CAK stimulates CDK with phosphorylation; wee1 kinase puts an inhibitory phosphate (taken off by CDC25). CAK only phosphorylates CDKs when there is a cyclin. Since phosphorylation can occur twice there is not one exact spot where it can be phosphorylated.

Which of the following statements about BrdU labeling technique is TRUE? A. BrdU labels cells regardless of whether they are replicating or not. B. BrdU labeling cannot be combined with any other labeling technique. C. BrDU substitutes for uridine during DNA replication. D. This technique only works on living cells. E. BrdU does not label neurons in adult brain as there is no adult neurogenesis in the brain.

Answer: D. This is because Brdu replaces thymidine and is a form of "metabolic labeling." The cell must be alive to replicate itself because it is a way that we can track which cells are dividing. In the slides, Brdu was labeled red and the nuclei were labeled blue; if they took in Brdu (thus showing replication), they will appear purple.

Which of the following statements DOES NOT describe fast cellular responses to signals? A. They involve changes in activity of existing proteins. B. they involve cell surface receptors. C. They are of short duration and reversible. D. They are fast because they are not mediated by multistep signaling pathways. E. They do not involve changes in gene expression.

Answer: D. Explanation: Fast cellular signals are hydrophilic. Slow signals are hydrophobic and involve intracellular receptors.

Which of the following statements is FALSE? A. Calmodulin undergoes a substantial conformational change upon binding to Ca2+. B. Ca2+ released from the ER can bind to cytosolic calmodulin. C. Ca2+ bound calmodulin binds to the same site on CaM kinase that the inactive state of CAM kinase is bound by the catalytic domain. D. Ca2+ entering through voltage-gated Ca2+ channels cannot bind to cytosolic calmodulin. E. Ca2+- free calmodulin does not bind to CAM Kinase.

Answer: D. Ca2+ entering through voltage-gated Ca2+ channels cannot bind to cytosolic calmodulin. When bound to Ca2+, Ca2+ constricts and activates its boa constrictor power. Ca2+ released from the ER. And Ca2+ released from the ER is upstream (calmodulin was actually an example of the Ca2+ effects)

Which of the following statements is FALSE? A. Some but not all receptors are ion channels, and some but not all ion channels are receptors. B. Some synaptic neurotransmitter receptors are ion channels while others are GPCRs. C. Some but not all receptors are transcription factors are receptors. D. Some but not all receptors are enzymes, and some but all not enzymes are receptors. E. GPCRs are the only proteins in cells that bind to G proteins.

Answer: E.

Which of the following statements is FALSE? A. There are a number of different CDKs in eukaryotic cells. B. The activity of CDK protein cycles up and down during the cell cylce. C. There are a number of different cyclins in eukaryotic cells. D. Different cyclins regulate different CDKs. E. The expression level of CDK proteins cycles up and down during the cell cycle.

Answer: E. The CDK expression level is constant; it is the cyclins that cycle up and down.

Death receptors stimulate apoptosis by stimulating cytochrome c release from mitochondria. T/F.

False. Death receptors are an extrinsic pathway and has nothing to do with cytochrome C. There are TNF (tumor necrosis factors) which bind to TNF receptors which binds to death domains FADD and TRADD which cleaves Procasp 8 and executioner caspases which leads to apoptosis.

The main substrates for phosphorylation by activated receptor tyrosine kinases are downstream signaling molecules.

False. It transautophosphorylates! Although MAP Kinase is one of the downstream effects of RTKS, it is far downstream.

Fast ionotropic signaling that activates ion channelcoupled receptors that selectively pass Cl ions take Vm farther away from the threshold for firing an action potential.

True. Na+ and Ca2+ takes Vm closer to threshold (along with Ach and Glu) and K+ and Cl- (along with GABA and Gly) take it farther from threshold.

Neurotrophins inhibit apoptosis by inhibiting cytochrome c release from mitochondria. T/F.

True. Neurotrophins prevent the BAD protein from binding the BCL2 which opens up the ion channel BAX which lets ions in, decreasing the mitochondrial potential and letting out Cytochrome C which will lead to Apoptosis.