cell bio final exam
if DNA is damaged or incompletely replicated in S phase, the inhibition of which of these molecules prevents the cell from entering M phase?
Cdc25
the activation of S-Cdk initiates
DNA replication
which of the following processes occurs only in the S phase of the cell cycle?
DNA replication
which one of the following can give rise to cancer-promoting mutations?
DNA replication errors inhalation of tobacco smoke exposure to ionizing radiation exposure to excess sunlight
the activation of S-Cdk helps prevent
DNA replication occurring more than once each cycle
which of the following correctly matches the phase of the eukaryotic cell cycle with an event that takes place in that phase?
M phase ---- cytokinesis
DNA replication occurs only in the
S phase
how do SNPs differ from mutations?
SNPs are more common in a population
what is the difference between a malignant and benign tumor?
a malignant tumor invades and colonizes other tissues, while a benign tumor does not
which of the following statements are true?
activated G1-Cdks and G1/S-Cdks help drive cells through G1 into S phase activated S-Cdk initiates DNA replication
which of the following statement is false?
activated M-Cdk triggers the onset of cytokinesis this is false because the activated M-Cdk triggers entry into M phase, where the replicated chromosomes will be distributed into two daughter cells
Cdk activity is regulated in several ways.
active: Cdk bound to cyclin, threonine in T loop phosphorylated inactive: Cdk/cyclin bound to p27, T loop in active site, Cdk alone
which type of epithelial cell junction plays a major role in an epithelial sheets ability to develop tension and change its shape?
adherens junction
what is the best description of connective tissue?
all of its cells are sparsely distributed in the extracellular matrix
based on Gregor Mendel's experimentation, yellow peas were assigned the allele genotype symbol uppercase "Y" and green peas were assigned the allele genotype symbol lowercase "y." the progeny of a true-breeding plant with yellow peas YY and one with green peas yy will have which of the following?
all yellow peas only
which of the following is the term for variant versions of a gene?
alleles
gap junctions
allow an electrical and a metabolic coupling between attached cells allow inorganic ions to move directly between attached cells they can open or close as needed allow the cytoplasm of two adjacent cells to be continuous with each other
what does the spindle assembly checkpoint, which blocks the initiation of anaphase until all chromosomes are properly attached to the mitotic spindle, depend on?
an inhibitory signal produced by inappropriately attached chromosomes
the cell-cycle control system monitors the tension on the kinetochores to ensure that ___
anaphase does not occur until the sister chromatids are correctly attached to the spindle
the cell-cycle control system monitors the tensions on the kinetochores to ensure that
anaphase does not occur until the sister chromatids are correctly attached to the spindle
the cell-cycle control system uses Cdk inhibitory proteins to do what?
arrest the cell cycle at specific transition points
what are main functions of the kinetochore?
attaching the sister chromatids to the dynamically growing and shrinking microtubules sensing tension when sister chromatids are attached to opposite poles of the spindle
what are the main functions of the kinetochore?
attaching the sister chromatids to the dynamically growing and shrinking microtubules sensing tension when sister chromatids are attached to opposite poles of the spindle
the loss of its cyclin causes a Cdk to do what?
become inactive
what gives the plant cell wall its tensile strength?
cellulose
in animal connective tissues, tensile strength is chiefly provided by which one of the following?
collagen fibrils and fibers
cyclins vary in
concentration at different stages of the cell cycle
which of the following animal tissues is characterized by a plentiful extracellular matrix?
connective
stem cells hold great promise both for studying cell fate determination and organ development and for clinical use, such as blood stem cell transplants to treat patients whose own immune systems have been severely impaired. clinicians also hope that stem cells can be coaxed into specific cell types to treat diseases in which that cell type is damaged, such as replacing neurons in Parkinson's disease. in 2008, researchers assessed the ability of neurons derived from reprogrammed fibroblasts to ameliorate the symptoms of Parkinson's disease in a rat model. based on your knowledge of stem cells and cell differentiation, what intermediate step was necessary to convert fibroblasts into neurons?
converting fibroblasts into induced pluripotent stem cells
the expression levels of different ___ fluctuate throughout the cell cycle
cyclins
which of the following is false?
cyclins help activate Cdks by phosphorylating them
which of the following could cause the cell to prematurely enter anaphase and the sister chromatids to separate?
defect in the spindle assembly checkpoint
cyclins are
degraded at specific timed in the cell cycle
what drives the reassembly of the nuclear envelope?
dephosphorylation of claims lamins, which are phosphorylated and disassembled by the mitotic Cdk, are dephosphorylated in telophase and can reassemble the nuclear envelope
the reassembly of the nuclear envelop at telophase depends on which of the following?
dephosphorylation of nuclear lamina and nuclear pore proteins - this triggers the breakdown of the nuclear envelope and desphosphorylation allows these proteins to reassemble and the nuclear envelope and lamina to reform
which of the following animal cell types, under appropriate conditions, can be kept proliferating indefinitely in culture and yet retain unrestricted developmental potential?
embryonic stem cells
cell-cycle control system
ensures that all DNA is replicated before M phase begins ensures that all chromosomes are attached to the mitotic spindle before the chromosomes are segregated to the two daughter cells ensures that the environment is favorable for the cell to initiate DNA replication
cyclins have no
enzymatic activity on their own
the inactivation of M-Cdk leads to which of the following?
exit from mitosis
true or false: a stem cell can only produce a single type of differentiated cell
false
true or false: apoptosis is a form of programmed cell death in which cells kill themselves by migrating to the bloodstream where they are carried to the liver for destruction
false
true or false: during mitosis, most mammalian cells flatten out to prepare for cleavage
false
true or false: survival factors act primarily by stimulating cell division
false
a fibroblast can attach indirectly to collagen via which type of extracellular matrix protein?
fibronectin - provides a linkage between the cell and collagen; part of the fibronectine molecule binds to collagen, while another part forms an attachment site for integrins
mendel crossed true-breeding plants producing yellow peas with true-breeding plants producing green peas, and found that the hybrid of offspring all had yellow peas. which allele is recessive?
green pea allele
mendel chose to study traits that are inherited in a discrete fashion. what does this mean?
he studied traits that did not become "blended" in subsequent generations
what attaches epithelial cells to the basal lamina?
hemidesmosomes
if the cell is deprived of mitogens for a prolonged period of time, it will enter a non-proliferating state in which it may remain for how long?
hours, days, weeks, the remaining lifetime cells can withdraw from the cell cycle for prolonged periods, either temporarily or permanently
Rb is an important protein for controlling cell proliferation by blocking entry into S phase. how does it exert its effect?
in its unphosphorylated state, Rb is active and blocks transcriptional regulators
which term best describes the process by which maternal and paternal chromosomes are shuffled and distributed randomly during meiosis 1?
independent assortment - the resulting gametes will receive novel assortments of maternal and paternal alleles
some cancer cells are missing a key protein needed to repair double-strand DNA breaks. they survive by relying on alternative DNA repair mechanisms. to treat these cancers, researchers have developed drugs that do which of the following?
inhibit alternative DNA repair mechanisms
which type of protein in a fibroblast's plasma membrane attaches to the extracellular matrix on the outside of the cell and (through adapter molecules) to actin inside the cell?
integrin
in desmosomes, cadherin molecules are anchored inside an epithelial cell to which type of cytoskeletal filament?
intermediate filaments
the entire period between one M phase and the subsequent M phase is called what?
interphase
which of the following statements about the cell-cycle control system is not true?
it ensures that M phase is completed before cytokinesis begins but, cytokinesis is part of M phase
what is true of the basic organization and machinery of the cell cycle?
it is essentially the same in all eukaryotes
what must happen for a Cdk to be active?
it must bind to its cyclin partner
which of the following mutations is not typically found in a genetic screen?
lethal mutations
why is loop 2 important for p53 function?
loop 2 helps position a critical arginine for binding DNA
which two processes together constitute the M phase of the cell cycle?
mitosis and cytokinesis
in most cases, how many mutations are required for a normal cell to turn into a cancer cell?
more than 3
when a cell is actually injured, it usually dies by which process?
necrosis
many of the genes mutated in individual tumors are involved with which of the following regulatory pathways?
pathways regulating the cell's response to DNA damage or stress pathways governing the initiation of cell division
which of the following are the plant equivalent of a gap junction?
plasmodesmata - they are cytoplasmic channels, lines with plasma membrane, that penetrate cell walls to connect neighboring plant cells
sexual reproduction generates genetic diversity by which processes?
production of novel allele combinations genetic recombination
5 stages of mitosis in order
prophase, prometaphase, metaphase, anaphase, telophase
why does the nuclear envelope break down at the start of prometaphase?
proteins that form the nuclear pores and nuclear lamina become phosphorylated
why does the nuclear envelope break down at the start of prometaphase?
proteins that form the nuclear pores and nuclear lamina becomes phosphorylated
which cancer causing gene can be activated by a single mutation in only one allele?
proto-oncogene
which method is the best way for identifying rare, large-effect mutations?
sequencing the exons of affected individuals, as well as their parent and sibilings
attachment of sister chromatid pairs to opposite poles of the spindle creates tension in the kinetochores, which ____
signals that the sister chromatids are ready to be separated
each sister chromatid in a pair must attach to the opposite pole of the spindle for the
sister chromatids to be segregated properly
which of the following occurs at specific times in the cell cycle?
some cyclins are ubiquitylated and degraded in proteasomes
Cdk inhibitors inhibit the function of cyclin-dependent protein kinases. different inhibitors display varying mechanisms of Cdk inhibition. which of the following might a Cdk inhibitor block in order to block Cdk function?
substrate binding ATP binding cyclin binding
which of the following is true of the basal lamina
supports epithelial cells by interacting with integrals in the basal plasma membrane thin, though sheet of extracellular matrix contains a specialized type of collagen type IV
attachment of sister chromatid pairs to opposite poles of the spindle creates
tension in the kinetochores, which signals that the sister chromatids are ready to be separated
what accounts for the difference in the curve shapes depicting concentration of M-cyclin versus M-Cdk activity during the cell cycle?
the M-Cdk complex is not activated until M-cyclin is bound and M-Cdk is dephosphorylated
which of the following statements about S-Cdk is false?
the activation of S-Cdk helps prevent the onset of M phase
which of the following is not true of the basal lamina?
the basal lamina lines the cytosolic side of the epithelial cell's basal plasma membrane
if a chromosome is attached to two microtubules from opposite poles and one of the microtubules is experimentally severed, what occurs?
the chromosomes migrates quickly to the pole to which it is still attached
which feature of glycosaminoglycans (GAGs) allows the extracellular matrix in cartilage to resist compression?
the negative charges on GAGs attract sodium ions, which draw water into the extracellular matrix to form a water-filled gel
which of the following statements is false?
the pairing of homologous chromosomes during prometaphase is called bi-orientation rather, the attachment of duplicated chromosomes, or sister chromatids, to microtubules from opposite spindle poles is called bi-orientation
which of the following statements about cells in G0 is false?
their cell-cycle control system is dismantled irreversibly
which of the following is inconsistent with the function of gap junctions?
they allow ATP-driven pumps to move substances between attached cells
what is true of induced pluripotent stem (iPS) cells?
they behave like embryonic stem cells
which of the following statements about cells in G0 is true?
they can be stimulated to proliferate if the surrounding tissue is damaged they can divide if the need arises but normally do so infrequently they retain the ability to reassemble the cell-cycle control system
what is true of cadherin proteins?
they link epithelial cells together by binding to similar cadherins in adjacent epithelial cells
which of the following statements described how growth factors stimulate animal cell enlargement?
they stimulate intracellular protein synthesis
epithelial cells line body cavities and, in organs like the intestine, separate the extracellular environment (intestinal lumen) from the body. the barrier function of epithelial tissues is important for maintaining homeostasis and preventing infections from gut-associated microbiota and viruses. some bacteria and viruses compromise this barrier function, aiding their pathogenesis. which of the following structures, most critical to the barrier function of epithelial tissue, is targeted by these infectious agents?
tight junctions
which epithelial cell junctions serve to seal neighboring cells together so that water-soluble molecules cannot easily leak between them?
tight junctions - seal neighboring cells together so that water-soluble molecules cannot easily lead between them
which of the following is responsible for the most cancer cases?
tobacco smoke
true or false: even perfectly healthy cells may undergo apoptosis
true
true or false: in the presence of severe DNA damage, the transcription regulator p53 can promote cell death.
true
true or false: many cells in normal animal tissues require extracellular signals from other cells to avoid apoptosis. this could be a mechanism for ensuring that cells survive only when and where they are needed.
true
true or false: most cases of cervical cancer are caused by a viral infection
true
true or false: protons-oncogenes can play an important role in controlling the division of normal cells
true
true or false: the rate of cell turnover varies in different tissue types
true
the p53 and Tumor Growth animation demonstrates that mice can develop lymphoma in certain tissues lacking p53. suppose different p53 gene sequences were added back to the lymphoma in mice. for each of the following, predict whether the lymphoma in the mice would grow or shrink over time. sort the treatments into the Tumor Growth or Tumor Regression boxes.
tumor growth: add a DNA sequence lacking 90% of the p53 gene, add p53 that does not bind to Zn2+, add p53 with Arg248 altered to alanine tumor regression: add a stable p53 that binds better to DNA than wild-type p53
which class of cancer-critical gene must be inactivated to promote the development of cancer?
tumor suppressor gene
