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Cell Bio Exam 4
Terms in this set (134)
When DNA replication proceeds along a template, which of the following best describes the directionality of synthesis?
in the 5'-to-3' direction
At a replication fork, how is the leading strand synthesized?
At a replication fork, how is the lagging strand synthesized?
Consider this image that represents DNA replication along with the "end-replication problem," and then answer the question. Using your knowledge of telomerase enzyme and chromosomal size, choose the statement that correctly describes the information in the figure.
Telomerase activity would solve the end-replication problem, as this enzyme is involved in telomere lengthening.
What does depurination refer to?
the loss of A or G bases from DNA
How does ultraviolet radiation in sunlight typically damage DNA?
It causes two adjacent pyrimidine bases to become covalently linked.
What potential outcomes are possible after replication in a DNA molecule with a depurination modification that is left unrepaired?
The DNA molecule is missing one nucleotide pair
The DNA molecule contains the normal sequence.
(Not The DNA molecule contains an extra three nucleotide pairs, The DNA molecule is converted into RNA.)
What type of enzyme removes damaged DNA from the rest of the DNA molecule?
What type of enzyme fills in the gap after damaged DNA has been removed?
What type of enzyme seals the newly added (repaired) DNA to the rest of the DNA molecule?
Which option correctly describes the two strands of DNA in a double helix?
antiparallel in orientation
Which chemical group is at the 3' end of a DNA strand?
a hydroxyl group
What type of bond connects nitrogenous bases between two strands of DNA in a complementary base pairing fashion?
Prokaryotes have chromosomes that are circular in structure. Which of the following would such chromosomes lack?
In the light microscope, DNA molecules are most visible in which of the following?
in a cell that is dividing
In the living cell, histone proteins pack DNA into a repeating array of DNA-protein particles called what?
What is the term that describes the complex of DNA and proteins that makes up a eukaryotic chromosome?
What structure in an interphase eukaryotic cell is the site of ribosomal RNA transcription?
What are the specialized DNA sequences that are at the ends of most eukaryotic chromosomes called?
Which of the following is true for most genes?
A gene is a segment of DNA that contains the instructions for making a particular protein.
A gene is a segment of DNA that contains the instructions for making a particular RNA.
A gene is a unit of heredity that contains instructions that dictate the characteristics of an organism.
What does each eukaryotic chromosome contain?
one long double-stranded DNA molecule
The tails of the core histone proteins can be chemically modified by the covalent addition of what type of chemical group?
acetyl, methyl and phosphate
What is the general name given to the most highly condensed form of chromatin?
One of the first steps in obtaining a karyotype (such as that shown below of a cancer cell) is treating cells with a drug that stalls cells in mitosis. Why must cells arrest in mitosis for karyotype analysis?
Only mitotic chromosomes are highly condensed and visible with a light microscope.
Which of the following statements about nucleosomes is false?
Nucleosomes are found only in mitotic chromosomes.
True: A nucleosome consists of DNA wrapped around eight histone proteins, plus a short segment of linker DNA.
Nucleosomes convert a DNA molecule into a chromatin thread about one-third the length of the initial DNA.
Nucleosomes represent the first and most fundamental level of chromatin packing.
Nucleosomes can be seen in the electron microscope.
How do chromatin-remodeling complexes work?
They use the energy from ATP hydrolysis to alter the arrangement of nucleosomes, rendering certain regions of the DNA more accessible to other proteins.
Which of the following statements is FALSE?
A cell will temporarily decondense its chromatin to silence genes during differentiation.
True: A cell will temporarily decondense its chromatin to give proteins rapid, localized access to specific DNA sequences.
A cell will temporarily decondense its chromatin to allow access to specific DNA sequences for replication, repair, or gene expression.
A cell can permanently condense and silence an entire chromosome during development.
When a cell divides, its chromatin structures will typically be inherited by its daughter cells.
Which of the following is a function of the protein component of chromosomes?
It packages the DNA strands.
If one end of a DNA strand has a phosphate group on it, the chemical group on the other end must be
The technique whereby human chromosomes are stained and identified is called a
What is a function of the nucleolus?
to assemble ribosomal RNA and proteins into ribosomes
When are chromosomes in their most compacted form?
Which of the labels in the following figure shows a nucleosome core particle?
The one showing only the yellow histone wrapped in DNA
How does methylation of histone tails affect the accessibility of DNA?
It can have different effects depending on the location.
Researchers sought to grow blood vessels in a lab for implantation into patients with clogged coronary arteries. To avoid immune rejection, they wanted to grow vessels by starting with patients' own vascular smooth muscle cells (SMCs). However, most patients requiring coronary artery replacement are elderly, and their vascular SMCs do not divide often enough to grow a new vessel. To get around this problem, the researchers introduced into the cells the gene coding for a particular protein in a format through which the gene would be transcribed and the protein produced. What gene was introduced into the elderly patients' SMCs to allow continued cell divisions?
The loss of purine bases from a strand of DNA is typically caused by which of the following?
A spontaneous chemical reaction?
NOT deamination or replication error
In the absence of repair, what would the replication of a double helix containing a mismatch yield?
one DNA molecule with the normal sequence and one DNA molecule with a mutated sequence
The mismatch repair system recognizes mismatched base pairs, removes a portion of the DNA strand containing the error, and then resynthesizes the missing DNA using the correct sequence as a template. But what if the mismatch repair system instead removed a piece of the DNA strand that contained the correct sequence? What would replication of this improperly repaired sequence produce?
two DNA molecules bearing the same mutation
What is true of a newly synthesized DNA strand of a human chromosome?
It is produced by a mixture of continuous and discontinuous DNA synthesis from multiple replication origins.
In a DNA double helix, which strand serves as the template during replication?
Both strands serve as templates during replication.
Determine whether the following statement is true or false: Most cancers arise from cells that have accumulated multiple mutations.
What is the name of the type of damage caused by an improperly paired base in the DNA?
Which of the following is NOT a common source of DNA damage for cells in our bodies?
soap (Other=replication fork problems, spontaneous loss of amino groups on cytosine, UV light
Shown here is the end of a newly replicated chromosome. Which strand will telomerase elongate?
the template of lagging strand
What is the first step that must occur to repair damage on one strand of the double helix?
The damaged region must be removed.
What is the most general term for a change in a single nucleotide pair?
Consider the image of somatic cell versus gamete mutations and then answer the question. Which of these statements is consistent with the information presented in the figure?
Mutation A is heritable to offspring because the mutation took place in the germ line.
Determine whether the following statement is true or false: Viruses do not encode all of the enzymes necessary to replicate themselves.
For a retrotransposon, reverse transcriptase produces DNA copies using which of the following as a template?
Most of the genetic variation in the human genome takes what form?
What is true of a reporter gene?
It can reveal when a gene is expressed.
It is a gene whose product can be visually monitored.
(NOT It cannot reveal where a gene is expressed.)
Which of the following terms describes a mouse in which a particular gene has been genetically eliminated?
Why are transgenic animals used to model human diseases in which mutant genes play a major part?
Transgenic approaches in humans are unethical.
Genes can be inactivated by introducing a ___________ molecule with a nucleotide sequence that matches the gene to be inactivated.
Transgenic plants can be produced using the ability of plants to
be manipulated to form a mature plant from cultured transgenic cells.
In our human ancestors, the enzyme lactase, which allows us to digest the milk sugar lactose, was produced only during infancy. Today, many adults can digest lactose, while others cannot. Which group was born with a point mutation in the regulatory DNA of their lactase genes?
adults who can digest lactose
You are a virologist. A friend asks you how reverse transcriptase inhibitors help treat HIV. You explain that inhibition of reverse transcriptase directly prevents the following step of the HIV viral life cycle.
production of DNA from RNA genome
Determine whether the following statement is true or false: In sexually reproducing organisms, only mutations that occur in the germ line are passed along to progeny.
In humans, the globin gene family evolved through which process?
repeated rounds of duplication and mutation
Determine whether the following statement is true or false: Two people selected at random from anywhere on Earth are likely to be identical with respect to 99.9% of their nucleotides.
Mutations that occur in germ-line cells are the only ones that lead to evolutionary change because
germ cells form progeny.
How do point mutations typically arise?
A mutation in the ___________ of the gene encoding the enzyme lactase enables expression of this gene in adults.
The transcription of an integrated retroviral DNA in the genome functions to supply what products for the replication virus?
more copies of the genome and protein for the viral coat/envelope
(NOT more RNA genome copies or RNA for translation into protein for the viral coat/envelope)
Nucleic acid hybridization, which can be used to detect any given DNA or RNA sequence in a mixture of nucleic acid fragments, relies on what factor?
a single strand of DNA or RNA forming a double helix with another nucleic acid strand of the complementary nucleotide sequence.
Genetic engineering in plants is made simpler by what fact?
Transgenic plants can be grown from almost any type of plant cells transfected with DNA in culture.
Which of the following is considered a reporter protein?
green fluorescent protein
In which organism is silencing genes by RNA interference (RNAi) particularly easy since the animals can be fed E. coli that has been genetically engineered to produce the double-stranded RNAs that trigger RNAi?
Consider the following image of genes being highlighted on two homologous chromosomes and then answer the question regarding this experimental result. What technique was likely used to generate the experimental result that is shown above?
in situ hybridization
Organisms with a mutation in a specific human disease-causing gene
are potential models for that human disease.
The entire period between one M phase and the subsequent M phase is called what?
What must happen for a Cdk to be active?
It must bind to its cyclin partner.
The inactivation of M-Cdk leads to which of the following?
exit from mitosis
Most of the diversity in the rates of cell division in the adult body lies in variations in the time that each cell spends in which phase(s)?
G1 phase and G0 phase
The mitotic spindle begins to assemble in which phase of the cell cycle?
What is the contractile ring made of?
actin and myosin
In dividing plant cells, a new cell wall is formed between two sets of chromosomes via a structure called a phragmoplast, which is built by vesicles largely originating from which organelle?
When a cell is acutely injured, it usually dies by which process?
Which of the following statements describes how growth factors stimulate animal cell enlargement?
They stimulate intracellular protein synthesis.
Fibroblasts are the major cellular component in which tissues?
What is the best description of connective tissue?
All of its cells are sparsely distributed in the extracellular matrix.
Which epithelial cell junctions serve to seal neighboring cells together so that water-soluble molecules cannot easily leak between them?
Which is true of cadherin proteins?
They link epithelial cells together by binding to similar cadherins in adjacent epithelial cells.
Which type of epithelial cell junction plays a major role in an epithelial sheet's ability to develop tension and change its shape?
What attaches epithelial cells to the basal lamina?
Which of the following are the plant equivalent of a gap junction?
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
Which statement is true about stem cells?
They can divide for the lifetime of the organism.
Which of the following can give rise to cancer-promoting mutations?
inhalation of tobacco smoke
exposure to ionizing radiation
DNA replication errors
exposure to excess sunlight
What does the phosphorylation of Cdc25 by M-Cdk do?
It activates Cdc25, which in turn activates more M-Cdk.
The anaphase-promoting complex or cyclosome (APC/C) triggers the onset of anaphase by doing which of the following?
triggering the destruction of the cohesins that hold the sister chromatids together
One approach to killing cancer cells is to induce apoptosis. Which of the following are reasonable approaches that researchers can take to induce apoptosis in cancer cells?
inhibiting the Bcl2 protein
activating the Bax protein
NOT inhibiting the G1-cyclin-dependent kinase protein or inhibiting the p53 protein
Mutations that prevent Bcl2 family proteins Bax and Bak from interacting with the outer mitochondrial membrane would have which effect?
preventing the release of cytochrome c and inhibiting apoptosis
Soon after nerve growth factor (NGF) was discovered, investigators injected newborn mice with antibodies that inactivated it. Compared to control mice, those that received the antibody showed massive amounts of nerve cell death. After a week of daily antibody injections, up to 99% of the neurons in certain parts of the nervous system of these mice were gone. What do these results suggest?
NGF is a survival factor for developing neurons.
Investigators interested in studying the activation of apoptosis inject cytochrome c into the cytosol of two types of mammalian cells: cells that are normal and cells in which Bak and Bax have been inactivated by mutation. How would these cells be predicted to respond?
Both cell types will undergo apoptosis.
Which of the following statements is false?
The death-promoting members of the Bcl2 family include Bcl2 itself.
True: Some Bcl2 family members promote apoptosis, whereas others inhibit apoptosis.
Some death-inhibiting members of the Bcl2 family inhibit apoptosis by blocking cytochrome c release from mitochondria.
Bax and Bak are death-promoting members of the Bcl2 family that induce the release of cytochrome c from mitochondria into the cytosol.
Determine whether the following statement is 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.
Determine whether the following statement is true or false: Cell growth, unlike cell proliferation, does not depend on the cell-cycle control system.
Determine whether the following statement is true or false: During mitosis, most mammalian cells flatten out to prepare for cleavage.
The reassembly of the nuclear envelope at telophase depends on which of the following?
dephosphorylation of nuclear lamins and nuclear pore proteins
The expression levels of different ___________ fluctuate throughout the cell cycle.
cyclins (not cdks)
The slow rise of S cyclin levels throughout G1 phase is due to ___________, and the abrupt decrease is caused by ___________.
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.
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.
In response to DNA damage, the ___________ protein is phosphorylated and activates the transcription of a Cdk inhibitor to halt cell cycle progression.
What is the function of condensins?
to coil sister chromatids into a compact form
Shown in the figure is the structure of a bipolar mitotic spindle. Which element(s) is/are the interpolar microtubules?
The ones in the middle
What determines the position of the cleavage furrow of the dividing cell?
The interpolar microtubules send signals to form a cleavage furrow between the poles.
The contractile ring is composed of
actin and myosin.
Which of the following cells died by apoptosis?
The unexploded one
In response to an apoptotic stimulus, initiator caspases
cleave and activate executioner caspases.
During vertebrate development, a sheet of epithelial tissue invaginates to form the neural tube, a structure that eventually forms the spinal cord and brain. Mutations that interfere with the function of which proteins would be most likely to disrupt the epithelial sheet movement that drives this developmental process?
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
Watch the animation about angiogenesis, and then answer the questions. Formation of new capillaries is a regulated process that occurs in a series of steps. Put the following steps of angiogenesis in the correct order.
Stimulation of endothelial cell by VEGF
Endothelial cell extension of filopodia
Formation of capillary sprout
Pinocytic vesicles fusing to form large vacuoles
Creation of a lumen that runs through capillary sprout
The drug Avastin binds and inhibits VEGF. How does this drug help treat cancer?
Angiogenesis is inhibited, blocking formation of new capillaries to the tumor.
The cancer cells are starved of oxygen.
Not: The drug directly kills cancer cells.
New capillaries form and aid in delivery of chemotherapy to the tumor.
Knowledge of the driver mutations underlying cancer has led to targeted therapeutics, such as the protein kinase inhibitor imatinib (trade name Gleevec) in cases of chronic myeloid leukemia. Cancer cells often become resistant to a given drug, so researchers continue searching for new drugs that target proteins that contribute to the cancerous phenotype. One recent promising approach uses drugs that lead to ubiquitination and proteasomal degradation of the target protein. Which of the following mutated proteins are good candidates for this approach?
proteins with gain-of-function mutations
Not: proteins with loss-of-function mutations
tumor suppressor genes
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
In animal connective tissues, tensile strength is chiefly provided by which one of the following?
collagen fibrils and fibers
Fibroblasts play a role in doing which of the following?
A fibroblast can attach indirectly to collagen via which type of extracellular matrix protein?
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?
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?
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.
True: The basal lamina is a thin, tough sheet of extracellular matrix.
The basal lamina supports epithelial cells by interacting with integrins in the basal plasma membrane.
The basal lamina contains a specialized type of collagen type IV.
In desmosomes, cadherin molecules are anchored inside an epithelial cell to which type of cytoskeletal filament?
In the intestine, what do Wnt proteins promote?
proliferation of the stem cells and precursor cells at the base of each intestinal crypt
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 cancer-causing gene can be activated by a single mutation in only one allele?
Which class of cancer-critical gene must be inactivated to promote the development of cancer?
tumor suppressor gene
Determine whether the following statement is true or false: Having one mutated copy of the APC gene is enough to cause colorectal cancer.
What is an epithelium?
a sheet of cells joined tightly together
The figure shows the attachment of a cell to a collagen molecule in the extracellular matrix. What is the identity of the molecule labeled B?
Integrin (inside the plasma membrane)
What is the difference between a malignant tumor and a metastasis?
A metastasis is a tumor in different distant tissue.
An oncogene is different from a tumor suppressor gene in that
oncogenes have mutations causing increased activity of the protein.
Cancer cells often lack normal DNA damage response and cell-cycle control mechanisms. Why does this make them more susceptible to DNA-damaging chemotherapies?
Cancer cells might ignore the normal mechanisms that halt the cell cycle in response to damage, and subsequent division with damage leads to death.
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