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72 Cards in this Set
- Front
- Back
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The signal transduction pathway involves what 3 things?
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a signal, a receptor, transduction, and effects.
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Membrane receptors include?
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ion channels, protein kinases, G protein-linked receptors, and cytoplasmic receptors.
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events of signal transduction may be direct
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occurring at the plasma membrane
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events of signal transduction may be indirect
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involving the formation of a second messenger.
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soluble signals sucha s steroids my find their receptors where?
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in the cytoplasm
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Signals? (3)
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Polypeptides, amino acid derivatives and steriods
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Second messengers include?
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cyclic AMP, lipid-derived substances, calcium ions.
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ultimate cell response to a signal may be? (3)
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the opening of membrane ion channels, the alteration of enzyme activities, or a change in gene transcription.
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Which of the following does not occur during signal transduction?
a) Ligand binding to receptor b) Confromational change of the signal c) Conformational change of the receptor protein d) Alteration of cellular activity. |
Answer: b
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Secondary messengers function to
a) Amplify the signal b) Bind to the active site of the receptor c) Result in multiple effects from a single signal d) Both “a” and “c”. |
Answer: d
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Cytoplasmic receptors only bind
a) Small signals that can diffuse through the plasma membrane b) Secondary messengers like cAMP c) Hydrophyllic molecules d) All of the above |
Answer: a
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Signal transduction is regulated in which of the following ways
a) The amount of signal present can be regulated b) Enzymes in the pathway convert active forms of proteins to inactive froms. c) Signals are denatured d) None of the above |
Answer: b
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I. Based on your knowlegde of prokaryotic and eukaryotic cell structure and function, how might signal transduction differ in prokaryotes and eukaryotes?
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Siganl transduction in prokaryotes is limited to ony one cell; there is no nuclear membrane to cross, and cascades tend to be simpler with fewer intermdiate steps..no signals having to go through nuclear membrane
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II. Describe how protein kinases and G protein-linked receptors may interact in a signal transduction cascade.
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G protein-linked receptors frequently expose the protein kinase activities of effector molecules
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III. Epinephrine initiates signal transduciton pathyway that involves production of cyclic AMP and leads to the breakdown of glycogen to glucose. Given that caffeine blocks the activity of cAMP phosphodieasterase, propose a mechanism by which caffeine ingestion leasds to heighted alertness and sleeplessness.
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glycogen is an energy source of the cell. The hormone also stimlates a burst of energy and faster heart rate.
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IV. Cyclic AMP is second messenger in many different cascades. How can the same messenger act in different ways in different cells?
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cAMP binds to ion channel proteins AND other kinase in the cell or cells and thus, can turn on or off certain processes all at once.
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VI. Give one example of how toxins can use cellular communication to advance its effects on a cell.
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Cholora toxin. Toxin recognizes epithelial cells of the gut and places a transmembrane receptor into them. This receptor allows access of “chain A” which than chemically modifiys the G- protien so that the latter losses the ability to communicate and “turn-off” soduim pump leading to cell dehydration.
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Cell division consists of three steps
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of the genetic material (DNA), partitioning of the two DNA molecules to separate portions of the cell, and division of the cytoplasm.
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A cell can be stimulated to begin a division cycle by
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its internal cyclin-Cdk complexes and by external controls such as growth factors and hormones
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During interphase? what happens
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the DNA in chromatin is wound around cores of histone proteins to form nucleosomes. DNA folds over and over again, packing itself within the nucleus. When mitotic chromosomes form, it folds even more.
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Replicated chromosomes consist of two chromatids that are held together along their length by
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cohesin proteins.
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At mitosis, most of the cohesin is removed, except?
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at the centromere region
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Additionally, condensin proteins coat the chromatids, which?
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make them more compact
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Mitosis can be divided into several phases, called
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prophase, prometaphase, metaphase, anaphase, and telophase.
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During prophase?
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the chromosomes condense and appear as paired chromatids
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During prometaphase?
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the chromosomes move toward the middle of the spindle
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In metaphase ?
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they gather at the middle of the cell with their centromeres on the equatorial plate
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At the end of metaphase?
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the centromeres holding together the chromatid pairs separate
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during anaphase?
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of the pair, now called a daughter chromosome, migrates to its pole along the microtubule track
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During telophase?
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the chromosomes become less condensed. The nuclear envelopes and nucleoli re-form, thus producing two nuclei whose chromosomes are identical to each other and to those of the cell that began the cycle.
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Animal cell cytoplasm usually divides by ?
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a furrowing of the plasma membrane
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In plant cells, cytokinesis is accomplished by?
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vesicle fusion and the synthesis of new cell wall material.
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caspases are?
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the enzymes that break down specific cell constituents.
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cytoskeleton plays a key roles in cell division by?
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supplying the protein structures necessary for mitosis.
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What happens during the mitotic metaphase?
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Answer: The chromosomes line up in the center of the spindle (metaphase plate) which is usually near the middle of the cell. This movement is thought to develop as a dynamic equilibrium is reached between spindle fibers tugging in opposite directions on a region of the chromosomes known as a centromere from each pole of the cell. The chromatids are the large and visible at this point and consist of pairs of “sister” chromatids.
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What events characterize mitotic anaphase?
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Answer: During anaphase, the two former chromatids of each replicated chromosome (sister chromatids) are pulled to opposite poles by depolymerization of those microtubules in the spindle apparatus that are attached to the centromeres.
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Describe the difference between centromeres and centrioles.
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Answer: Centromere are where the duplicated chromosomes are attached and consists of protein complexes. The centrosomes consists of a pair of centrioles and are referred to as the mitotic tubule organizing center (MTOC).
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Describe the levels of “packing” by which the genetic information contained in DNA is condensed into chromosomes.
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Answer: see figure 16.21 book. The DNA double helix is wrap around histone molecules and forms “nucleosomes”. They are further packaged into chromatin fibers where the nucleosome wrap around each other. During mitosis there is an increase in packaging making the chromatids visible during the metaphase during the M phase of the cell cycle.
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How and why do prokaryotes and eukaryotes cells divide?
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Answer: Cell division is necessary for the reproduction, growth and repair of organisms. Cell division must be initiated by a reproductive signal. Before a cell can divide the genetic material must be replicated and segregated to separate portions of the cell. Cytokinesis then divides the cytoplasm into two cells. In prokaryotes most cellular DNA is circular and reproduces by binary fission. In eukaryotes cells divide by mitosis which in general is similar to binary fission, but differs in detail as eukaryotes have a nucleus.
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How do cells die?
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Answers: Cells die by necrosis or they may self-destruct by apoptosis, a genetically programmed series of events that includes the fragmentation of its DNA.
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Which statement about mitosis is not true?
A. A single nucleus gives rise to two identical daughter nuclei B. The daughter nuclei are genetically identical to the parent nucleus. C. The centromeres separate at eth onset of anaphase D. Homologous chromosomes at prophase exchange genetic material E. The centrosomes organize the microtubules of the spindle fiber |
Answer: D
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Which statement about the cell cycle is not true?
A. It consists of mitosis and interphase B. The cell’s DNA replicates during G1 C. A cell can remain in G1 for weeks or much longer D. DNA is not replicated during G2 E. Cells enter the cell cycle as a result of internal or/and external control |
Answer: B
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DNA is
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a double-stranded helix in which the strands are antiparallel and the bases are held together by hydrogen bonding
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Each of the four bases pairs with its complement
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A with T and C with G
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This structure accounts for
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the genetic information, mutation, and replication functions of DNA.
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which proteins assist with DNA replication?
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Many proteins, most notably DNA polymerases
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The replication of DNA is
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semiconservative and proceeds in both directions from each origin of replication. The leading strand grows continuously, but synthesis of the lagging strand is discontinuous
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Circular chromosomes replicate from
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a single origin
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linear chromosomes replicate from
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multiple origins
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Telomeres does what
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comprise the ends of eukaryotic chromosomes and are important in maintaining chromosomal stability
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Loss of telomeres due to the activity of the enzyme telomerase is associated with
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aging and with cancers.
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Errors in DNA replication are repaired by three different mechanisms
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proofreading, mismatch repair, and excision repair.
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Which direction does replication go?
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Replication goes in both directions from the origin of replication. That is to say that each strand of DNA is replicated, and from each origin, two replication forks move in opposite directions.
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How can replication proceed along the DNA if the two strands are going in opposite directions?
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There are different modes of polymerization for the two growing strands. One newly formed strand (the leading strand) is formed continuously from its 5’ end to its 3’ end at the replication fork on the exposed 3’ to 5’ template strand. The other strand (the lagging strand) is formed semi-discontinuously in small fragments, called Okazaki fragments. The fragments of the lagging strand are linked together by DNA ligase.
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Where does the primer come from?
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The enzyme primase uses a DNA strand as a template and creates a complementary RNA strand that is the primer for DNA synthesis.
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How does proofreading improve replication fidelity?
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Spontaneous mutation of bases and insertion of the wrong nucleotide would normally lead to an error every 104 to 105 bases. However, the proofreading capability of the DNA polymerases allows mismatched nucleotides to be removed, reducing the errors to one in 10^9 to 10^10.
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How is replication tied to cell division?
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Replication is tied to cell division by several proteins including the origin recognition complex, replication proteins. The process is controlled by cyclins, proteins produced during interphase that bind to cyclin¬dependent kinases and activate replication.
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1. Do DNA polymerase enzymes alsofunction as exonucleases?
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Most DNA-polymerase enzymes also have exonuclease activity.
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2. Define processivity and indicate the importance of this concept in DNA replication.
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The processivity of a DNA polymerase is the number of nucleotides incorporatedbefore the enzyme dissociates from the template. The higher this number, the more efficient the replication process
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3. How does proofreading take place in the process of replication
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When an incorrect nucleotide is introduced into a growing DNA chain as a result of mismatched base pairing, DNA polymerase acts as a 3_-exonuclease, removing the incorrect nucleotide. The same enzyme then incorporates the correct nucleotide.
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4. Can methylation of nucleotides play role n DNA replication? Is so how?
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Prokaryotes methylate their DNA soon after replication. This aids the process ofmismatch repair. The enzymes that carry out the process can recognize the correctstrand by its methyl groups.The newly formed strand, which contains the incorrect base, does not have methyl groups.
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Reception
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A signal molecule binds to a receptor protein, causing it to change shape
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The binding between a signal molecule (ligand) and receptor is
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highly specific
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A shape change in a receptor is often what?
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the initial transduction of the signal
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Most signal receptors are
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plasma membrane proteins
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Most water-soluble signal molecules bind to
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specific sites on receptor proteins in the plasma membrane
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What are “Kinases”?A) They are small substrates that bind to proteins.
B) They are ATP molecules that bind to enzymes C) They are proteins that transfers ATP to another Protein D)They are enzymes that transfer phosphate groups to themselves or other enzymes. E) They are enzymes that use ATP as a source of energy to drive unfavorable reactions. |
D)
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Receptor tyrosine kinases are
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membrane receptors that attach phosphates to tyrosines
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A receptor tyrosine kinase can
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trigger multiple signal transduction pathways at once
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A ligand-gated ion channel receptor does what?
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acts as a gate when the receptor changes shape
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receptor tyrosine kinase does what?
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can trigger multiple signal transduction pathways at once
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Would you expect “ion-gated” transport to be A) Facilitated-Diffusion controlled
B) Activated controlled C) Simple Diffusion controlled D) None of the above. |
A)
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