Chapter 18 Questions

Programmed cell death occurs ________________. (a) by means of an intracellular suicide program. (b) rarely and selectively only during animal development. (c) only in unhealthy or abnormal cells. (d) only during embryonic development.

(a) by means of an intracellular suicide program.

Mitogens are _____. (a) extracellular signals that stimulate cell division. (b) transcription factors important for cyclin production. (c) kinases that cause cells to grow in size. (d) produced by mitotic cells to keep nearby neighboring cells from dividing.

(a) extracellular signals that stimulate cell division.

Which of the following does not occur during M phase in animal cells? (a) growth of the cell (b) condensation of chromosomes (c) breakdown of nuclear envelope (d) attachment of chromosomes to microtubules

(a) growth of the cell

Cytokinesis in animal cells ________________. (a) requires ATP . (b) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane. (c) is often followed by phosphorylation of integrins in the plasma membrane. (d) is assisted by motor proteins that pull on microtubules attached to the cell cortex.

(a) requires ATP .

Which organelle fragments during mitosis? (a) endoplasmic reticulum (b) Golgi apparatus (c) mitochondrion (d) chloroplast

(b) Golgi apparatus

Which of the following statements is false? (a) DNA synthesis begins at origins of replication. (b) The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk. (c) The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle. (d) DNA synthesis can only begin after prereplicative complexes assemble on the ORCs.

(b) The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk.

Which of the following events does not usually occur during interphase? (a) Cells grow in size. (b) The nuclear envelope breaks down. (c) DNA is replicated. (d) The centrosomes are duplicated.

(b) The nuclear envelope breaks down.

A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________. (a) reassemble its nuclear envelope at telophase. (b) disassemble its nuclear lamina at prometaphase. (c) begin to assemble a mitotic spindle. (d) condense its chromosomes at prophase.

(b) disassemble its nuclear lamina at prometaphase.

Progression through the cell cycle requires a cyclin to bind to a Cdk because _________. (a) the cyclins are the molecules with the enzymatic activity in the complex. (b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity. (c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. (d) without cyclin binding, a cell-cycle checkpoint will be activated.

(b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity.

Which of the following statements about the anaphase-promoting complex (APC) is false? (a) It promotes the degradation of proteins that regulate M phase. (b) It inhibits M-Cdk activity. (c) It is continuously active throughout the cell cycle. (d) M-Cdk stimulates its activity.

(c) It is continuously active throughout the cell cycle.

How does S-Cdk help guarantee that replication occurs only once during each cell cycle? (a) It blocks the rise of Cdc6 concentrations early in G1. (b) It phosphorylates and inactivates DNA helicase. (c) It phosphorylates the Cdc6 protein, marking it for destruction. (d) It promotes the assembly of a prereplicative complex.

(c) It phosphorylates the Cdc6 protein, marking it for destruction.

At the end of DNA replication, the sister chromatids are held together by the ___________. (a) kinetochores. (b) securins. (c) cohesins. (d) histones.

(c) cohesins.

Which of the following statements about apoptosis is true? (a) Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. (b) The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. (c) Bax and Bak promote apoptosis by binding to procaspases in the apoptosome. (d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.

(d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? (a) Cells would not be able to replicate their DNA. (b) The mitotic spindle could not assemble. (c) Cells would get larger and larger. (d) The cells produced would get smaller and smaller.

(d) The cells produced would get smaller and smaller.

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? (a) at the transition between G1 and S (b) when cells enter G0 (c) during M (d) at the end of G2

(d) at the end of G2

The G1 DNA damage checkpoint ________________. (a) causes cells to proceed through S phase more quickly. (b) involves the degradation of p53. (c) is activated by errors caused during DNA replication. (d) involves the inhibition of cyclin-Cdk complexes by p21.

(d) involves the inhibition of cyclin-Cdk complexes by p21.

Disassembly of the nuclear envelope ________________. (a) causes the inner nuclear membrane to separate from the outer nuclear membrane. (b) results in the conversion of the nuclear envelope into protein-free membrane vesicles. (c) is triggered by the phosphorylation of integrins. (d) must occur for kinetochore microtubules to form in animal cells.

(d) must occur for kinetochore microtubules to form in animal cells.

Name the stage of M phase in which of the following events occur. Place the numbers 1-8 next to the letter headings to indicate the normal order of events. A. alignment of the chromosomes at the spindle equator B. attachment of spindle microtubules to chromosomes C. breakdown of nuclear envelope D. pinching of cell in two E. separation of two centrosomes and initiation of mitotic spindle assembly F. re-formation of the nuclear envelope G. condensation of the chromosomes H. separation of sister chromatids

A. 5, metaphase B. 4, prometaphase C. 3, prometaphase D. 8, cytokinesis E. 2, prophase F. 7, telophase G. 1 prophase H. 6, anaphase

Irradiated mammalian cells usually stop dividing and arrest at a G1 checkpoint. Place the following events in the order in which they occur. (a) production of p21 (b) DNA damage (c)inhibition of cyclin-Cdk complexes (d) accumulation and activation of p53

B, D, A, C

The cell cycle consists of an alternation between __________________, which appears as a period of dramatic activity under the microscope, and a preparative period called __________________, which consists of three phases called __________________, __________________, and __________________. During M phase, the nucleus divides in a process called __________________, and the cytoplasm splits in two in a process called __________________. The cell-cycle control system relies on sharp increases in the activities of regulatory proteins called __________________, or __________________, to trigger S phase and M phase. Inactivation of __________________ is required to exit from M phase after chromosome segregation. - APC - Cdks - condensation - cyclin-dependent kinases - cytokinesis - G2 phase - interphase - intraphase - kinesins - M phase - metaphase - microtubules - mitosis - myosins - S phase - G1 phase - M-Cdk - S-Cdk - G1-Cdk - meiosis

The cell cycle consists of an alternation between M PHASE, which appears as a period of dramatic activity under the microscope, and a preparative period called INTERPHASE, which consists of three phases called G1 PHASE, S PHASE, and G2 PHASE. During M phase, the nucleus divides in a process called MITOSIS, and the cytoplasm splits in two in a process called CYTOKINESIS. The cell-cycle control system relies on sharp increases in the activities of regulatory proteins called CYCLIN-DEPENDENT KINASES, or CDKS, to trigger S phase and M phase. Inactivation of M-CDK is required to exit from M phase after chromosome segregation.

The four phases of the cell cycle, in order, are G1, __________________, __________________, and __________________. A cell contains the most DNA after __________________ phase of the cell cycle. A cell is smallest in size after __________________ phase of the cell cycle. Growth occurs in __________________, __________________, and __________________ phases of the cell cycle. A cell does not enter mitosis until it has completed __________________ synthesis. - DNA - M - protein - G1 - nucleotide - S - G2 - organelle

The four phases of the cell cycle, in order, are G1, S, G2, and M. A cell contains the most DNA after S phase of the cell cycle. A cell is smallest in size after M phase of the cell cycle. Growth occurs in G1, S, and G2 phases of the cell cycle. A cell does not enter mitosis until it has completed DNA synthesis.

The survival, __________________, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface __________________ and trigger various intracellular signaling pathways. One class of signal molecules, called __________________, stimulates cell division by releasing the molecular brakes that keep cells in the __________________ or __________________ phase of the cell cycle. Members of a second class of signal molecules are called __________________, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called __________________, inhibits __________________ by regulating members of the __________________ family of proteins. In addition to such stimulatory factors, some signal proteins such as __________________ act negatively on other cells, inhibiting their survival, growth, or proliferation. - anaphase - annihilation - apoptosis - arrestase - Bcl2 - biosynthetic - cascades - caspase - Cdk - cyclin - differentiation - G0 - G1 - G2 - growth factors - interphase - ligand - M - mitogens - myostatin - nourishment - nutrition - phosphatases - proliferation - receptor - S - survival - factors - transcription

The survival, PROLIFERATION, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface RECEPTOR and trigger various intracellular signaling pathways. One class of signal molecules, called MITOGENS, stimulates cell division by releasing the molecular brakes that keep cells in the G0 or G1 phase of the cell cycle. Members of a second class of signal molecules are called GROWTH FACTORS, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called SURVIVAL FACTORS, inhibits APOPTOSIS by regulating members of the BCL2 family of proteins. In addition to such stimulatory factors, some signal proteins such as MYOSTATIN act negatively on other cells, inhibiting their survival, growth, or proliferation.

You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is least likely during this experiment? (a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase. (b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase. (c) G1 cyclins will be expressed during S phase. (d) S-Cdk targets will be phosphorylated during S phase.

c) G1 cyclins will be expressed during S phase.