cell bio 18 & 20

both types of arrest

-Cdk is unable to phosphorylate its substrates.

neither type of arrest

-Cyclins are phosphorylated and destroyed.

S-phase arrest,

-The Cdc25 phosphatase is inhibited.

interact with the cell cortex

-aster microtubules

stabilized by interactions with each other via motor proteins

-interpolar microtubules

link chromosomes to a spindle pole

-kinetochore microtubules

G1 arrest, an

-p53 activates the transcription of a Cdk inhibitor.

Which type of junction involves a connection to the actin cytoskeleton?

adherens junctions

Proteoglycans in the extracellular matrix of animal tissues

allow cartilage to resist compression.

A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is the

amount of extracellular matrix in connective tissues.

Tight junctions

are formed from claudins and occludins.

Condensins

assemble into complexes on the DNA when phosphorylated by M-Cdk.

Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells?

assembly of the contractile ring

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated?

at the end of G2

Hemidesmosomes are important for

attaching epithelial cells to the extracellular matrix.

Which of the following statements about cancer is FALSE?

A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell.

Which of the following genetic changes cannot convert a proto-oncogene into an oncogene?

A mutation that introduces a stop codon immediately after the codon for the initiator methionine.

Name the stage of M phase in which the following events occur. Place the numbers 1-8 next to the letter headings to indicate the normal order of events.

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

Which of the following statements about tumor suppressor genes is FALSE?

Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells.

Examine the schematic representation of centrosome duplication in Figure 18-13. By analogy with DNA replication, would you classify centrosome duplication as conservative or semiconservative? Explain your answer.

Centrosome duplication is semiconservative. The paired centrioles in the centrosome separate, and each serves to nucleate the assembly of a new centriole. As a consequence, each new centrosome consists of one old and one new centriole. Thus, centrosome duplication is analogous to DNA replication, in which the new double helix consists of one old DNA strand and one newly replicated DNA strand.

Which of the following statements about collagen is FALSE?

Collagen synthase organizes the mature collagen molecules into ordered collagen fibrils.

MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which of the following statements is NOT a legitimate conclusion from the control experiment?

Components of an interphase nucleus are insufficient to cause mitotic spindle formation.

Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2?

The cell would enter M phase under conditions when normal cells would not.

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only?

The cells produced would get smaller and smaller.

Which of the following statements is FALSE?

The cleavage furrow always forms in the middle of the cell.

blood vessels

bring oxygen and remove waste

Programmed cell death occurs

by means of an intracellular suicide program.

A metastasis is

a secondary tumor in a different part of the body that arises from a cell from the primary tumor.

Induced pluripotent stem (iPS) cells

can be created by the expression of a set of key genes in most somatic cell types, including cells derived from adult tissues.

Adherens junctions

can be used to bend epithelial sheets into tubes.

A pluripotent cell

can give rise to all the tissues and cell types in the body.

Cells that are terminally differentiated

can no longer undergo cell division.

An adult hemopoietic stem cell found in the bone marrow

can undergo self-renewing divisions for the lifetime of a healthy animal.

Apoptosis differs from necrosis in that necrosis

causes cells to swell and burst, whereas apoptotic cells shrink and condense.

The principal microtubule-organizing center in animal cells is the

centrosome.

At the end of DNA replication, the sister chromatids are held together by the

cohesins.

Which of the following molecules is NOT found in plants?

collagen

lymphocytes

combat infection

Mouse embryonic stem (ES) cells

come from the inner cell mass of early embryos.

Levels of Cdk activity change during the cell cycle, in part because

cyclin activity change during the cycle.

A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to

disassemble its nuclear lamina at prometaphase.

A cell that is terminally differentiated will

dismantle the cell-cycle control system.

macrophages

dispose of dying cells

Cells in the G0 state

do not divide

Mitogens are

extracellular signals that stimulate cell division.

The concentration of mitotic cyclin (M cyclin)

falls toward the end of M phase as a result of ubiquitylation and degradation.

Cohesins are required to make the chromosomes more compact and thus to prevent tangling between different chromosomes.

false

Sister chromatids are held together by condensins from the time they arise by DNA replication until the time they separate at anaphase.

false

The centromere nucleates a radial array of microtubules called an aster, and its duplication is triggered by S-Cdk.

false

Therefore, the cell-cycle control system operates primarily by a timing mechanism, in which the entry into one phase starts a timer set for sufficient time to complete the required tasks. After a given amount of time has elapsed, a molecular "alarm" triggers movement to the next phase.

false

The plasmodesmata in plants are functionally most similar to which animal cell junction?

gap junction

Which of the following does not occur during M phase in animal cells?

growth of the cell

Which of the following would NOT explain the results with the mutant?

inability to begin M phase

You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could NOT be responsible for the behavior of this strain of yeast?

inactivation of an enzyme that ubiquitylates M cyclin

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by

inhibiting cyclin transcription.

A cell can crawl through a tissue because of the transmembrane __________ proteins that can bind to fibronectin outside of the cell.

integrin

At desmosomes, cadherin molecules are connected to

intermediate filaments.

The G1 DNA damage checkpoint

involves the inhibition of cyclin-Cdk complexes by p21.

A basal lamina

is a thin layer of extracellular matrix underlying an epithelium.

A malignant tumor is more dangerous than a benign tumor because

its cells invade other tissues.

Cadherins

mediate cell-cell attachments through homophilic interactions.

Which word or phrase below best describes the phase in mitosis depicted in Figure 18-29?

metaphase

Disassembly of the nuclear envelope

must occur for kinetochore microtubules to form in animal cells.

fibroblasts

organize connective tissue

Plasmodesmata

permit small molecules to pass from one cell to another.

When a terminally differentiated cell in an adult body dies, it can typically be replaced in the body by a stock of

proliferating precursor cells.

Ras is a GTP-binding protein that is often defective in cancer cells. A common mutation found in cancer cells causes Ras to behave as though it were bound to GTP all the time, which will cause cells to divide inappropriately. From this description, the normal Ras gene is a/an

proto-oncogene.

Schwann cells

provide electrical insulation for axons

Fibroblasts organize the collagen of the extracellular matrix by

pulling the collagen into sheets or cables after it has been secreted.

Cytokinesis in animal cells

requires ATP.

Sister chromatid separation occurs because __________ are destroyed by the APC/C.

securins

Progression through the cell cycle requires a cyclin to bind to a Cdk because

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

A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes?

the jiggling movement of chromosomes at the metaphase plate

Which of the following is NOT an example of a connective tissue?

the layer of photoreceptors in the eye

Which type of junction contributes the most to the polarization of epithelial cells?

tight junctions

Both multicellular plants and animals have

tissues composed of multiple different cell types.

The artificial introduction of three key __________ into an adult cell can convert the adult cell into a cell with the properties of ES cells.

transcription factors

Each centrosome contains a pair of centrioles and hundreds of γ-tubulin rings that nucleate the growth of microtubules.

true

Microtubule-dependent motor proteins and microtubule polymerization and depolymerization are mainly responsible for the organized movements of chromosomes during mitosis.

true

Statement 1: Generally, in a given organism, the S, G2, and M phases of the cell cycle take a defined and stereotypedamount of time in most cells.

true

Irradiated mammalian cells usually stop dividing and arrest at a G1 checkpoint. Place the following events in the order in which they occur.

1.DNA damage 2.accumulation and activation of p53 3.production of p21 4.inhibition of cyclin-Cdk complexes

Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. How many of each of the following structures will the cell have at mitotic prophase? A. sister chromatids B. centromeres C. kinetochores D. centrosomes E. centrioles

: A—16; B—16; C—16; D—2; E—4

Which of the following statements is FALSE?

Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition.

You create cells with a version of the origin recognition complex, ORC, that cannot be phosphorylated by S-Cdk and thus cannot be inactivated. Which of the following statements describes the likely consequence of this change in ORC?

Cells will replicate some regions of the genome more than once in a cell cycle.

Which of the following statements about apoptosis is TRUE?

Apoptosis can be promoted by the release of cytochrome c into the cytosol from mitochondria.

Which of the following statements about gap junctions is FALSE?

Because gap junctions only allow uncharged molecules to pass through, they are not used for electrically coupling cells.

Which letter is associated with the line that is pointing to the interpolar microtubules in Figure 18-29?

E

You engineer yeast cells that express the M cyclin during S phase by replacing the gene regulatory sequences of the M cyclin gene with those of the S cyclin gene. 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?

G1 cyclin-Cdks will be activated earlier in G1.

Which organelle fragments during mitosis?

Golgi apparatus

Which of the following statements is TRUE?

In anaphase B, microtubules associated with the cell cortex shorten.

Which of the following statements about integrins is FALSE?

Integrins use adaptor proteins to interact with the microtubule cytoskeleton.

Which of the following statements about the anaphase-promoting complex (APC) is FALSE?

It is continuously active throughout the cell cycle.

How does S-Cdk help guarantee that replication occurs only once during each cell cycle?

It phosphorylates and inactivates Cdc6.

Which of the following statements about kinetochores is TRUE?

Kinetochores assemble onto chromosomes during late prophase.

Which of the following statements about cellulose is FALSE?

Microtubules are directly attached to the outside surface of the plasma membrane to form tracks that help orient the cellulose polymers.

Which of the following statements is FALSE?

Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall.

Which of the following statements about the cell cycle is FALSE?

Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.

Which of the following statements about organoids is FALSE?

Organoids can only be made for organs that are made up of a single type of differentiated cell.

Which of the following statements is FALSE?

Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye.

Which of the following statements about animal connective tissues is TRUE?

Proteoglycans can resist compression in the extracellular matrix.

After the nuclear envelope breaks down, microtubules gain access to the chromosomes and, every so often, a randomly probing microtubule captures a chromosome and ultimately connects to the kinetochore to become a kinetochore microtubule of the spindle.

TRUE

Which of the following statements is FALSE?

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

Which of the following statements about plant cell walls is TRUE?

The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall.

Which of the following statements is TRUE?

The mitotic spindle helps segregate the chromosomes to the two daughter cells.

Which of the following events does NOT usually occur during interphase?

The nuclear envelope breaks down.

APC is a tumor suppressor and acts in the Wnt signaling pathway to prevent the TCF complex from turning on Wnt-responsive genes. Mice that lack the gene encoding TCF4 do not have the ability to maintain the pool of proliferating gut stem cells needed to renew the gut lining. What do you predict will happen in mice that lack the APC gene?

They will have inappropriate proliferation of gut stem cells.

Which of the following is NOT good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution?

Yeast cells have only one Cdk, whereas humans have many Cdks.