Study guide

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

inhibiting cyclin transcription.

Which of the following statements is FALSE?

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

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

The cells produced would be smaller than if G1 were also present.

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

cohesins.

A cell that is terminally differentiated will

dismantle the cell-cycle control system.

Which of the situations below will enhance microtubule shrinkage?

addition of a drug that inhibits GTP exchange on free tubulin dimers

You are studying nuclear lamins and use recombinant DNA technology to alter the coding sequence of a nuclear lamin gene. The altered gene codes for a nuclear lamin protein that can no longer be phosphorylated during prophase of mitosis. What do you predict would happen if the cell only had the altered nuclear lamin gene (and not the unaltered version)?

Nuclear lamins will no longer disassemble properly during mitosis.

Figure 17-7 shows an electron micrograph of a myofibril within a skeletal muscle fiber; various regions and points along the fibril have been labeled. Which of the following statements is true about this myofibril's contraction?

Point B will move closer to point C.

Which of the following statements about organellar movement in the cell is FALSE?

Only the microtubule cytoskeleton is involved in organellar movement.

Which of the following conditions would decrease the likelihood of skeletal muscle contraction?

addition of a drug that blocks Ca2+ binding to troponin

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

A mutant yeast strain stops proliferating when shifted from 25°C to 37°C. When these cells are analyzed at the two different temperatures, using a machine that sorts cells according to the amount of DNA they contain, the graphs in Figure 18-1 are obtained. Which of the following would not explain the results with the mutant?

inability to begin M phase

Which of the following components is NOT important for ciliary movement?

sarcoplasmic reticulum

All intermediate filaments are of similar diameter because

the central rod domains are similar in size and amino acid sequence.

Which of the following statements about the cytoskeleton is FALSE?

Covalent bonds between protein monomers hold together cytoskeletal filaments.

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

cyclin activity changes during the cycle.

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.

The G1 DNA damage checkpoint

involves the inhibition of cyclin-Cdk complexes by p21.

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 of the following statements about skeletal muscle contraction is FALSE?

The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.

Actin-mediated movement involves the coordination of many events in the cell. Which of the following is NOT required for cell crawling?

release of Ca2+ from the sarcoplasmic reticulum

Which of the following statements about skeletal muscle cells is true?

The cells possess multiple nuclei.

Figure 17-4A shows how the movement of dynein causes a sperm cell's flagellum to bend. If the polarity of the adjacent doublets of microtubules is reversed (see Figure 17-4B), what do you predict would happen?

Bending would occur, except that the right microtubule doublet would move down relative to the left one.

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(n)

proto-oncogene.

Mouse embryonic stem (ES) cells

come from the inner cell mass of early embryos.

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.

What part of an epithelial tissue needs to be degraded to allow tumor cells to spread to the rest of the body?

basal lamina

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.

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.

A basal lamina

is a thin layer of extracellular matrix under lying an epithelium

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

Normally, a signaling pathway can be illustrated as R