Cell biology Test 4

Which of the following statements is FALSE? a. Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition. b. Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive. c. Inhibiting the Cdc25 phosphatase will delay the G2/M transition. d. The activating phosphatase (Cdc25) removes the phosphates from mitotic Cdk that were added by Wee1, so that M-Cdk will be active.

A. Cdc25 dephosphorylation of Weel activated the kinase, promoting the G2/M transition. The Cdc25 phosphatase acts to dephosphorylate M-Cdk and does not dephosphorylateWee1. Furthermore, Wee1 activation would inhibit M-Cdk activity, which would inhibit (and notpromote) the G2/M transition.

Induced pluripotent stem (iPS) cells a. can be created by the expression of a set of key genes in most somatic cell types, including cells derived from adult tissues. b. require a supply of donor egg cells, as is the case for embryonic stem cells. c. can differentiate into a greater variety of adult tissues than embryonic stem cells. d. have been used to create human clones

A. can be created by the expression of a set of key genes in most somatic cell. PS cells do not require donor egg cells and are made from adult (and not embryonic)cells. Embryonic stem cells can differentiate into all tissue and cell types. Human clones have notbeen created using iPS cells.

Adherens junctions a. can be used to bend epithelial sheets into tubes. b. are most often found at the basal surface of cells. c. are found only in adult tissues. d. involve fibronectin and integrin interactions.

A. can be used to bend epithelial sheets into tubes.

Which of the following statements about integrins is FALSE? a. Integrins use adaptor proteins to interact with the microtubule cytoskeleton. b. Integrins can switch to an activated state by binding to an extracellular matrix molecule. c. Integrins can switch to an activated state by binding to an intracellular protein d. An activated integrin molecule takes on an extended conformation.

A. integrins use adaptor proteins to interact with the microtubule

Sister chromatid separation occurs because __________ are destroyed by the APC/C. a. securins b. cohesins c. kinetochores d. condensins

A. securins The APC/C initiates sister chromatid separation by triggering destruction of securin, which results in activation of separase. Separase then cleaves the cohesins that hold the sister chromatids together.

Cells that are terminally differentiated a. will undergo apoptosis within a few days. b. can no longer undergo cell division. c. are unable to move. d. no longer produce RNAs.

B. can no longer undergo cell division Terminally differentiated cells no longer divide. The life of a terminally differentiated cell depends on the cell type; although terminally differentiated cells in the intestine typically die within a few days, neurons in the brain can last for a lifetime. Some terminally differentiated cells can still move and transcribe and translate genes

Which of the following is NOT an example of a connective tissue? a. bone b. the layer of photoreceptors in the eye c. the jellylike interior of an eye d. cartilage

B. the layer of photoreceptors in the eye The layer of photoreceptors in the eye is considered an epithelial sheet.

After mitosis occurs, the two daughter cells are at a "crossroads". The cell must decide whether to keepdividing or not. What are the three options for a cell at this point in the cell cycle.

G0, G1, terminally differentiate

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? 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 cyclin-Cdks will be activated earlier in G1. d. S-Cdk targets will be phosphorylated during S phase.

C. G1 cyclin-Cdks will be activated earlier in G1. The activity of G1 cyclin-Cdks should not be affected by S-Cdk (which normally occurs in S phase) or M-Cdk (which likely now exists within the cell due to the inappropriate expression of M cyclin from the S cyclin promoter).

Apoptosis differs from necrosis in that necrosis a. requires the reception of an extracellular signal. b. causes DNA to fragment. c. causes cells to swell and burst, whereas apoptotic cells shrink and condense. d. involves a caspase cascade.

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

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 molecules is NOT found in plants? a. cellulose b. lignin c. collagen d. pectin

C. collagen

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.

C. cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. Cdks require cyclins for enzymatic activity. Cyclins have no enzymatic activities themselves, and cyclin binding to Cdk activates the Cdk. As far as we know, cyclin-Cdk binding is not directly monitored by checkpoints.

The concentration of mitotic cyclin (M cyclin) a. rises markedly during M phase. b. is activated by phosphorylation. c. falls toward the end of M phase as a result of ubiquitylation and degradation. d. is highest in G1 phase.

C. falls toward the end of M phase as a result of ubiquitylation and degradation. The concentration of mitotic cyclin rises gradually during G2 and it is ubiquitylated and degraded during late M phase.

Which type of junction contributes the most to the polarization of epithelial cells? a. adherens junctions b. desmosomes c. tight junctions d. gap junctions

C. tight junctions

How are gap junctions different from adheren junctions and desmosomes ?

GJ: connect cytoplasms of adjacent cells and ar formed by connexon channels

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 Cells will check whether the DNA is fully and correctly replicated at the end of G. It does not make sense to monitor DNA replication before S phase because DNA replication has not yet occurred. When cells enter G0, they do not replicate their DNA. During M phase, chromosomes are condensed for chromosome segregation, so it would be difficult for the cell to examine the replicated DNA for errors at that point.

Which word or phrase below best describes the phase in mitosis depicted in Figure 18-29? a. anaphase b. prometaphase c. S-phase check point d. metaphase

D. metaphase

Which of the following statements about animal connective tissues is TRUE? a. Enzymes embedded in the plasma membrane synthesize the collagen in the extracellular matrix extracellularly. b. In connective tissue, the intermediate filaments within the cells are important for carrying the mechanical load. c. Cells can attach to a collagen matrix by using fibronectin, an integral membrane protein. d. Proteoglycans can resist compression in the extracellular matrix.

D. proteoglycans can resist compression in the extracellular matric. Collagen is synthesized within the cell and reaches the extracellular environment through exocytosis. In connective tissues, the extracellular matrix carries the mechanical load. Cells attach to the collagen matrix with the use of integrins, which span the plasma membrane; integrins then interact with fibronectin, which binds to collagen.

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

D. the cells produced would get smaller and smaller. The cells produced would get smaller and smaller, as they would not have sufficient time to double their mass before dividing.

The cell cycle can be arrested at both G1 and G2/M check points if DNA damage is detected. Describe in detail one example of this process (be specific - what proteins are involved, and which CDK-Cyclin complexes are inhibited

P53 pathway in G1 that activates p21, or ATM/ATR that acts on cdc25

Describe in detail the differences between a tumor suppressor gene and a proto-oncogene

Tumor suppressor - inhibitory protein that requires loss-of-function mutations in both copies (recessive) can inherit one bad copy and get loss-of-function in other by any number of events. Proto-oncogene = gain of function mutation that make protein overactive (only need one copy to gain function), gene amplification, translocation, mutation can all give rise to gain of function

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? a. Cells will enter S phase prematurely. b. Cells will replicate some regions of the genome more than once in a cell cycle. c. ORC will be unable to bind to DNA. d. DNA helicases will not be able to open up the double helix at the replication origin.

b. DNA helicases will not be able to open up the double helix at the replication origin. If ORC is not properly inactivated (and thus remains active), ORC could bind to DNA and reassemble a prereplicative complex on a DNA molecule that has already undergone replication. The assembly of an inappropriate prereplicative complex would lead to an inappropriate reinitiation of replication.

Which of the following statements about cancer is FALSE? a. Viruses cause some cancers. b. Tobacco use is responsible for more than 20% of all cancer deaths. c. A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell. d. Chemical carcinogens cause cancer by changing the nucleotide sequence of DNA.

c. A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell. Multiple mutations are required to convert a normal cell into a cell that has all the properties needed to make it cancerous.

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 a. tumor suppressor. b. oncogene. c. proto-oncogene. d. gain-of-function mutation.

c. proto-oncogene. The normal Ras gene is a proto-oncogene. Only the mutated form of Ras is an oncogene and a gain-of-function mutation.

Mouse embryonic stem (ES) cells a. can only be grown in the laboratory. b. can give rise to all tissues and cell types in the body except germ cells. c. can be made in the lab from human iPS cells. d. come from the inner cell mass of early embryos.

d. come from the inner cell mass of early embryos Mouse ES cells are cells that are dissociated from the inner cell mass of early embryos. These cells are produced naturally in embryos and can be isolated and grown in the lab. ES cells can give rise to all tissues and cell types of the body, including germ cells. An organism's genes determine what an embryo grows up to become, and thus human iPS cells can only be used to generate human cells.

What is the order of the entire cell cycle. Include all the phases.

prophase• prometaphase• metaphase• anaphase• telophase• cytokinesis