Exam 4 cell biology

Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. How many centrioles will the cell have at mitotic prophase? a. 2 b. 4 c. 16 d. 32

b. 4

Fibroblasts organize the collagen of the extracellular matrix by _____. a. cutting and rejoining the fibrils. b. processing procollagen into collagen. c. twisting fibrils together to make ropelike fibers. d. pulling the collagen into sheets or cables after it has been secreted.

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

Which of the following statements about the cell cycle is false? a. Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells. b. An unfavorable environment can cause cells to arrest in G1. c. A cell has more DNA during G2 than it did in G1. d. The cleavage divisions that occur in an early embryo have short G1 and G2 phases.

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

Certain proto-oncogenes become oncogenes when they acquire mutations that cause them to act in a dominant hyperactive manner. a. True b. False

a. True

The binding of a cyclin to a Cdk is required for Cdk enzymatic activity. a. True b. False

a. True

The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall. a. True b. False

a. True

A metastasis is _____a. a. a secondary tumor in a different part of the body that arises from a cell from the primary tumor. b. a cell that is dividing in defiance of normal constraints. c. a part of the primary tumor that has invaded the surrounding tissue. d. the portion of the cancerous tumor that displays genetic instability.

a. a secondary tumor in a different part of the body that arises from a cell from the primary tumor. All tumors, benign or malignant, divide in defiance of normal constraints. A malignant tumor will invade the surrounding tissue while a metastasis is found at a distant site from the original tumor. The genetic instability seen in cancer cells is not limited to metastases.

Which type of junction involves a connection to the actin cytoskeleton? a. adherens junctions b. desmosomes c. gap junctions

a. adherens junctions

Induced pluripotent stem (iPS) cells _____ a. can be created by the expression of a set of key genes in most somatic cell types. 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.

a. can be created by the expression of a set of key genes in most somatic cell types.

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.

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.

All of the following occur during M phase except: 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 Cell size increases throughout interphase and not during M phase. All of the other phenomena are observed in M phase.

A cell can crawl through a tissue because of the transmembrane _______ proteins that can bind to fibronectin outside of the cell. a. integrin b. collagen c. gap junction d. claudin

a. integrin

Plasmodesmata _____ a. permit small molecules to pass from one cell to another. b. are found only in animal cells. c. are closed by the neurotransmitter dopamine. d. provide tensile strength.

a. permit small molecules to pass from one cell to another.

Sister chromatid separation occurs at the time that __________ are destroyed. 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.

Which of the following genetic changes cannot convert a proto-oncogene into an oncogene? a.A mutation that introduces a stop codon immediately after the codon for the initiator methionine. b.A mutation within the coding sequence that makes the protein hyperactive. c.An amplification of the number of copies of the proto-oncogene, causing overproduction of the normal protein. d.A mutation in the promoter of the proto-oncogene, causing the normal protein to be transcribed and translated at an abnormally high level.

a.A mutation that introduces a stop codon immediately after the codon for the initiator methionine. A mutation that introduces a stop codon immediately after the codon for the initiator methionine will result in no protein being produced.

A pluripotent cell can give rise to all the tissues and cell types in the body. a.True b. False

a.True

Which protein is responsible for activating nucleases that destroy DNA? a. Initiator caspases b. Executioner caspases

b. Executioner caspases

Enzymes embedded in the plasma membrane translate the collagen. a. True b. False

b. False

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

b. False Cells with one copy of a tumor suppressor gene should behave normally, because tumor suppressor genes generally work in a recessive manner.

Mouse iPS cells can generate human tissues. a.True b. False

b. False 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.

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

b. False Multiple mutations are required to convert a normal cell into a cell that has all the properties needed to make it cancerous.

A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is the _____ a. ability of connective-tissue cells such as fibroblasts to change shape. b. amount of extracellular matrix in connective tissues. c. ability of connective tissues to withstand mechanical stresses. d. numerous connections that connective-tissue cells make with each other.

b. amount of extracellular matrix in connective tissues. Cells in connective tissue tend to be scattered throughout the extracellular matrix and make few or no contacts with each other, unlike nerve cells or epithelial cells.

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.

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 lamins at prometaphase c. begin to assemble a mitotic spindle d. condense its chromosomes at prophase

b. disassemble its nuclear lamins at prometaphase If the lamins cannot be phosphorylated during mitosis, the cells will be unable to disassemble their nuclear lamina, preventing the breakdown of the nuclear envelope at prometaphase.

At desmosomes, cadherin molecules are connected to _____ a. actin filaments. b. intermediate filaments. c. microtubules. d. gap junctions.

b. intermediate filaments.

A basal lamina_____. a. is a thin layer of connective-tissue cells and matrix underlying an epithelium. b. is a thin layer of extracellular matrix underlying an epithelium. c. is attached to the apical surface of an epithelium. d. separates epithelial cells from each other.

b. is a thin layer of extracellular matrix underlying an epithelium.

Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. How many centromeres will the cell have at mitotic prophase? a. 2 b. 4 c. 16 d. 32

c. 16

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

c. S-Cdk phosphorylates and inactivates Cdc6. The phosphorylation and inactivation of Cdc6 ensures that replication occurs once and only once during each cell cycle. The concentration of Cdc6 rises early in G1, independent of S-Cdk. Cdc6 guides the assembly of the prereplicative complex at an origin. By phosphorylating Cdc6, S-Cdk inactivates it, so that once an origin fires and replicates, Cdc6 cannot reinitiate replication. S-Cdk phosphorylates and activates DNA helicases.

An adult hemopoietic stem cell found in the bone marrow _____ a. will occasionally produce epidermal cells when necessary. b. can produce only red blood cells. c. can undergo self-renewing divisions for the lifetime of a healthy animal. d. will express all the same transcription factors as those found in an unfertilized egg.

c. can undergo self-renewing divisions for the lifetime of a healthy animal. Stem cells undergo self-renewing divisions. Adult stem cells are specialized, and thus an adult hemopoietic stem cell does not produce epidermal cells and also stably expresses the transcriptional regulators that ensure that its progeny will become blood cells. An adult hemopoietic stem cell has the ability to produce all the many types of cell in the blood.

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

A cell that is terminally differentiated will __________________. a. replicate its DNA. b. reenter the cell cycle only once a year. c. dismantle the cell-cycle control system. d. arrest after S phase.

c. dismantle the cell-cycle control system. A terminally differentiated cell cannot reenter the cell cycle.

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

c. falls during 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 M phase.

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 gene. b. oncogene. c. proto-oncogene.

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.

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

Hemidesmosomes are important for _____ a. epithelial sheets to change shape to form tubes. b. linkages to glycosaminoglycans. c. forming the basal lamina. d. attaching epithelial cells to the extracellular matrix.

d. attaching epithelial cells to the extracellular matrix.

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.

A malignant tumor is more dangerous than a benign tumor because _____ a. its cells are proliferating faster. b. it causes neighboring cells to mutate. c. its cells attack and phagocytose neighboring normal tissue cells. d. its cells invade other tissues.

d. its cells invade other tissues.

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 Cdc6 d. must occur for kinetochore microtubules to form in animal cells

d. must occur for kinetochore microtubules to form in animal cells In animal cells, kinetochore microtubules cannot form if the chromosomes in the nucleus are separated from the microtubules in the cytoplasm because of the presence of the nuclear envelope.