Bio chapter 10 exam 3

cell cycle

ordered sequence of events through which a cell passes between one cell division and the next, ordered series of events involving cell growth and cell division that produces two new daughter cells

interphase

period of the cell cycle leading up to mitosis; includes G1, S and G2 phases (the interim period between two consecutive cell divisions)

gene

physical and functional unit of heredity, a sequence of DNA that codes for a protein

locus

position of a gene on a chromosome

binary fission

prokaryotic cell division process

kinetochore

protein structure associated with the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase

condensin

proteins that help sister chromatids coil during prophase

quiescent

refers to a cell that is performing normal cell functions and has not initiated preparations for cell division

centromere

region at which sister chromatids are bound together; a constricted area in condensed chromosomes

retinoblastoma protein (Rb)

regulatory molecule that exhibits negative effects on the cell cycle by interacting with a transcription factor (E2F)

centriole

rod-like structure constructed of microtubules at the center of each animal cell centrosome

tumor suppressor gene

segment of DNA that codes for regulator proteins that prevent the cell from undergoing uncontrolled division

chromatid

single DNA molecule of two strands of duplicated DNA and associated proteins held together at the centromere

metaphase

stage of mitosis during which chromosomes are aligned at the metaphase plate

telophase

stage of mitosis during which chromosomes arrive at opposite poles, decondense, and are surrounded by a new nuclear envelope

anaphase

stage of mitosis during which sister chromatids are separated from each other

prometaphase

stage of mitosis during which the nuclear membrane breaks down and mitotic spindle fibers attach to kinetochores

cell plate

structure formed during plant cell cytokinesis by Golgi vesicles, forming a temporary structure (phragmoplast) and fusing at the metaphase plate; ultimately leads to the formation of cell walls that separate the two daughter cells

septum

structure formed in a bacterial cell as a precursor to the separation of the cell into two daughter cells

nucleosome

subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins

histone

one of several similar, highly conserved, low molecular weight, basic proteins found in the chromatin of all eukaryotic cells; associates with DNA to form nucleosomes

origin

(also, ORI) region of the prokaryotic chromosome where replication begins (origin of replication)

G1 Phase

(also, first gap) first phase of interphase centered on cell growth during mitosis

mitosis

(also, karyokinesis) period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase

G2 Phase

(also, second gap) third phase of interphase during which the cell undergoes final preparations for mitosis

Compare and contrast a human somatic cell to a human gamete.

Human somatic cells have 46 chromosomes, including 22 Homologous pairs and have one pair of nonhomologous sex chromosomes. This is the 2N, or diploid, condition. Human gametes have 23 chromosomes, one each of 23 unique chromosomes. This is the n, or haploid, condition

Explain the difference between a proto-oncogene and a tumor-suppressor gene.

A proto-oncogene is a segment of DNA that codes for one of the positive cell cycle regulators. If that gene becomes mutated so that it produces a hyperactivated protein product, it is considered an oncogene. A tumor suppressor gene is a segment of DNA that codes for one of the negative cell cycle regulators. If that gene becomes mutated so that the protein product becomes less active, the cell cycle will run unchecked. A single oncogene can initiate abnormal cell divisions; however, tumor suppressors lose their effectiveness only when both copies of the gene are damaged.

At which of the cell-cycle checkpoints do external forces have the greatest influence? a. G1 checkpoint b. G2 checkpoint c. M checkpoint d. G0 checkpoint

A. G1 checkpoint

Which negative regulatory molecule can trigger cell suicide (apoptosis) if vital cell cycle events do not occur? a. p53 b. p21 c. retinoblastoma protein (Rb) d. cyclin-dependent kinase (Cdk)

A. p53

Separation of the sister chromatids is a characteristic of which stage of mitosis? a. prometaphase b. metaphase c. anaphase d. telophase

Anaphase

Describe how the duplicated bacterial chromosomes are distributed into new daughter cells without the direction of the mitotic spindle.

As the chromosome is being duplicated, each origin moves away from the starting point of replication. The chromosomes are attached to the cell membrane via proteins; the growth of the membrane as the cell elongates aids in their movement.

FtsZ proteins direct the formation of a _______ that will eventually form the new cell walls of the daughter cells. a. contractile ring b. cell plate c. cytoskeleton d. septum

B cell plate

Chromosomes are duplicated during what stage of the cell cycle? a. G1 phase b. S phase c. prophase d. prometaphase

B. S phase

An organism's traits are determined by the specific combination of inherited _____. a. cells. b. genes. c. proteins. d. chromatids.

B. genes

A diploid cell has_______ the number of chromosomes as a haploid cell. a. one-fourth b. half c. twice d. four times

C. Twice

What is the main prerequisite for clearance at the G2 checkpoint? a. cell has reached a sufficient size b. an adequate stockpile of nucleotides c. accurate and complete DNA replication C. d. proper attachment of mitotic spindle fibers to kinetochores

C. accurate and complete DNA replication

Many of the negative regulator proteins of the cell cycle were discovered in what type of cells? a. gametes b. cells in G0 c. cancer cells d. stem cells

C. cancer cells

___________ are changes to the order of nucleotides in a segment of DNA that codes for a protein. a. Proto-oncogenes b. Tumor suppressor genes c. Gene mutations d. Negative regulators

C. gene mutations

Which eukaryotic cell-cycle event is missing in binary fission? a. cell growth b. DNA duplication c. karyokinesis d. cytokinesis

C. karyotinesis

A gene that codes for a positive cell-cycle regulator is called a(n) _____. a. kinase inhibitor. b. tumor suppressor gene. c. proto-oncogene. d. oncogene

C. proto-oncogene

What steps are necessary for Cdk to become fully active?

Cdk must bind to a cyclin, and it must be phosphorylated in the correct position to become fully active.

Which of the following is the correct order of events in mitosis? a. Sister chromatids line up at the metaphase plate. The kinetochore becomes attached to the mitotic spindle. The nucleus reforms and the cell divides. Cohesin proteins break down and the sister chromatids separate. b. The kinetochore becomes attached to the mitotic spindle. Cohesin proteins break down and the sister chromatids separate. Sister chromatids line up at the metaphase plate. The nucleus reforms and the cell divides. c. The kinetochore becomes attached to the cohesin proteins. Sister chromatids line up at the metaphase plate. The kinetochore breaks down and the sister chromatids separate. The nucleus reforms and the cell divides. d. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins break down and the sister chromatids separate. The nucleus reforms and the cell divides.

D

If the M checkpoint is not cleared, what stage of mitosis will be blocked? a. prophase b. prometaphase c. metaphase d. anaphase

D. anaphase

The first level of DNA organization in a eukaryotic cell is maintained by which molecule? a. cohesin b. condensin c. chromatin d. histone

D. histone

A mutated gene that codes for an altered version of Cdk that is active in the absence of cyclin is a(n) _____. a. kinase inhibitor. b. tumor suppressor gene. c. proto-oncogene. d. oncogene.

D. oncogene

Which of the following events does not occur during some stages of interphase? a. DNA duplication b. organelle duplication c. increase in cell size d. separation of sister chromatids

D. separation of sister chromatids

Identical copies of chromatin held together by cohesin at the centromere are called _____. a. histones. b. nucleosomes. c. chromatin. d. sister chromatids.

D. sister chromatids

Unpacking of chromosomes and the formation of a new nuclear envelope is a characteristic of which stage of mitosis? a. prometaphase b. metaphase c. anaphase d. telophase

D. telophase

Briefly describe the events that occur in each phase of interphase.

During G 1 , the cell increases in size, the genomic DNA is assessed for damage, and the cell stockpiles energy reserves and the components to synthesize DNA. During the S phase, the chromosomes, the centrosomes, and the centrioles (animal cells) duplicate. During the G 2 phase, the cell recovers from the S phase, continues to grow, duplicates some organelles, and dismantles other organelles.

p53 can trigger apoptosis if certain cell-cycle events fail. How does this regulatory outcome benefit a multicellular organism?

If a cell has damaged DNA, the likelihood of producing faulty proteins is higher. The daughter cells of such a damaged parent cell would also produce faulty proteins that might eventually become cancerous. If p53 recognizes this damage and triggers the cell to self-destruct, the damaged DNA is degraded and recycled. No further harm comes to the organism. Another healthy cell is triggered to divide instead.

What cell-cycle events will be affected in a cell that produces mutated (non-functional) cohesin protein?

If cohesin is not functional, chromosomes are not packaged after DNA replication in the S phase of interphase. It is likely that the proteins of the centromeric region, such as the kinetochore, would not form. Even if the mitotic spindle fibers could attach to the chromatids without packing, the chromosomes would not be sorted or separated during mitosis.

Outline the steps that lead to a cell becoming cancerous.

If one of the genes that produce regulator proteins becomes mutated, it produces a malformed, possibly non-functional, cell-cycle regulator. This increases the chance that more mutations will be left unrepaired in the cell. Each subsequent generation of cells sustains more damage. The cell cycle can speed up as a result of loss of functional checkpoint proteins. The cells can lose the ability to self-destruct.

List some reasons why a cell that has just completed cytokinesis might enter the G0 phase instead of the G1 phase.

Many cells temporarily enter G 0 until they reach maturity. Some cells are only triggered to enter G 1 when the organism needs to increase that particular cell type. Some cells only reproduce following an injury to the tissue. Some cells never divide once they reach maturity.

Rb is a negative regulator that blocks the cell cycle at the G1 checkpoint until the cell achieves a requisite size. What molecular mechanism does Rb employ to halt the cell cycle?

Rb is active when it is dephosphorylated. In this state, Rb binds to E2F, which is a transcription factor required for the transcription and eventual translation of molecules required for the G 1 /S transition. E2F cannot transcribe certain genes when it is bound to Rb. As the cell increases in size, Rb becomes phosphorylated, inactivated, and releases E2F. E2F can then promote the transcription of the genes it controls, and the transition proteins will be produced.

List the regulatory mechanisms that might be lost in a cell producing faulty p53.

Regulatory mechanisms that might be lost include monitoring of the quality of the genomic DNA, recruiting of repair enzymes, and the triggering of apoptosis.

Eukaryotic chromosomes are thousands of times longer than a typical cell. Explain how chromosomes can fit inside a eukaryotic nucleus

The DNA double helix is wrapped around histone proteins to form structures called nucleosomes. Nucleosomes and the linker DNA in between them are coiled into a 30-nm fiber. During cell division, chromatin is further condensed by packing proteins.

Describe the general conditions that must be met at each of the three main cell-cycle checkpoints.

The G 1 checkpoint monitors adequate cell growth, the state of the genomic DNA, adequate stores of energy, and materials for S phase. At the G 2 checkpoint, DNA is checked to ensure that all chromosomes were duplicated and that there are no mistakes in newly synthesized DNA. Additionally, cell size and energy reserves are evaluated. The M checkpoint confirms the correct attachment of the mitotic spindle fibers to the kinetochores

Name the common components of eukaryotic cell division and binary fission.

The common components of eukaryotic cell division and binary fission are DNA duplication, segregation of duplicated chromosomes, and the division of the cytoplasmic contents.

What is the relationship between a genome, chromosomes, and genes?

The genome consists of the sum total of an organism's chromosomes. Each chromosome contains hundreds and sometimes thousands of genes, segments of DNA that code for a polypeptide or RNA, and a large amount of DNA with no known function.

Chemotherapy drugs such as vincristine (derived from Madagascar periwinkle plants) and colchicine (derived from autumn crocus plants) disrupt mitosis by binding to tubulin (the subunit of microtubules) and interfering with microtubule assembly and disassembly. Exactly what mitotic structure is targeted by these drugs and what effect would that have on cell division?

The mitotic spindle is formed of microtubules. Microtubules are polymers of the protein tubulin; therefore, it is the mitotic spindle that is disrupted by these drugs. Without a functional mitotic spindle, the chromosomes will not be sorted or separated during mitosis. The cell will arrest in mitosis and die.

Describe the similarities and differences between the cytokinesis mechanisms found in animal cells versus those in plant cells.

There are very few similarities between animal cell and plant cell cytokinesis. In animal cells, A ring of actin fibers is formed around the periphery of the cell at the former metaphase plate. The actin ring contracts inward pulling the plasma membrane toward the center of the cell until the cell is pinched in two. In plant cells, a new cell wall must be formed between the daughter cells. Because of the rigid cell wall's of the parent cell, contraction of the middle of the cell is not possible. Instead, a cell plate is formed in the center of the cell at the former metaphase plate. The cell plate is formed from golgi vessicles that contain enzymes, protein, and glucose. The vesicles fuse and the enzymes build a new cell wall from the proteins and glucose. The cell plate Grows toward, and eventually fuses with, the cell wall of the parent cell.

cleavage furrow

a constriction formed by the actin ring during animal-cell cytokinesis that leads to cytoplasmic division

gamete

a haploid reproductive cell or sex cell (sperm or egg)

FtsZ

a tubulin-like protein component of the prokaryotic cytoskeleton that is important in prokaryotic cytokinesis (name origin: Filamenting temperature-sensitive mutant Z)

mitotic spindle

apparatus composed of microtubules that orchestrates the movement of chromosomes during mitosis

Attachment of the mitotic spindle fibers to the kinetochores is a characteristic of which stage of mitosis? a. prophase b. prometaphase c. metaphase d. anaphase

b. Prometaphase

p21

cell cycle regulatory protein that inhibits the cell cycle; its levels are controlled by p53

p53

cell cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis

diploid

cell, nucleus, or organism containing two sets of chromosomes (2n)

haploid

cells, nucleus, or organism containing one set of chromosomes (n)

homologous chromosomes

chromosomes of the same morphology with genes in the same location; diploid organisms have pairs of homologous chromosomes (homologs), with each homolog derived from a different parent

G0 Phase

distinct from the G1 phase of interphase; a cell in G0 is not preparing to divide

cytokinesis

division of the cytoplasm to form two separate daughter cells

cell-cycle checkpoint

mechanism that monitors the preparedness of a eukaryotic cell to advance through the various cell cycle stages

karyokinesis

mitotic nuclear division

oncogene

mutated version of a normal gene involved in the positive regulation of the cell cycle

proto-oncogene

normal gene that when mutated becomes an oncogene

cylin-dependent kinase (Cdk)

one of a group of protein kinases that helps to regulate the cell cycle when bound to cyclin; it functions to phosphorylate other proteins that are either activated or inactivated by phosphorylation

cyclin

one of a group of proteins that function that act in conjunction with cyclin-dependent kinases to help regulate the cell cycle by phosphorylating key proteins; the concentration of cyclins fluctuate throughout the cell cycle

metaphase plate

the equatorial plane midway between two poles of a cell where the chromosomes align during metaphase

mitotic phase

the period of the cell cycle when duplicated chromosomes are distributed into two nuclei and the cytoplasmic contents are divided; includes karyokinesis and cytokinesis

S phase

the second, or synthesis phase, of interphase during which DNA replication occurs

prophase

the stage of mitosis during which chromosomes condense and the mitotic spindle begins to form

genome

total genetic information of a cell or organism