Chapter 12: The Cell Cycle

Question 1

Cell division is essential for

Answer 1

The perpetuation of life. It provides for the development, growth, and repair of multicellular organisms; and the reproduction of unicellular organisms

Question 2

A cell’s complement of DNA is called its

Answer 2

Genome

Question 2

A genome is organized into

Answer 2

Chromosomes

Question 3

Each eukaryotic chromosome is

Answer 3

A very long, linear DNA molecule with associated proteins that help structure the chromosome and control the activity of genes

Question 4

The entire complex of DNA and protein is called

Answer 4

Chromatin

Question 5

Duplicated chromosomes consist of

Answer 5

Two identical sister chromatids are attached along their length by proteins known as cohesion (attachment known as sister chromatid cohesion)

Question 6

Each sister chromatid has a

Answer 6

Centromere: a region where proteins bind to specific centromeric DNA sequences and hold the chromatids closely together

Question 7

When sister chromatids separate each is considered a

Answer 7

Chromosome

Question 8

Meiosis produces

Answer 8

Daughter cells that have half the number of chromosomes as the parent cell; when a sperm fertilizes an egg (both of which are formed by meiosis in animals), the chromosome number is restored, and the somatic cells of the new offspring again have two sets of chromosomes

Question 9

How many chromosomes are in your somatic cells?

Answer 9

46

Question 10

How many chromosomes are in your gametes?

Answer 10

23

Question 11

How many chromatids are in one of your somatic cells that has duplicated its chromosomes prior to mitosis?

Answer 11

92 (each duplicated chromosome consists of two sister chromatids)

Question 12

What event is common to all three subphases of interphase

Answer 12

Cell growth (produces proteins and cytoplasmic organelles)

Question 13

What key event happens during the S phase?

Answer 13

Duplication of the chromosomes, which is crucial for eventual division of the cell (DNA synthesis)

Question 14

Describe one chromosome as it proceeds through an entire cell cycle, starting with G1 of interphase and ending with telophase of mitosis

Answer 14

G1 phase - chromosome consists of a long, thin chromatin fiber made of DNA and associated proteins; growth and metabolic activities occur

S phase - (still chromatin fiber) chromosomes are duplicated and DNA is synthesized

G2 phase - growth and metabolism continue

Mitotic phase- cell division consisting of mitosis and cytokinesis

Prophase - sister chromatids become condensed into discrete chromosomes and the mitotic spindle begins to form

Prometaphase - kinetochore fibers from opposite ends of the mitotic spindle attach to the kinetochores of sister chromatids

Metaphase - chromosomes are all aligned at the metaphase plate

Anaphase - the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell

Telophase - The chromatin fiber uncoils and is surrounded by a reforming nuclear membrane; daughter nuclei are forming and cytokinesis has typically begun

Question 15

What is MPF?

Answer 15

Known as a “maturation-promoting factor” or “M-phase-promoting factor” it is a complex that is only activated when bound to a cyclin-dependent kinase and triggers the passage past the G2 checkpoint into M phase

Question 16

Describe the concentrations of MPF throughout the cell cycle

Answer 16

It has a high concentration as it triggers mitosis but is reduced at the end of mitosis because it depends on the concentration of cyclin in the cell

Question 17

Describe the concentrations of Cdk throughout the cell cycle

Answer 17

Constant throughout the cycle but rises and falls with changes in the concentration of its cyclin partner

Question 18

Describe the concentrations of cyclin throughout the cell cycle

Answer 18

Has a cyclically fluctuating concentration in the cell (increases during G1, S, and G2, and breaks down at the end of mitosis)

Question 19

In addition to phosphorylating proteins and other kinases that initiate mitotic events, MPF can

Answer 19

Activate a protein breakdown process that destroys its cyclin component and thus MPF activity during anaphase

Question 20

The Cdk portion of the complex remains to

Answer 20

Associate with new cyclin synthesized during the S and G2 phases of the next cycle

Question 21

If a mammalian cell does not receive a go-ahead signal at the G1 checkpoint, the cell will usually exit the cell cycle to a nondividing state called

Answer 21

The G0 (Gzero) phase

Question 22

An internal signal is required to move past the M phase checkpoint into

Answer 22

Anaphase

Question 23

Density-dependent inhibition of cell division appears to involve

Answer 23

The binding of cell-surface proteins of adjacent cells, which sends a cell-division-inhibiting signal to both cells

Question 23

Only after all chromosomes are attached at their _________ to __________ is the enzyme separate activated and the cohesions holding sister chromatids together are cleaved

Answer 23

Kinetochores; spindle microtubules

Question 23

Certain nutrients and regulatory proteins called ________ _________ have been found to be essential for cells to divide in culture.

Answer 23

Growth factors

Question 24

Most animal cells also show ________ _________ and must be attached to a substratum in order to divide

Answer 24

Anchorage dependence

Question 25

When grown in cell culture, cancer cells do not exhibit

Answer 25

Density-dependent inhibition or anchorage dependence, do not depend on growth factors to divide, do not undergo apoptosis when appropriate, and may continue to divide indefinitely instead of stopping after the typical 20 to 50 divisions of normal mammalian cells in culture

Question 26

Cells in culture that can divide indefinitely are said to have undergone

Answer 26

Transformation

Question 27

When a normal undergoes changes that begin its conversion to a cancer cell, the body's immune system may destroy it. If it proliferates, a mass of abnormal cells develops within a tissue. A _________ __________ remains at its original site and can be removed by surgery

Answer 27

Benign tumor

Question 28

The cells of a __________ ___________ are considered to be transformed cells. They have significant genetic changes that enable them to invade and disrupt the functions of one or more organs

Answer 28

Malignant tumor, an individual with a malignant tumor is said to have cancer

Question 29

Malignant tumor cells lose their attachment to other cells and may enter the blood and lymph systems and spread to other sites, a process called

Answer 29

Metastasis

Question 30

Radiation treatment preferentially affects cancer cells because

Answer 30

They are unable to repair the resulting DNA damage

Question 31

Chemotherapy involves drugs that

Answer 31

Affect stages in the cell cycle and therefore target actively dividing cells

Question 32

Most cells that will no longer divide are in this phase

Answer 32

G zero

Question 33

Sister chromatids separate and chromosomes move apart in this phase

Answer 33

Anaphase

Question 34

Mitotic spindle begins to form in this phase

Answer 34

Prophase

Question 35

Cell plate forms or cleavage furrow pinch cells apart in this phase

Answer 35

Telophase

Question 36

Replication of DNA occurs in this phase

Answer 36

S phase

Question 37

Chromosomes line up at central plane during this phase

Answer 37

Metaphase

Question 38

Nuclear membranes form around separated chromosomes during this phase

Answer 38

Telophase

Question 39

Chromosomes become visible during this phase

Answer 39

Prophase

Question 40

Kinetochore-microtubule interactions move chromosomes to the midline during this phase

Answer 40

Metaphase

Question 41

Restriction point occurs in this phase

Answer 41

G1 phase

Question 42

One of the differences between prokaryotic binary fission and eukaryotic mitosis is that

Answer 42

The duplicated signle chromosome does not separate along a mitotic spindle in prokaryotic cells (prokaryotes do not do mitosis because they do not have a nucleus)

Question 43

A plant cell has 12 chromosomes at the end of mitosis. How many chromosomes would it have in the G2 phase of its next cell cycle

Answer 43

12

Question 44

How many chromatids would this plant cell have in the G2 phase of its cell cycle

Answer 44

24

Question 45

The longest part of the cell cycle is

Answer 45

Interphase

Question 46

In animal cells, movement of the chromosomes is accomplished using ___________, but division of the cytoplasm requires the action of __________

Answer 46

Microtubules; actin filaments

Question 47

In eukaryotic organisms, chromosomes are duplicated

Answer 47

Before mitosis (in S phase)

Question 48

When do chromatids become chromosomes

Answer 48

When cohesins are degraded by separase (in anaphase)

Question 49

A cell in this phase has the least amount of DNA

Answer 49

G zero

Question 50

What is not true of a cell plate

Answer 50

It results from the fusion of microtubules in a dividing plant cell (actually is golgi vesicles)

Question 51

A cell that passes the restriction point in G1 will most likely

Answer 51

Undergo chromosome duplication

Question 52

During cell division, cyclin combines with Cdk to form a complex called MPF; this complex

Answer 52

Moves the cell past the G2 checkpoint into mitosis and promotes the degradation of cyclin, but leaves Cdk intact

Question 53

What initiates the separation of sister chromatids

Answer 53

Activation of a regulatory protein complex and the enzyme separase after all kinetochores are attached to microtubules

Question 54

Knowledge of the cell cycle control system will be most beneficial to understanding

Answer 54

Cancer

Question 55

Vinblastine is a chemotherapeutic drug used to treat certain cancers. It acts by interfering with microtubule assembly. The effectiveness of vinblastine must be related to

Answer 55

Disruption of mitotic spindle formation (prevents cell division during metaphase)

Question 56

Checkpoints in cell division

Answer 56

G1 checkpoint - (the most important) G2 checkpoint - a cyclin-Cdk complex in animal cells called MPF acts at the checkpoint as a go-ahead signal, triggering the events of mitosis M checkpoint - (internal signal) anaphase does not begin until all the chromosomes are properly attached to the spindle at the metaphase plate. S phase checkpoint - stops cells with DNA damage from proceeding in the cell cycle