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Chapter 12 The Cell Cycle > Concept 12.2: The mitotic phase alternates with interphase in the cell cycle > Flashcards

Concept 12.2: The mitotic phase alternates with interphase in the cell cycle Flashcards

1
Q

In 1882, a German anatomist named ____________________ developed dyes that allowed him to observe, for the first time, the behavior of chromosomes during mitosis and cytokinesis.

A

Walther Flemming

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2
Q

In fact, Flemming coined the terms

A

mitosis and chromatin

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3
Q

includes both mitosis and cytokinesis, is usually the shortest part of the cell cycle

A

mitotic (M) phase

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4
Q

The mitotic phase alternates with a much longer stage called

A

interphase

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5
Q

interphase often accounts for about

A

90% of the cycle

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6
Q

Interphase can be divided into three phases:

A

the G1 phase (“first gap”), the S phase (“synthesis”), and the G2 phase (“second gap”)

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7
Q

the first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis

A

G1 phase

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8
Q

the synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated

A

S phase

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9
Q

the second gap, or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs

A

G2 phase

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10
Q

The G phases were misnamed as “gaps” when they were first observed because the cells appeared inactive, but we now know that intense metabolic activity and growth occur throughout

A

interphase

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11
Q

During all three phases of interphase, in fact, a cell grows by producing proteins and cytoplasmic organelles such as

A

mitochondria and endoplasmic reticulum

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12
Q

Duplication of the chromosomes, crucial for eventual division of the cell, occurs entirely during the

A

S phase

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13
Q

a cell grows (G1), continues to grow as it copies its chromosomes (S), grows more as it completes preparations for

A

cell division (G2), and divides (M).

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14
Q

The daughter cells may then

A

repeat the cycle.

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15
Q

watch animation the cell cycle

A
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16
Q

A particular human cell might undergo one division in

A

24 hours

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17
Q

Of this time, the M phase would occupy less than 1 hour, while the S phase might occupy

A

10–12 hours, or about half the cycle.

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18
Q

The rest of the time would be apportioned between the

A

G1 and G2 phases.

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19
Q

The G2 phase usually takes 4–6hours; in our example, G1 would occupy about 5–6hours.

A

5-6 hours

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20
Q

G1 is the most variable in length in different types of

A

cells.

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21
Q

Mitosis is conventionally broken down into five stages:

A

prophase, prometaphase, metaphase, anaphase, and telophase

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22
Q

Overlapping with the latter stages of mitosis, cytokinesis completes the

A

mitotic phase.

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23
Q

study figure 12.7 exploring mitosis in animal cell, watch bioflix animation mitosis and video animal mitosis

A
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24
Q

Many of the events of mitosis depend on the ________________, which begins to form in the cytoplasm during prophase.

A

mitotic spindle

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25
Q

This structure consists of fibers made of microtubules and associated

A

proteins.

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26
Q

While the mitotic spindle assembles, the other microtubules of the cytoskeleton partially disassemble, providing the material used to construct the

A

spindle.

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27
Q

The spindle microtubules elongate (polymerize) by incorporating more subunits of the protein tubulin (see Table 6.1) and shorten (depolymerize) by

A

losing subunits.

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28
Q

In animal cells, the assembly of spindle microtubules starts at the ____________, a subcellular region containing material that functions throughout the cell cycle to organize the cell’s microtubules.

A

centrosome

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29
Q

A pair of centrioles is located at the center of the centrosome, but they are not essential for cell division: If the centrioles are destroyed with a laser microbeam, a spindle nevertheless forms during

A

mitosis.

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30
Q

centrioles are not even present in plant cells, which do form

A

mitotic spindles.

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31
Q

During interphase in animal cells, the single centrosome duplicates, forming two centrosomes, which remain near the

A

nucleus.

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32
Q

The two centrosomes move apart during prophase and _____________ of mitosis as spindle microtubules grow out from them.

A

prometaphase

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33
Q

By the end of prometaphase, the two centrosomes, one at each pole of the spindle, are at opposite ends of the

A

cell.

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34
Q

An _________, a radial array of short microtubules, extends from each centrosome.

A

aster

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35
Q

The spindle includes the

A

centrosomes, the spindle microtubules, and the asters.

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36
Q

a structure made up of proteins that have assembled on specific sections of DNA at each centromere

A

kinetochore

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37
Q

The chromosome’s two kinetochores face in

A

opposite directions.

38
Q

During prometaphase, some of the spindle microtubules attach to the kinetochores; these are called

A

kinetochore microtubules (The number of microtubules attached to a kinetochore varies among species, from one microtubule in yeast cells to 40 or so in some mammalian cells.)

39
Q

When one of a chromosome’s kinetochores is _____________ by microtubules, the chromosome begins to move toward the pole from which those microtubules extend.

A

“captured”

40
Q

However, this movement comes to a halt as soon as microtubules from the opposite pole attach to the

A

kinetochore on the other chromatid.

41
Q

At metaphase, the centromeres of all the duplicated chromosomes are on a

A

plane midway between the spindle’s two poles.

42
Q

This plane is called the ____________________, which is an imaginary plate rather than an actual cellular structure

A

metaphase plate,

43
Q

Meanwhile, microtubules that do not attachto kinetochores have been elongating, and by metaphase they overlap and interact with other

A

nonkinetochore microtubules from the opposite pole of the spindle

44
Q

By metaphase, the microtubules of the asters have also grown and are in contact with the

A

plasma membrane.

45
Q

watch video spindle formation during mitosis

A
46
Q

The structure of the spindle correlates well with its function during .

A

anaphase

47
Q

Anaphase begins suddenly whenthe cohesins holding together the sister chromatids of each chromosome are cleaved by an enzyme called

A

separase.

48
Q

Once separated, the chromatids become individualchromosomes that move toward opposite ends of the

A

cell.

49
Q

How do the kinetochore microtubules function in this poleward movement of chromosomes? Apparently, two mechanisms are in play, both involving

A

motor proteins.

50
Q

Results of a cleverly designed experiment suggested that motor proteins on the kinetochores “walk” the chromosomes along the microtubules, which depolymerize at their kinetochore ends after the motor proteins have passed (Figure 12.9). (This is referred to as the

A

“Pac-man” mechanism because of its resemblance to the arcade game character that moves by eating all the dots in its path.)

51
Q

However, other researchers, working with different cell types or cells from other species, have shown that chromosomes are “reeled in” by

A

motor proteins at the spindle poles and that the microtubules depolymerize after they pass by these motor proteins at the poles.

52
Q

The general consensus now is that both mechanisms are used and that their relative contributions vary among

A

cell types.

53
Q

study figure 12.9 and watch animation microtubule depolymerization

A
54
Q

In a dividing animal cell, the nonkinetochore microtubules are responsible for elongating the whole cell during

A

anaphase.

55
Q

Nonkinetochore microtubules from opposite poles overlap each other extensively during

A

metaphase

56
Q

During anaphase, the region of overlap is reduced as motor proteins attached to the microtubules walk them away from one another, using

A

energy from ATP.

57
Q

As the microtubules push apart from each other, their spindle poles are pushed apart, elongating the

A

cell.

58
Q

At the same time, the microtubules lengthen somewhat by the addition of

A

tubulin subunits to their overlapping ends

59
Q

As a result, the microtubules continue to

A

overlap.

60
Q

At the end of anaphase, duplicate groups of chromosomes have arrived at opposite ends of the elongated

A

parent cell.

61
Q

Nuclei re-form during

A

telophase.

62
Q

Cytokinesis generally begins during anaphase or telophase, and the spindle eventually disassembles by

A

depolymerization of microtubules.

63
Q

watch animation mitosis

A
64
Q

In animal cells, cytokinesis occurs by a process known as

A

cleavage.

65
Q

The first sign of cleavage is the appearance of a __________________, a shallow groove in the cell surface near the old metaphase plate

A

cleavage furrow

66
Q

On the cytoplasmic side of the furrow is a contractile ring of

A

actin microfilaments associated with molecules of the protein myosin.

67
Q

The actin microfilaments interact with the

A

myosin molecules, causing the ring to contract

68
Q

The contraction of the dividing cell’s ring of microfilaments is like the pulling of a drawstring. The cleavage furrow deepens until the parent cell is pinched in two, producing

A

two completely separated cells, each with its own nucleus and its own share of cytosol, organelles, and other subcellular structures.

69
Q

figure 12.10 cytokinesis in animal and plant cells, and watch video cytokinesis in an animal cell

A
70
Q

Cytokinesis in plant cells, which have cell walls, is markedly different. There is no

A

cleavage furrow.

71
Q

Instead, during telophase, vesicles derived from the Golgi apparatus move along microtubules to the middle of the cell, where they coalesce, producing a

A

cell plate.

72
Q

Cell wall materials carried in the vesicles collect inside the

A

cell plate as it grows

73
Q

The cell plate enlarges until its surrounding membrane fuses with the

A

plasma membrane along the perimeter of the cell.

74
Q

Two daughter cells result, each with its own plasma membrane. Meanwhile, a new cell wall arising from the contents of the cell plate forms between the

A

daughter cells.

75
Q

watch animation cytokinesis, figure 12.11

A
76
Q

Prokaryotes (bacteria and archaea) can undergo a type of reproduction in which the cell grows to roughly double its size and then

A

divides to form two cells.

77
Q

The term __________________, meaning “division in half,” refers to this process and to the asexual reproduction of single-celled eukaryotes, such as the amoeba in Figure 12.2a.

A

binary fission

78
Q

However, the process in eukaryotes involves mitosis, while that in prokaryotes

A

does not.

79
Q

In bacteria, most genes are carried on a single bacterial chromosome that consists of a

A

circular DNA molecule and associated proteins.

80
Q

In some bacteria, the process of cell division is initiated when the DNA of the bacterial chromosome begins to replicate at a specific place on the chromosome called

A

the origin of replication, producing two origins.

81
Q

As the chromosome continues to replicate, one origin moves rapidly toward the opposite end of the

A

cell

82
Q

While the chromosome is replicating, the cell

A

elongates.

83
Q

hen replication is complete and the bacterium has reached about twice its initial size, proteins cause its plasma membrane to pinch inward, dividing the parent bacterial cell into two daughter cells. In this way, each cell inherits a complete

A

genome.

84
Q

figure 12.12 bacterial cell division by binary fission, animation cell division in bacteria

A
85
Q

In most bacterial species studied, the two origins of replication end up at opposite ends of the cell or in some other very specific location, possibly anchored there by

A

one or more proteins.

86
Q

Polymerization of one protein resembling eukaryotic actin apparently functions in bacterial chromosome movement during cell division, and another protein that is related to tubulin helps pinch the plasma membrane inward, separating the

A

two bacterial daughter cells.

87
Q

Given that prokaryotes preceded eukaryotes on Earth by more than a billion years, we might hypothesize that mitosis evolved from simpler

A

prokaryotic mechanisms of cell reproduction

88
Q

As eukaryotes with nuclear envelopes and larger genomes evolved, the ancestral process of binary fission, seen today in bacteria, somehow gave rise to

A

mitosis.

89
Q

Variations on cell division exist in different groups of organisms. These variant processes may be similar to mechanisms used by ancestral species and thus may resemble steps in the evolution of mitosis from a

A

binary fission-like process presumably carried out by very early bacteria

90
Q

Possible intermediate stages are suggested by two unusual types of nuclear division found today in certain

A

unicellular eukaryotes—dinoflagellates, diatoms, and some yeasts

91
Q

These two modes of nuclear division are thought to be cases where ancestral mechanisms have remained relatively unchanged over evolutionary time. In both types, the nuclear envelope remains intact, in contrast to what happens in most

A

eukaryotic cells.

92
Q

figure 12.13 mechanisms of cell division in several groups of organisms, video nuclear envelope breakdown

A

Chapter 12 The Cell Cycle (4 decks)

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