Chapter 2: Mitosis and Meiosis Flashcards Preview

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Flashcards in Chapter 2: Mitosis and Meiosis Deck (134)
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1

What is a sister chromatid?

During interphase, the cell’s DNA replicates, producing an identical copy of each DNA molecule. By the end of mitosis, one copy of each DNA molecule has been moved to each daughter cell.

2

The terminology associated with DNA replication can be confusing.

Before DNA replication, each individual DNA molecule and its associated proteins is considered a single, unreplicated chromosome.

The product of DNA replication is still considered a single chromosome (a replicated chromosome) even though it contains two identical DNA molecules, or sister chromatids.

During mitosis, the sister chromatids separate, at which point each chromatid is considered an individual (unreplicated) chromosome.

Key structures involved in mitosis: the two sister chromatids of each duplicated chromosome begin to attach to the mitotic spindle by means of their kinetochores. The centrosomes anchor the mitotic spindle at opposite ends of the cell.

3

The cell cycle can be divided into 2 principle stages:

interphase and the mitotic (M) phase

Interphase consists of 3 subphases: G1, S, and G2. During interphase, the cell grows and copies its chromosomes in preparation for cell division.

The mitotic phase includes mitosis (division of the nucleus, which itself is divided into further subphases) and cytokinesis (division of the cytoplasm).

4

A number of cellular structures are involved in physically separating the duplicated chromosomes into two daughter nuclei during mitosis.

Which of the following statements does not correctly describe the role of a cellular structure in mitosis?
Every chromosome is attached to the mitotic spindle by two sets of microtubules, one extending from each pole of the cell.
The kinetochore is the structure that holds the sister chromatids together.
The centrosomes are the organizing centers for the formation of the mitotic spindle in animal cells.
During mitosis, the attachment of the sister chromatids to each other at the centromere is broken, permitting the chromatids to separate.

The kinetochore is NOT the structure that holds the sister chromatids together.

In animal cells, the assembly of spindle microtubules starts at the centrosomes.

The mitotic spindle is composed of microtubules that are organized by the centrosomes as they migrate to the poles of the cell early in mitosis.

The 2 sister chromatids of a replicated chromosome are most closely attached at their centromeres.

During prometaphase, a protein structure called the kinetochore appears on each sister chromatid at the position of the centromere. The spindle microtubules attach to the kinetochore, which is the motor that moves the chromosome along the spindle microtubules.

5

Prokaryotic DNA Replication

Need to replicate DNA with each cell division, eg. E. coli.

NO nuclear membrane.

Generally circular DNA molecule.

6

2 major processes of Eukaryotic DNA replication

Mitosis: produces 2 identical daughter cells

Meiosis: reduces genetic material content & number of chromosomes by exactly one half. Essential for sexual reproduction.

7

Kinetochore

Kinetochore proteins bind to centromeric proteins

Allows attachment to spindle fibers (made of alpha, beta, gamma tubulin), which facilitates transport to poles

8

centromere

The specialized heterochromatic chromosomal region at which sister chromatids remain attached after replication,and the site to which spindle fibers attach to the chromosome during cell division. Location of the centromere determines the shape of the chromosome during the anaphase portion of cell division. Also known as the primary constriction.

The shape of the chromosome during anaphase of mitosis is determined by the position of the centromere.

9

cytokinesis

The division or separation of the cytoplasm during mitosis or meiosis.

10

chromatin

The complex of DNA, RNA, histones, and nonhistone proteins that make up uncoiled chromosomes, characteristic of the eukaryotic interphase nucleus.

11

centrosome

Region of the cytoplasm containing a pair of centrioles.

12

chromatin

The complex of DNA, RNA, histones, and nonhistone proteins that make up uncoiled chromosomes, characteristic of the eukaryotic interphase nucleus.

Chromatin is the combination or complex of DNA and proteins that make up the contents of the nucleus of a cell

13

centrosome

Region of the cytoplasm containing a pair of centrioles.

the centrosome is the main microtubule organizing center of the animal cell as well as a regulator of cell-cycle progression.

14

Sister chromatids

A sister chromatid refers to either of the two identical copies formed by the replication of a single chromosome, with both copies joined together by a common centromere.

15

unreplicated chromosome

Before DNA replication, each individual DNA molecule and its associated proteins is considered a single, unreplicated chromosome.

During mitosis, the sister chromatids separate, at which point each chromatid is considered an individual (unreplicated) chromosome.

16

single chromosome (a replicated chromosome)

The product of DNA replication is still considered a single chromosome (a replicated chromosome) even though it contains two identical DNA molecules, i.e., sister chromatids.

17

The cell cycle can be divided into two principle stages:

interphase and the mitotic (M) phase.

18

Every chromosome is attached to the mitotic spindle by....

two sets of microtubules, one extending from each pole of the cell.

19

centrosomes

The centrosomes are the organizing centers for the formation of the mitotic spindle in animal cells.

20

During mitosis, the attachment of the sister chromatids to each other at the .....

....centromere is broken, permitting the chromatids to separate.

21

Role of checkpoints in the cell cycle

Checkpoints are control points in the cell cycle where “stop and go” signals regulate whether or not a cell continues to the next part of the cycle.

For example, cells that pass through the G1 checkpoint usually complete the cell cycle and divide. If a cell does not pass through the G1 checkpoint, it exits the cell cycle and enters a nondividing state called the G0 phase.

22

What distinguishes the G2 phase from the S phase?

Once the cell passes through the G1 checkpoint, it enters the S phase, followed by the G2 phase.

23

G1 checkpoint

A point in the G1 phase of the cell cycle when a cell becomes committed to initiating DNA synthesis and continuing the cycle or withdraws into the G0 resting stage.

24

G0

A nondividing but metabolically active state that cells may enter from the G1 phase of the cell cycle

25

Which two statements correctly describe the processes that occur in the S and G2 phases?

DNA replication occurs in the S (synthesis) phase. The S phase is followed by the G2 phase, which is when the centrosome replicates.

26

Which three of the following processes occur during the M phase of the cell cycle?

formation of the mitotic spindle
separation of sister chromatids
cytokinesis


The M phase of the cell cycle consists of both mitosis (the division of the nucleus) and cytokinesis (the division of the cell’s cytoplasm). DNA replication and replication of the centrosome both occur before mitosis begins.

27

checkpoints

The cell cycle is controlled by 3 internal checkpoints that evaluate the condition of the genetic information.

A checkpoint is one of several points in the eukaryotic cell cycle at which the progression of a cell to the next stage in the cycle can be halted until conditions are favorable.

Damage to DNA and other external factors are evaluated at the G1 checkpoint; if conditions are inadequate, the cell will not be allowed to continue to the S phase of interphase.

The G2 checkpoint ensures all of the chromosomes have been replicated and that the replicated DNA is not damaged before cell enters mitosis.

The M checkpoint determines whether all the sister chromatids are correctly attached to the spindle microtubules before the cell enters the irreversible anaphase stage.

28

Phases of the cell cycle

Many organisms contain cells that do not normally divide. These cells exit the cell cycle before the G1 checkpoint.

Once a cell passes the G1 checkpoint, it usually completes the cell cycle--that is, it divides.

The first step in preparing for division is to replicate the cell’s DNA in the S phase.
In the G2 phase, the centrosome replicates.
In early M phase, the centrosomes move away from each other toward the poles of the cell, in the process organizing the formation of the mitotic spindle.
At the end of the M phase when mitosis is complete, the cell divides (cytokinesis), forming two genetically identical daughter cells.

29

When are sister chromatids present?

Sister chromatids play an essential role in ensuring that each daughter cell receives genetic material that is identical to that which was present in the original parent cell.

Sister chromatids form when the DNA molecule in each chromosome is duplicated during the S phase. Until the sister chromatids separate in early anaphase, they are joined at one or more regions along their length. Once the sister chromatids separate, each chromatid becomes a full-fledged chromosome.

30

Changes in DNA content during the cell cycle

Once a cell passes the G1 checkpoint, its DNA is replicated during the S phase of interphase. Replication means that an exact copy of the DNA in each chromosome is made, thus doubling the cell’s DNA content.

Only once cytokinesis is completed at the end of telophase does the cell’s DNA content return to the level found in G1 cells.

Sister chromatids form when DNA replicates in the S phase. The sister chromatids become individual chromosomes once they separate in early anaphase.

Similarly, the cellular DNA content doubles in the S phase when the DNA replicates. However, the cell’s DNA content does not return to its normal (undoubled) levels until after cytokinesis is complete and two daughter cells have formed.

The condensation state of the DNA is not related to the presence or absence of sister chromatids. The DNA condenses in prophase and remains condensed until after the sister chromatids separate and the new daughter cells begin to form. In late telophase/cytokinesis, the emphasis shifts to cell growth and DNA replication for the next cell cycle. For these processes to occur, the DNA needs to be de-condensed so it is accessible to the cellular machinery involved in transcription.