Top1-Ch2-P19-24

Question 2

Before cell division what happens with the centromere?

Answer 2

Before cell division a multiprotein complex called a kinetochore assembles on the centromere, later, spindle microtubules attach to the kinetochore.

Question 3

Chromosomes are classified into four types based on the location of the centromere? What are the names?

Answer 3

metacentric, submetacentric, acrocentric, and telocentric

Question 3

Name the letter classification of the two arms of a chromosome?

Answer 3

short arms of submetacentric and acrocentric is allocated letter p - (short arm)

The other arm is letter q - (long arm)

Question 4

Telomeres?

Answer 4

The natural tips of a whole linear chromosome. It protects and stabilises the chromosome ends.

Question 5

In preparation for cell division what does each chromosome do?

Answer 5

It replicates, making a copy of itself. These two initially identical copies are called sister chromatids and are held together at the centromere. Each sister chromatid consists of a single molecule of DNA.

Question 6

What is the cell cycle?

Answer 6

It is the life story of a cell.

Question 7

What are checkpoints?

Answer 7

It is when progression through the cell cycle is regulated at key transition points.

Question 8

What are the two major phases of the cell cycle?

Answer 8

Interphase - the period between cell divisions when the cell grows, develops and functions. Critical events necessary for cell division also take place.

M phase - (mitotic phase) - the period of active cell division - it includes mitosis (the process of nuclear division) and cytokinesis (cytoplasmic division)

Question 9

Name the three subphases of interphase

Answer 9

G₁, S and G₂

Question 10

Explain G₁

Answer 10

G₁ (for gap 1) is when the cell grows and proteins for cell division are synthesised, lasting several hours. Near end of G₁ a critical point called G₁/S checkpoint holds the cell in G₁ until it has all enzymes necessary for DNA replication. Cell is committed to divide passed this checkpoint.

Prior to G₁/S checkpoint cells may exit from active cell cycle and go to nondividing G₀ phase (a stable state). Cells can reenter G₁ after any period of time. Some cells never enter G₀ but continuously cycle.

Question 11

Explain S phase of cell cycle?

Answer 11

It is after G₁ phase. S phase (for DNA synthesis) is when each chromosome duplicates. If DNA synthesis is blocked (by drugs or mutation) the cell will not undergo mitosis. Before the S phase each chromosome is unreplicated but after the S phase each chromosome is composed of two chromatids.

A chromatid contains the replicated DNA of each individual chromosome, which are joined by a centromere, for the process of cell division (mitosis or meiosis).

Question 12

Explain G₂ phase of cell cycle?

Answer 12

Gap 2. Important G₂/M checkpoint is reached near end of G₂, which is passed only if cell’s DNA is undamaged. After G_2/M checkpoint cell is ready to divide and enters M phase. Throughout interphase chromosomes are relaxed, but not uncoiled. Condition changes dramatically when interphase closes and cell enters M phase.

Question 13

How long does a typical mammalian cell spend at each subphase within interphase. Ie G₁, S, G₂?

Answer 13

• G1 : 10 hours
• S : 9 hours
• G2 : 4 hours

Question 14

Name the six stages of the M phase of the cell cycle? Briefly explain M phase.

Answer 14

Five stages of mitosis (prophase, prometaphase, metaphase, anaphase, and telophase) and cytokinesis.

Note: M phase is a continuous process and its separation into these six stages is arbitrary.

M phase is when copies of cell’s chromosomes (sister chromatids) separate and cell undergoes division. Separation of sister chromatids is critical process that results in complete set of genetic information for each of the resulting cells.

Question 15

Prophase?

Answer 15

The mitotic spindle (an organised array of microtubules that move the chromosomes in mitosis) forms. In animal cells the spindle grows out from a pair of centrosomes that migrate to opposite sides of the cell. In each cetrosome is a special organelle (the centriole) which is also composed of microtubules. Some plant cells do not have cetrosomes or centrioles but they do have mitotic spindles.

Question 16

Prometaphase?

Answer 16

Nuclear membrane disintegrates. Then for each chromosome a microtubule from one centrosome anchors to the kinetochore of one of the sister chromatids. The same occurs with a microtubule from the opposite centrosome anchoring to the other sister chromatid.

Question 17

Chromatid?

Answer 17

A chromatid is one-half of two identical copies of a replicated chromosome. During cell division, the identical copies are joined together at the region of the chromosome called the centromere. They are known as sister chromatids. Once the paired sister chromatids separate from one another in anaphase of mitosis, each is known as a daughter chromosome.

Question 18

Centrosome?

Answer 18

Is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression.

Question 19

Metaphase?

Answer 19

The chromosomes arrange in a single plane along the metaphase plate between the two centrosomes. Centrosomes are now at opposite ends of cell with microtubules radiating outward and meeting in the middle of the cell.

Question 20

Six stages of M phase picture from lectures

Answer 20

Question 21

Cell cycle picture from book

Answer 21

Question 22

Anaphase?

Answer 22

Sister chromatids separate and move towards opposite spindle poles

Question 23

Telophase?

Answer 23

Chromsomes arrive at spindel poles. Nuclear membrane re-forms and the chromosomes relax.

Question 24

Cytokinesis?

Answer 24

Cytoplasm divides; cell wall forms in plant cells. In many cells this is simultaneous with telophase.

Question 25

Cell cycle summary from lecture notes

Answer 25