Topic 9: Cell Cycle

Question 1

What is the cell cycle?

Answer 1

The mechanism through which somatic cells of eukaryotes can divide producing two daughter cells which are genetically identical to each other and the parent cell for one parent cell.

Question 2

What are the key events of the cell cycle?

Answer 2

Interphase: reproduction of DNA by parent cell
Mitosis: organisation of chromosome followed by their separation into two identical groups at different poles of the parent cell.
Cytokinesis: division of parent cells into two identical daughter cells

Question 3

What are the three stages of interphase?

Answer 3

Gap 1
Synthesis
Gap 2

Question 4

What is the gap 1 stage of interphase?

Answer 4

• Cell undergoes growth increasing the cell cytosol, synthesising proteins that are needed for DNA replication.
• The mitochondria of the cell divide and in the cases of photosynthetic plants, their chloroplasts also divide..
• It is near the end of this stage that the cell will either commit to continuing the cell cycle or will drop out and not divide. If the latter occurs the cell enters a non dividing quiscent g0 stage.

Question 5

What is the synthesis stage of interphase?

Answer 5

The parent cell synthesis or replicates its DNA, the genetic material of the cell. At the end of the s stage the parent cell contains 2 identical DNA copies.

Question 6

What is the gap 2 stage of intephase?

Answer 6

Further growth of the cell occurs in preparation for division. In addition the synthesis of proteins occurs including those that form the microtubules of the spindle. By the end of interphase the cell had doubled its size.

Question 7

What is a chromosome?

Answer 7

-A chromosome is composed of a single molecule of DNA. Somatic cells contain 2 sets of chromosomes, one from
mother and father.
-When chromosomes are copied they go from being single stranded to double stranded. Chromosomes are only visible during cell division.

Question 8

What does semiconservative mean?

Answer 8

Each daughter DNA molecule consists of one old and one newly synthesised strand.

Question 9

How does DNA replicate?

Answer 9

• A polynucleotide chain is build up during replication by adding complementary DNA units according to the sequence of bases on the template strand.
• As the old strands unzip from each other, a new strand is synthesis against each old strand. The sequence of bases of the newly synthesised strand is complementary to that of the old strand.

Question 10

When are chromosomes visible?

Answer 10

Chromosomes are only visible during cell division and are initially observed to be compose of two chromatids.

Question 11

What is mitosis?

Answer 11

Mitosis completes the division of the nucleus and involves a number of different stages, prophase, metaphase anaphase and telophase.

Question 12

What are the stages of mitosis?

Answer 12

PROPHASE:
Metaphase
Anaphase
Telophase

Question 13

What is prophase?

Answer 13

• Chromosomes become visible early in mitosis, gradually becoming thicker and shorter
• Later the chromosomes become double stranded, held together at the Centromere.
• The replicated centrioles move apart
• Microtubules of the mitotic spindle continue to extend from the centrioles.

Question 14

What is metaphase?

Answer 14

• Mitotic spindle is fully formed between the pair of centrioles at the two poles of the spindle.
• The double stranded chromosomes (each strand called a chromatid) line up around the equator of the cell. From each side they form. Line across the middle of the cell.
• The nuclear membrane has disappeared.

Question 15

What is anaphase?

Answer 15

• Each centromere divides so that the single stranded copies of each chromosome move to opposite ends of the cell as the tubules shorten.
• The migration is orderly and results in one copy of each chromosome moving toward each end of the spindle.

Question 16

What is telophase?

Answer 16

The chromosomes become thinner and less obvious. A new nuclear membrane behind to form around each group of chromosomes completing the process of mitosis.

Question 17

What is cytokinesis?

Answer 17

The final stage of cell division following mitosis when the cytosol and organelles surround each nucleus and are distributed around the new nuclei.

Question 18

What is the difference between animal and plant cells during cytokinesis?

Answer 18

ANIMAL-the bridge of cytoplasm between the two nuclei narrows as the plasma membrane pinches in to separate the nuclei and cytoplasm into the 2 new cells.

PLANT-A new cell plate forms between two groups of chromosomes and develops into a new cell wall for each of the newly produced cells.

Question 19

What are the checkpoints in the cell cycle?

Answer 19

G1-check of the DNA to ensure that it is not damaged or incomplete.

G2-replicated DNA of the cell is checked for completeness and lack of damage.

M-ensures that the sister chromatids are attached to the correct microtubules of the spindle

Question 20

What is the purpose of cell replication?

Answer 20

GROWTH enables part of an organism or whole organism to increase in size

REPAIR AND MAINTENANCE replacement of old cells as they wear out and replacement of damaged cells after injury.

REPRODUCTION in unicellular organisms

DIFFERENTIATION in growing organisms cells that divide by mitosis may become differentiated, eg growing tips of plants, mammalian embryo.