6.2 Mitosis

Question 1

Why is mitosis important?

Answer 1

• needed for growth of multicellular organisms and for repairing damaged tissues
• necessary for asexual reproduction
• produces 2 daughter cells that are clones (genetically identical) to the parent cell

Question 2

What is the structure of chromosomes in mitosis?

Answer 2

Before mitosis can occur, all of the DNA in the nucleus is replicated during interphase.
As mitosis begins, the chromosomes are made up of two chromatids that are joined in the middle by a centromere.
Two chromatids on the same chromosome are called sister chromatids.

When mitosis is over, the chromosomes only consist of one chromatid in the new daughter cells

Question 3

What are the four stages of mitosis?

Answer 3

Prophase, metaphase, anaphase, telophase

Mitosis is a continual process but is described in these stages

Question 4

Describe what happens and what you can see at prophase

Answer 4

1) during prophase, chromatin fibres (made up of his tone proteins and DNA) begin to coil and condense to form chromosomes. The nucleolus disappears and the nuclear membrane/ envelope begins to breakdown
2) centrioles move to opposite ends of the cell, forming a network of protein fibres across it called the spindle

Question 5

Describe what happens at metaphase

Answer 5

• the chromosomes (each with two chromatids) line up along the spindle equator/ metaphase plate and become attached to the spindle by their centromere
• at the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can ontinue

Question 6

Describe what happens at anaphase

Answer 6

• the centromeres divide, separating each pair of sister chromatids
• the spindles contract, pulling chromatids to opposite ends of the cell, centromere first

Question 7

Describe what happens at telophase

Answer 7

• the chromatids reach the opposite poles on the spindle
• they uncoil and become long, thin chromosomes again
• a nuclear envelope forms around each group chromosomes, so there are now two nuclei
• nucleolus is formed
• cytokinesis begins

Question 8

What is cytokinesis?

Answer 8

The actual division of the cell into two separate cells. Cytokinesis begins during telophase

Question 9

Describe cytokinesis in animals cells

Answer 9

• in animals cells a cleavage furrow forms around the middle of the cell
• the cell-surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle to form two cells

Question 10

Describe cytokinesis in plant cells

Answer 10

• plant cells have cell wall and therefore its not possible for a cleaver furrow to form
• vesicles from the Golgi apparatus, assemble where the metaphase plate was formed and then fuse with each other and the cell surface membrane, divine the cell into two
• new section of cell wall then from along the new sections of membrane