2.6.2 The Stages Of Mitosis

Question 1

Mitosis and The Stages

Answer 1

Mitosis is the process of nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent cell nucleus
- they have the same number of chromosomes as the parent cell
Although mitosis is, in reality, one continuous process, it can be divided into four main stages
These stages are:
- prophase
- metaphase
- anaphase
- telophase
Most organisms contain many chromosomes in the nuclei of their cells
- e.g. humans have 46 chromosomes, in 23 pairs
Half of these chromosomes are from the farther, and half from their mother
- i.e. one from each parent in each pair

Question 2

Prophase

Answer 2

Chromosomes condense and are now visible when stained
The chromosomes consist of two identical chromatids and sister chromatids (each containing one DNA molecule) that re joined together at the centromere
The two centrosomes (replicated in the G2 -G squared - phases just before the prophase) move towards opposite poles (opposite end of the nucleus)
Spindle fibres (protein microtubules) begin to emerge from the centrosomes (consist of two centrioles in animal cells)
The nuclear envelope (nuclear membrane) breaks down into small vesicles
The nucleus disappears

Question 3

Metaphase

Answer 3

Centrosomes reach opposite poles
Spindle fibres (protein microtubules) continue to extend from centrioles
Chromosomes line up at the of the equator of the spindle (also known as the metaphase plate) so they are equidistant to the two centrosomes poles
Spindle fibres (protein microtubules) reach the chromosomes and attach to the centromeres
- this attachment involves specific proteins called kinetchores
Each sister chromatid is attached to spindle fibre originating from opposite poles

Question 4

Anaphase

Answer 4

The sister chromatids separate at the centromere (the centromeres divide in two)
Spindle fibres (protein microtubules) begin to shorten
The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres (protein microtubules)

Question 5

Telophase

Answer 5

Chromosomes arrive at opposite poles and begin to decondense
Nuclear envelopes (nuclear membrane) begin to reform around each set of chromosomes
The spindle fibres break down
New nucleoli form within each nucleus