Topic 2---A: Cell structure and division- 4. Cell division- Mitosis

Question 1

When does the cell cycle start?

Answer 1

It starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical daughter cells.

Question 2

What does the cell cycle consist of?

Answer 2

G1- gap phase 1
S- synthesis
G2- gap phase 2
M- mitosis
So it consists of a period of cell growth and DNA replication called interphase and a period of cell division called mitosis.

Question 3

What is interphase?

Answer 3

• It’s cell growth
• It is subdivided into three separate growth stages (G1,S,G2)
• The cell carries out normal functions but also prepares to divide.
• The cells DNA is unravelled and replicated to double it’s genetic content .
• The organelles are also replicated so it has spare ones and it’s ATP content is increased which provides the energy needed for cell division.

Question 4

What occurs in the gap phase 1 stage? (cell cycle)

Answer 4

• The cell grows and new organelles and proteins are made.
  (protein synthesis)

Question 5

What occurs in the synthesis stage? (cell cycle)

Answer 5

The cell replicates it’s DNA ready to divide by mitosis

Question 6

What occurs in the gap phase 2 stage? (cell cycle)

Answer 6

The cell keeps growing and proteins needed for cell division are made.

Question 7

What occurs in the mitosis stage? (cell cycle)

Answer 7

The cycle starts and ends here.
Nuclear division (division of the nucleus occurs to produce 2 daughter cells)

Question 8

What happens in mitosis?

Answer 8

A parent cell divides to produce two genetically identical daughter cells

Question 9

What are the stages in mitosis?

Answer 9

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 10

What are the structure of chromosomes in mitosis?

Answer 10

• As mitosis begins, the chromosomes are made up of two strands joined in the middle by a centromere.
• The separate strands are called chromatids.
• Two strands on the same chromosome are called sister chromatids. (there are 2 strands because each chromosome has already made an identical copy of itself during interphase).
• When mitosis is over the chromatids end up as one-strand chromosomes in the new daughter cells.

Question 11

Prophase

Answer 11

• The chromosomes condense getting shorter and fatter.
• Tiny bundles of protein called centrioles start moving to opposite ends of the cell.
  -This forms a network of protein fibres across it called the spindle.
• The nuclear envelope breaks down and chromosomes lie free in the cytoplasm.

Question 12

Metaphase

Answer 12

• The chromsomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.

Question 13

Anaphase

Answer 13

• The centromeres divide separating each pair of sister chromatids.
• The spindles contract pulling chromatids to opposite poles of the spindle, centromere first.
• This makes the chromatids appear v-shaped.

Question 14

Telophase

Answer 14

• The chromatids reach the opposite poles on the spindle.
• They uncoil and become long and thin again so are now chromosomes.
• A nuclear envelope forms around each group of chromosomes so there are now two nuclei.
• Cytokinesis occurs which starts in anaphase and finishes in telophase.
• There are now two daughter cells that are genetically identical to the original cell and to each other.

Question 15

Why is mitosis important?

Answer 15

• Growth and repair of cells because some cells need replaced if their damaged
• Asexual reproduction (cloning)
• Proliferation

Question 16

Function of a centromere

Answer 16

• Holds sister chromatids together
• Attatches chromosomes to spindle fibres

Question 17

How do you find the time in a stage of mitosis ?

Answer 17

You divide the number of cells in a specific stage by the total number of cells undergoing mitosis then multiply it by the total time

Question 18

How does a tumour form?

Answer 18

• Mitosis and the cell cycle are controlled by genes so when cells have divided enough times to make enough new cells, they stop.
• But if theres a mutation in a gene that controls cell division, the cells can grow out of control so the cells keep dividing to make more and more cells forming a tumour.

Question 19

Cancer treatments

Answer 19

Some treatments for cancer are designed to control the rate of cell division in tumour cells by dirupting the cell cycle.

Question 20

Chemotherapy (cancer treatments)

Answer 20

• Prevent the synthesis of enzymes needed for DNA replication so if these aren’t produced the cell is unable to enter the synthesis phase disrupting the cell cycle and forcing the cell to kill itself.

Question 21

Benign tumour

Answer 21

• Slow growing
• Stays in one location
• Usually harmless
• Can be removed by surgery

Question 22

Malignant tumour

Answer 22

• Cells divide quickly uncontrollable
• More dangerous
• Difficult to treat as their spread out