Mitosis and the cell cycle

Question 1

What is a general definition of mitosis?

Answer 1

Normal cell division for growth, repair and asexual reproduction which occurs in somatic cells (normal body cells)

Question 2

What does cell division by mitosis produce?

Answer 2

Two genetically identical daughter cells (clones)

Question 3

What does it mean when a cell is diploid (2n)?

Answer 3

When cells have both chromosomes from each homologous pair. In human cells a diploid cell has 46 chromosomes

Question 4

Why is mitosis important in repairing/ replacing cells?

Answer 4

• If cells are damaged through injury the healing process involves mitosis to produce cells which are genetically the same
• When celos need to be replaced constantly throughout life it is mitosis which produces the replacement cells e.g top layer of skin

Question 5

Why is mitosis important in growth?

Answer 5

-when sperm cell fertilises an ovum the nuclei fuse together to make a zygote. The zygote divided by mitosis so that all the cells in the new organism have exactly the same information- all the cells will contain exactly same alleles to give the same phenotype

Question 6

Why is mitosis important in asexual reproduction?

Answer 6

-asexual reproduction means that one parent plant produces genetically identical clones. This is helpful as one organism can produce many offspring very quickly if weather conditions aren’t changing

Question 7

What needs to happen to a cell before it can do mitosis? Explain the conditions needed for this step to happen.

Answer 7

• The DNA has to be replicated so that each daughter cell can have a copy of every gene
• During DNA replication the DNA needs to be diffuse (uncoiled so its can unzip)
• Chromosomes therefore will not be visible as distinct structures within the nucleus during DNA replication
• DNA will only be visible as chromatin

Question 8

What happens to the chromosomes just before cell division? Explain this process

Answer 8

• They condense (x shaped)= becomes coiled and supercoiled into distinct molecules which can be seen down a microscope and wrap DNA around histones
• by condensing the chromosomes become more compact so a large amount of DNA can be fitted into a small space and so that when the 2 daughter cells separate the DNA is organised and doesn’t get tangled up with other chromosomes

Question 9

What is the cell cycle? State when it starts and ends and the different periods it consists of

Answer 9

• The events which take place as one parent cell divides to produce two new daughter cells which then grow to full size.
• Starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells
• has a period of cell growth called interphase and a period called M, when cell division occurs by mitosis (division of nucleus) and cytokinesis (division of cytoplasm)

Question 10

What is the first section of interphase? Describe what happens at this stage of the cell cycle

Answer 10

Gap phase 1:

Cell grows and new organelles and protein is made

Question 11

What is the second section of interphase? Describe what happens at this stage of the cell cycle

Answer 11

Synthesis:
Cell duplicates it’s DNA through DNA replication ready for cell division. This has created the X shaped chromosome made of two chromatids

Question 12

What is the third section of interphase? Describe what happens at this stage of the cell cycle

Answer 12

Gap phase 2:

• Cells keep growing and proteins needed for cell division are made
• Protein synthesis of microtubules for spindle also occur

Question 13

What is meant by G 0 phase?

Answer 13

When some cells don’t undergo further cell division (cell cycle arrest) e.g red blood cells and nerve cells

Question 14

What are the 4 stages of mitosis?

Answer 14

IPMAT: =
Prophase 
Metaphase 
Anaphase 
Telophase

Question 15

What happens during stage 1 of mitosis, prophase?

Answer 15

• the chromosomes condense getting shorter and fatter
• centrioles start moving to opposite ends of the cell forming the spindle
• the nuclear envelope breaks down

Question 16

What happens during stage 2 of mitosis, metaphase?

Answer 16

-chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere

Question 17

What happens during stage 3 of mitosis, anaphase?

Answer 17

• the centromeres divide

- the spindle pulls the chromatids apart towards opposite poles of the cell

Question 18

What happens during stage 4 of mitosis, telophase?

Answer 18

• chromatids reach opposite poles on spindle
• they uncoil and become long and thin (diffuse) again
• the nuclear envelope reforms and the chromatids are now known as chromosomes again. There are now 2 nuclei

Question 19

What happens in cytokinesis,the stage that occurs shortly after mitosis?

Answer 19

• the cytoplasm divides and two genetically identical daughter cells are formed
• cell division by mitosis is complete and each daughter cell starts the interphase part of the cell cycle

Question 20

What factors are essential to a cell to make sure that the two daughter cells are identical?

Answer 20

1) Cell has grown to right size
2) Cell divides at the right time
3) Chromosomes are in their correct position during mitosis
4) Replicated DNA is error-free
5) Cell doesn’t divide too often as excessive cell growth can lead to a tumour

Question 21

What are checkpoints in the cell cycle and when do they occur?

Answer 21

• points of the cell cycle where the completion of processes is checked
• they are controlled by proteins acting as growth-factors (cyclin and cyclin-dependent kinases)
• there are 3 checkpoint which occur at various stages of the cell cycle

Question 22

What point of the cycle does the G1 checkpoint occur and what does it check for at this stage?

Answer 22

-Occurs at the end of G1 phase, before entry into S phase

• cell size
• nutrients
• growth factors
• DNA damage

-if successfully passed then DNA can be replicated in S phase, if not cell enters G 0

Question 23

What point of the cell cycle does the G2 checkpoint occur and what does it check for?

Answer 23

-Occurs at end of G2 phase, before mitotic phase

• cell size
• DNA damage
• DNA replication

-once checkpoint has been passed mitosis begins

Question 24

What point of the cell cycle does the spindle assembly checkpoint occur and what does it check for?

Answer 24

• Occurs at metaphase of mitosis
• if the chromosomes have attached to the spindle and are aligned at the equator
• if checked cell will move on to anaphase