Mitosis

Question 1

What are the 2 types of cell divisions?

Answer 1

• Mitosis - produces 2 daughter cells that have the same number of chromosomes as the parent cell and each other.
• Meiosis - produces 4 daughter cells, each with half the number of chromosomes of the parent cell.

Question 2

What is mitosis?

Answer 2

A cell division that allows each daughter cells to have an exact copy of DNA as the parent cell.
Except in mutation.

Question 3

When does mitosis occur?

Answer 3

When the cell is not dividing - this is called interphase.

Question 4

What does G1, S, G2, and M stand for?

Answer 4

G1 - Gap 1 - presynthesis
S - Synthesis
G2 - Gap 2 - postsynthesis
M - Mitotic division phase

Question 5

What is interphase?

Answer 5

G1, S, G2 together is considered as interphase.
It’s where DNA replication takes place.
G1 - Cells grow physically larger, make copies of the organelles and make molecular building blocks for later stages.
S - The cell synthesizes a complete copy of the DNA in its nucleus, it also duplicates centrosomes which are needed to separate the DNA in M stage.
G2 - Cell grows more, make proteins and organelles and begins to reorganize the contents ready for mitosis. When G2 ends, mitosis begins.

Question 6

What happens to the DNA after it’s been duplicated?

Answer 6

They remain joined at a place called the centromere.

Question 7

IPMAT?

Answer 7

Interphase
Prophase
Metaphase
Anaphase
Telophase

Question 8

Describe what happens in prophase.

Answer 8

• There are early prophase and late prophase (prometaphase).
• Early
  1) The chromosomes start to condense (so it’s easier to pull apart later on)
  2) Animal cells contain centrioles, each moves to the opposite ends (poles) of the cell. From each of the centrioles, spindle fibers develop which goes across the cell from pole to pole. (collectively, they are called spindle apparatus). Its job is to organize and move around the chromosomes.
  3) The nucleolus disappears.
  ( Because plants do not have centrioles but they do develop spindle apparatus, so it shows that centrioles are not essential for spindle fiber formation).
• Late
  1) The chromosomes finish condensing, so they are very compact.
  2) The nuclear envelope breaks down so it releases chromosomes free into the cytoplasm.
  3) These chromosomes are drawn towards the equator of the cell by the spindle fibers attached to the centromere.

Question 9

Describe what happens in metaphase.

Answer 9

• In metaphase, chromosomes are made up of 2 chromatids, each chromatid is an identical copy of DNA from the parent cell.
• The chromatids are joined by the centromere.
• Microtubules from the poles are attached to the centromere and the chromosomes are pulled along the spindle apparatus and line up at the equator of the cell.

Question 10

Describe what happens in anaphase.

Answer 10

• The centromeres divide into 2 and the spindle fibers pull the individual chromatids apart.
• The chromatids move to the opposite poles of the cell, now can be referred to as chromosomes.
• The energy required is provided by mitochondria which gather around the spindle fibers.
  ( If the cell were treated with chemicals that damages the spindle fibers, the chromosomes will remain in the middle, unable to pull apart and reach the poles.)

Question 11

Describe what happens in telophase and cytokinesis.

Answer 11

• Chromosomes reach their poles and become longer and thinner, finally disappearing altogether leaving just a widely spread chromatin.
• The spindle fibers go away and nuclear envelopes and nucleolus reform.
• The cytoplasm forms and it divides it into 2 separate cells is the stage of cytokinesis.

Question 12

What’s the process of cell division is prokaryotic cells?

Answer 12

• Binary fission.

Question 13

What happens during binary fission?

Answer 13

• Circular DNA molecule replicates and both copies attach to the cell membrane.
• Plasmids also replicate.
• The cell membrane begins to grow between the 2 DNA molecules and pinch inward, dividing the cytoplasm into 2.
• A new cell wall is formed between the 2 molecules of DNA, dividing the original cell into 2 daughter cells, each with a single copy of the circular DNA and a variable number of plasmids.

Question 14

How do viruses replicate?

Answer 14

• As viruses are non-living, they cannot undergo cell divisions.
• They can only replicate by attaching to host cells with the attachment protein on their surface.
• Then they inject the nucleic acid into the host cell.
• The genetic information of the injected viral nucleic acid would provide ‘instructions’ for the host cell’s metabolic processes to start producing viral components, nucleic acid, enzymes, and structural proteins and make new viruses.

Question 15

What is the importance of mitosis?

Answer 15

It produces daughter cells that are genetically identical to parent cells.

Question 16

Why is it essential to make exact copies of existing cells?

G, R, R

Answer 16

• Growth - Haploid cells fuse to form diploid cells, it has all the genetic materials to make a new organism. If the new organism needs to resemble the parent cell, all the cells grow from this original cell must be genetically identical and mitosis ensures this happens.
• Repair - When a cell is damaged or has died, the replacement cell must have identical genes so they can have identical structure and function.
• Reproduction - Single-celled organisms divide by mitosis to give 2 new organisms, all genetically identical to the parent organism.