Eukaryotic cell division (Mitosis)

Question 1

Why do multicellular organisms need mitosis?

Answer 1

For development from a fertilised cell

For growth to an adult

For repair and replacement.

Question 2

Does every cell have the same DNA?

Answer 2

Yes, except for the mutations.

Question 3

What happens in G1 stage, before mitosis?

Answer 3

The cell grows. All organelles and cytoplasmic components, including centrioles in animal cells replicate.

Question 4

What happens in S phase, before mitosis?

Answer 4

Synthesis of DNA (replicates the DNA for preparation)

Question 5

What happens in G2 phase, before mitosis?

Answer 5

Second growth phase. All enzymes needed to aid in cell division are produced.

Question 6

What happens in interphase?

Answer 6

Chromosomes are duplicated (but condensed)

Centrosomes which are involved in the development of spindle fibres (consisting of a pair of centrioles)

Question 7

What happens in prophase?

Answer 7

• Chromosomes start to become visible (they developed into two sister chromatids connected by centromeres)
• Centrosomes start to seperate and the spindle is developed (microtubules form this). Cytoskeleton also disassembles as they form.
• 46 chromosomes and 92 chromotids
• Nuclear envolope starts to disintergrate

Question 8

What happens in pro-metaphase?

Answer 8

• Nuclear envelope finishes disintegrating.
• Centrosomes have moved to opposite poles of the cell which are connected by microtubules (Non-kinetochore and kinetochore)
• Sister chromatids connected by the centromere which connects to the kinetochore, which connects to the kinetochore microtubules.

Question 9

What happens in metaphase?

Answer 9

• Chromatids line up at central metaphase plate.

- Organised through kinetochore microtubules. Whole structure is called a spindle.

Question 10

What happens in Anaphase?

Answer 10

• Sister chromatids are ripped apart (degradation of proteins that hold them, freeing the individual chromosomes.
• Kinetochore microtubules get shorter at the centromere. Non-kinetochore get longer and push the two sides of the cell apart.
• One lot of genetic info up and one down for both cells to have a complete set.

Question 11

What happens in telophase?

Answer 11

• The cleavage furrow forming (made of actin filaments)
• Nuclear envelope develops to surround the genetic info (chromosomes start decondensing)
• Nucleolus forms
• Spindle disassembles (broken down into tublin monomers which can be used for the cytoskeleton later.

Question 12

What happens in cytokinesis?

Answer 12

This is how the cytoplasm divides.
In animal cells the actin filaments that make up the cleavage furrow split it.
In plant cells this is when the cell wall is produced. Vesicles form the cell plate as actin can’t divide the cells.

Question 13

Why are there cell cycle checkpoints?

Answer 13

To assure that the process is happening correctly. If it isn’t the cell cycle will stop and correct it or will stop the cell from dividing.

Question 14

What are the checkpoints in the cell cycle?

Answer 14

G1/S
G2/M
Spindle (assuring that all chromosomes have attached to the spindles in preparation for anaphase)

Question 15

What does cell cycle regulation depend on?

Answer 15

Growth factors
Size of the cell
Nutritional state of the cell

Question 16

How long does the cell cycle take?

Answer 16

Takes 10-20 hours on average.

Question 17

Give examples of what cells go through the cell cycle a lot and what ones don’t.

Answer 17

Skin cells - a lot

Neurons and mature muscle cells - very rarely.