Cell Division

Question 1

What occurs during Prophase?

Answer 1

Early:
- Chromosomes condense and become visible.
- Two sister chromatids joined at the centromere.
- Centrioles split and move to opposite ends of cell.
- The centrioles produces proteins called the mitotic spindle.

Late:
- Nuclear envelope breaks down.
- Free chromosomes in cytoplasm.

Question 2

What occurs during metaphase?

Answer 2

• Nuclear envelope is completely gone.
• Spindle fibres attach to the centromeres of each chromosome.
• The chromosomes line up at the equator of the cell.
• Pulled by spindle fibres so they line up.

Question 3

What occurs during anaphase?

Answer 3

• The chromosomes are pulled apart at the centromere.
  The spindle fibres begin pulling the sister chromatids away from each other to opposite poles of the cell.
• Chromosomes split into two V-shaped sister chromatids.

Question 4

What occurs during telophase?

Answer 4

• Chromatids reach opposite poles of the cell. They uncoil and become long and thin again.
• The nuclear envelope reforms around each set. Two nuclei.
• Cell prepares to spilt the cytoplasm and its contents.
• Cleavage furrows forms.
• Cytokinesis - cell divides into 2 identical daughter cells.

Question 5

How does telophase differ in plant cells?

Answer 5

• Plant cells have cell walls so it not possible for a cleavage furrow to form.
• Vesicles from the Golgi apparatus begin to assemble in the same place as where the metaphase plate was formed.
• The vesicles fuse with each other and the cell surface membrane, dividing the cell into two.
• New sections of cell wall then form along the new sections of membrane.

Question 6

What is cell division called in yeast?

Answer 6

budding

Question 7

G1 checkpoint?

Answer 7

Checks cell size
Monitors nutrients levels
Monitors growth factors
Checks for DNA damage

Question 8

G2 checkpoint?

Answer 8

Checks for correct DNA replication
Checks for DNA damage
Checks cell size.

Question 9

metaphase/spindle assembly checkpoint?

Answer 9

Checks that spindle fibres are attached to chromosomes. If it fails, can result in wrong chromosome numbers in each cell.

Question 10

How is passing of checkpoints controlled?

Answer 10

• Passing of checkpoints is a result of the enzyme kinase bonding to cyclin, forming a cyclin-dependant kinase complex (CDK).
• CDK complexes activate important cell cycle proteins by adding a phosphate group to proteins (phosphorylation) which changes the tertiary structure of checkpoint proteins, moving to the next stage of the cell cycle.

Question 11

What is meant by pluripotent stem cells?

Answer 11

• Can differentiate into any adult cells.
• Cannot form whole organisms of extra-embryonic/placental tissues