1.5 Cell division & differentiation

Question 1

What is cell division?

Answer 1

Process by which cells double their content, then divide to produce two daughter cells which have half of the cell contents each

Question 2

What are the three cycles in the cell cycle?

Answer 2

1. Chromosome cycle = DNA replication and segregation
2. Cytoplasmic cycle = organelle replication and physical division (cytokinesis)
3. Centrosome cycle = replication of the mitotic spindle

Question 3

What is the G1 phase?

Answer 3

Start point of the cycle
G = Gap
Phase of normal cell activity e.g., biosynthesis
Often the longest phase

Question 4

What is the S phase?

Answer 4

S = Synthesis
Phase of synthesis, cell contents double (DNA and cytoplasm)
Time varies depending on DNA content
Chromosomes duplicate to form sister chromatids

Question 5

What is the G2 phase?

Answer 5

Second gap phase
Normal biosynthesis
Only when all DNA replicated

Question 6

What is the M phase?

Answer 6

Mitosis
Very short phase
Involves both mitosis and cytokinesis
6 distinct stages

Question 7

What is the G0 phase?

Answer 7

Where a cell exits cell cycle

Can be transient or permanent - can exit if conditions are fulfilled

Question 8

Describe the mechanics of cell division

Answer 8

2 different cytoskeletal machines

• mitotic spindle - microtubules
• contractile ring - actin and myosin

Question 9

What is the mitotic spindle?

Answer 9

Spindle formed by the centrosome (organelle)
- contains a pair of cylindrical centrioles
1 centrosome = 1 pole of the spindle

Question 10

What is the contractile ring?

Answer 10

Consists of both actin and myosin filaments

• forms under plasma membrane at the equator of the cell
• contracts to divide in 2 but not like a muscle contraction

Question 11

What is prophase?

Answer 11

Chromosomes condense

- outside the nucleus, mitotic spindle begins to assemble

Question 12

What is prometaphase?

Answer 12

Nuclear membrane breaks down
Spindle and chromosomes now meet
Attachment is via kinetochores
Spindle begins to move to poles of the cell

Question 13

What is metaphase?

Answer 13

Sister chromatids align on cell equator

Forms the metaphase plate

Question 14

What is anaphase?

Answer 14

Sister chromatids separated by separase
Chromosomes separated by: 
- spindle poles moving outwards 
- microtubules shorten 
- chromosome slides along microtubule

Question 15

What is telophase?

Answer 15

Chromosomes arrive at poles + decondense
Nuclear envelope forms
Cells spilt in 2

Question 16

What is cytokinesis?

Answer 16

Starts in anaphase, ends in telophase
Actinomyosin ring assembles under the cel membrane
Contraction of this ring spilts the cell into two

Question 17

What are the two steps in differentition?

Answer 17

1. Specification = capable of autonomous differentiation in isolation but can be reversed, not fate committed
2. Determination = when the cell differentiates into a specific cell type, even when placed amongst another cell type, irreversible and fate committed