The Cell Cycle and Mitosis

Question 1

What is Cell Theory?

Answer 1

• All organisms are composed of 1 or more cells
• Cells are the smallest units of life
• Cells arose by replication & division of a pre-existing cell

Question 2

Why is cell division required in multicellular organisms?

Answer 2

• During development in juveniles
• In adult somatic tissues, millions of cells need to be replaced every second due to injury and death
• Many cells are ‘dormant’ for the majority of their life-span, but must retain proliferative potential and response to appropriate cues

Question 3

What happens if cell division goes wrong?

Answer 3

Cancer may develop = a disease of uncontrolled cell division

Question 4

What is mitosis?

Answer 4

Transmission of the genome from one generation to the next

Question 5

When does mitosis occur?

Answer 5

Prequisites are completion of S-phase synthesis, sufficient growth and genome intact (no DNA Damage)

-Precision is vital and errors can be lethal

Question 6

What are the three central C’s in Mitosis?

Answer 6

Chromosomes
-cargo condensed chromatids

Centrosomes
-cytoskeletal components

Centromeres

• central constriction
• kinetochore formation

Question 7

What are the stages of Mitosis?

Answer 7

Prophase
Metaphase
Anaphase
Telophase

Question 8

What occurs in Prophase?

Answer 8

• Chromosome condenses
• They compact into short rods called chromatids
• Cohesion is lost between the arms of the chromatids which remain glued together only at the centromere
• Nuclear envelope disintegrates - chromosomes are liberated
• Centrosomes separate to opposite sides of the nucleus and nucleate microtubules

Question 9

How are microtubules nucleated?

Answer 9

Eg5 responsible! Kinesin - A microtubule motor protein

Question 10

How are microtubules inhibited?

Answer 10

Monopolar spindles

Question 11

What does chromosome movement depend on?

Answer 11

The mitotic spindle, a structure composed of microtubules

Question 12

What is chromosome congression? Process?

Answer 12

The search and capture of Chromosomes

• Capture of chromosomes starts as a stochastic process (random) - we call this ‘search and capture’
• Errors and inappropriate connections are made and need to be corrected

Question 13

What is prometaphse?

Answer 13

• Chromosomes ‘congress’ to the centre of the cell
• Microtubules nucleates by the centrosomes from a bipolar spindle
• Kinetochores are captured by microtubules

Question 14

What is Metaphase?

Answer 14

• Chromosomes form a metaphase ‘plate’ - are aligned at the cell centre, remain condensed and cohesed
• Microtubules maintain a symmetrical bipolar spindle
• Cells WAIT until a signal tells them to separate the chromosomes this place is known as the Spindle Checkpoint

Question 15

What occurs at the Spindle Assembly Checkpoint (SAC)

Answer 15

Mad2 moniters microtubule attachment

BubR1 moniters tension across the centromere

Question 16

What determines the Mitotic Exit?

Answer 16

Determined by the SAC and Cylin B expression which regulates the activity of the master mitotic regulator, cdk1

Question 17

What is the process of Anaphase (A)?

Answer 17

• Cohesion is lost from sister chromatids
• Chromosomes move to opposite spindle poles
• Centrosomes remain same distance apart
• Cdk1 is inactivated

Question 18

What is the process of Anaphase (B)?

Answer 18

• Chromosomes continue to move to opposite poles
• Centrosome-centrosome distance increases
• Midzone microtubules slide past each other
• Cleavage pane determined

Question 19

What occurs at Telophase?

Answer 19

• Chromosomes at opposite ends of the cell start to decondense
• Nuclear envelope starts to reform
• Thick bundles of interdigitating microtubules between the chromatin masses
• Cleavage furrow formed and ingressing

Question 20

What occurs during cytokinesis?

Answer 20

• Chromosomes decondense and are packaged into nuclei

- Cell constricts into two identical daughter cells

Question 21

What proteins are involved in cytokinesis?

Answer 21

Actin and Myosin (same molecules used in muscle contraction)

Question 22

What occurs if mitosis doesn’t occur properly?

Answer 22

Defects in mitosis can cause loss or gain of whole chromosomes
-A form of genomic instability referred to as CIN (Chromosomal Instability)