4.6-4.7: Regulation Of The Cell Cycle

Question 1

Throughout the cell cycle, there are checkpoints. What are checkpoints? (2)

Answer 1

• control points that regulate the cell cycle

- cells receive stop/go signals

Question 2

What are the major checkpoints?

Answer 2

G1, G2, M (spindle)

Question 3

What is the most important checkpoint?

Answer 3

G1

Question 4

What happens in the G1 checkpoint?

Answer 4

• checks for cell size, growth factors, and DNA damage

Question 5

What are the Stop and Go signals of the G1 checkpoint?

Answer 5

Go - cell completes the whole cell cycle

Stop - cell enters a non-dividing (quiescent) state known as G0 phase

Question 6

As stated in the G1 checkpoint, the stop signal is that the cell renters a non-dividing state known as G0 phase. What happens to these cells? (2)

Answer 6

• some cells stay in G0 forever (muscle/nerve cells)

- some cells can be called back into the cell cycle

Question 7

What does the G2 checkpoint check for?

Answer 7

• checks for completion of DNA replication and DNA damage

Question 8

What are the Stop and Go signals of the G2 Checkpoint?

Answer 8

Go - cell proceeds to mitosis
Stop - cell cycle stops and the cell will attempt to repair damage
— if damaged cannot be repaired, the cell will undergo apoptosis

Question 9

What does the M (spindle) checkpoint check for?

Answer 9

• checks for microtubule attachment to chromosomes at the kinetochores at metaphase

Question 10

What are the stop and go signals of M checkpoint?

Answer 10

Go - cell proceeds to anaphase and completes mitosis

Stop - cell will pause mitosis to allow for spindles to finish attaching to chromosomes

Question 11

What does the regulation of the cell cycle (internally) involve? (3)

Answer 11

Involves an internal control system that consisted of:

• proteins known as cyclin
• enzymes known as cyclin - dependent kinases

Question 12

What are cyclins? (3)

Answer 12

• proteins
• concentration varies (fluctuates)
• cyclins are synthesized and degraded at specific stages of the cell cycle

Question 13

What are cyclin - dependent kinases (CDK)? (3)

Answer 13

• concentration is constant through each phase of the cell cycle
• varying levels of Different Cylyns in each stage
• active ONLY when it’s specific cyclin is present

Question 14

Each cyclin-CDK complex has a specific regulatory effect. How?

Answer 14

• Active CDK Complexes phosphorylate target proteins, which help regulate key events in the cell cycle

Question 15

What are 3 external cell cycle regulators?

Answer 15

1. Growth factors
2. Contact (or density) inhibition
3. Anchorage dependence

Question 16

What are growth factors and what do they do? (3)

Answer 16

1. Hormones released by cells that stimulate cell growth
   2. Signal transduction pathway is initiated
2. CDKs are activated leading to progression through the cell cycle

Question 17

What is contact (or density) inhibition? (2)

Answer 17

• cell surface receptors recognize contact with other cells

- initiates signal transduction pathway that stops the cell cycle in G1 phase

Question 18

What is anchorage dependence?

Answer 18

• cells rely on attachment to other cells or the extracellular matrix to divide

Question 19

How can normal cells be cancerous and why? (2)

Answer 19

• Through DNA mutations

- DNA mutations change the DNA

Question 20

How many mutations on average do cancer cells accumulate?

Answer 20

• 60 or more on genes that regulate cell growth

Question 21

What does a normal cell do in a cell cycle? Ex. What do they follow, divide, die? (3)

Answer 21

• follow checkpoints
• divide on average 20-50 times in culture (in petri dishes)
• go trough apoptosis when there are significant errors

Question 22

What do cancers cells do in a cycle? (3)

Answer 22

• do not follow checkpoints
• divide infinitely when in culture (considered to be immortal)
• evade apoptosis and continue dividing with errors

Question 23

How do cancer cells evade apoptosis?

Answer 23

• they have telomeres that do not degrade and therefore never get the signal for apoptosis

Question 24

The uncontrollable growth of cancer cells can lead to a ______. What is it? (2)

Answer 24

• tumour

- a mass of tissue formed by abnormal cells

Question 25

What is a benign tumour? (2)

Answer 25

• cells are abnormal but not consider cancerous yet

- cells remain at only the tumour site and are unable to spread elsewhere in the body

Question 26

What is a malignant tumour?

Answer 26

• mass of cancerous cell that lose their anchorage dependency (can move to other tissues) and can leave the tumour site

Question 27

What is metastasis? (2)

Answer 27

• when cells separate from the tumour and spread elsewhere in the body
• via lymphatic then circulatory system

Question 28

What are three ways to minimize your risk of developing cancer?

Answer 28

1. Do not smoke
2. Eat healthy and drink water
3. Protect your skin from sun using SPF

Question 29

How does smoking cause cancer?

Answer 29

• nicotine causes mutations in cells at high rates

Question 30

How does eating healthy and drinking water prevent cancer?

Answer 30

• fatty foods and dehydration can affect the functions of cells

Question 31

How does sunscreen prevent cancer?

Answer 31

• sun is damaging to skin cells and can cause mutations to occur after exposure