1: Cell Cycles and Cancer

Question 1

What is the cell cycle?

Answer 1

the sequence of events between one cell division and the next

Question 2

State the main phases of a cell cycle.

Answer 2

interphase and cell division

Question 3

Describe (briefly) interphase.

Answer 3

very active phase in the life of a cell when many metabolic reactions occur

Question 4

Which metabolic reactions happen only in interphase?

Answer 4

• DNA replication in the nucleus

- and protein synthesis in the cytoplasm

Question 5

What happens to the number of mitochondria and chloroplasts in the cytoplasm?

Answer 5

the numbers increase as they grow and divide

Question 6

How many phases in interphase? Name them all.

Answer 6

three:

• G1 phase
• S phase
• G2 phase

Question 7

What happens in S phase? Why?

Answer 7

cell replicates all the genetic material in its nucleus, so that after mitosis both the new cells have a complete set of genes

Question 8

Which phase in interphase does a cell stay at if it will not divide again?

Answer 8

G1 - they will never divide again so do not need to prepare to mitosis

Question 9

What happens at the end of interphase?

Answer 9

the cell begins mitosis, where the nucleus divides to form two genetically identical nuclei

Question 10

What happens at the end of mitosis?

Answer 10

cytokinesis - the cytoplasm of the cell starts to divide and two cells are formed, each containing one nucleus

Question 11

What are cyclins?

Answer 11

a group of proteins used to ensure that tasks in the cell cycle are performed at the correct time and that the cell only moves on to the next stage of the cycle when it is appropriate

Question 12

Describe how cyclins act in general.

Answer 12

• cyclins bind to enzymes called cyclin-dependent kinases
• kinases then become active and attach phosphate groups to other proteins in the cell
• attachment of phosphate triggers other proteins to become active and carry out tasks specific to one of the phases of the cell cycle

Question 13

How many main types of cyclins are there in human cells?

Answer 13

4

Question 14

How do cyclins control the cell cycle? What does this ensure?

Answer 14

• cell can only only progress to the next stage in the cell cycle when the relevant cyclin reaches a ‘threshold level’
• cyclins therefore control the cell cycle.
• ensures that cells divide when new cells are needed, but not at other times

Question 15

Sketch a cyclin concentration graph over 4 phases of the cell cycle (3 phases in interphase and mitosis). (p15)

Answer 15

should have 4 cyclins: D, E, A, B

Question 16

How were cyclins discovered?

Answer 16

serendipity - happy accident:

• Tim Hunt doing research into protein synthesis in sea urchin eggs
• he noticed a protein that increased and decreased in concentration repeatedly, the increase/decrease corresponded with particular phases of the cell cycle
• he named the protein cyclin
• discovery partly due to luck but also due to being observant and realizing the significance of an unexpected observation

Question 17

What is ‘oncogenesis’?

Answer 17

formation of tumours

Question 18

Where does the process of oncogenesis start?

Answer 18

with mutations in genes involved in the control of the cell cycle called oncogenes

Question 19

What must happen for control of the cell cycle to be lost?

Answer 19

mutation must occur in SEVERAL oncogenes in the same cell

Question 20

The chance of mutation occurring in several oncogenes in the same cell is minute. How come human cells get cancer?

Answer 20

body contains billions of cells, any one of which could have mutations in its oncogenes, so the overall risk is significant

Question 21

What increases the risk of tumour formation?

Answer 21

anything that increases the chance of mutation

Question 22

What are mutagens?

Answer 22

chemical substances that can cause mutations

Question 23

Name two causes of tumour formation.

Answer 23

• mutagens - chemical substances that can cause mutations

- ionizing radiation

Question 24

What happens when control of the cell cycle is lost?

Answer 24

cell undergoes repeated uncontrolled divisions that produce a mass of cells called a primary tumour

Question 25

What is often the case with primary tumours?

Answer 25

• they are often benign

Question 26

What qualities does a tumour have if it is ‘benign’?

Answer 26

• does not grow rapidly

- does not spread

Question 27

What is the opposite of ‘benign’ when describing tumours? What qualities does this sort of tumour have?

Answer 27

• malignant
• grows rapidly
• spreads

Question 28

What can happen if a cell becomes detached from the primary tumour?

Answer 28

• cell carried elsewhere in body

- develops into a secondary tumour

Question 29

Define metastasis.

Answer 29

the spreading of cells to form tumours in a different part of the body

Question 30

When is a patient said to have cancer? What happens if cancer is not treated?

Answer 30

• when they have a secondary tumour

- if not treated, the cancer will likely lead to the patient’s death

Question 31

What is the relationship between cigarette smoking and the death rate due to cancer?

Answer 31

positive correlation - more cigarettes smoked per day = higher chance of developing cancer of the lung and some other organs

Question 32

What does the correlation between smoking cigarettes and the death rate due to cancer prove by itself?

Answer 32

that there is a correlation. It does not prove that smoking cigarettes CAUSES cancer in some organs

Question 33

“There is evidence that chemicals in tobacco smoke are … and therefore …. (cancer causing)”.

Answer 33

1. mutagenic

2. carcinogenic