Cell Division

Question 1

What is the cell cycle?

Answer 1

Cell cycle is the sequence of events between one cell division and the next

Question 2

What are the two main phases of cell cycle?

Answer 2

1. Interphase: when the cell is engaged in metabolic activity and is preparing for mitosis
2. Cell division (M phase): cell is divided to create two genetically identical daughter cells

Question 3

What are the 3 phases that make up the interphase?

Answer 3

1. G1 phase: cell grows and prepares for DNA replication
2. S phase: synthesis stage (DNA is replicated)
3. G2 phase: cell finishes growing and organelles are duplicated

Question 4

What are the 2 phases that make up the M phase?

Answer 4

1. Mitosis: nuclear division

2. Cytokinesis: cellular division

Question 5

What is chromatin?

Answer 5

DNA is usually loosely packed within the nucleus, known as chromatin

Question 6

What is chromosome?

Answer 6

DNA is temporarily tightly packed into a condensed form, known a chromosomes. This is done through a process known as super coiling.

Question 7

What are sister chromatids?

Answer 7

After DNA replication in the S phase, each chromosome is replicated to form sister chromatids. These sister chromatids are separated into two chromosomes during mitosis

Question 8

What is mitosis?

Answer 8

The division of the nucleus into two genetically identical daughter nuclei

Question 9

What are the 4 phases of mitosis?

Answer 9

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 10

What happens during prophase? (3 points)

Answer 10

1. DNA supercoils (chromatin => sister chromatids), to prevent breaking of DNA
2. Paired centrosomes move to opposite poles and form microtuble spindle fibers
3. Nuclear membrane breaks down and the nucleus dissolves

Question 11

What happens during metaphase? (2 points)

Answer 11

1. Microtubule spindle fibers from both centrosomes connect to the centromere of each sister chromatids
2. Microtubule depolymerization causes spindle fibers to shorten in length, causing sister chromatids to align along center of the cell

Question 12

What happens during anaphase? (2 points)

Answer 12

1. Continued contraction of spindle fibre results in sister chromatids splitting and forming two separate genetically identical chromosomes
2. Genetically identical chromosomes move to the opposite poles of the cell

Question 13

What happens during telophase? (3 points)

Answer 13

1. Spindle fibres dissolve
2. Chromosomes => chromatin
3. Nuclear membranes reform around each chromosome set

Question 14

What is cytokinesis?

Answer 14

Division of the cytoplasm to form two cells

Question 15

How is cytokinesis carried out in animal cells?

Answer 15

Plasma membrane at the equator is pulled inwards until it meets in the centre of the cell, dividing it into two

Question 16

How is cytokinesis carried out in plant cells?

Answer 16

Vesicles fuse together and form an early cell plate which extends and becomes a cell wall, dividing the cell into two

Question 17

What is the mitotic index?

Answer 17

number of cells in mitosis / total number of cells

Question 18

What are cyclins?

Answer 18

Family of proteins that control the progression of the cell cycle. They activate cyclin dependent kinase (CDKs) which control cell cycle processes through phosphorylation.

Question 19

How are cyclins used to control cell cycle?

Answer 19

1. cyclin and CDK form a complex which binds to other proteins and activate it via phosphorylation
2. the phosphorylated protein will trigger some specific event in the cell cycle
3. after the event has occurred, the cycle is degraded and the CDK is rendered inactive

Question 20

What are the 4 types of cyclins?

Answer 20

Cyclin D: triggers G1 and G1 => S phase
Cyclin E: prepares cell for DNA replication
Cyclin A: activates DNA replication
Cyclin B: promotes assembly of the mitotic spindle and other tasks in the cytoplasm to prepare for mitosis

Question 21

What is a tumour?

Answer 21

Abnormal cell growth caused by uncontrolled cell division

Question 22

What is a cancer?

Answer 22

Diseases caused by the growth of tumours are collectively known as cancers

Question 23

Why do cancer cells avoid immune detection?

Answer 23

They are not foreign bodies, just abnormally functioning body cells

Question 24

What are carcinogens?

Answer 24

Cancer-causing agents

Question 25

What are mutations?

Answer 25

Random changes to the base sequence of genes

Question 26

What are oncogenes?

Answer 26

An oncogene is a gene that has the potential to cause cancer

Question 27

What are the two causes of cancer?

Answer 27

1. Mutation to proto-oncogenes
   - they code for proteins that stimulate the cell cycle and promote cell growth and proliferation
   - mutation causes it to become an oncogene, and leads to uncontrolled growth and cell division
2. Inactive tumour suppressor genes code for proteins - function is to repress cell cycle progression and promote apoptosis

Question 28

What are mutagens?

Answer 28

An agent that causes mutation

1. physical (radiation like X-rays)
2. chemical (reactive oxygen species)
3. biological (viruses)

Question 29

What is metasis?

Answer 29

The spread of cancer from one location (primary tumour) to another; patients with secondary tumours are said to have cancer

Question 30

What are the 4 reasons why cells may divide mitotically?

Answer 30

1. Tissue repair/replacement
2. Organismal growth
3. Asexual reproduction
4. Development of zygotes