CELLS : Mitosis/Cancer

Question 1

What is mitosis?

Answer 1

Cell division that results in each of the daughter cells having exact copies of the DNA of the parent cell.

Question 2

What are the products of mitosis?

Answer 2

Two daughter cells that have genetically identical nuclei to the parent cell.

Question 3

What is mitosis needed for?

Answer 3

• Growth of multicellular organisms.
• Repairing damaged tissues.
• Reproduction in single-celled organisms.

Question 4

Draw the cell cycle:

Answer 4

Question 5

What does the cell cycle consist of?

Answer 5

• Cell growth and DNA replication called interphase.
• Mitosis

Question 6

What is interphase subdivided into?

Answer 6

Three seperate growth stages:

• Gap phase 1 = cell grows and new organells and protiens are made.
• Synthesis = cell replicates its DNA, ready to divide by mitosis.
• Gap phase 2 = cell keeps growing and proteins needed for cell division are made.

Question 7

What are the four stages of mitosis?

Answer 7

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 8

What type of process is mitosis?

Answer 8

A continuous one.

Question 9

What happens during interphase?

Answer 9

• Cell carries out normal functions, but is preparing to divide.
• DNA is unravelled and replicated, to double its genetic content.
• Organelles also replicated so it has spare ones, and ATP content is also increased.

Question 10

What does ATP do?

Answer 10

Provides the energy for cell division.

Question 11

What happens during prophase?

Answer 11

• Chromosomes condense and become visible, getting shorter and thinner.
• Centrioles move to opposite poles.
• Spindle fibres develop from the centrioles, forming spindle apparatus.
• Nucleolus disappears and nuclear membrane breaks down, leaving chromosomes free in the cytoplasm of the cell.

Question 12

What are centrioles?

Answer 12

Organelles within an animal cell, that spindle fibres develop from.

They are made of tiny bundles of protein.

Question 13

What are spindle fibres collectively known as?

Answer 13

Spindle apparatus.

Question 14

How do we know centrioles are clearly not essential to spindle fibre formation?

Answer 14

Plant cells lack centrioles yet still develop a spindle apparatus.

Question 15

What happens during metaphase?

Answer 15

• Chromosomes line up along the equator of the cell, pulled by microtubules from the poles.
• They are attached to the spindle apparatus by their centromere.

Question 16

What happens during anaphase?

Answer 16

• Centromeres divide into two, separating each pair of sister chromatids.
• Spindle fibres contract, pulling chromatids to opposite poles of the spindle, centromere first.
• Chromatids now appear as v-shapes.

Question 17

What provides the energy for anaphase?

Answer 17

The mitochondria, which gathers around the spindle fibres.

Question 18

What happens during telophase?

Answer 18

• Chromatids reach opposite poles on the spindle.
• They uncoil and become long and thin again - now known as chromosomes again.
• Eventually, they disappear altogether leaving only widely spread chromatin.
• Nuclear envelope reforms, so there are two nuclei.
• Cytoplasm divides through cytokinesis.

Question 19

What is chromatin?

Answer 19

A mass of material found in the nucleoplasm that contains the genes of the organism.

It separates into chromosomes during cell division.

Question 20

What are the two strands of the chromosome joined by?

Answer 20

The centromere.

Question 21

What are the separate arms of a chromosome called?

Answer 21

Chromatids.

Question 22

As mitosis begins, why does each chromosome have two strands?

Answer 22

Because they have already made an identical copy of themself during interphase.

Question 23

How long does each stage of mitosis take?

Answer 23

It varies for each stage.

Therefore, we must calculate it.

Question 24

How do you calculate the length of each stage of the cell cycle?

Answer 24

• Count how many cells are undergoing mitosis.
• Count how many cells are in the specific stage of mitosis.
• Divide number of cells in specific stage by total number of cells undergoing mitosis - this suggests the proportion of time the cells spend in the specific stage of the cell cycle.
• Convert the cell cycle duration into minutes.
• Times this number by your calculated fraction.

Question 25

What are the **three stages of the cell cycle?**

Answer 25

* Interphase * Nuclear division * Cytokinesis

Question 26

What is **cancer a result of?**

Answer 26

Damage to genes that regulate mitosis and the cell cycle. This leads to uncontrolled growth and division of cells.

Question 27

What is cancer?

Answer 27

A group of diseases caused by uncontrollable cell division.

Question 28

What is a **tumour?**

Answer 28

A group of abnormal cells resulting from uncontrollable growth and division of cells. ## Footnote *It becomes cancerous if it changes from benign to malignant.*

Question 29

Describe how **mitosis** can lead to the **formation of a tumour:**

Answer 29

* Mitosis is how most cells divide. * It is controlled by two genes. * A mutation in one of these results in uncontrolled mitosis. * Mutant cells mostly die. * However, some survive and are capable of dividing to form clones of themselves. * This forms tumours.

Question 30

What is the **difference** between **malignant** and **benign tumours?**

Answer 30

* Malignant tumours grow rapidly, whereas benign ones grow more slowly. * Malignant tumours can spread to other tissues, whereas benign tumours are more compact. * Malignant tumours are more likely to be life-threatening, whereas benign tumours are less likely to be life-threatening.

Question 31

What is the **treatment of cancer** designed to do?

Answer 31

Control the rate of cell division by disrupting the cell cycle. This kills the tumour cells, and hence cancer growth ceases.

Question 32

What are the problems with **cancer treatments?**

Answer 32

* Also disrupt the cell cycle of normal cells (although they are more effective in the cell cycles of cancer cells, as they divide more often). * Common body cells killed are those that divide rapidly, eg hair-producing cells. *This explains the hair loss frequently seen in patients undergoing chemotherapy.*

Question 33

Describe some cell cycle **targets** of cancer treatments?

Answer 33

* **G1 (cell growth and protein production) -** chemotherapy prevetns the synthesis of enzymes needed for DNA replication. So the cell is unable to enter the synthesis phase (S), disrupting cell cycle and forcing cell to be killed. * **S phase (DNA replication) -** radiation and some drugs damage DNA. This means at checkpoints before and after S phase, severe damage of DNA is detected, so the cell is killed - preveting further tumour growth.