Mitosis and the Cell Cycle

Which type of cells undergo the cell cycle?

Most eukaryotic cells

Name 2 types of eukaryotic cell that do not undergo the cell cycle.

Neurones and white blood cells

What are the 3 phases of the cell cycle?

• Interphase

• Mitosis

• Cytokinesis

What is phase 1 of the cell cycle?

Interphase

What can be said about the time taken for interphase to take place, compared to the other phases of the cell cycle?

Interphase takes the longest amount of time (by far)

Why are chromosomes not visible during interphase of the cell cycle?

The chromatin is uncondensed

Which 3 things happen during interphase of the cell cycle?

• Cell grows

• DNA replicates

• Cell makes copies of every organelle

What are the 4 stages of mitosis?

Prophase, metaphase, anaphase, telophase

What happens during mitosis (in broad terms)?

The nucleus divides in 2

What is a centrosome?

An organelle made up of two centrioles

Which organisms have centrosomes in their cells?

Only animals

What do centrioles do?

Produce spindle fibres

What happens during prophase?

• Chromatin condenses to form chromosomes

• Nuclear envelope breaks down

• Centrioles move to opposite poles of the cell

• Centrioles start producing spindle fibres

What happens during metaphase?

• Spindle fibres attach to centromeres of chromosomes

• Chromosomes line up at the equator of the cell

What happens during anaphase?

• Centromere splits

• Spindle fibres contract to pull the chromatids to opposite poles of the cell

What happens during telophase?

• Nuclear envelope reforms

• Chromatids decondense back to chromatin

• Spindle fibres break down

What happens during cytokinesis (in broad terms)?

The entire cell splits into 2 new cells

How does cytokinesis take place in animal cells?

The cell membrane pinches in until the cell is divided into two

How does cytokinesis take place in plant cells?

• A layer of cellulose forms in the middle of the cell

• When this cellulose layer is thick enough, it forms 2 new cell walls and the cell splits

What can be said about the daughter cells formed during mitosis?

They are genetically identical to one another and to the original parent cell

What are four purposes of mitosis?

• Proliferation of white blood cells

• Asexual reproduction

• Growth

• To repair damaged tissue

How do you calculate mitotic index?

number of cells in field of view undergoing mitosis / total number of cells in field of view

What does the mitotic index tell us?

The proportion of cells in a population that are currently undergoing mitosis

What can uncontrolled tissue growth lead to the formation of?

Tumours

What is uncontrolled mitosis caused by?

Mutations in the genes controlling the rate of mitosis

What do most cancer treatments aim to do?

Prevent mitosis

What are two things a cancer treatment can do in order to prevent mitosis?

• Prevent DNA replication

• Prevent centrioles from producing spindle fibres

What is a negative aspect of cancer treatments?

They also affect healthy body cells

Why are cancer treatments still considered effective, despite affecting healthy body cells?

Cancer cells divide much faster than healthy body cells, so the negatives outweigh the positives, as cancer cells are mainly affected