Mitosis & life cycle

What processes take place during interphase?


G1, S and G2

What occurs during G1?
(3)

1. The first growth phase

2. Cellular components (excluding chromosomes) are duplicated

3. Cell increases in size

What occurs during S stage
(2)

1. Synthesis phase

2. DNA is replicated in the nucleus (Each of the chromosomes are duplicated by the cell)

What occurs during G2?
(5)

1. Second growth stage

2. Cell continues to increase in size

3. Proteins needed for cell division is made

4. Cell double checks duplicated chromosomes for errors

5. DNA mutations are checked for (if present apoptosis occurs)

What are checkpoints?


The control mechanisms of the cell cycle

Where is G1 checkpoint and what is checked?
(4 checks)

End of G1 phase before entry to S

• Cell size

• Nutrients

• Growth factors

• DNA damage

If checks not met , enters G0

When is G2 checkpoint and what is checked?
(3 checks)

End of G2 phase, before start of mitotic phase

• Cell size

• DNA replication

• DNA damage

What is G0 and why would cells enter it? (3 reasons)

The phase when a cell permanently or temporarily leaves the cycle

• Differentiation (a cell that becomes specialized to carry out a particular function can no longer divide)

• DNA of a cell may be damaged

• Lymphocytes in an immune response (can re-enter G1)

When is a cell viable to enter mitotic phase? (3)

• When it is right size (end of G2)

• Full set of DNA that is error free (end of S)

• Chromosomes are found along the equator during mitosis

  • Chromosomes should be attached to spindles and have aligned (spindle assembly checkpoint (metaphase))

Stages of mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

What happens during prophase?
(3)

1. Chromatin fibres condense and coil to form chromosomes that will take up stain to be visible

2. The nuclear envelopes begins to dissolve/break down

3. Centrioles start moving to opposite ends of cell, forming spindle fibres

What happens during metaphase? (3)

1. Chromosomes (each with 2 chromatids) are moved by spindle fibres and align on the metaphase plate

2. Become attached to spindle by their centromere

3. At metaphase checkpoint, cell checks all chromosomes are attached to the spindle before mitosis can continue

What happens during anaphase?
(1)

1. Centromeres divide, separating each pair of chromatids and pulling them to opposite poles of the side by the shortening/contraction of spindle fibres

What happens during telophase?


1. Chromatids reach the poles are now called chromosomes

2. Two new sets of chromosomes assemble at each pole

3. Nuclear envelope reforms around them so are now 2 nuclei

4. Chromosomes uncoil and nucleolus is formed

What happens during cytokinesis? (1)

1. The cell (cytoplasm) divides into 2 separate cells

There are now 2 genetically identical daughter cells

What takes place during the cell cycle?
(3)

1. Interphase (G1, S and G2)

2. Mitosis

3. Cytokinesis

What does the cell cycle lead to?

2 genetically identical (daughter) cells

How does cytokinesis occur in animal cells?
(2)

1. A cleavage furrow forms around the middle of the cell

2. Cytoskeleton pulls cell surface membrane inwards until it is close enough to fuse around the middle, forming 2 cells

How does cytokinesis occur in plant cells?

Forms a cell plate along centre of cell to make cell wall before it lyses

1. Vesicles from Golgi apparatus begin to assemble in the same place where the metaphase plate was formed

2. Vesicles fuse with each other and the cell surface membrane, dividing the cell into 2

3. New sections of the cell wall form along new sections of membrane

What is the significance of mitosis? (2)

1. Asexual reproduction in plants, animals and fungi

2. To make genetically identical daughter cells for growth, replacement and repair of tissues

What is mitosis?


Nuclear division that produces 2 genetically identical diploid daughter cells