Cell Cycle & Mitosis Flashcards
What are the 3 stages of the cell cycle?
- Interphase - biosynthesis and DNA replication
- Mitosis - nuclear division
- Cytokinesis - cell cleavage
What are the 3 stages of interphase?
- G1 - first growth phase
- S - synthesis phase
- G2 - second growth phase
What happens to the cell during interphase?
- DNA is replicated and checked for errors in the nucleus
- protein synthesis occurs in the cytoplasm
- mitochondria & chloroplasts grow and divide - increasing in number
- normal metabolic processes occur
What happens during G1?
Proteins from which organelles are synthesised are produced and organelles replicate, cell grows in size.
What happens during S?
DNA is replicated in the nucleus
What happens during G2?
Cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors.
How is the cell cycle controlled?
Using checkpoints - G1, G2, M checkpoints
What is checked at the G1 checkpoint?
Cell size, nutrients, growth factors, DNA damage is checked before the cell can trigger DNA replication.
What is checked at the G2 checkpoint?
Cell size, DNA damage and DNA replication is checked before the process of mitosis is initiated.
What is checked at the M checkpoint?
Spindle assembly checkpoint - all chromosomes must have attached to spindles and be aligned before mitosis can proceed.
What is meant by G0?
G0 is the phase when the cell leaves the cycle either temporarily or permanently.
Why do cells enter G0?
- Differentiation - cells that become specialised are no longer able to divide and leave the cycle indefinitely
- DNA damage - cannot divide and enters a period of permanent cell arrest
- Senescent cells - most cells only divide a limited number of times, eventually becoming senescent. This increases with age.
What are the four stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
What happens in prophase?
- Chromatin fibres coil up and condense to form chromosomes
- Nucleolus disappears and the nuclear envelope begins to disintegrate
- Protein microtubules form the spindle fibres - centrioles migrate to opposite poles of the cell to aid in spindle formation
- Spindle fibres attach to centromeres and move the chromosomes to the centre of the cell
By late prophase, nuclear envelope has disappeared
What happens in metaphase?
Chromosomes are moved by the mitotic spindle to form a plane in the centre of the cell called the metaphase plate where they are held in place.
The chromosomes line along the metaphase plate equator.
What happens in anaphase?
The sister chromatids separate:
Centromeres holding the pair of chromatids together in each chromosome divide - chromatids are pulled to opposite poles by shortening spindle fibres.
How are chromatids characterised by their V shape?
The V shape comes as a result of them being dragged by centromeres through the liquid cytosol.
What happens in telophase?
The chromatids have reached the poles and are now called chromosomes.
- nuclear envelope reforms, chromosomes uncoil and nucleolus is formed.
How does cytokinesis work in animal cells?
A cleavage furrow forms around the middle of the cell. The cell surface membrane is pulled inwards by the cytoskeleton until it fuses around the middle.
Two genetically identical daughter cells are formed.
How does cytokinesis work in plant cells?
Cell walls prevent the formation of a cleavage furrow.
- golgi vesicles assemble where the metaphase plate was formed. They fuse with each other and the cell surface membrane, and the cell is divided into 2.
What is cancer?
The unregulated, uncontrolled division of cells which happens too frequently.
What are the issues of cancerous cells?
They have issues with communicating with healthy cells and carrying out normal cell functions.
They can secrete their own growth hormone to divert blood vessels to cancerous cells.
What are the causes of cancer?
- genetic inheritance
- excessive UV exposure
- exposure to toxins / radiation
- damage / spontaneous mutations of genes that encode proteins involved in cell cycle regulation (checkpoint proteins).
What are HeLa cells?
An immortal cell line derived from cervical cancer cells - can divide indefinitely under the right conditions due to activation of the enzyme telomerase.
