6 Cell division Flashcards
What are the main two phases in the cell cycle of eukaryotic cells?
1) Interphase
2) Mitotic phase
What is interphase?
Growth period of the cell cycle between cell divisions. Consists of stages G1, S, G2.
What happens during interphase?
- DNA is replicated and checked for errors in the nucleus.
- Protein synthesis occurs in the cytoplasm.
- Mitochondria grow and divide, increasing in number in the cytoplasm.
- Chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number.
- The normal metabolic processes of cells occur.
What are the three stages of interphase?
1) G1- The first growth phase: cell grows in size, new organelles and proteins are made, organelles replicate.
2) S- synthesis phase: DNA is replicated in the nucleus.
3) G2- The second growth phase: the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors.
What is the mitotic phase? What stages does it involve?
1) Mitosis- the nucleus divides.
2) Cytokinesis- The cytoplasm divides and two cells are produced.
What is G0?
- G0 is the name given to the phase when the cell leaves the cycle, either temporarily or permanently.
- There are a number of reasons for this including :
1) Differentiation- A cell that becomes specialised to carry out a particular function is no longer able to divide. It will carry out this function indefinitely and not enter the cell cycle again.
2) The DNA of a cell may be damaged, in which case it is no longer viable. A damaged cell can no longer divide and enters a period of permanent cell arrest. The majority of normal cells only divide a limited number of times and eventually become senescent.
3) As you age, the numbers of these cells in your body increases. Growing number of senescent cells have been linked with many age related diseases, such as cancer and arthritis.
4) A few types of cells that enter G0 can be stimulated to go back into the cell cycle and start dividing again, for example lymphocytes in an immune response.
What are checkpoints?
Control mechanisms of the cell cycle.
Why do cells divide by mitosis?
1) Growth: In order for organisms to increase in size, they must increase the overall number of cells that they are made from.
2) Repair : Cells need to be replaced as they mostly do not survive indefinitely.
3) Asexual reproduction: In plants and some animal cells. Offspring produced by asexual reproduction are identical to their parents and each other.
What is the G1 checkpoint?
This checkpoint is at the end of the G1 phase, before entry into S phase. If the cell satisfies the requirements of this checkpoint, it is triggered to begin DNA replication. If not, it enters a resting state. (G0) G1 checks for: - Cell size - Nutrients - Growth factors - DNA damage
What is the G2 checkpoint?
This checkpoint is at the end of the G2 phase, before the start of the mitotic phase. In order for this checkpoint to be passed, the cell has to check for a number of factors such as: cell size, DNA replication, DNA damage
What does the spindle assembly checkpoint check for?
It checks for chromosome attachment to spindle.
What are chromatids?
Chromatids are two identical copies of DNA held together at a centromere.
What are the four stages of mitosis?
1) Prophase
2) Metaphase
3) Anaphase
4) Telephase
What happens during prophase?
1) The chromotin fibres begin to coil and condense to form chromosomes.
2) Protein microtubules form spindle-shaped structures linking the poles of the cell.
3) Centrioles start moving to the opposite poles of the cell.
4) The nuclear envelope breaks down.
What happens during metaphase?
1) The chromosomes line up along the middle of the cell and become attached to the spindle by their centromere.
2) They form a plane in the centre of the cell, called the metaphase plane, and then held in position.
What happens during anaphase?
1) The centromeres holding together the pairs of chromatids in each chromosome divide during anaphase.
2) The chromatids are separated and pulled to opposite poles of the cell by the shortening spindle fibres.
What happens during telephase?
1) The chromatids have reached the poles and are now called chromosomes.
2) The two new sets of chromosomes assemble at each pole and the nuclear envelope reforms around them.
3) The chromosomes start to uncoil and the nucleolus is formed.
What happens during cytokinesis 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 is close enough to fuse around the middle forming two cells.
What happens during cytokinesis in plant cells?
- Plant cells have cell walls so it is not possible for a cleavage furrow to be formed.
- Vesicles from Golgi apparatus begin to assemble in the same place as where the metaphase plate was formed.
- The vesicles fuse with each other and the cell surface membrane, dividing the cell into two.
- New sections of cell wall then form along the new sections of membrane.
What is meiosis?
- A type of cell division that happens in the reproductive organs to produce gametes.
- The nucleus divides twice producing four haploid cells.
- Cells formed by meiosis are all genetically different because each new cell ends up with a different combination of chromosomes.
What happens in Meiosis I?
1) Prophase I
2) Metaphase I
3) Anaphase I
4) Telephase I
5) Cytokinesis
What happens during Prophase I?
- The chromosomes condense, getting shorter and fatter.
- The chromosomes then arrange themselves into homologous pairs and crossing-over occurs.
- Centrioles start moving to opposite ends of the cell, forming spindle fibres.
- The nuclear envelope breaks down.
What happens during Metaphase I?
- The homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres.
What happens during Anaphase I?
- The spindles contract, separating the homologues pairs- one chromosome goes to each end of the cell.
