2.3 - Eukaryotic Cell Division: Mitosis Flashcards
What is the cell cycle?
Is the regulated process that all body cells ina multicellular organism use to grow and divide
What are the three main stages of this process?
- Interphase
- Mitosis
- Cytokinesis
Interphase
- This is the preparation phase
- G1 (Growth Phase 1)
This is the first growth phase of the cell, synthesis of RNA, proteins, and organelles replicate. Cell increases in size. - S (Synthesis Phase)
Replication of each chromosome in the nucleus and are converted into chromatids. They are now called sister chromatids (joined at the centromere) - G2 (Second Growth Phase)
Cell continues to grow in size. Duplicated DNA is checked for errors, energy stores are increased, and enzymes are increased. End of G2 checkpoint.
What is the G0 phase?
Where the cell leaves the cell cycle either temporarily or permanently because the DNA may be damaged or the cell is no longer able to divide
The different checkpoints for the cell cycle:
G1 checkpoint:
Checks:
- cell is the correct size
- nutrients/chemicals are present
- Growth factors present
- any damage to DNA
G2 checkpoint:
checks:
- cell is the correct size
- DNA has been replicated without damage
Spindle assembly checkpoint:
Checks:
- chromosome attachment to the spindle
What is the need for checkpoints?
The checkpoints are used to control the mechanisms of the cell
What might happen if the DNA is not checked?
- mutation in the DNA sequence
- Faulty DNA produced
- Error in copying daughter cells
- Daughter cells will not receive identical genetic information
- proteins not made or do not function properly
MITOSIS: PMAT (prophase)
- chromosome condense and thicken
- consists of sister chromatids joined at the centromere
- two centrioles migrate to opposite poles of the cell
- spindle fibres attach to specific areas on the centromeres
- nuclear envelope disappears
MITOSIS: PMAT (metaphase)
- individual sister chromatids are moved by the spindle fibres to align at the metaphase plate at the centre of the cell
- sister chromatids are attached to the spindle fibres by the centromere
MITOSIS: PMAT (anaphase)
- centromeres holding the pairs of chromatids in each chromosome divide
- sister chromatids separate
- spindle contracts (fibres shorten)
- each chromatid is pulled by its centromere to opposite poles of the cell
MITOSIS: PMAT (telophase)
- chromatids have reached opposite poles of the cell
- they uncoil and decondensed so they become long and thin again
- now called chromosomes
- spindle fibres break down
- nuclear envelope reforms and encloses around the chromosomes at each pole
Cytokinesis:
- where the cell surface membrane + cytoplasm divides
- in animal cells a ‘cleavage furrow’ forms
- in plant cells a ‘cell plate’ forms
- results in 2 genetically identical daughter cells being formed
How to find the cell cycle length?
length of time in stage = (observed number of cells in stage/ total number of cells observed) x total length of cell cycle
how to calculate the mitotic index?
mitotic index = number of cells with visible chromosomes/ total number of cells
( x 100 if needed as a percentage)
Importance of the cell cycle
- Growth
- Repair
- Asexual Reprodution
- Growth
- mitosis allows organisms to grow by increasing the number of cells.
- as the organism develops from a single fertilised egg into a multicellular entity, mitosis ensures that each new cell contains the same genetic material as the original which is crucial for producing tissues and organs that function correctly.
- Repair
- mitosis is essential for replacing damaged or dead cells
- mitosis generates new cells to replace those that are lost or damaged, aiding in the healing process.
- this ensures that tissues maintain their structure and function
- Asexual Reproduction
- in single-celled organisms and certain plants, mitosis is used for asexual reproduction.
- The process produces offspring that are genetically identical to the parent as there is no fusion of gametes.
- This allows for rapid production of many identical individuals in favourable conditions
- mitosis ensures genetic consistency across cells
