M2 Cell Division Flashcards
What occurs 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 (some eg. cell respiration, also occur throughout cell division)
What are the three stages of interphase?
- G1 - the first growth phase: proteins from which organelles are synthesised are produced and organelles replicate. The cell increases in size.
- Synthesis phase: DNA is replicated in the nucleus.
- G2 - the second growth phase: the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for energy.
What is G0?
G0 is the phase when the cell leaves the cycle, either temporarily or permanently. Reasons include:
- Differentiation (a cell that becomes specialised is no longer able to divide so it will not enter the cell cycle again)
- DNA becomes damaged, in which case it is no longer viable (a damaged cell can no longer divide and enters a period of permanent cell arrest (G0) , the majority of cells only divide a limited number of times and eventually become senescent)
- Age (as you age the number of these cells in your body increases)
A few types of cells that enter G0 can be stimulated to go back into the cell cycle and start dividing again, eg. lymphocytes.
What do checkpoints control in the cell cycle?
- Checkpoints are the control mechanisms of the cell cycle.
- They monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase.
What does the G1 checkpoint do?
- It is at the end of G1 phase, before entry into S phase.
- If the cell satisfies the requirements it is triggered to begin DNA replication, if not it enters G0
- G1 checkpoint checks for cell size, nutrients, growth factors (appropriate growth conditions) and DNA damage.
What does the G2 checkpoint do?
- G2 checkpoint is the end of G2 phase, the start of the mitotic phase.
- The cell checks a number of factors, including if DNA has been replicated without error.
- If the checkpoint is passed, the cell initiated the molecular processes that signal the beginning of mitosis.
- The G2 checkpoint checks for cell size, DNA replication and DNA damage.
What does the spindle assembly checkpoint/metaphase checkpoint do?
- This checkpoint is at the point in mitosis where all of the chromosomes should be attached to spindle fibres and have aligned.
- Mitosis cannot proceed until this checkpoint is passed.
- It is checking for chromosome attachment to the spindle.
Compare mitosis and meiosis
- Mitosis has 2 daughter cells, meiosis has 4 daughter cells.
- Mitosis has 1 nuclear and 1 cytoplasmic division, meiosis has 2 nuclear and 2 cytoplasmic divisions.
- Mitosis creates diploid cells (chromosomes arranged in pairs) and meiosis creates haploid cells (chromosomes not arranged in pairs)
- Crossing occurs only in meiosis
- Mitosis occurs for growth, repair, replacement and asexual reproduction.
- Meiosis occurs for sexual reproduction (production of gametes)
What needs to occur before mitosis?
(interphase)
- All of the DNA in the nucleus is replicated during interphase. Each DNA molecule is converted into two identical DNA molecules (chromatids)
- The two chromatids are joined together at a region called the centromere.
Describe prophase (mitosis)
- Chromatin fibres begin to coil and condense to form chromosomes
- The nucleolus where RNA synthesis occurs disappears The nuclear membrane begins to break down
- Protein microtubules form spindle-shaped structures linking the poles of the cell. The fibres are necessary to move chromosomes before division.
