5.2 - Cell Replication Flashcards
Mitosis and meiosis
Mitosis
- Forms 2 identical cells from 1 parent cell
- Used for growth and repair of dead/damaged cells
- Used for asexual reproduction in which offspring are genetic clones of their parent
Meiosis
- ## Creates gametes that are genetically unique
Cell cycle
- Series of events that occur over the life of a eukaryotic cell
- 2 main stages: interphase and mitosis/cytokinesis (cell division)
Cells spend most of their lives in interphase.
Phases:
- G0: “resting” - the cell is performing its function
- G1 cell growth: cellular contents excluding chromosomes are duplicated
- S synthesis: each chromosome is duplicated
- G2 proofreading: duplicated chromosomes are checked for errors and necessary repairs are made
- M mitosis: nucleus divides
- Cytokinesis: cytoplasm divides, forming 2 diploid daughter cells
Interphase
- Occurs in the S phase of the cell cycle
- DNA replicates
- DNA is not yet compacted into chromosomes, rather it is spread out and called “chromatin”
Stages
- Resting: Gap 0 (G0)
- Interphase: Gap 1 (G1), Synthesis (S), Gap 2 (G2)
Chromosome/chromatid/chromatin
2 chromatids: a chromosome
1 chromatid: made of chromatin fibres
Chromatin: DNA wrapped around histone proteins
When chromatin is condensed, it becomes chromatid.
In increasing order of complexity: chromatin → chromatid → chromosome
Interphase
Gap 0
- Occurs in the Resting phase
- Cell has left the cycle and stopped dividing
- Usually occurs within or outside of G1 phase
- Allows the cell to carry out its other specialised functions
Interphase
Gap 1
- First stage of interphase
- Cells increase in size
- Has a checkpoint control mechanism that ensures everything is ready for DNA synthesis
Interphase
Synthesis
- 2nd stage of Interphase
- DNA replication occurs (in preparation for mitosis)
Interphase
Gap 2
- Final stage of Interphase
- Cell continues to grow with replicated DNA
- Another checkpoint ensures everything is ready for mitosis
- Checkpoints are controlled by tumour suppressors, transcription genes, proteins and enzymes
- If something is wrong in G2, apoptosis occurs: programmed cell death
After Synthesis phase in Interphase, the cell DOES NOT divide immediately. The time between DNA replication and actual cell division is separated by Gap 2
Mitosis
- Cells with duplicated chromosomes divide into 2 identical daugther cells
- PMAT cycle
Prophase
- 1st stage of mitosis
- Chromatin material shortens and thickens by coiling, and DNA separates out into chromosomes
- Each chromosome contains 2 copies of DNA
- Each copy is called a sister chromatid, joined by a single centromere
- Spindle fibres begin to form
- Nuclear membrane distintegrates
At this stage, DNA REPLICATION has already occured (in the synthesis phase)
Metaphase
- 2nd stage of mitosis
- Chromosomes aligh along the equator of the cell (metaphase plate)
- Each sister chromatid attaches to a spindle fibre originating from oppsosite poles
Anaphase
- 3rd stage of mitosis
- Centromere are cleaved, allowing the sister chromatids to separate
- Spindle fibres pull chromsomes by their centromeres to opposite sides of the cell
Telophase
- 4th and final stage of mitosis
- Daughter chromosomes gather at opposite poles of the cell
- Spindle fibre breaks down
- Nuclear membrane and nucleolus reappear
- Chromosomes also uncoil into chromatin again.
Cytokinesis
- Division of the cytoplasm occurs
- Begins in the late stages of telophase in mitosis
- Cytoplasm furrows and splits into 2 daughter cells, as the cell membrane starts constricting
- A contractile ring made of microfilamnets causes the cell to constrict in the centre, just beneath the plasma membrane
- Contractile ring shrinks at the equator of the cell, pinching the plasma membrane inward → forms a cleavage furrow
