2.1.6: Cell Division, cell diversity and cellular organisation Flashcards
What are the 3 key processes within the cell cycle ?
- Interphase
- Mitosis or meiosis
- Cytokinesis
What is included within interphase ?
G1,S,G2
Which is the longest stage in the cell cycle ?
Interphase
What are the key processes that occur within interphase ?
- Protein synthesis
- DNA replication
- Mitochondria grow and divide
How is the cell cycle regulated and controlled ?
Checkpoints
What happens within G1 stage of interphase ?
- Organelles except the chromosomes duplicate
- Protein synthesis for proteins involved in synthesising organelles occurs
What is checked at the G1 checkpoint ?
- Size
- Nutrients
- Growth factors
- DNA damage
What happens within the S stage of interphase ?
DNA is replicated in the nucleus and each of the chromosomes is duplicated
What happens in the G2 phase of interphase ?
- Cell continues to grow
- Energy stores increase
- DNA checked for copying errors
What is checked at the G2 checkpoint ?
- Cell size
- DNA copying errors / damage
What happens in the G0 stage of interphase ?
Cell can :
- Leave cycle
- Specialise
- Go into rest period
What does mitosis lead to ?
Genetically identical diploid cells
What does meiosis lead to ?
Genetically identical haploid cells
What is the checkpoint before cytokenesis ?
Chromosomes attached to spindle fibres
What is cytokenesis ?
Cytoplasmic division of cell at the end of mitosis or meiosis which brings about the separation into 2 daughter cells
How does cytokenesis occur in animals ?
Cytoskeleton causes cell membrane to draw inwards
How does cytokenesis occur in plants ?
Cell membrane splits due to fusing of vesicles from golgi
What are the 4 stages of mitosis ?
Prophase
Metaphase
Anaphase
Telophase
What happens in early prophase ?
- Chromosomes condense and become visible
- Nucleolus disappears and nucleolus breaks down
- Centrioles move to opposite poles of the cell in animal cells
- Centrioles make protein microtubules which form spindle fibres
What happens in late prophase ?
Spindle fibres attach to centromeres on sister chromatids of chromosomes
What happens in metaphase ?
- Chromosomes are moved by spindle fibres to align along the metaphase plate (equator)
- Spindle fibres are released from centrioles and attach to centromere
- Spindle assembly checkpoint
What happens in anaphase ?
- Centromeres divide and chromatids are pulled to opposite poles of cell by spindle fibres ( form a ‘V’ shape whilst being dragged through liquid cytosol)
What is required for anaphase ?
ATP from respiration in mitochondria
What happens in telophase ?
- Chromatids have reached poles
- 2 sets of chromatids assemble to form chromosomes
- Spindle fibres disintegrate
- Nuclear envelope reforms
What is different for mitosis in plants vs animals ?
- In the meristem (tips of roots and shoots) not in stem cells
- No centrioles, instead tubulin protein threads are made in cytoplasm
Give 3 significances of mitosis in life cycles
- Growth
- Tissue repair
- Asexual reproduction in plants, animals and fungi
How do you calculate the mitotic index ?
number of cells in mitosis
————————————– x100
total number of cells
What happens in prophase 1 of meiosis ?
- Homologous chromosomes pair to form bivalents
- Same as mitosis
What happens in metaphase 1 of meiosis ?
- Homologous chromosomes are moved by spindle fibres to form a metaphase plate at the equator of the cell
What happens in anaphase 1 of meiosis ?
- Homologous chromosomes are pulled apart to each pole by spindle fibres
What happens in telophase ?
- Homologous chromosomes have reached poles
- Spindle fibres disintegrate
- Nuclear envelope reforms
What is different about the second half of meiosis compared to mitosis ?
- In anaphase 2 the spindle fibres attach to centromere on sister chromatids not homologous chromosomes
- 2 nuclear divisions result in 4 genetically different haploid cells
Summarise the 3 ways that meiosis can introduce genetic variation
- Crossing over in prophase 1
- Independent assortment of homologous chromosomes or sister chromatids
- Random mutations
How do you work out the number of variations of a chromosomes in an organism ?
number of chromosomes
2