6 - CELL DIVISION/ DIFFERENTIATION Flashcards
What are the two main phases of the cell cycle?
Interphase, where cells are prepared for division
M phases, where cells undergo cytokinesis and mitosis
What is the difference between cytokinesis and mitosis?
Mitosis is a type of nuclear division which results in the creation of 2 new identical daughter cells, whereas cytokinesis is a process of cytoplasmic division which takes place afterwards.
Describe the growth phase (G1) of interphase.
- Cells grow and organelles duplicate
- Transcription and translation take place
- Biosynthesis of proteins and enzymes required for S phase takes place
Describe the resting phase (G0) with phase G1.
- Trigger at restriction point
- Cells either undergo differentiation, apoptosis (programmed cell death) or sensescence (biological deterioration)
- Some cells may remain in this phase for a long time or indefinitely
Describe the synthesis phase (S) of interphase.
- DNA replication takes place
- Chromatids (pairs of chromosome replicates) are produced
- Genes active in all cell types (housekeeping) replicate first
- Genes used in certain/specialised cells are replicated last
- Rapid due to susceptibility to mutations
Describe the gap 2 phase (G2) of interphase.
- Cells grow
- Chemicals are released to stimulate proteins, these cause spindles to form and chromosomes to condense in the M phase
What are the two main checkpoints of the cell cycle?
The G1/S checkpoint, also called restriction point and the G2/M checkpoint
What is their purpose?
- to prevent uncontrolled division that would lead to tumours
- to detect and repair damage to DNA (i.e that caused by UV light)
- ensuring the cycle cannot be reversed
- ensuring the DNA is only duplicated once during each cell cycle
What is a spindle?
A slender mass of microtubules
Describe the prophase of mitosis.
- chromosomes shorten and thicken (condense)
- the nuclear envelope breaks down
- centrioles (from centrosomes) move to opposite ends of the cells where cytoskeleton fibres extend out from, forming spindle
Describe the metaphase of mitosis.
- spindle fibres attach to the centromeres (region in chromosome where chromatids link)
- it manouveures them so they line up at the equator of the cell
Describe the anaphase of mitosis.
- centromere of each chromosome splits
- spindle pulls on threads of chromatids to opposite poles of the cell through the use of motor proteins
Describe the telophase of mitosis.
- chromosomes are fully seperate and reach opposite poles of cell
- nuclear envelope forms around the 2 new sets of chromosomes, forming 2 nuclei containing genetically identical material
- even distribution of organelles takes place
- mitosis is now complete
Compare the formation of animal and plant cells after mitosis is complete.
In animal cells, the plasma membrane folds inwards and nips in the cytoplasm, whereas in plant cells an end plate forms (where the equator of the spindle was), where a new plasma membrane and cellulose cell-wall material are then laid.
What are homologous chromosomes?
Matching chromosomes containing the same genes at the same loci but different alleles