2.1.6 Cell Division, Cell Diversity And Cellular Organisation Flashcards
Types of cell division
Eukaryotic cells: enter cell cycle and divide by mitosis or meiosis
Prokaryotic cells: undergo binary fission
Viruses: do not undergo cell division as they are non-living
3 Key stages of the cell cycle
Interphase (G1, S, G2)
Nuclear division (mitosis or meiosis)
Cytokinesis
Interphase
Longest stage in the cell cycle
G1:
Protein synthesis occurs - make proteins involved in synthesising organelles
Organelles replicate
Cell is checked that it’s correct size, correct nutrients + no damaged DNA.
S:
DNA is replicated
G2:
Cell continues to grow, energy stores increase
Newly replicated DNA is checked for copying errors at checkpoint
If DNA damaged, cell attempts to repair DNA
Mitosis
Creates two genetically identical diploid cells
Used for growth, tissue repair = asexual reproduction in plants, animals + fungi
Prophase
- Chromosomes condense + thicken.
- Centrioles separate + move to opposite poles of the cell.
- Centrioles create spindle fibres
Metaphase
- Chromosomes align along the metaphase plate
- Spindle fibres are released from centrioles + attach to the centromere of chromatids
- Spindle assembly checkpoint occurs.
Anaphase
- Spindle fibres start to shorten and move towards the centrioles + pull the chromatids towards the opposite poles.
- Causes the centromere to divide into two + individual sister chromatids are pulled to each opposite pole.
- Requires energy in the form of ATP - provided by respiration in mitochondria.
Telophase
- Chromosomes at each pole of the cell + become longer + thinner again.
- Spindle fibres disintegrate + nuclear membrane reforms.
Cytokinesis
- Cytoplasm splits into two genetically identical cells.
Animals: Cleavage furrow forms in middle of the cell + cytoskeleton causes the cell membrane to draw inwards until the cell splits in two
Plants: Cell membrane splits into new cells due to fusing of vesicles from Golgi.
Cell wall forms new sections around the membrane to complete the division.
Meiosis
Two nuclear divisions which result in four genetically different haploid daughter cells
How are genetic differences introduced in meiosis
Independent assortment of homologous chromosomes
Crossing over
Crossing over
During prophase 1 - homologous chromosomes pair to form bivalents.
Crossing over genetic material can occur between non-sister chromatids of bivalents.
Breaks can occur in genetic material where chromatids cross over and parts of the chromatids are exchanged between the homologous pairs.
Results in new combinations of alleles in the resulting gamete.
Independent Assortment
During metaphase 1- homologous pairs of chromosomes line up opposite each other on either side of the equator.
Random on which side the paternal and maternal chromosome aligns.
Each gamete receives different combinations of the maternal = paternal chromosomes.
Metaphase 2: sister chromatids line up on equator + same thing happens
