Chapter Six: Cell Divisions Flashcards
How does cell division occur in eukaryotic and prokaryotic cells, and viruses?
- eukaryotic: enters the cell cycle and divides by mitosis or meiosis
- prokaryotic: by binary fission
- viruses don’t undergo cell division since they’re not living
What are the three key stages of the cell cycle?
- interphase (G1, S, G2)
- nuclear division (mitosis or meiosis)
- cytokinesis
What is interphase? what happens in each part of interphase?
- interphase is the longest stage in the cell cycle
G1:
- protein synthesis occurs to make proteins involved in synthesising organelles
- organelles replicate
- cell is checked that it’s the correct size, has the correct nutrients , growth factors, and that there’s no damaged DNA
S phase:
- DNA is replicated
G2:
- cell continues to grow, energy stores increase, and newly replicated DNA is checked for copying errors
What does mitosis create, what is it used for, and what are the four key stages?
- creates two identical diploid cells
- used for growth, repair, and asexual reproduction in plants, animals, and fungi
the four key stages are:
1. prophase
2. metaphase
3. anaphase
4.telophase
What happens during prophase? what do plant cells have and don’t have in this stage?
- chromosomes condense and become visible. in animal cells, centrioles separate and move to opposite poles of cell
- centrioles create spindle fibres that are released from both poles, making a spindle apparatus that attach to the centromere and chromatids on the chromosome later
- plant cells have a spindle apparatus but don’t have centrioles
What happens during metaphase? what checkpoint occurs?
- chromosomes align along equator of cell
- spindle fibres released from centrioles and attaches to the centromere and chromatids
- spindle assembly occurs to ensure that every chromosome has attached to a spindle fibre before mitosis can proceed into anaphase
What happens during anaphase? what happens to the centromere? what does this stage require?
- spindle fibres start to shorten and move towards the centrioles to pull the centromere and chromatids they’re bound to towards the opposite poles
- this causes the centromere to divide into two and the individual chromatids are pulled to each opposite’s pole
- stage requires energy in the form of ATP which is provided by respiration in the mitochondria
What happens during telophase?
- chromosomes are at each pole and become longer and thinner again
- spindle fibres disintegrate, nuclear membrane reforms
What happens during cytokinesis? how are the cells split in animal cells and plant cells?
- the cytoplasm splits into two genetically identical cells
- in animal cells, a cleavage furrow forms in the middle of the cell and the cytoskeleton causes the cell membrane to draw inwards until the cell splits into two
- in plant cells, the cell membrane splits into two new cells due to the fusing of vesicles from the Golgi apparatus. the cell wall forms new sections around the membrane to complete the division into two cells
What is meiosis? what is a haploid and a diploid? how are genetic differences introduced in meiosis?
- meiosis: two nuclear divisions which result in four, genetically different haploid daughter cells
- haploid (n): one copy of each chromosome
- diploid (2n): two copies of each chromosome
- introduced by the two key processes in meiosis:
1. independent assortment of homologous chromosomes
2. crossing over
What difference happens in prophase 1?
- homologous chromosomes pair up, forming bivalents. the chromosomes being brought together causes the chromatids to tangle (crossing over)
What difference happens in metaphase 1? what happens during metaphase 1? what is independent assortment and what does it result in?
- the homologous pairs of chromosomes assemble along the metaphase plate instead of individual chromosomes
- the homologous pairs of chromosomes line up opposite each other on either side of the equator, it is random on which side of the equator the paternal and maternal chromosome of each pair aligns (independent assortment)
- independent assortment results in genetic variation
