A concise and clear overview of the key concepts covered in chapter 6. These notes make biology easy to understand and are a good place to start your revision and boost your grades.
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CELL DIVISION
CHAPTER 6
The Cell Cycle
Sequence of events which leads to the division
of cells and the formation of genetically identical
daughter cells
•In eukaryotic cells, the cycle has two main
phases: INTERPHASE and MITOTIC phase
Interphase
• Long periods of normal working and growth
• Where a cell spends most its life
• Not actively dividing
• DNA replication + checked for errors in nucleus
• Protein synthesis in cytoplasm
• Mitochondria grow and divide, increasing in number
• Chloroplasts grow and divide
• Normal metabolic processes of cells occur
• The 3 stages of interphase are G1, S and G2
• G1: the first growth phase, organelles (except
chromosomes) replicate. The cell increases in size.
• S: synthesis phase, DNA is replicated in the nucleus
• G2: second growth phase, grows in size, energy
stores increase and DNA is checked for errors
Mitotic Phase G0
• Cell division involves 2 phases: mitosis and •When the cell leaves the cycle, either temporarily or permanently for…
cytokinesis •Differentiation: cells that become specialise can no longer divide, It will not
• Mitosis: nucleus divides enter the cell cycle again
•The DNA may be damaged: can no longer divide and enters permanent cell
• Cytokinesis: cytoplasm divides and two cells are
arrest, cells only divide a number of times and eventually become senescent
made
•As you age, growing numbers of senescent cells can cause cancers and arthritis
•A few cells which enter G0 can be triggered to re enter the cell cycle for
example white blood cells for the immune system
Control of the cell
•Ensures that daughter cells have correct DNA and
are correct size
•Checkpoints control the cycle Mitosis
•They occur at: •Growth, replacement of cells, repair of cells, asexual reproduction
• End of G1 - checks size, nutrients, growth factors •Before mitosis happens, all the DNA must be copied. Each DNA molecule
(chromosome) is converted into 2 identical DNA molecules, called chromatids,
and DNA damage
attached by the centromere. It is necessary for them to be kept together so they
• End of G2 - checks size, DNA replication and DNA
can be transported and segregated equally into 2 daughter cells.
damage
• Metaphase/ spindle assembly checkpoint - checks
chromosomes have attached to spindles
Stages of Mitosis
• 4 stages: Prophase, Metaphase, Anaphase
and Telophase
•These stages can be easily seen in in the growing
root tips of plants, when they are stained
, Prophase
•Nuclear envelope breaks down
•Protein microtubules form spindle shaped
structures linking the poles of the cell.
•Centrioles appear at poles of cell
•Centrioles produce spindle fibres that attach to
the sister chromatids at the centromere
Metaphase
•Sister chromatids line up along the equator,
forming the metaphase plate (single file)
•Moved by spindle fibres
Anaphase
•Spindles contract, pulling the sister chromatids
apart from the centromere to the poles
Telophase
•Plasma membrane pinches to form a cell
cleavage which splits into 2 cells =
CYTOKINESIS
•Nuclear membrane reforms, chromosomes
relax/uncoil and centrioles disappear
The exception
•Only meristem cells of plants can carry out
mitosis and cytokinesis
•Plant cells lack centrioles and can’t create a
cell cleavage due to the cell wall, instead the
wall reforms in the middle
•Yeast remain attached after mitosis. This is
known and budding
Meiosis KEY WORDS
•One chromosome from each homologous pair is put into each •Allele: different versions of the same gene
daughter cell •Zygote: a diploid cell resulting form the fusion of two
•It produces cells with just one copy of each chromosome (haploid haploid gametes
cells) •Gamete: an organisms reproductive cells
•Fertilisation: combining of two 2 gametes and the
genetic material
•Haploid: half the chromosomes of the number of the
•Genes at
parent cell
same
•Diploid: 2 copies of every chromosome
location on
•Homologous pairs: one from mother, one from father
each
chromosome
Meiosis
• IPMATPMAT
• Mitosis + extra, then mitosis
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