cell cycle

Cell Mitosis is the process of cell division where a parent cell divides into two daughter cells, each with the same number of chromosomes as the parent cell. It consists of stages like prophase, metaphase, anaphase, and telophase.

Meiosis is a type of cell division that produces gametes with half the number of chromosomes as the parent cell. It involves two rounds of division, resulting in four daughter cells with genetic variation.

3 phases:

  • interphase

  • mitosis

  • cytokinesis

INTERPHASE

dna replication, growth and cell preparation for mitosis

  • 90% of the time of a cell cycle is spent in interphase

  • preps for cell reproduction

  • not a resting phase, but this stage is not visible under light microscope as the chromosomes are not condensed

G1 (gap 1) phase

  • cells grows

  • synthesises proteins needed for gene regulation

  • organelles duplicate - mitochondria, chloroplasts

  • non dividing cells enter G0 stage - brain cells and neurons

S (synthesis) phase

  • all dna in chromosomes are replicated

  • the parent cell contains 2 identical copies of dna

G2 (gap 2) phase

  • synthesis of proteins needed for spindle

  • cells grow and prepare for mitosis

MITOSIS

organisation and chromosome separation

  • after fertilisation, mitosis duplicated zygote

  • creates 2 genetically identical daughter cells

  • used to grow body parts, develop tissues and replace dead cells

Mitosis phases

nucleus divides to produce 2 nuclei with 46 unduplicated chromosomes each

prophase

  • chromosomes condense and form chromatids

  • spindle apparatus forms

  • nucleolus and nuclear membrane disappear

metaphase

  • chromosomes line up at cell equator

  • spindle fibers attached to centromere

anaphase

  • sister chromatids separated and moved to opposite poles

telophase

  • chromosomes uncoil

  • spindle apparatus disappear

  • nuclear envelopes form around each chromosome cluster

cytokenesis

  • animals: indentation of cell surface in late anaphase, the cleavage furrow

  • plants: formation of cell plate

BINARY FISSION

  • cell cycle in prokaryotes

  • very fast process

  • the dna molecule is replicated

  • cell increases size

  • two dna molecules are pulled to separate poles and a membrane forms between the separating cells

  • 2 daughter cells are formed by a single parent cells.

CELL CYCLE CHECK POINTS

  • cell cycle undergo apoptosis due to dna damage, spindle break or chromosome failure.

  • cell cycle has 3 checkpoints - G1, G2 and mitosis

    • G1 checkpoint - checks for DNA damage, stop cycle if damage not repaired, apoptosis if damage is irreparable.

    • G2 checkpoint - checks dna damage and cell size

    • mitosis (metaphase/anaphase) checkpoint - checks the spindle fibres and chromosome misalignment

the mitotic spindle

  • spindle fibers grow from centrioles to middle of cell

  • anchor double stranded chromosomes at kinetochore in metaphase