Cell Cycle and Cell Growth, Death, and Differentiation Summary

Eukaryotic Cell Cycle

  • A division of the nucleus (mitosis) followed by a division of the cytoplasm (cytokinesis).

  • The cell passes through a series of discrete stages or phases to accomplish this task.

  • Results in the production of two genetically identical daughter cells.

Interphase

  • The longest part of the cell cycle.

  • Cells are not always dividing; mitosis takes up about 10-15% of the cell cycle.

  • The rest of the time cells are doing other things.

  • Interphase is made up of the following sub-phases:

    • G1 phase

    • S phase

    • G2 phase

  • The genetic material in the nucleus is in the form of chromatin fibres. Discrete chromosomes are not visible.

Chromatin

  • Chromatin is a substance within a chromosome consisting of DNA and protein.

  • The major proteins in chromatin are histones, which help package the DNA in a compact form that fits in the cell nucleus.

Interphase - G1

  • Grows to almost double its original size by increasing the volume of cytosol.

  • Replicating organelles.

  • Synthesising proteins needed for DNA replication to occur in S phase.

G0 Phase

  • Cells not required to divide, rest in G0 phase.

  • Cells in G0 are either:

    • Terminally differentiated (fully specialized and no longer divide e.g. nerve cells)

    • Quiescent (dormant but can re-enter the cell cycle e.g. liver cells can regenerate)

Interphase – S Phase

  • S = synthesis

  • What is being synthesized? DNA

  • DNA is being replicated or copied.

  • This ensures the new cells being produced by mitotic cell division, each get a copy of the genetic material.

  • Single chromosome becomes a replicated chromosome.

  • DNA replication is semi-conservative.

DNA Replication

  • DNA molecules are replicated in S phase.

  • A single chromosome becomes a replicated chromosome (sister chromatids).

  • These will become daughter chromosomes after mitosis.

  • Two strands of DNA unwind.

  • Nucleotides are added following the base pairing rules (A-T, C-G).

  • Two DNA molecules are formed, exact copies of each other, each containing one new strand and one original strand.

  • This is called the Semi-conservative model.

Interphase – G2

  • Another period of growth, increasing the volume of the cytosol.

  • Increase its energy store in preparation for division.

  • Proteins needed for division are synthesised.

M Phase: Mitosis

  • 'division of the nucleus'

  • PMAT:

    • Prophase

    • Metaphase

    • Anaphase

    • Telophase

  • Mitosis and Cytokinesis are part of Cell Division.

  • G2 phase: Preparation for mitosis.

  • G1 phase: Cell growth.

  • S phase: DNA replication.

Prophase

  • Chromosomes condense and become visible.

  • Centrioles move to opposite sides (poles) of the cell.

  • Nuclear membrane begins to breakdown.

  • Spindle fibres begin to form.

Centrioles

  • These are small, cylindrical organelles that are found in animal cells and the cells of some other organisms.

  • They are responsible for controlling the movement of spindle fibres, which are made of microtubules.

  • Microtubules are used for cell structure, and transport of cellular components.

  • Plant cells can lack centrioles: they build vesicles using the Golgi apparatus to achieve a similar function.

Metaphase

  • Spindle fibres are now fully formed and attach to the centromere of each chromosome.

  • Chromosomes are aligned along the equator of the cell.

Anaphase

  • Spindle fibres contract.

  • This splits the centromere and pulls sister chromatids to opposite poles of the cell.

Telophase

  • Chromosomes pack together near poles.

  • Nuclear membranes form around the chromosomes.

  • Spindle fibres break down and disappear.

Cytokinesis

  • ‘splitting of the cytoplasm’

  • Restores the original size of the cell (maintains SA:V).

  • Divides organelles between the two daughter cells.

  • At the end of cytokinesis, the parent cell has completed its journey through the cell cycle.

  • = 2 genetically identical daughter cells.

Cytokinesis in Animal Cells

  • Plasma membrane pinches inwards on both sides.

  • Creates a cleavage furrow.

  • Cleavage furrow continues inwards until both sides meet.

  • Cell separates = 2 genetically identical daughter cells.

Cytokinesis in Plant Cells

  • Presence of a cell wall means that a cleavage furrow cannot be formed.

  • Vesicles accumulate in the middle of the cell.

  • Cell plate begins down the midline of the parent cell form in telophase.

  • At the conclusion of cytokinesis, a new cell wall has assembled.

  • Cell separates = 2 genetically identical daughter cells.

Animal vs. Plant Cell Cytokinesis Summary

  • Animal Cell

    • A contracting ring of actin filaments forms at the cell center.

    • The filaments constrict, forming a cleavage furrow.

    • The furrow meets, forming 2 daughter cells.

  • Plant Cell

    • The Golgi Vesicles accumulate at the metaphase plate.

    • The vesicles fuse to form the Cell Plate.

    • The cell plate fuses with the cell wall, forming 2 daughter cells.

Binary Fission in Prokaryotes vs. Mitosis in Eukaryotic Cells

Binary Fission

  • Binary fission is a simpler and faster process than mitosis.

  • It occurs in prokaryotic cells (bacteria and archaea) that lack a nucleus and other complex organelles.

  • The single circular DNA molecule replicates, and the two copies attach to the cell membrane. The cell elongates, and the plasma membrane pinches inward to divide the cell into two identical daughter cells.

Comparison

  • Mitosis involves several phases (prophase, metaphase, anaphase, telophase) and results in two genetically identical daughter cells.

  • Binary fission is a simpler process that does not involve these distinct phases.

  • Key Differences:

    • Complexity: Mitosis is more complex, involving the breakdown and reformation of the nuclear envelope and the precise alignment and separation of chromosomes.

    • Genetic Material: Mitosis deals with multiple linear chromosomes, whereas binary fission involves a single circular DNA molecule.

Similarities and Differences in Cell Division for Plant and Animal Cells

Similarities

  • Both plant and animal cells undergo mitosis, which ensures that the genetic material is equally divided between the two daughter cells.

  • The basic stages of mitosis (prophase, metaphase, anaphase, telophase) are similar in both plant and animal cells.

  • Both cell types also undergo cytokinesis, which is the physical separation of the cytoplasm to form two distinct cells.

Differences

  • Centrioles: Animal cells have centrioles that help organize the spindle fibres during mitosis. Plant cells do not have centrioles; instead, they use other structures to organize the spindle fibres.

  • Cytokinesis: Cytokinesis differs significantly between plant and animal cells. In animal cells, the cell membrane pinches off in the middle to form two daughter cells (cleavage furrow). In plant cells, a cell plate forms in the middle of the cell, which eventually becomes the new cell wall separating the two daughter cells.