The Cell Cycle & Cell Reproduction

Intro Animation

• Reproduction– A single-celled organism can divide to become two

living organisms (next generation of the species)– A multicellular organism can grow from a single

cell created by fertilization (zygote)

• Growth– Division of a single cell can result in numerous

cells– DNA is passed from one cellular generation to the

next

• Repair– Damaged cells can repair themselves as they

spend time in interphase

This amoeba is undergoing cell division to create a genetically identical daughter cell.

Paramecium

These dividing bone marrow stem cells are undergoing mitosis to give

rise to new blood cells

• The cell cycle (in eukaryotes) • Includes two MAIN stages…

1. Interphase = cell growth, metabolism, replication of DNA, preparation for cell division

2. M Phase = nuclear division and splitting of the cytoplasm/cell

Interphase

• The period of time before M Phase

• Interphase is divided into 3 phases: G1, S, and G2.

• Proteins are made, organelles are constructed, DNA is replicated, and materials needed for cell division are produced.

The M Phase: Mitosis and Cytokinesis

• Mitosis- the process by which the nucleus of the cell divides into two nuclei, each with the same number and kinds of chromosomes as the parent cell.

• Cytokinesis- the process by which the cytoplasm divides and the cell splits, forming two cells.

Four Phases of Mitosis

•Prophase

•Metaphase

•Anaphase

•Telophase

Early Prophase

• Centriole pairs move toward opposite poles (animal cells)

• Spindle fibers begin to extend from centrioles. Form asters

• Duplicated chromosomes form as long threads

Late Prophase

• Nuclear membrane breaks down

• Nucleolus disappears

• Chromosomes clearly visible and begin to move to equator of cell

Metaphase

•Spindle fibers align the chromosomes along the middle of the cell nucleus. (metaphase plate)•At the end of this stage, sister chromatids (aka. chromosomes) begin to separate

Anaphase

Early Anaphase: Sister chromatids separate and move to opposite sides of the cell. Late AnaphaseSister chromatids move to poles

• Centrioles and spindle fibers disappear

• Chromosomes begin to stretch out/become uncondensed

• Cleavage furrow/cell plate begins to form

Telophase

• New membranes form around the chromatids forming daughter nuclei.

Cytokinesis: Animal vs. Plant Cells

• Cytokinesis in animal cells begins with the formation of a cleavage furrow

• This is the site at which the cytoplasm is divided between the 2

• The cleavage furrow appears during telophase

• Contractile ring pinches cell in two

Cytokinesis: Animal vs. Plant Cells

• Cytokinesis is quite different in plant cells

• During telophase, a new cell wall begins to form at the metaphase plate

• This is called a cell plate

• The plant cell continues to grow this cell wall until it divides the cell into 2

Results of Mitosis

•Mitosis is the division of a NUCLEUS

•Mitosis produces two new nuclei that have the SAME number of chromosomes as the original nucleus.

•MITOSIS IS ASEXUAL

ONE PARENT = 2 IDENTICAL DAUGHTER CELLS

Mitosis Animation