Cell Cycle & Mitosis The phases in the life of a cell are called THE CELL CYCLE. The CELL CYCLE is an orderly sequence of events that extends from the time a cell first arises until it divides. The cell cycle consists of two parts: INTERPHASE & CELL DIVISION

Roles of Cell Reproduction Replacement of worn out or dead cells Growth (some stuff never stops – e.g. your nails & hair) Maintain proper surface area to volume ratio so that cell transport can occur efficiently. Cell Reproduction is also known as CELL DIVISION.

Mitosis vs. Meiosis Mitosis – for growth and development (focus right now) Meiosis – only produces gametes (What is this?)

Some Terms Daughter Cell – offspring of a parent cell Chromosome – structure made of coiled or condensed DNA Asexual Reproduction – one parent (no egg or sperm)

Chromatin & Proteins Chromosomes are made up of a material called CHROMATIN, which is a combination of DNA & protein molecules. Protein molecules organize chromatin and control activity of its genes.

More Terms...These can be Confusing! Single Strand of CHROMATIN (DNAs normal structure in the nucleus) – Image #3 Two SISTER CHROMATIDS joined at a CENTROMERE (After replication)-Image #4 Replicated or double stranded CHROMOSOME after it condenses. Each half is still considered a SISTER CHROMATID during cell cycle. -Image #5

Another view…

General Information Humans have 46 total chromosomes, or 23 pairs. Eukaryotic (What is this?) organisms contain small proteins called HISTONES which assist in folding and packaging the long DNA molecules. DNA is copied through the process of REPLICATION.

The Cell Cycle Two Major Phases: Cell Growth=INTERPHASE Cell Division MITOSIS & CYTOKINESIS

Interphase Period of Cell Growth – NOT PART OF MITOSIS!!! Three Phases to Interphase G1 – Number of organelles and cytoplasm in the cell increases so the cell must grow to accompany this S – DNA replication takes place G2 – cell makes the final preparations to begin division

DNA Replication What happens? DNA molecule makes a copy of itself Where does it happen? In the nucleus Why does it happen? So when the cell divides each new cell will have a copy of all the DNA in the original cell

Interphase

Other Interphase Fun It is the longest phase of the cell cycle and the cell is carrying out all of its normal activities including converting food into a form of energy the cell can use. The cell IS NOT dividing during interphase. Chromosomes HAVE NOT condensed yet (still in chromatin form) and ARE NOT visible under a light microscope.

Mitosis Actual process of NUCLEAR DIVISION, which means the nucleus and chromosomes divide Four Phases: Prophase, Metaphase, Anaphase, Telophase Cytokinesis is the period of cellular division when organelles and cytoplasm divide into two new daughter cells.

Prophase Sister chromatids condense to become thicker and visible under a light microscope. Nucleolus & nuclear membrane disappears. Microtubules that make up spindle fibers begin to assemble.

Prophase

Metaphase Chromosomes are moved to the middle of the cell by the spindle fibers attached to the centromeres.

Anaphase Sister chromatids of each chromosome are pulled by the spindle fibers toward the opposite ends of each cell. Sister chromatids are SEPARATED from each other.

Anaphase

Telophase New nuclear membranes begin to form around the chromosomes at either end of the cell. Nucleoli reforms Process of mitosis is complete. Cell membrane begins to pinch the cell in two as cytokinesis begins.

Cytokinesis CYTOPLASM of the cell divides into two new cells called DAUGHTER CELLS. In animal cells a CLEAVAGE FURROW forms. In plant cells a CELL PLATE forms. Mitosis and Cytokinesis result in TWO new cells that are genetically IDENTICAL.

Cytokinesis

Words of Cellular Reproduction Gene Chromosome Centromere Sister Chromatids Chromatin Mitosis Prophase Interphase Metaphase Telophase Anaphase cytokinesis