Cell Cycle and Cell Division We all began as a single cell (fertilized egg). This cell gave rise to all cells in our bodies. Each cell goes through a cycle called the CELL CYCLE, consisting of 2 processes: interphase and mitosis (cell division)

Interphase makes up most of a cell’s life when it is not dividing by mitosis. Interphase is divided into 3 phases: G 1 = rapid growth S = growth and DNA synthesis (DNA replication) G 2 = growth and preparation for cell division

Mitosis (Cell Division) A cell goes through cell division called MITOSIS It only occurs in body (somatic) cells It does not occur in sex cells

In Mitosis... 2 daughter cells are formed from the cell Each new cell has a complete set of genetic information (DNA) In humans, there are 46 chromosomes in each body cell 46

Mitosis involves 4 main phases that occur in a specific order: PROPHASE METAPHASE ANAPHASE TELOPHASE

Prophase The chromosomes condense and become visible. The nucleolus disappears. The centrioles move towards the poles (ends) of the spindles and spindle fibres form. The nuclear membrane breaks down.

Metaphase The sister chromatids align at the mid-point of the spindle fibres in the centre of the cell and equidistant from each pole. The chromosomes attach to the spindle fibres at the centromeres.

Anaphase The shortest of the phases, it is when the chromatids separate and move towards opposite poles. The microtubules attached to each of the poles pull the chromatids apart.

Telophase – The spindle fibres are disassembled. – The nuclear membrane forms around each set of chromosomes. – The chromosomes lengthen and disappear

Cytokinesis This is the physical division of the cytoplasm of eukaryotic cells into two daughter cells after mitosis.

What is the difference between MITOSIS in plant cells and animal cells? A cleavage furrow forms in animal cells to divide the cytoplasm into 2 new cells A cell plate forms in plant cells to divide the cytoplasm into 2 new cells (the cell plate constructed between the 2 cells is the new cell wall)

What is the importance of the Cell Cycle and Mitosis? Ensures that the number of chromosomes in all nuclei of body cells remains constant Cells that die are replaced by new cells Injured tissue can be repaired (i.e., skin and bones) Cells can be replaced to keep a healthy body

What happens during AGING? As cells die, they are not replaced or are replaced more slowly The various body systems begin to change structurally and functionally as cells die Hypothesis: As cells age, they can’t repair themselves or they can’t pass instructions along to new cells