Cell Cycle

Cell Reproduction When a cell divides in two cells Cells need to grow larger because there is a limit to cell size Needed to replace dead cells Composed to MITOSIS and CYTOKINESIS

Chromosome Replication Chromosomes are uncoiled and duplicated CHROMATIDS are the two identical strands of a duplicated chromosome joined at the centromere

Cell Cycle Interphase Rest/growth phase Cell grows bigger Chromosomes are uncoiled and duplicated

Cell Cycle Prophase Preparing for mitosis Chromosomes begin to coil And condense into visible threads Centrioles move to the opposite ends of the cell The spindle fibers form between the centriole pairs Nuclear membrane breaks down and disappears

Cell Cycle Metaphase Middle stage of mitosis Paired chromatids begin to move towards the center of the cell between the two centrioles

Cell Cycle Anaphase Leaving stage of mitosis Each pair of chromatids splits at the centromere and becomes a single chromosome so there are TWICE as many chromosomes Chromatids move to opposite ends of the cell

Cell Cycle Telophase The last stage Nuclear membranes form around the two new sets of chromosomes Spindle disappears Chromosomes begin to uncoil and gradually become less visible Now two nuclei in the cell

Cell Cycle Cytokinesis “Dividing materials Division of organelles and the other substances in the cytoplasm into roughly equal halves In animal cells, an indent forms in the cell membrane and deepens until the cell is pinched into half In plant cells, a cell plate enlarges until it reaches the outer surface splitting the cell in half

Diploid = (2n) There are double the number of chromosomes Example: human body cells have 46 chromosomes Haploid = (1n) There are half the number of chromosomes in the cells Example: human sperm and egg cells have 23 chromosomes

In mitosis the number of chromosomes are the same from cell to cell In meiosis the number of chromosomes are halved When fertilization occurs… the chromosome numbers double to form body cells

Meiosis For the production of gametes Interphase chromosomes duplicate

Meiosis Prophase I Metaphase I - Chromosomes coil and become visible - Nuclear membrane disappears (crossing over may occur) Spindle forms Metaphase I - Chromosomes move to the middle and line up beside each other (crossing over may occur)

Meiosis Anaphase I Telophase I Cytokinesis Chromosomes move apart Paired chomosomes uncoil Nuclear membrane forms Spindle disappears Cytokinesis - TWO CELLS

Meiosis 7. Prophase II Paired chromatids coil Spindle forms Nuclear membrane disappears Metaphase II Chromosomes line up in the middle of the cell 9. Anaphase II - each chromosome splits - move to the opposite ends of the cell

MEIOSIS Telophase II - chromosomes uncoil - nuclear membrane form Cytokinesis - Total of 4 cells from one cell

QUIZ QUIZ 2