The Cell Cycle• Cells have distinct phases of growth, reproduction and normal functions

The Cell Cycle

• The cell cycle has four main stages– Regular

pattern of growth, DNA replication, and cell division

The Cell Cycle

• Main Stages- gap 1, synthesis, gap 2, and mitosis– Gap 1 (G₁): cell growth and

normal functions– DNA synthesis (S): copies

DNA– Gap 2 (G₂): additional growth– Mitosis (M): includes division

of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)

• Do all cells divide at the same rate?

The Cell Cycle

• Why do you think skin cells only have a life span of about 2 weeks?

• Some cells divideonly rarely- G₀ phase

The Cell Cycle• Cell size is limited

– Volume increases faster than surface area

• Which cell has the largest surface area?• Which cell has the largest surface area-to-volume ratio?• Which has the larger ratio of surface area to volume, a tennis ball or a soccer ball?• Why is a suitable cell size important?

Mitosis and Cytokinesis

• Cells divide during mitosis and cytokinesis• Chromosomes condense at start of mitosis

Mitosis and Cytokinesis

• DNA wraps around proteins (histones) that condense it

• Chromatin- DNA plus proteins

• Chromatid- half of a duplicated chromosome

• Centromere- hold sister chromatids together

• Telomeres- found on end of DNA molecules and protect them

Mitosis and Cytokinesis

• Mitosis and cytokinesis- produce two genetically identical daughter cells

• Interphase prepares the cell to divide– DNA is duplicated

• Mitosis divides the cell’s nucleus in four phases– Prophase, Metaphase,

Anaphase, Telophase

• Mitosis 1 video

Mitosis and Cytokinesis

• Mitosis divides the cell’s nucleus in four phases– Prophase- chromosomes condense and spindle fibers form,

nuclear envelope breaks down

Mitosis and Cytokinesis

• Metaphase- chromosomes line up in the middle of the cell– Chromosomes are connected to spindle fiber

Mitosis and Cytokinesis

• Anaphase- sister chromatids separate to opposite sides of the cell

Mitosis and Cytokinesis

• Telophase- new nuclei form and chromosomes begin to uncoil– Two new nuclear

envelopes will form

Mitosis and Cytokinesis

• Cytokinesis- division of cytoplasm– Usually occurs at same

time of telophase

• Cytokinesis differs in animal and plant cells– Animal- membrane

pinches closed– Plant- cell plate forms

• Mitosis 2 Video