Post on 19-Jan-2016
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