Cells have distinct phases of growth, reproduction and normal functions
The cell cycle has four main stages – Regular pattern of growth, DNA replication, and cell division
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?
Why do you think skin cells only have a life span of about 2 weeks? Some cells divide only rarely- G₀ phase
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?
Cells divide during mitosis and cytokinesis Chromosomes condense at start of mitosis
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- 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 divides the cell’s nucleus in four phases – Prophase- chromosomes condense and spindle fibers form, nuclear envelope breaks down
Metaphase- chromosomes line up in the middle of the cell – Chromosomes are connected to spindle fiber
Anaphase- sister chromatids separate to opposite sides of the cell
Telophase- new nuclei form and chromosomes begin to uncoil – Two new nuclear envelopes will form
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