Cell Cycle, Lecture notes of Cell Biology

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SC Standards

B2.6, B2.7, B2.

 Objectives:  Summarize the steps of the cell cycle  Explain why cells need to be small

• State Standards: B2.6, B2.7, and B2.

 We have learned that the basic unit of life is the cell.  Like all living things, the cell goes through a cycle of growth and reproduction.  The sequence of growth and division of a cell is called the Cell Cycle.  Most of the cell’s life is spent in in the growth phase known as interphase.

 Made up of three phases : G1, S, and G

 The shortest phase in the cycle is the cell division phase known as mitosis and cytokinesis.

 Once a cell becomes a certain size, it will divide into two cells  The larger a cell grows  The more demands on the cell’s DNA

 Proteins and other substances are not produced quick

enough for a large cell to maintain.

 The more demands on the cell’s membrane

 Nutrients and wastes have a hard time crossing the

membrane because of the lack of surface area.

 The important point is that the surface area to the volume

ratio gets smaller as the cell gets larger.

 Thus, if the cell grows beyond a certain limit, not enough

material will be able to cross the membrane fast enough to

accommodate the increased cellular volume. When this

happens, the cell must divide into smaller cells with

favorable surface area/volume ratios, or cease to function.

 What are the three main parts of the cell cycle?  What are the three parts of interphase?  In which stage do the chromosomes double?  In which stage are proteins made?  When are centrioles made?  In which phase of the cell cycle do sister chromatids appear?

 Mitosis follows interphase.  During mitosis, one parent cell divides into two daughter cells.  All somatic cells ( cells that are not sex cells that make eggs & sperm) undergo mitosis.  There are FOUR phases of Mitosis (PMAT):  Prophase  Metaphase  Anaphase  Telophase

 1 st and longest phase in mitosis  Chromosomes in the cell condenses  Nuclear envelope disappears.  Centrioles (organelle that produces spindle fibers) have separated and move to opposite ends of the cell.  Spindle fibers form and radiate toward the center of the cell.

 Centromeres that join the sister chromatids split.  Sister chromatids separate becoming individuals chromosomes.  Separated chromatids move to opposite poles of the cell.

 Last phase of mitosis  Chromosomes (each consisting of a single chromatid) uncoil.  A nuclear envelope forms around the chromosomes at each pole of the cell.  Spindle fibers break down and dissolve.  Cytokinesis begins.

 During which phase does the nuclear envelope disappear?  Which phase does it reappear?  During which phase are sister chromatids pulled apart?  When phase do the sister chromatids line up in the middle?  What is the longest phase of mitosis?  What is the shortest phase of mitosis?

 Cytokinesis is the division of the cytoplasm into two individual cells.  Each new cell has its own nucleus and organelles  Different process in animal and plant cells:  In animals: the cell membrane forms a cleavage furrow that will pinch into two cells.  In plants: the cell plate forms midway between the divided nuclei, which gradually develops into a separating membrane. The cell plate is formed by the cell wall of the plant cell. Cell Plate