Chapter 10 Section 2

 The cell cycle is a repeating sequence of cellular growth and division during the life of a cell.  The life of a eukaryotic cell cycles through phases of growth, DNA replication, preparation for cell division, and division of the nucleus and cytoplasm.  The cell cycle is made up of five phases. The first three phases together are known as interphase. The remaining two phases make up cell division (mitosis).

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 Interphase: 1 st phase of the cell cycle where the cell is not dividing but is growing and preparing to divide  The “Prep” Phase  Consists of 2 Gap Phases and Synthesis Phase  Skin cells: spend less time in interphase ▪ Why?: they divide often  Nerve cells: spend more time in interphase ▪ Why?: they divide seldom

 During the G1 phase cells grow rapidly as the cell builds more organelles  G1 occupies a major portion of the cell’s life  Checkpoint:  Cell checks surroundings before it copies DNA  If favorable conditions and cell is healthy/large enough it will enter synthesis phase

 During the S Phase, the cell’s DNA is copied  At the end of the phase, the cell’s nucleus has 2x as much DNA  Each chromosome consists of 2 identical chromatids that are attached to a centromere

 During G2 the cell continues to grow and divide  Microtubules (hollow protein fibers) are formed and organized in cytoplasm  Checkpoint:  Check for any mistakes in copied DNA  Enzymes correct mistakes that are found  Ensures DNA of daughter cells will be identical to DNA of original cell  Proteins double-check that cell is large enough to divide  If pass may begin to divide=mitosis