Cell Cycle All Change is a miracle to contemplate; but it is a miracle taking place every second. – Henry David Thoreau

Do cells grow?  Yes, but just enough to have double of what is needed.  Organelles, cytoplasm, membrane, etc  When we are babies we have fewer cells than when we are adults. Our cells divide and create more cells as we grow.  All cells are generally the same size.  A small plant and a large plant have the same size cells.  The muscle tissue on an elephant and the muscle tissue of a mouse have the same size cells.

Why do cells have to divide?  Because growing too big has consequences.  Becomes less efficient in 3 ways…  1. DNA becomes overworked.  2. Small cells are much easier/faster to replicate.  3. The main consequence is that it is much harder to move materials across the cell membrane.  Surface Area : Volume (ratio)

High Surface Area to Volume Ratio  Surface Area/Volume (Look on Test)  The smaller the cell is, the greater the surface area to volume ratio.  This means there is more area for materials to be transported through the membrane.  What the cell wants is a higher Surface Area than the volume. BUT…  Volume increases faster than Surface Area.

Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume

What is the cell cycle?  It is the series of events that cells go through in order to grow and divide.  Called a “cycle” because it is an ongoing/continuous process.

3 Basic Types  1. Binary Fission in prokaryotes (Bacteria)  2. Cell division (Mitosis) in eukaryotes for the purpose of growth and repair.  3. Cell division (meiosis)that produces sex cells (gametes)

Prokaryotic Cell Division  Relatively simple…  These cells reproduce through binary fission.  First: the genetic information is copied.  Then the cell divides in two.  Each new cell receives an exact copy of the genetic information.  These daughter cells are exactly identical.

Binary Fission  Is a type of asexual reproduction  Benefits  Reproduce quickly  All information comes from one parent  Same number of chromosomes as parent cell  Non-benefit  Reduces genetic variation  Population cannot adapt as quickly

Eukaryotic Cell Division  2 distinct part to the Cell Cycle  1. Interphase (Between phase)  2. M Phase (Mitosis and cytokinesis)

Interphase  Resting Stage  Looks like the cell is resting.  Majority of time is spent here.  DNA Chromatin  3 phases of Interphase  G 1 phase: the cell grows & carries out routine functions. (increase in size)  2. S phase: chromosomes are copied.  Critical: because each daughter cell needs a complete set.  The number of chromosomes in cells is constant within a species.  Humans= 46 chromosomes or 23 pairs  3. G 2 phase: cell prepares for nucleus to divide.  Cell grows & produces additional organelles & cytoplasm.

M Phase  Mitosis  Division of the nucleus to form two nuclei.  Ensures each new cell gets a copy of every chromosome.  Takes the least amount time, but has the most action.

Mitosis - General Chromosomes have replicated & are visible # of centromeres = # of chromosomes

Mitosis – General Cont’d Each daughter cell receives its own copy of the parent cell’s DNA Each daughter cell receives its own copy of the parent cell’s DNA Occurs in body cells – somatic cells

Cytokinesis  Still a part of the M phase…but NOT a part of mitosis!  This is the division of the organelles and cytoplasm.

Disruptions in the cell cycle…  We are made up of many kinds of specialized cells.  Skin cells, muscle cells, red blood cells, liver cells, it goes on and on.  Cell divide to make other cells, like themselves.  Cells continue to grow until they touch another cell.  The cell cycle is controlled by proteins call cyclins.

Continued…  Disruptions lead to diseases, such as…  Cancer  Causes abnormal cells to form or an unusually large number of cells to form.  These cells do not respond to signals that regulate the growth of most cells  If these cells join together into a large mass, it is called a tumor. And they grow at a faster rate.  Many have a defect in a gene called p53.  The cell cycle can be disrupted when…  DNA is not copied correctly.  Environmental factors: radiation, tobacco smoke, other pollutants. (mutagens)

Cancer Loss of control during the cell cycle can lead to cancer Cancer cells do not show contact inhibition and they divide uncontrollably Can result from a single nucleotide change in the DNA! Cancer Cells YouTube

1. In which phase of the eukaryotic cell cycle is the genetic material duplicated? A. G 1 phaseC. G 2 phase B. 2 nd - S phaseD. M phase (MITOSIS) 2. Which two phases of the cell cycle make up cell division? A. G 1 & CytokinesisC. G 2 phase & Cytokinesis B. Interphase & mitosisD. Mitosis & Cytokinesis