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

We are made up of many kinds of specialized cells.  Skin cells, muscle cells, red blood cells, liver cells, it goes on and on. somatic cells All of these body cells AKA: somatic cells must remain identical so they divide to make more cells, like themselves.

Do cells grow?  Yes, but just enough to have double of what is needed.  Organelles, cytoplasm, membrane, etc  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. It is much harder to move materials across the cell membrane.  Surface Area : Volume

Surface Area to Volume Ratio 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.

Functions of Cell Division 20 µm 100 µm 200 µm (a)Reproduction. An amoeba, single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). (b) Growth and development This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).

Chromosomes  All eukaryotic cells store genetic information in chromosomes.  Human cells have 46 chromosomes.  23 nearly-identical pairs  They contain the blue print for protein production 50 µm

Structure of Chromosomes  Chromosomes are composed of a complex of DNA and protein called chromatin that condenses during cell division Short Arm Long Arm Sister Chromatids Bands Centromere

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 Types of Cell Cycles Binary FissionMitosisMeiosis PROKARYOTESEUKARYOTES Reproduction (clones) Growth & repair (identical cell copies) Sex cells (gametes)

Prokaryotic Cell Division BINARY FISSION  1. Genetic information is copied.  2. Then the cell divides in two.  Each new cell receives an exact copy of the genetic information.  These daughter cells are exactly identical.

Eukaryotic Cell Division 2 part 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  1. 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.  3. G 2 phase: cell prepares for nucleus to divide.  Cell grows & produces additional organelles & cytoplasm.

M Phase  Mitosis- PMAT  Division of the nucleus to form two nuclei.  Ensures each new cell gets a copy of every chromosome.  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 Cell Cycle…but NOT a part of mitosis!  This is the division of the organelles and CYTOPLASM.

Disruptions in the cell cycle…  The cell cycle is controlled by proteins call cyclins.  Disruptions lead to diseases, such as…  Cancer  Causes abnormal cells to form or an unusually large number of cells to form.  If these cells join together into a large mass, it is called a tumor. What can cause disruptions?  The cell cycle can be disrupted when…  DNA is not copied correctly.  Environmental factors: radiation, tobacco smoke, other pollutants.

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