World Builders™                                                                    Session Four  --  Microbiology             

                Eukaryotes and Prokaryotes    

The presence of oxygen in the atmosphere made larger, more complex cells possible.

 

         Here is another copy of the  diagram of a eukaryote cell compared with a prokaryote cell. 

Characteristics of Eukaryotes and Prokaryotes

Eukaryotes

Prokaryotes

Roughly (if a spherical cell)
           10 times the diameter 
         100 times the surface area
        1000 times the volume
                                     of a prokaryote.

DNA is in paired chromosomes
DNA is in a nucleus contained in a
         membrane

Larger ribosomes

Contain additional structures such as
     Mitochondria        Chloroplasts
 that are "live-in" prokaryotes

Have additional structures to help with cell 
organization and functioning

About one tenth the size of a eukaryote

 

 

DNA is a loop
DNA floats in the cytoplasm


Small ribosomes

some are anaerobic (poisoned by oxygen)
some can live with oxygen or without it
some use oxygen

have a lot of biochemical diversity

So What is in These Cells?

Prokaryotes and Eucaryotes:

    The Cell Membrane encloses the cell.  Water and nutrients are admitted through the cell wall, and wastes are expelled.  Bacteria and plant cells also have a protective cell wall, but animals have a membrane without a wall. 

    
Cytoplasm is the watery stuff that fills the cell, provides a medium in which to move the molecules around.   The cytoplasm is full of chemicals: dissolved oxygen and / or carbon dioxide, amino acids, simple sugars, molecules of carbohydrates, proteins, or lipids (fats).   More than half of the cell contents is water.

     In eukaryotes the inside of the cell is full of membranes that guide and contain and compartmentalize the cell contents.

     Ribosomes do protein synthesis.  I think of them as being like workers in a fast food place.  When the cell needs proteins, the ribosomes get information about how to make the proteins by copying a piece of the DNA.  That is like taking the order.

The proteins are made of amino acids, which are floating in the cytoplasm.  The ribosome collects the amino acids which fill the order.  It puts the amino acids together correctly.  That is like assembling  and packing up the items on the order.

When the order is complete, the protein folds up and is ready to use.  The folding up is the customer's smile!

Eukaryotes Only   

     The Nucleus contains the DNA, the material that holds the genetic code, the instructions for how to make the cell and control its processes.  The nucleus is contained in a membrane which keeps all the DNA together. In Eukaryotes, ribosomes are made inside the nucleus by a structure called the nucleolus.

    The Vacuole is a container within a single membrane.  It may hold water, food, or wastes -- whatever the cell is storing or transporting.  In a plant cell the vacuole stores water.  In plant cells, the vacuole can occupy about 55% to 95% of the cell volume.  When the vacuole is full of water it helps to support the cell wall of the plant cell.

Mitochondria and Chloroplasts are called organelles.

     Mitochondria are found in all eukaryotic cells.  They are the "energy factories" of the cells, doing respiration..  They use oxygen as they work.  They process the glucose that the chloroplasts make and release energy that powers the entire cell.  They are small and oval shaped, and were once free-living prokaryotes.   

     Mitochondria have their own DNA and their own small ribosomes.  They are enclosed in two membranes.  They divide themselves by binary fission.  

     Chloroplasts are found in algae and plants.  They are cyanobacteria that moved into  eukaryotic cells long ago.  They have their own DNA loops and their own little ribosomes. They are enclosed by three specialized membranes.

     Chloroplasts do photosynthesis.  They capture the carbon in carbon dioxide and link it to other atoms to make organic compounds.  They release oxygen into the atmosphere.  What they do benefits the whole cell.

     Chloroplasts are larger than mitochondria.  It is their productive work that makes much of the life on earth possible by providing oxygen and materials for the construction of biomass (leaves, twigs, roots, etc) that support animals and decomposers.

     Chloroplasts are well treated by the plants.  Plants supply the chloroplasts with water and minerals, and turn their leaves toward the sun so that the chloroplasts can function well.   What a great partnership!

     Other contents of the eukaryotic cell include the endoplasmic reticulum (membranes that create paths for the movement of contents in the cell), the Gogli body, and the cytoskeleton, which provides support and helps in cell organization.

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