P ROKARYOTIC & E UKARYOTIC C ELLS

 As you have already learned, everything is made up of living cells.  And the cells themselves are made up of many different parts.  There are many different cells that do many different things, but all of these cells fall into one of the two main categories:  Prokaryotic cells &  Eukaryotic cells

W HAT THE WORDS MEAN Prokaryotes  Pro = before  Karyose = kernel, which represents the nucleus  So prokaryotes occurred before cells with a nucleus  Ex. Bacteria Eukaryotes  Eu = true  Karyose = kernel, the nucleus  So eukaryotes are the cells with a true nucleus  Ex. Found in animals, plants, and fungi (yeast)

W HAT THEY HAVE IN COMMON  DNA  Cell (plasma) membrane  Ribosomes  Simple in Prokaryotic, complex in Eukaryotic  Cytoplasm  Allow the flow of nutrients and wastes to enter and leave the cell  Have similar metabolic ( life processes) like photosynthesis and respiration  Require a supply of energy  Made from the same basic chemicals  Carbohydrates, proteins, nucleic acid, fats, minerals, and vitamins

D IFFERENCES  That’s what they have in common, but there are significant differences too.  The two main ones are age and structure.

A GE D IFFERENCES  Scientists believe that prokaryotic cells (in the form of bacteria) were the first life forms on earth. They are considered “primative” and originated 3.5 billion years ago. That is 2 billion years before eukaryotic cells and billions of years before our earliest ancestor, the hominids.  4.6 billion years ago – Earth was formed  3.5 billion years ago – the first life arose: prokaryotic bacteria  1.5 billion years ago – eukaryotic cells arose  500 million years ago – multi-celled eukaryotes arose  3 million years ago – our earliest ancestor, the hominids, appeared

S TRUCTURAL D IFFERENCES  Eukaryotic cells contain two important things that prokaryotic cells do not:  A nucleus  Membrane bound organelles

DNA  Although both contain DNA:  The DNA in eukaryotic cells in in the membrane bound nucleus  The DNA in prokaryotic cells floats around in the cell in what we call a Nucleoid – not a real structure, just a word to describe the inside of the cell where the nuclear material sits

O RGANELLES  The organelles in eukaryotic cells allow them to perform more complex functions than prokaryotic cells.  Prokaryotic cells do not have organelles like eukaryotic cells.  Both have ribosomes, but they are much more complex in Eukaryotic cells.

C HLOROPLASTS AND MITOCHONDRIA  Evidence suggests that chloroplasts and mitochondria were once bacteria that developed a symbiotic relationship with cells that have a nucleus  Chloroplasts and mitochondria have their own DNA that is not a part of the cells.  Yes, plants have both chloroplasts and mitochondria.

S IZE  Eukaryotic cells are about 10 times larger than prokaryotic cells.

C ELL W ALL Both have a cell wall, but they are made up of different substances. Well, eukaryotic plant cells do.

F LAGELLA & C ILIA  Flagella and cilia are the structures that help cells move.  Eukaryotic flagella are more complex than prokaryotic flagella.

C HECK FOR U NDERSTANDING Eukaryotic and Prokaryotic Cell Structure Cell StructureProkaryotic Cell Typical Animal Eukaryotic Cell Cell MembraneYes Cell WallYesNo Cilia or FlagellaYes, simpleYes, complex Endoplasmic ReticulumNoYes Golgi ComplexNoYes LysosomesNoYes MitochondriaNoYes NucleusNoYes RibosomesYes, simpleYes, complex

N EW D ISCOVERIES  Until recently, it was thought that only eukaryotic cells existed in multi-celled groups like in organs and tissue. Recent discoveries suggest that some prokaryotic cells do too.  This is just one more example of how new discoveries are always changing what we know – or think we know.  But that is what makes science so exciting!  sler_on_how_bacteria_communicate.html sler_on_how_bacteria_communicate.html