An Introduction to
Prokaryotes, Eukaryotes,
and Viruses
Classification Schemes for Living Matter
• Historical Basis for Classification of Living Matter
• First classification outlined by Linnaeus in 1735
• A simple classification (Animale, Vegetabile)
• Since 1735, the classification of living matter has
continued to change and develop as technology
advances.
Image source: http://en.wikipedia.org
3 Domain, 6 Kingdom Classification
• 1990 Carl Woese proposed a 3 domain classification system
• Classification is largely a result of molecular analysis of 16S ribosomal RNA genes
Prokaryotes
Eukaryotes
Image source: http://en.wikipedia.org
Cells of Eukaryotes and Prokaryotes
Eukaryote = 10µM
Prokaryote = 1-2µM
Image source: http://www.ncbi.nlm.nih.gov/bookshelf
The Prokaryotes
Prokaryotes
• Mostly tiny, single-celled
organisms
• Surrounded by a cell wall
• Lack extensive internal
compartments. No (limited)
membrane-bound organelles
• No nucleus
• Absorb nutrients through cell
wall or generate own nutrients
by photosynthesis
Image source: http://en.wikipedia.org
A Closer Look into a Prokaryotic Cell
A Closer Look into a Prokaryotic Cell
• Many prokaryotic
genomes consist of dsDNA
organized as a single
circular chromosome.
(Linear dsDNA genomes
also exist.)
• In addition to the single
circular chromosome, some
prokaryotes also have
additonal genes on smaller
plasmids (circular or linear).
Image source: http://textbook of bacteriology.net
The Eukaryotes
• Single-celled or multicellular
organisms
• Do not have a cell wall
• Contain several membranebound organelle
• Presence of a nucleus
• Nutrient acquisition by
photosynthesis, absorption,
ingestion.
Eukaryotes
A Closer Look into a Eukaryotic Cell
Image source: http://micro.magnet.fsu.edu/cells/animals/animalmodel.html
Additional Resources
A summary essay comparing prokaryotes and
eukaryotes
Cells Alive – A website demonstrating size
differences in cells and viruses. Also contains a
simple tutorial on differences between
prokaryotes and eukaryotes
What is a virus?
• Viruses are unlike prokaryotes
and eukaryotes. A virus must
infect a cell and use the host cell
machinery to replicate.
• Viruses are approximately 100
times smaller than bacteria and
must be observed with an
electron microscope.
Source: CDC PHIL #1873;
http://www.cgl.ucsf.edu;
Hatfull laboratory
Anatomy of a Virus
A virion consists of:
1. Nucleic Acid: DNA or
RNA, single or double
stranded
2. Capsid: A protein coat
that encapsulates and
protects the genomic
material
3. Envelope (optional): A
lipid layer surrounding
the capsid derived from
the host cell membrane.
Viral Hosts
• Viruses infect just about anything! Plants, Animals, Fungi,
Protists, Bacteria.
• Viruses can be specific for a particular host or may infect
a number of different hosts.
• Many new viruses are being discovered each year!
What have I learned?
• After listening to this presentation, you
should be able to:
Compare and contrast structural features
of prokaryotic and eukaryotic cells.
Discuss the host range and structural
features of a virion.
END