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Cell Architecture
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Classification of organisms
“Five kingdom system:”
Divide all organisms into groups (kingdoms)-different groups have different combinations of cell
parts (organelles)
! Prokaryota
! Animalia
! Plantae
! Fungi
! Protista
Classification by molecular biology
Modern systems divide organisms into groups-(domains, kingdoms)—on the basis of DNA
sequences
The more we learn, the more complex the situation
This chart only classifies eukarya, again on the basis of DNA
us
S.L. Baudauf, Science 300:1703, 13 June 2003
Prokaryotes
! Bacteria, Archaea
! Simplest structure
Plasma Membrane
Thin sheet 7-9 nm (0.007-0.009 !m) thick
Composition: lipid (fat) and protein
Found in all cells
Functions:
! serves as platform for biochemical reactions
! recognizes outside stimuli
! controls transport of molecules (and larger
things) into and out of cell.
Cell Wall
Thick net (variable width) surrounding the plasma
membrane; rigid
Found in most prokaryotes (bacteria, archaea); also
plants, fungi, some protists
Composition: peptidoglycan, cellulose, chitin, etc.
(long molecules, porous net)
Functions
! limits the size of cell
! controls cell growth
Nucleoid
Nucleic acid (DNA, a long, stringy molecule) in center
of cell
Function: contains information that controls...
! cell functions (metabolism)
! growth of cell
! reproduction
Ribosomes
Small, solid spheroids (0.02 !m diameter)
Nucleic acid (RNA) and protein, two subunits each
Ave. 30,000 per cell
Function
! synthesis of proteins
Eukaryotes
! Plants, Animals, Fungi, Protists
! Complex cell structures
! Multicellular organisms, with specialized cells
Organelles in prokaryotes that are the
"same" in eukaryotes
Plasma membrane
Cell wall (in plants, fungi, some protists)
Ribosomes
Nucleus (nuclei)
Spheroid, 10-20 !m diameter
Present in all eukaryotes: usually
one per cell (more? coenocytic or
syncitial)
Surrounded by nuclear envelope,
a double membrane
Chromatin (DNA + protein):
! Nucleosomes
! Chromosomes
! Centromeres
! Telomeres
Nucleolus: makes ribosomes
Function: like nucleoid of prokaryotes
Mitochondrion (-dria)
Spheroid ca. 1 !m diameter
Surrounded by a double membrane
Crista (-ae): inner membrane folds
Matrix: liquid gel center
Function: directs energy transformation,
metabolism
Found in all eukaryotic cells: 1 to 10,000 (ave.
100) per cell
Mitochondria in cornial cells are long and tubular
a and d and green in c and f is autofluorescence
b and e and red in c and f is a fluorescent dye absorbed by mitochondria
Plastid
Spheroid 5 !m diameter
Found in plants and some protists
! Double membrane
! Thylakoids
! Stroma
Functions depend on type:
! Chloroplast (green)
! Leukoplast (white)
! Chromoplast (colored)
! Proplastids
Organelles in prokaryotes and eukaryotes
! Plasma membrane
! Cell wall (in prokaryotes, plants, fungi, some
protists—not animals)
! Ribosomes
! Nucleoid/nucleus
! Mitochondrion (eukaryotes, not prokaryotes)
! Plastids (plants, protists, not prokaryotes,
fungi, or animals)