bio2230_cell_types 1/21/04
BIOL 2230 REEDER
CELL TYPES BASED ON MORPHOLOGY AND ORGANIZATION
I. Cellular Life
A. Biochemical and Genetic Activities
l. Tremendous similarities in the biochemical activities and genetics of all cellular life forms
a. DNA as the chief heritable genetic material
b. Similar mechanisms of fermentation and aerobic respiration utilized for the formation
and storage of energy as well as photosynthetic processes
c. Almost identical methods of protein synthesis, nucleic acid synthesis, and polysaccharide
synthesis
2. Important morphological variations exist resulting in two structural types of cells composing
the majority of life (viruses as the exception): procaryotic and eucaryotic
B. Cell Morphology and Organization
l. Procaryotic
a. Represented by members of the Kingdoms Eubacteria and Archaebacteria
b. Considered to be the most primitive cellular life forms as well as the oldest (fossilized
cyanobacterium dated 3.8 to 3.5 billion years old).
l) Absence of internal lipid membranous organelles in the cell's cytoplasm such as the
nucleus, mitochondria, chloroplasts, lysosomes, endoplasmic reticulum, etc.
a) Possess ribosomes that are smaller than eucaryotic ribosomes: 70s in prokaryotes,
80s in eukaryotes.
2) Cytoplasmic streaming absent for internal transport due to a lack of microtubules;
simple diffusion related with the cell's small size is sufficient for intercellular
transport
3) Most prokaryotes possess a cell wall external to the cytoplasmic membrane
containing peptidoglycan (polymer of amino acids and sugars), which is not found in
eucaryotic cell walls; some Gram neg. types lack a wall completely (Mycoplasma)
4) Endocytosis can only occur on soluble material, therefore, no phagocytosis; external
digestion with a secretion of enzymes.
5) Lacks a true nucleus: the genetic material is not separated from the cytoplasm by a
distinct two-layered nuclear membrane; instead, the DNA is in the cytoplasm.
a) Also, the DNA is not organized into multiple distinct chromosomes, but exists as
a circular, single, continuous thread attached to the cytoplasmic membrane at a
certain number of sites (nucleoid); haploid
b) The chromosome also lacks the histone proteins in its DNA chromosome
structure
c) Small circular pieces of extrachromosomal DNA, called plasmids, are also found
in the cytoplasm that confer certain auxiliary metabolic capabilities
6) A procaryotic gene is transcribed directly into messenger RNA; requires no
enzymatic removal of "nonsense" intervening sequences (introns) followed by
splicing together to make functional RNA as normally occurs in eucaryotes.
7) Typically of very small size: a cell's size affects its growth rate because of the
relationship between a cell's surface area & volume of its contents
a) Surface-to-volume ratio for a typical bacterium is 20 times greater than that for a
typical human cell: procaryotic cells meet their nutritional needs easily & grow
rapidly
