I. Eukaryotic cells - Can be unicellular (protists such as yeast, paramecium and amoebae) or multicellular (a system of division of labor such as fungi, animals, and plants).
A. First appeared 1.5 billion years ago.
B. Distinguishing characteristics (in comparison to prokaryotes)..
1. Generally larger than prokaryotic cells - generally 20 -> 50 micrometers, but can even be up to meters in length.
2. Eukaryotic DNA works in much the same way as prokaryotic DNA and the same code is used, however there are some distinct differences as well:
a) Eukaryotic DNA is enclosed by a membrane making a well defined nucleus.
b) Eukaryotic DNA tends to have protein bound to it forming chromatin (chromosomes). The regulating proteins (also found in prokaryotes) turn on and off genes. The histones (in larger mass but less important) help fold eukaryotic DNA.
c) The DNA has repeated and 'junk' areas (e.g. introns).
d) The DNA has free ends and is not bound to any membranes.
e) Replication starts at several points.
3. The nucleus containerizes the DNA.
a) Nuclear structure of the membrane.
(1) Double membrane