sedimentation rate are unaffected by the antibiotic. This enables the antibiotic to
kill bacterium and not the body that is infected by the bacterium.
For example, erythromycin and chloramphenicol, popular antibiotics, kill
bacteria whose subunits have a sedimentation rate of 50S. Streptomycin and
gentamycin affect bacteria whose subunits have a 30S sedimentation rate.Inclusions
An inclusion is a storage area that serves as a reserve for lipids, nitrogen, phos-
phate, starch, and sulfur within the cytoplasm. Scientists use inclusions to iden-
tify types of bacteria. Inclusions are usually classified as granules.- Granule inclusion.Membrane-free and densely packed, this type of inclu-
sion has many granules each containing specific substances. For example,
polyphosphate granules, also known by the names metachromatic gran-
ulesand volutin, have granules of polyphosphate that are used to synthe-
size ATP and are involved in other metabolic processes. A polyphosphate
granule appears red under a microscope when stained with methylene blue. - Vesicle inclusion.This is a protein membrane inclusion commonly found
in aquatic photosynthetic bacteria and cyanobacteria such as phytoplank-
ton, which suspends freely in water. These bacteria use vesicle inclusions
to store gas that give the cell buoyancy to float at a depth where light, car-
bon dioxide (CO 2 ), and nutrients—all required for photosynthesis—are
available.
Eukaryotic Cells
Aeukaryotic cell(Fig. 4-6) is larger and more complex than a prokaryotic cell
and found in animals, plants, algae, fungi, and protozoa. When you look at a
eukaryotic cell with a microscope you’ll notice a highly organized structure of
organelles that are bound by a membrane. Each organelle performs a specialized
function for the cell’s metabolism. Eukaryotic cells also contain a membrane-
bound nucleus where the cell’s DNA is organized into chromosomes.
Depending on the organism, a eukaryotic cell may contain external projec-
tions called flagella and cilia. These projections are used for moving substances
along the cell’s surface or for moving the entire cell. Flagellamove the cell in a
wavelike motion within its environment. Ciliamove substances along the cell’s(^78) CHAPTER 4 Prokaryotic and Eukaryotic Cells