 Eucaryotes have a true nucleus and a number of cellular organelles inside the cytoplasma.  The plasma membrane is made of proteins and phospholipides that form a bilayer structure.  One major difference is the presence of sterols in the cytoplasmic membrane.

 The nucleus of eucaryotic cells contains chromosomes as nuclear material (DNA molecules with some closely associated small proteins), surrounded by a membrane  The nucleolus is in an area in the nucleus and is the site of ribosome synthesis.  Many chromosomes contain small amounts of RNA and basic proteins called histones attached to the DNA.

 DNA synthesis  Nuclear division  Cell division  Cell separation

 The M phase consists of mitosis where the nucleus divides, cytokinesis where the cell splits into separate doughter cells.  All of the phases between one M phase and the next are known as the interphase.  The interphase is divied into three phases: G1, S, and G2.  In the S phase the cell replicates its nuclear DNA.  Checkpoints exist for entry into the S and M phases and exit from M phase.  Cells may also be in a Go state, which is a resting state where there is no growth.

 Certain procaryotic and eucaryotic organisms contain flagella- long, filamentous structures that are attached to one end of the cell and are responsible for the motion of the cell.  The cytoskeleton refers to filaments that provide an internal frame work to organize the cells’ s internal activities and control its shape.  Cilia are flagella like structures. Only one group of protozoa, called ciliates, contains cilia.

 Fungi are heterotrophs.  larger than bacterial cells  Two major groups of fungi are yeasts and molds.

 Yeasts can reproduce by asexual or sexual means  Asexual reproduction is by either budding or fission.  In budding, a small bud cell forms on the cell, which gradually enlarges and separates from the mother cell.  Asexual reproduction by fission is similat tho that of bacteria.  In fission, cells grow to a certain size and divide into two equal sizes.  Sexual reproduction of yeasts involves the formation of a zygote from fusion of two haploid cells, each having a single set of chromosomes.

 Molds are filamentous fungi and have a mycelial structure.  The mycelium is a highly branched system of tubes that contains mobil cytoplasm with many nuclei.  Long, thin filaments on the mycelium are called hyphae.  Certain branches of mycelium may grow in the air, and asexual spores called conidia are formed on these aerial branches.  Some molds reproduce by sexual means and form sexual spores. These spores provide resistance against heat, freezing, drying, and some chemical agents.

 The phycomycetes are algalike fungi ; they don’t posses chlorophyll and cannot photosynthesize. Aquatic and terrestrial molds belong to this category.  The ascomycetes form sexual spores called ascospores, which are contained within a sac. Some molds of the genera Neurospora and Aspergillus and yeasts belong to thsi category.  The basidiomycetes reproduce by basidiospores, which are extended from the stalks of specialized cells called the basidia. Mushrooms are basidiomycetes.  Only asexually reproducing molds are the deuteromycetes (fungi imperfecti). Some pathogenic fungi such as Trichophyton, which causes athlete’ s foot, belong to this category.

 Algae are unicellular organisms. Some plantlike multicellular structures are present in marine waters.  All algae are photosynthetic and contain chloroplasts, which impart the green color to the organisms.  The chloroplasts are the sites of chlorophyll pigments and are responsible to the photosynthesis.  Some algae contain silica or calcium carbonate in their cell wall.  Diatoms containing silica in their cell wall are used as filter aids in industry.  Some algae, such as Chlorella, Scenedesmus, Spirullina, and Dunaliella, are used for waste water treatment with simultaneous single-cell protein production.

 Protozoa are unicellular, motile, relatively large eucaryotic cells that lack cell walls.  Protozoa obtain food by ingesting other small organisms, such as bacteria, or other food particles.  Protozoa are uninucleate and reproduce by sexual or asexual means.  They are classified on the basis of their motion.  The amoebae move by ameboid motion, whereby the cytoplasm of the cell flows forward to form a pseudopodium (false foot), and the rest of the cell flows toward this lobe.  The flagellates move using their flagella.  Trypanosomes move by flagella and cause of number of diseases in humans.

 The ciliates move by motion of a large number of small appendages on the cell surface called cilia.  The sporozoans are nonmotile and contain members that are human and animal parasites.

 Viruses are very small and are obligate parasites of other cells, such as bacterial, yeast, plant, and animal cells.  Viruses cannot store free energy and are not functionally active except when inside their host cells.  Viruses contain either DNA (DNA viruses) or RNA (RNA viruses) as genetic material.  DNA stands for deoxyribonucleic acid, and RNA is ribonucleic acid.  In free living cells, all genetic information is contained on the DNA, whereas viruses can use either RNA or DNA to encode such information.  This nuclear material is covered by a protein code called a capsid.  Some viruses have an outher envelope of a lipoprotein and some do not.  Viruses infected bacteria are called bacteriophages.

 Some bacteriophages have a hexagonal head, tail, and tail fibers.  Bacteriophages attach to the cell wall of a host cell with tail fibers, alter the cell wall of the host cell, and inject the viral nuclear material into the host cell.  Bacteriophage nucleic acids reproduce inside the host cells to produce more phages.  Host cells lyse or break apart and phase particles are released, which can infect new host cells. This mode of reproduction of viruses is called the lytic cycle.  In some cases, phage DNA may be incorporated into the host DNA, and the host may continue to multiply in this state, which is called the lysogenic cycle.

Michael L. Shuler and Fikret Kargı, Bioprocess Engineering: Basic Concepts (2 nd Edition),Prentice Hall, New York, James E. Bailey and David F. Ollis, Biochemical Engineering Fundementals (2 nd Edition), McGraw-Hill, New York, REFERANSLAR