Prokaryotic and Eukaryotic Cells Structure and Function
In general microbes or microorganisms may be either prokaryotic (bacteria) or eukaryotic (protists, fungi, and some animals). However, there are some microbial organisms that appear to be intermediates between prokaryotes and eukaryotes (they possess a nucleus but do not have mitochondria or chloroplasts, an example is Giardia intestinalis. Prokaryotes differ from eukaryotes in several ways including but not limited to:
Characteristics Prokaryotic Eukaryotic Types bacteria (monerans) protists, fungi, plants, and animals Organization unicellular usually multicellular (exception some protists) Cell size small (0.1-10um) larger (10-100um) Membrane-bound organelles absent present Reproduction asexual asexual and sexual DNA circular linear Proteins assoc. with DNA Basic Histone Plasma membrane No sterols Sterols Ribosomes 70S 80S Cytoskeleton Absent present
PROKARYOTIC CELLS
Key Functions of Cells A boundary that keeps the cellular contents separate from the external environment but allows for the transfer of some substances into and out of the cell. Replication of DNA Synthesis of cellular components The ability to obtain energy through metabolic processes
Appendages are basically involved in movement or adhesion Flagella (singular flagellum) are cellular appendages that consist of three parts: a filament that rotates for movement a hook where the filament attaches a basal body that anchors the hook to the cell the arrangement of the hook/basal body articulation allows the hook with its filament to rotate 360 o
Arrangements of Flagella polar - flagella are attached at one or both ends of the cell monotrichous - a single flagellum at one end lophotrichous - multiple flagella arising from one or both ends amphitrichous a single flagellum arises from each end peritrichous - flagella are randomly dispersed over the cell surface
are modified flagella that occur in spirochetes Axial filaments
Non-locomotor appendages Pili are longer and sparser than fimbriae. fimbriae are involved in adhesion and pili (found only in Gram - bacteria) are involved in conjugation ( a mating process).
Cell envelopes differ between taxa but they basically consist of three layers: The capsule or slime layer (outermost layer) differs greatly in thickness, organization and chemical composition depending on the bacterial species. T Beneath the outer layer lies the cell wall. The cell membrane is a thin flexible sheet that surrounds the contents of the bacterial cell. Its functions include: transport, energy extraction, nutrient processing, and synthesis
An important tool in the identification of bacteria is the Gram stain. Some bacteria are Gram + while others are Gram - (some however, do not show a Gram reaction). Gram + bacteria stain purple (the color of the primary dye) and Gram - bacteria stain pink (the color of the counterstain or second dye). The Gram stain is a differential staining technique because different species of bacteria stain differently. The difference is a result of the composition of the cell wall. The Gram Stain
The protoplasm or cytoplasm is the dense gelatinous solution within the cell membrane that is the primary site for the cell s biochemical and synthetic processes. The following are found within the protoplasm of the prokaryotic cell:
chromatin body or the bacterial chromosome nucleoid or nuclear region of the cell that is associated with the chromatin body
plasmids are tiny circular extrachromosomal strands of DNA ribosomes are small structures consisting of RNA and proteins that are involved in protein synthesis
inclusions or granules are areas where nutrients are concentrated Endospores are dormant structures produced by some species of Bacillus and Clostridium.
Shapes and arrangements of bacteria There are six common shapes of bacteria: coccus, bacillus, coccobacillus, vibrio, spirochete, and spirullum and there are several arrangements of these cells: single, chains (strepto-), clusters (staphylo-), pairs (diplo-) etc.
Eukaryotic Cell
Cell Membrane Cell membrane Structure Components Arrangement Functions include Barrier Transport (know diffusion, osmosis, facilitated diffusion and active transport) Recognition (e.g., self vs. non-self) Reception (for protein hormones) Adhesion
Nucleus Structure and Function membrane similar to cell membrane (similar function) Nucleolus (formation of ribosomes) Chromosomes (gene expression) Nucleoplasm (matrix)
Ribosomes Structure rrna Proteins Function Site of protein formation (translation) Found in both prokaryotes and eukaryotes (different structurally)
Endoplasmic Reticulum Structure membranous system of tunnels and sacs Rough with ribosomes on surface Smooth- no ribosomes on surface Function Rough protein synthesis Smooth- lipid synthesis
Golgi Apparatus Structure also membranous, kind of like a stack of pancakes Function processing of lipids and proteins
Lysosomes Structure membrane bound sac containing hydrolytic enzymes Function digestion
Mitochondria Structure cigarshaped, double membrane-bound organelle Function Energy transfer by ATP synthesis
Chloroplast Structure Also cigar or spindle shaped, double membrane-bound, green Function Site of photosynthesis
OTHER STUCTURES Cell walls, not in animal cells Vacoules Cytoskeleton Cytoplasm