MAJOR CHARAC OF BACTERIA and EUCARYOTIC CELL STRUCTURE

• Morphological characteristics of bacteria refer to cell shape, size and structure; cell arrangement; occurrence of special structures and developmental forms; staining reactions; motility and flagellar arrangement.
• Centrioles play roles in eukaryotic cell division and in the formation of cilia and flagella.
• Chemical composition of bacteria refers to the chemical constituents of the cell, for example, presence of lipopolysaccharide in cell walls, teichoic acids or capsule.
• Cultural characteristics of bacteria include nutritional requirements and physical conditions required for growth and the manner in which growth occurs.
• Metabolic characteristics of bacteria refer to the way in which the cells obtain and use their energy, carry out chemical reactions and regulate these reactions.
• Antigenic characteristics of bacteria are special large chemical components (antigens) of the cell, distinctive for certain kinds of microorganisms.
• Genetic characteristics of bacteria are characteristics of the hereditary materials of the cells (deoxyribonucleic acid or DNA) and occurrence and function of other kinds of DNA that may be present, such as plasmids.
• Pathogenicity of bacteria refers to the ability to cause disease in various plants or animals or other microorganisms.
• Ecological characteristics of bacteria refer to the habitat and the distribution of the organisms in nature and the interactions between and among species in natural environment.
• Eucaryotic cells have a true nucleus, in that their DNA is enclosed by a nuclear membrane.
• Most animal and plant cells are 10 to 30 um in diameter, about 10 times larger than most prokaryotic cells.
• The cell is enclosed and held intact by the cell membrane, which is also referred to as the plasma, cytoplasmic, or cellular membrane.
• Structurally, the cell membrane is a mosaic composed of large molecules of proteins and phospholipids (certain types of fats).
• The cell membrane regulates the passage of nutrients, waste products and secretions into and out of the cell.
• The cell membrane has the property of selective permeability, allowing only certain substances to enter and leave the cell.
• The cell membrane is similar in structure and function to all of the other membranes found in eukaryotic cells.
• The nucleus controls the functions of the entire cell and it has three components: nucleoplasm, chromosomes, and the nuclear membrane.
• Eucaryotic chromosomes consist of linear DNA molecules and proteins (histones and nonhistone proteins).
• Genes are located along the DNA molecules.
• Each gene contains the genetic information that enables the cell to produce one or more gene products.
• Most gene products are proteins but some genes code for the production of two types of ribonucleic acid (RNA): ribosomal ribonucleic acid (rRNA) and transfer ribonucleic acid (tRNA) molecules.
• The organism’s complete collection of genes is referred to as that organism’s genotype (or genome).
• When observed using a transmission electron microscope, a dark (electron dense) area can be seen in the nucleus, called the nucleolus, where rRNA molecules are manufactured.
• The rRNA molecules then exit the nucleus and become part of the structure of ribosomes.
• The cytoplasm of eukaryotic cells encompasses the substance inside the plasma membrane and outside the nucleus.
• The cytoplasm is the substance in which various cellular components are found.
• A major difference between eukaryotic and prokaryotic cytoplasm is that eukaryotic cytoplasm has a complex internal structure, consisting of exceedingly small rods called microfilaments and intermediate filaments and cylinders called microtubules, forming the cytoskeleton.
• The cytoskeleton provides support and shape and assists in transporting substances through the cell (and even in moving the entire cell, as in phagocytosis).
• Within the cytoplasm of eucaryotic cells there is an extensive network of flattened membranous sacs, or cisterns, called the endoplasmic reticulum, or ER.
• The ER network is continuous with the nuclear envelope.
• The ER synthesizes lipids and stores lipids and proteins, and it provides a pathway for transport of those molecules to other parts of the cell.
• The ends of the cisterns can pinch off into small spheres called secretory vesicles, which then transport substances within the cell.
• Many lipids and proteins in the ER are transported to the Golgi complex in this manner as well.
• Two types of ER are found in most eucaryotic cells: rough ER, which has numerous ribosomes bound to it and thus looks rough through a microscope, and smooth ER, which has no ribosomes attached to it and thus is called smooth ER.
• Attached to the outer surface of rough ER are ribosomes, which are also found free in the cytoplasm.
• Ribosomes are the sites of protein synthesis in the cell.
• The ribosomes of eukaryotic ER and cytoplasm are somewhat larger and denser than those of prokaryotic cells.
• The eukaryotic ribosomes are 80S ribosomes, each of which consists of a large 60S subunit containing three molecules of rRNA and a smaller 40S subunit with one molecule of rRNA.
• Chloroplasts and mitochondria contain 70S ribosomes, which may indicate their evolution from prokaryotes.
• The ER expands into expanded areas that form secretory vesicles which can export substances from the cell and transport substances within it.