All bacteria have a cell wall except mycoplasma. wall functions in:

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1 Bacteria There are three basic shapes of bacteria: I. coccus (cocc ~i) ("berries") - They are round or spherical, but may be oval or elongated. When they divide or reproduce they may form different patterns depending on the species: diplococci - cocci remain together in pairs when they divide or reproduce (gonorrhea and one type of meningitis). streptococci - chains which vary in length (cause strep throat, tooth decay, used in producing yogurt). staphylococci -grapelike clusters of cells (cause food poisoning, toxic shock syndrome, numerous skin infections). sarcina - cubelike structure consisting of eight cocci (normal inhabitants of the skin). tetrads - a cluster of four cocci 2. bacillus (bacilli) ("little staff") - They are rod-shaped or cylinders. Some are short, long, slender, rectangular with squared ends, or club-shaped. They form some patterns similar to cocci: diplobacilli - pairs streptobacilli - chains staphylobacilli - clusters Small, short rods that resemble oval cocci are referred to as coccobacilli. 3. spiral - They are cylindrical and convoluted (curved) to varying degrees. There are three spiral forms: a. spirillum (spirilla) - They are spirals or helices likecorkscrews, and they always have one or more twists. Their bodies are relatively rigid and they move by polar flagella. b. spirochetes - They are spiral with flexible bodies and move by axial filaments that wrap around the body. c. vibrios - They are curved rods shaped like commas.

2 Bacterial Cell Structures Surface LaTers i. Cell wall All bacteria have a cell wall except mycoplasma. wall functions in: The cell a. protection b. determining the shape of the bacteria c. contributing to the ability of some species to cause disease d. site of action of some antibiotics e. preventing bacteria from rupturing when the osmotic pressure inside the cell is greater than outside the cell Most bacteria can be divided into two groups based on the chemical and physical differences in their cell walls. A differential staining method, called the Gram stai~, separates the two groups. a. Gram-positive bacteria - The cell wall contains a large amount of peptidoqlycan. Peptidoglycan is composed of alternating units of disaccharides. The disaccharide is composed of the monosaccharides N-acetylmuramic acid (NAM) and N-acetyl~lucosamine (NAG). Rows of alternating NAM and NAG units are linked together by polypeptides. The cell wall consists of many layers of peptidoglycan linked together by polypeptides. Many Gram-positive bacteria also contain teichoic acid which is composed of alternating units of sugar alcohols (glycerol and ribitol) linked together by phosphates. During the Gram stain procedure, Grampositive bacteria retain crystal violet (purple) and iodine and they appear purple. When the peptidoglycan layer is removed from the bacteria, the remaining cell, surrounded only by a plasma membrane, is called a protoplast. b. Gram-neqative bacteria - The cell wall consists of one or a few layers of peptidoglycan. The cell wall does not contain teichoic acid. There is an outer layer of the cell wall which is composed of lipoproteins, lipopolysaccharides, and phospholidids. The layer functions as a barrier to certain antibiotics, detergents, digestive enzymes such as lysozymes, and body defense mechanisms. The lipopolysaccharide (LPS) is broken down into l i Did ~ which is an endotoxin that is toxic in the bloodstream or gastrointestinal tract. The polysaccharide portion contains sugars that function as antiqens. During Gram staining the crystal violet and iodine are not retained in the cell wall. A red counterstain, called safranin, is retained giving the bacteria a red color. When the peptidoglycan layer is removed from the cell the outer layer remains attached to the plasma membrane and the cell is referred to as a spheroplast.

3 2. Glycocal~x The cell wall is often surrounded by a glycocalyx, capsule, or slime layer in cocci and bacilli, but not spiral bacteria. Glycocalyx is a general term for substances that surround cells and is produced inside the cell and excreted to the cell surface. It consists of a viscous (sticky) gelatinous substance composed of polysaccharides, polypeptides, or both. If the substance is organized and firmly attached to the cell wall the glycocalyx is called a cadsule. If the substance is unorganized and only loosely attached to the cell wall the glycocalyx is described as a slime a er. The glycocalyx functions in: a. protecting against phagocytosis by neutrophi!s and macrophages b. allowing attachment to various surfaces for survival and growth c. protecting against dehydration 3. Cell or plasma membrane The cell or plasma membrane is a thin layer beneath the cell wall and it surrounds the cytoplasm. It mainly consists of proteins and phospholipids. The functions of the plasma membrane are: a. to regulate the movement of substances into and out of the cell by passive (diffusion, osmosis) and active transport mechanisms (main function) b. synthesizing cell wall components c. secretes proteins d. assists in DNA replication e. contains enzymes for cellular respiration and the production of ATP f. removal of waste products In some areas, the membrane folds and forms a round sac called a mesosome. The mesosome also contains folds and functions in metabolism and cell division.

4 External Structures I. Flaqella Flagella are long, thin threadlike strands of protein arranged in a spiral or helical pattern around a hollow center. They extend from the plasma membrane to the outside of the cell and are found in bacilli, spiral,.and a few cocci. Flagella rotate and propel the bacteria. The arrangement of flagella may be single at one end, one at~each end, two at one end, several at one end, or all over the cell. The number and arrangement of flagella are sometimes used to identify different genera of bacteria. 2. Pili and Fimbriae Pi!i and fimbriae are short, thin hairlike strands of protein arranged in a spiral or helical pattern around a hollow center. They are not involved in movement. Pill are longer than fimbriae and function in attaching some species of bacterial cells to each other. They are sometimes referred to as sex pili because they aid in the transfer of DNA from one cell to another during a process called conjuqation. Fimbriae are usually shorter than pili and function in attaching the bacteria to surfaces or to other cells. The attachment to cells of the body enhances the ability of the bacteria to cause disease (pathogenicity). 3. Axial filaments Axial filaments are only found in spirochetes. They consist of protein fibrils wound spirally around the length of the cell and are attached at the two ends of the cell. Rotation of the axial filament causes movement like a corkscrew. Internal Structures I. Cytoplasm The cytoplasm is the dense, semi-fluid substance inside of the plasma membrane. It is mainly composed of water and also contains enzymes and other proteins, carbohydrates, lipids, nucleic acids, and inorganic ions. Chemical reactions involved in metabolism occur in the cytoplasm. Structures in the cytoplasm include a nuclear reqion or nucleoid, ribosomes, and inclusions. I0

5 2. Nucleoid The nucleoid is a distinct area which contains a single, long, circular double-stranded molecule of DNA known as a bacterial chromosome. The bacterial chromosome contains the genetic information required for the cell s structures and functions. The bacterial chromosome differs from that of eukaryotic cells in that it is not associated with histone proteins and it is not surrounded by a membrane, separating it from the cytoplasm. Many bacteria also containextrachromosomal DNA called p!asmids. They consist of small, circular double-stranded DNA molecules that are not associated with the bacterial chromosome. Plasmids function in resistance to antibiotics and are referred to as R factors. They may also function in transferring DNA from one bacteria to another during the process of conjuqation and are referred to as F plasmids (fertility). 3. Ribosomes Ribosomes consist of RNA and protein and they function in protein synthesis. Bacterial ribosomes are made up of two protein subunits (large and small) and are smaller than those of eukaryotic cells. Antibiotics such as erythromycin, streptomycin, tetracycline, chloramphenicol, and qentamicin, all act by binding to the ribosome and interfering with its function, but they do not affect the ribosomes of eukaryotic cells. 4. Inclusions Inclusions include various qranules and vacuoles for storage of nutrients and reserve materials. Some inclusions are common to a wide variety of bacteria and others are limited to a few species and serve as a basis for identification. 5. Endospores Endospores are restinq or non-qrowinq structures that some Gram-positive bacteria such as Clostridium (botulism, gas gangrene, tetanus) and Bacillus (anthrax) produce when nutrients and/or water are unavailable. Endospores have thick walls and additional layers and are highly resistant to extreme heat, dehydration, toxic chemicals, and radiation. They can survive for hundreds of years. Formation of endospores is known as sporulation and they may form at the end, near the end, or in the center of the cell. The bacterial chromosome replicates and one of the chromosomes and a small portion of the cytoplasm are isolated by an ingrowth of the plasma membrane called a s_pore sept~un. The spore septum becomes a double-layered membrane surrounding the chromosome and cytoplasm and the structure is called a forespore. Thick layers of peptidoglycan form between the two membranes forming the cortex. A thick s_pore coat composed of protein then forms around the outside of the outer membrane. The spore coat functions in 11

6 resistance. The resulting endospore~contains little water, high amounts of calcitun ions, and diplocolinic acid which make it heat resistant. The bacterial cell degenerates or lyses and the endospore is released. Even though it contains DNA, ribosomes, and some enzymes, it is inactive metabolically and reproductively. When conditions become favorable the endospore coat and membrane layers are broken down by enzymes and water enters the endospore. Metabolism resumes and ~ermination occurs forming a veqetative cell.