Mic 101: L 5 SST Prokaryotic cells

Typical Prokaryotic cell

Morphology Size: μm diameter μm length Shape: three shapes common: 1.coccus = sphere 2.bacillus = rod 3.spiral = twisted Cell division by binary fission:

Morphology: Arrangement Cocci(singular Coccus) I.single coccus: II.diplococcus: daughter cells separate remain in pair III. streptococci: after division remain attached in chain IV.tetrad: division occurs in two planes and group as four V. sarcinae: division occurs in three planes and group as eight V. staphylococci: division occurs in multiple planes and form grape like structure

Morphology Bacilli (Singular Bacillus)  rods of various length:  oval to “hot dog”  -rods divide only along the short axis I. single bacillus II. diplobacilli:daughter cells separate remain in pair III. streptobacilli: chain after division IV. coccobacillus: short oval, often confused with cocci

Morphology Spiral one or more twists I. vibrio: curved rod II.spirillum: rigid helical shape, like corkscrew III. spirochete: flexible helical shape,  Most bacteria are monomorphic: always one shape  Some are genetically pleomorphic: have varied shapes within the population of a single species

The cell wall is the layer, usually semirigid, that lies just outside the plasma membrane. Functions It helps determine the shape of the cell. It helps protect the cell from osmotic lysis. It can protect the cell from toxic substances. In pathogens it can contribute to pathogenicity. The prokaryotic cell wall also is the site of action of several antibiotics.

After Christian Gram developed the Gram stain in 1884, it soon became evident that most bacteria could be divided into two major groups based on their response to the Gram-stain procedure Gram-positive bacteria stained purple Gram-negative bacteria colored pink or red The gram-positive cell wall consists of a single 20 to 80 nm thick homogeneous layer of peptidoglycan (murein) lying outside the plasma membrane. Gram-negative cell wall is quite complex. It has a 2 to 7 nm peptidoglycan layer covered by a 7 to 8 nm thick outer membrane.

Peptidoglycan is an enormous meshlike polymer composed of many identical subunits. The polymer contains two sugar derivatives, N-acetylglucosamine and N- acetylmuramic acid and several different amino acids. Three of these amino acids are not found in proteins: D-glutamic acid, D- alanine, and diaminopimelic acid. The backbone of this polymer is composed of alternating N- acetylglucosamine and Nacetylmuramic acid residues. A peptide chain of four alternating D- and L-amino acids is connected to the carboxyl group of Nacetylmuramic acid. Many bacteria replace diaminopimelic acid with another diaminoacid, usually L-lysine. Often the carboxyl group of the terminal D-alanine is connected directly to the amino group of diaminopimelic acid, but a peptide interbridge may be used instead.

Gram-positive bacteria normally have cell walls that are thick and composed primarily of peptidoglycan.Peptidoglycan in grampositive bacteria often contains a peptide interbridge In addition, gram-positive cell walls usually contain large amounts of teichoic acids, polymers of glycerol or ribitol joined by phosphate groups.Amino acids such as D-alanine or sugars like glucose are attached to the glycerol and ribitol groups. Two types of teichoic acid: Lipoteichoic acid –bound to membrane lipids Wall teichoic acid –linked to peptidoglycan

Gram-negative bacteria have a cell wall that is thinner than that of Gram-positive bacteria with one or few layers of peptidoglycan Outer membrane, lies above the peptidoglycan layer. The outer membrane is much thicker than the single peptidoglycan layer. Peptidoglycan is bonded to lipoproteins in the outer membrane. Does not contain teichoic acids. More susceptible to mechanical breakage.

Cell Wall

Ultra-structure: Cell Wall

Cell Wall 2. Gram Negative Cell Wall One or very few peptidoglycan layer and outer membrane Peptidoglycan linked with outermembrane by lipoprotein Space between peptidoglycan and outer membrane-periplasmic the peptidoglycan in periplasm Outer membrane contains lipoprotein,phospho lipid and lipopolysaccharide

Structure of plasma membrane Thin structure lying inside the cell wall and enclosing the cytoplasm. It is 5-10 nm thick, consists mainly of lipoprotein and is visible in some ultrathin sections examined with the electron microscope (EM. The cytoplasmic membrane is the physical and metabolic barrier between the interior and exterior of the bacterial cell. Changes with temperature, age, environment

The protein molecules in the membrane can be arranged in a variety of ways. Peripheral proteins- not embedded. associated firmly with inner or outer surface of the membrane; may function as enzyme. Integral proteins-firmly embedded in the membrane some penetrate the membrane completely. Some make channels through which substances enter and exit the cell. The membrane must be as viscous as olive oil to allow membrane protein to move freely enough to perform their functions without destroying the structure of the membrane. This dynamic arrangement of phospholipid and protein is referred to as the fluid mosaic model.

Ultra-structure: Membrane

Act as selective barrier through which materials can transport Selective permeability Can produce certain enzymes to break nutrients and produce energy Sometimes the pigments and enzymes of photosynthetic bacteria found in plasma membrane Function of plasma membrane

Flagella -long, filamentous appendages -used for motility Arrangements: a. monotrichous: one on one end b. amphitrichous: one or more on each end c. lophotrichous: two or more on one end d. peritrichous: all over cell

Ultra-structure of Flagella

Flagella Three basic structuere a. filament:  -made up of chains of flagellin protein form helix surrounding a hollow core  -sticks out beyond plasma membrane and cell wall b. hook:  Filament is attached to a wider structure called hook  -provides rotational movement of flagella  -solid, composed of hook protein c. basal body: -rod and disc structure -anchors flagellum to cell wall and plasmamembrane

Pili and Fimbrae  Pili are short, straight and thinner than flagella  composed of pilin protein  Used for attachment rather than movement  Fimbriae: 1.Evenly distributed 2.Adhere with any surfaces even cell 3.Few to several hundreds per cell

Cytoplasm the substance inside the plasma membrane ~80% water Contains proteins (enzymes), carbohydrates, lipids, ions includes some solid structures: 1.nucleoid, 2.ribosomes 3.Inclusions Nuclear Area / Nucleoid Single long double strand DNA in the bacterial chromosome Carry cells genetic info of cell 20% of cell volume is occupied by DNA

Prokaryotic ribosome -site of protein synthesis -composed of rRNA and protein -consist of 2 subunits: 30s + 50s = 70s prokaryotic ribosome 30s = one molecule of rRNA 50s=two molecule of rRNA

Endospore Produced under unfavorable condition formed by some Gram + bacilli (e.g Clostridium & Bacillus species) Exception Gram – bacteria Coxiella burnetii Endospore 1.dehydrated, thick wall structure 2. resistant to heat, toxins, radiation, etc 3.Formation of endospore process called sporulation 4.endospores can remain dormant for thousands of years 5.upon return of favorable conditions, endospores germinate into vegetative cells

Division of Prokaryotic cells

Binary Fission 1. Binary fission means formation of two from one 2. In adequate nutrition and favorable environment, cells gather nutrient material and elongate The DNA replicates and divides into two copies The cytoplasmic content divides into two equal parts by formation of septum Formation of cell wall in the daughter cell completes binary fission