Bacterial Cell Structure & Function Dr.Qurat-Ul-Ain Department Of Microbiology KEMU,Lahore

Two Basic Types of Cells Prokaryotic Cells (Prokaryotes) Eukaryotic Cells (Eukaryotes) ______________ _____________________

Size of Living Things 1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm 1mm = 1000 µm = 1000000nm 1 µm = 1000nm

Size of Bacteria Average bacteria 0.5 - 2.0 um in diam. RBC is 7.5 um in diam. Surface Area ~12 um^2 Volume is ~4 um Surface Area to Volume is 3:1 Typical Eukaryote Cell SA/Vol is 0.3:1 Food enters through SA, quickly reaches all parts of bacteria Eukaroytes need structures & organelles

Shapes of Bacteria Coccus Bacillus Coccobacillus Vibrio = curved Chain = Streptoccus Cluster = Staphylococcus Bacillus Chain = Streptobacillus Coccobacillus Vibrio = curved Spirillum Spirochete

Bacterial Structures Flagella Pili Capsule Plasma Membrane Cytoplasm Cell Wall Lipopolysaccharid es Teichoic Acids Inclusions Spores

Prokaryotes Cytoplasm: Also known as proto-plasm. Gel-like matrix of water, enzymes, nutrients, wastes, (organic n inorganic solutes) and gases and contains cell structures like numerous ribosomes and polysomes. No ER n memb.bound organelles. Shows signs of internal mobility like cytoplasmic streaming , amoeboid movement and formation and disappearance of vacoules. Location of growth, metabolism, and replication. Granules or inclusions: Bacteria’s way of storing nutrients. Staining of some granules aids in identification. Cytoplasm Granules

Prokaryotes Ribosomes: Small electron dense particles Involved in prt.synthesis 70 S(30 S + 50S) Different from host cell ribosomes in SR. Streptomycin interferes with bacterial metabolism sparing the host cell ribosomes. 3 types of RNAs: Ribosomal, transfer , mRNA Found within cytoplasm or attached to plasma membrane. Ribosomes

Plasma Membrane Separates the cell from its environment. Limits the protoplast Thin n elastic , can be only seen with electron microscope With the exception of mycoplasma , bacterial cytoplasmic memb.lacks sterol. Phospholipid molecules oriented so that hydrophilic,water-loving heads directed outward and hydrophobic ,water-hating tails directed inward. Proteins embedded in two layers of lipids (lipid bilayayer) FUNCTIONS: Semipermeable membrane Housing enzymes for cell wall, outer membrane synthesis, assembly n secretion of extractoplasmic n extracellular substances Generation of ATP Cell motility Mediation of chromosomal segragation during replication Hydrophilic hydrophobic Some materials can move across the membrane, others cannot.

Cell Wall Peptido-glycan Polymer (amino acids + sugars) Unique to bacteria Sugars; NAG & NAM N-acetylglucosamine N-acetymuramic acid D form of Amino acids used not L form Hard to break down D form Amino acids cross link NAG & NAM

Prokaryotes – Cell Wall Peptidoglycan is a huge polymer of interlocking chains of identical peptidoglycan monomers. Provides rigid support while freely permeable to solutes. Backbone of peptidoglycan molecule composed of two derivatives of glucose: - N-acetylglucosamine (NAG) - N-acetlymuramic acid (NAM) NAG / NAM strands are connected by inter- peptide bridges.

Prokaryotes - Cell Wall From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are: Gram Positive Gram Negative positive negative

Prokaryotes - Cell Wall Gram-Positive & Gram-Negative Peptidoglycan makes up as much as 90% of the thick, compact cell wall. Gram-negative More chemically complex and thinner. Peptidoglycan only 5 – 20% of the cell wall. Peptidoglycan not outermost layer, between the plasma membrane and the outer membrane. Outer membrane is similar to the plasma membrane, but is less permeable and composed of lipopolysaccharides (LPS). LPS is a harmful substance classified as an endotoxin, The space between the cell wall and the plasma membrane is called the periplasm.

Q: Why are these differences in cell wall structure so important? Gram-negative bacteria: fewer interpeptide bridges but have an outer membrane made of lipopolysaccharides LPS. Penicillins and cephalosporins interfere with linking of interpeptides, but can’t easily get to in gram- bacteria. Cell walls without enough of these intact cross-links are structurally weak, and disintegrate when cells divide. This is how penicillins and cephalosporins work. Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs. Microorganisms that do not contain peptidoglycan are not susceptible to these drugs.

Teichoic Acids Gram + only Glycerol, Phosphates, & Ribitol Attachment for Phages Participate in MG supply to the cell Antigenic determinant

Lipopolysaccharide (LPS) Endotoxin or Pyrogen Fever causing Toxin nomenclature Endo- part of bacteria Exo- excreted into environment Structure Lipid A Polysaccharide O Antigen of E. coli, Salmonella G- bacteria only Alcohol/Acetone removes primary stain durind gram’s staining.

Chapter 4

LPS (cont’d.) Appearance of Colonies Mucoid = Smooth (lots of LPS or capsule) Dry = Rough (little LPS or capsule) O Antigen of Salmonella and E. coli 2,000 different O Ags of Salmonella 100’s different O Ags of E. coli E. coli O157 O Ags differ in Sugars, not Lipid A

Cytoplasm 80% Water {20% Salts-Proteins) DNA is circular, Haploid Osmotic Shock important DNA is circular, Haploid Advantages of 1N DNA over 2N DNA More efficient; grows quicker Mutations allow adaptation to environment quicker Plasmids; extra circular DNA Antibiotic Resistance No organelles (Mitochondria, Golgi, etc.)

Prokaryotes - Glycocalyx Some bacteria have an additional layer outside of the cell wall called the glycocalyx. This additional layer can come in one of two forms: 1- Glycoproteins loosely associated with the cell wall. - Slime layer causes bacteria to adhere to solid surfaces and helps prevent the cell from drying out. - Streptococcus The slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities). Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque. Slime layer

Prokaryotes - Glycocalyx 2.Polysaccharides firmly attached to the cell wall. Capsules adhere to solid surfaces and to nutrients in the environment. Adhesive power of capsules is a major factor in the initiation of some bacterial diseases. Capsule also protect bacteria from being phagocitized by cells of the hosts immune system. Capsule

Prokaryotes – Surface Appendages Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces. Consist of delicate strands of proteins. Flagella: Long, thin extensions that allow some bacteria to move about freely in aqueous environments. Endoflagella: Wind around bacteria, causing movement in waves. Flagella Axial filaments Fimbria Pili

Flagella Motility - movement Swarming occurs with some bacteria Spread across Petri Dish Proteus species most evident Arrangement basis for classification Monotrichous; 1 flagella Lophotrichous; tuft at one end Amphitrichous; both ends Peritrichous; all around bacteria

Pili Short protein appendages Adhere bacteria to surfaces smaller than flagella Adhere bacteria to surfaces E. coli has numerous types K88, K99, F41, etc. Antibodies to it will block adherence. F-pilus; used in conjugation Exchange of genetic information

Endospores Resistant structure Location important in classification Heat, irradiation, cold Boiling >1 hr still viable Takes time and energy to destroy spores Location important in classification Central, Subterminal, Terminal Bacillus stearothermophilus -spores Used for quality control of heat sterilization equipment Bacillus anthracis - spores Used in biological warfare

Spore Formation This is what happens ………….. Cell

Spore forms in cell

Cell disintegrates

Spore is released

Spore starts to germinate

Spore continues to germinate

Now see as, in suitable conditions, the cell begins to divide (binary fission)………………………….

Prokaryotes – Arrangements of Cells Bacteria sometimes occur in groups, rather than singly. _________ divide along a single axis, seen in pairs or chains. _________ divide on one or more planes, producing cells in: - pairs (diplococci) - chains (streptococci) - packets (sarcinae) - clusters (staphylococci). Size, shape and arrangement of cells often first clues in identification of a bacterium. Many “look-alikes”, so shape and arrangement not enough for id of genus and species. Bacillus Coccus