Chapter 4

Prokaryotic organisms

Prokaryotic cell

Includes bacteria and archaea Thousands of species of bacteria differ by

morphology (shape), chemical composition, nutritional requirements, biochemical activities, and sources of energy

Bacteria divide by binary fission (asexual reproduction)

Size, shape, and arrangement

Most bacteria range in size between 0.2 micrometers (microns) to 2.0 microns

The basic shapes are cocci, bacilli, and spirilla

Cocci may occur in pairs (diplococci), in chains (streptococci), and in clusters (staphylococci)

Bacilli may appear as single rods, diplobacilli, streptobacilli, or coccobacilli

Other shapes

Spiral bacteria have one or more twists Curved rods (comma shaped) are vibrios Others called spirilla are corkscrew shaped and

move with whip-like appendages called flagella Spirochetes are helical and flexible and move by

axial filaments Most bacteria maintain a single shape and are

monomorphic, but some may have more than one shape and are pleomorphic

Structures external to cell wall

Glycocalyx means sugar coat, and is a sticky, gelatinous polymer that is outside the cell wall

If the glycocalyx is firmly attached to cell wall and is organized it is called a capsule

If the glycocalyx is unorganized and loosely attached it is called a slime layer

Streptococcus pneumoniae, Haemophilus influenzae, Bacillus anthracis have them

Flagella

These are long, filamentous appendages that help bacteria move (motile)

No flagella is called atrichous A single polar flagellum is monotrichous A tuft of flagella at each end is amphitrichous Two or more at one (or both) ends is

lophotrichous Flagella all over is peritrichous

Flagella

The flagellum has 3 basic parts: filament is the long, outermost region; a hook attaches to the filament; the basal body, which anchors the flagellum to the cell wall and plasma membrane

The basal body is a small central rod inserted into a series of rings

In gram negative bacteria, there are two pair of rings In gram positive bacteria, only the inner pair is

present

Motility

Bacteria have a ‘run and tumble’ movement thanks to flagella

A bacterium with flagella can move quickly toward or away from a stimulus

Bacteria moving toward chemical stimulus is positive chemotaxis

Bacteria moving away is negative chemotaxis Moving in response to light is phototaxis

Axial Filaments

Spirochetes are unique in structure and motility

Treponema pallidium causes syphilis, Borrelia burgdorferi causes Lyme disease

Spirochetes move by axial filaments, which spiral around the cell and cause a corkscrew like movement

Fimbriae and Pili

Many gram negative bacteria contain shorter hairlike appendages called fimbriae and pili

These are used for attachment and transfer of DNA

Fimbriae help cell stick to surfaces (Neisseria gonorrhoeae)

Pili (sex pili or conjugation pili) help cells transfer DNA in conjugation

Cell Wall

Helps maintain shape of the cell Keeps cell from rupturing Contributes to ability to cause disease Is the site of action of some antibiotics Helps tell differences in major types of

bacteria

Composition

Contains peptidoglycan which consists of repeating disaccharides attached by polypeptides that forms a lattice

Disaccharide portion has monosaccharides called N-acetyl glucosamine (NAG) and N-acetylmuramic acid (NAM)

Alternating NAG and NAM are linked to form a backbone, and adjacent rows are linked by polypeptides

Difference between gram positive and negative cells

Gram negative have an outer membrane

Gram positive cells do not have an outer membrane, so the peptidoglycan is exposed and more easily destroyed by antibiotics like penicillin

Gram negative vs. Gram positive

Gram positive cell wall has thick peptidoglycan

Gram negative has a thin layer Gram positive cell has teichoic acids which

help bind and regulate movement of cations in/out of the cells

Teichoic acids may also provide antigenic specificity which makes it easier to ID bacteria

Gram negative cells

Have thin layer of peptidoglycan and an outer membrane

The outer membrane (OM) has lipopolysaccharide (LPS), lipoprotein, and phospholipid

It has a negative charge which helps the bacteria avoid phagocytosis and complement (both are host defenses)

Gram negative OM

It also is a barrier to antibiotics, enzymes, etc. Has porins (proteins) which allow passage of

some material in and out LPS component has an O polysaccharide

portion and a lipid portion (lipid A) The O polysaccharide is an antigen and is

used to help ID the bacteria The Lipid A is a toxin (endotoxin) that can

cause fever and shock (endotoxin shock)

Atypical cells

Mycoplasma has no cell wall (causes walking pneumonia), but do have sterols to protect against rupture

Acid Fast Cell Walls- Mycobacterium and Nocardia have mycolic acid in cell wall, which causes these bacteria to clump and stick together.

Damage to cell wall by lysozyme causes either a spheroplast (gram negative) or a protoplast (gram positive)

Cell or Plasma Membrane

Encloses the cytoplasm Made of phospholipids (bilayer), proteins,

glycoprotein, glycolipid Arrangement is phospholipid bilayer Heads (hydrophilic), tails (hydrophobic) Selective permeability ATP production occurs here

Movement across membranes

Passive process-movement from high concentration to low without using ATP

Includes simple diffusion (alka seltzer example)

Facilitated diffusion-requires a protein transporter to allow movement across membrane

Osmosis-movement of water from greater water to less water

Osmosis

Movement produces osmotic pressure-this is the pressure needed to stop the flow of water across the membrane

3 types of osmotic solutions: isotonic-equal solid; no change in cell when placed in this type of solution

Hypotonic=less solid, cell will swell Hypertonic=greater solid; cell will shrink

Inside cell

Cytoplasm is 80% water and contains proteins, carbohydrates, lipids, inorganic ions, and contains the nuclear area, ribosomes, and inclusions

Nuclear area contains loop shaped DNA May have pieces of DNA called plasmids that

carry genes for resistance (resistance factors or R factors)

Inside cell continued

Ribosomes-sites of protein synthesis Contained in eukaryotic cells too, but different

because they are 80 S (Svedberg unit); 40 S + 60 S) Prokaryotic ribosomes are 70 S (30 S + 50 S) Inclusions are extra storage areas including gas

vacuoles, sulfur granules, land lipid inclusions Metachromatic granules -collectively known as

volutin, represents a reserve of inorganic phosphate Magnetosomes-inclusions of iron oxide found in

some gram negatives that act like magnets

Endospores

Form in gram positive rods when essential nutrients are depleted

Endospores are highly durable and can survive extremes of heat, dehydration, and exposure to toxins and radiation

Begin sporulation when a key nutrient becomes scarce

Endospores may remain dormant for years, and will eventually ‘germinate’ and become a vegetative cell again

Shapes, review

Shapes; cocci (spherical), bacilli (rods), vibrio (comma), spirochetes (spring), spirillum (helix)

Arrangements: Staphylo (clusters), strepto (chains), mono (single), diplo (pairs), tetrads (4), sarcina (8), palisade (side by side like a picket fence)

Pleomorphism-variable shapes like Corynebacterium