Prokaryotic cells

• cell membrane

• Cytoplasm

• Ribosomes

• Genetic material

All types of cells have these structures:

Binary fission

How do prokaryotes reproduce

• An area in the centre of the cytoplasm where DNA is kept

• DNA is a single fibril (chromosome)

The nucleoid

• negative regions of DNA associate with Mg2+ ions

• Histone-like proteins

• These allow for folding and coiling of the DNA

How is DNA kept in the nucleoid region

A collection of several structures that allow for protection, transportation, metabolism, and pathogenicity of bacteria

The cell envelope

• cell membrane: plasma or cytoplasmic

• Cell wall: gram + or -

• Capsule: either capsulated or non-capsulated

The layers of the cell envelope

• encloses the cells cytoplasm, defining the cell

• Made of a phospholipid bilayer, proteins, and hopaniods

• Proteins are integral (floating in the bilayer spanning the membrane) or peripheral ( associated with the inner membrane)

The cell membrane

Lipid molecules in the prokaryotic cell membrane that alter fluidity. Similar to sterol in eukaryotic CM’S

Hopanoids

• permeability & transport

• Electron transport & oxidative phosphorylation (ATP production)

• Excretion of hydrolytic exoenzymes and pathogenicity proteins

• Biosynthetic functions (enzymes to form phospholipids and CW)

• Chemotactic systems (receptors of attractants or repellants)

The functions of prokaryotic cell membrane

Types I - type VI, six pathways of protein secretion total

Excretion of hydrolytic exoenzymes and pathogenicity proteins In cell membrane function

• passive (concentration reliant from high to low)

~ simple: no proteins

~ facilitated: needs transport protein

• active: needs energy and transport proteins (low to high conc.)

Passive and active transport in CM

• group translocation: energy needed to phosphorylate a molecule in the transport process which is then used in metabolism

• Special transport: using special molecules like siderophores to transport iron locked in nature as Fe(OH)3

Group translocation and special transport in CM

• a rigid layer that surrounds the cell membrane

• Made of peptidoglycan

• Either gram + or -

The cell wall

• give shape and protect from osmotic lysis

• Protect from toxicities

• Components of the structure can make the cell pathogenic

• Site of action of several antibiotics

Functions of the cell wall

• backbone made of altering sugar derivatives N-acetylglucosamine and N-acetylmuramic acid

• Peptide interbridges in gram + only that link 2 tetrapeptide chains, in gram- its a continuous strand of chains between backbones

• Tetrapeptide side chains that attach to NAM. These contain L-alanine, D-glutamate, diaminopimelic acid (- only) or L-lysine (+ only), and D-alanine

The structure of peptidoglycan in the cell wall

• teichoic acids

• Polysaccharides

Special components of gram + CW’s

2 types: wall and lipo form

• responsible for walls negative charge

• Along with peptidoglycan allow for elasticity, porosity, and tensile strength

• Antigenic properties (EX. Forssman antigen)

• Attachment to host cells in strep

Teichoic acids

In some, these sugars such as mannose, arabinose or glucuronic acid are subunits

Polysaccharides in gram + CW’s

• outer membrane

• Lipopolysaccharide

• Porin channels

• Braun’s lipoprotein

• Periplasmic space

Special components of gram - CW’s

Bilayer structure that contains lipopolysaccharides on the outer layer. Also has porins

Outer membrane of CW in gram -

• located on the outer membrane to prevent entrance of hydrophobic materials

• Made of Glycolipids broken down into lipid A and polysaccharides

• Lipid A can act as endotoxin in some

• The polysaccharides are made of a core and side chain O antigen that is highly variable within species

Lipopolysaccharides on CW of gram -

• allow low molecular weight, hydrophilic molecules to enter

• Large antibiotics are unable to enter, giving gram - resistance to select antibiotics

• Permeability varies widely between species, where pseudomonas aeruginosa is 100 times less permeable than E. coli

Porin channels

Cross links between the outer membrane and peptidoglycan layers

• most abundant protein in gram - cells

• Stabilizes and hold the outer membrane in place

Braun’s lipoprotein

• the space between the inner and outer membranes, peptidoglycan layer and gel-like solution of proteins is in this area

Periplasmic space

• cell wall that contains lots of waxes/mycolic acids

• Cannot be stained with Gram stains

• Permeability lower than E. coli

• Causes the cell to be resistant to many antibiotics and harsh chemicals for killing

Acid-fast bacteria cell wall

• cell wall lacking bacteria that have to peptidoglycan

• Closer genetically to gram +

• Resistant to cell wall inhibiting antibiotics

Mycoplasmas

• lysozymes

• Autolysins hydrolytic enzymes

• Hydrolytic enzymes of higher organisms

Enzymes that attack the cell wall

• Found in human secretions

• Breakdown the peptidoglycan backbone

• In gram - the outer membrane prevents lysozyme entry

Lysozymes & the CW

• secreted by bacteria themselves to catalyze degradation to allow for turnover of peptidoglycan

• Used to grow the CW and in cell separation

• Causes dissolution of dead cells through the process of autolysis

Autolysins hydrolytic enzymes & the CW

• secreted by Ex. Protozoa and phagocytic cells

• Degrade CW and digest whole bacteria

Hydrolytic enzymes of higher organisms & the CW

• extracellular layer made of polymers of polysaccharides

• Also called slime layer or glycocalyx

The capsule

• contributes to invasiveness

• Protects from phagocytosis

• Adherence to host cells

Functions of the capsule