Prokaryotic cells

Cells with no membrane bound nucleus or organelles

• Similarities to eukaryotic cells– contain cell membranes that are lipid bilayers

– Both have DNA that encode genetic information

• DifferencesStructural – eukaryotes have membrane bound organelles and nucleus

Prokaryotic cells lack these

• Chemicalcell wall of bacteria contains

peptidoglycan

ribosomes are comprised of distinct subunits

• Size – Generally eukaryotes are 10 X larger than

prokaryotes.– Why is this important?• Small cells have larger surface to volume ratio – greater

contact with the environment therefore nutrients can enter and be distributed faster.• cells can be simpler and grow faster• Exception:

• Shapes:

• Round cocci• Rod bacilli• Spiral spirilla

Cocci may form chains tetrads or clusters depending upon the plane of division

Bacterial envelope

• Plasma membrane• Cell wall • Outer membrane

Gram negative bacteria have all 3 layersGram positive bacteria lack the outer

membrane

Bacterial envelope

• Plasma membrane

Regulates what enters and exits a bacteria

More protein in bacteria membranes than in eukaryotic membranes No mitochondria are present therefore ATP is generated by enzymes located on the cell membrane

No sterols in bacterial membrane

• Cell wall – Forms a chain mail like covering over the bacteria– Made up of peptidoglycan• Peptide units are made up of 4 amino acids and differ

between species• Glycan units are made of alternating chains of

N acetylglucosamine and N acetylmuramic acid

• Cell wall– Function is to provide shape and support • Some bacteria have turgor pressures of 350 lbs/square

inch• All bacteria have cell walls except a group of bacteria

called mycoplasmas. – Mycoplasmas are isotonic to their environment – – Antibiotics can damage some bacteria turning them into

L-forms – they lose their ability to make cell walls.

Mycoplasma pneumonia causes “ walking pneumonia”

• Differences in cell wall of GN and GP bacteria– Gram negative bacteria are 1 layer thick– Gram positive bacteria are many layer thick and

contain techoic acid • Techoic acids may function as passage ways for moving

ions inside and outside of cell – involve in structural integrity

Gram positive envelope

• Outer membrane – Gram negative bacteria only– Consists of a bi layer• Inner layer is phospholipid• Outer layer is lipopolysaccharide

– Act as barriers to polar as well as nonpolar molecules– Only H2O and gasses pass through this membrane

• How do nutrients get into gram negative cell?– PORINS – small pores in membrane formed by

proteins• Porins are embedded in membrane and act as

transport molecules

• LPS is known as endotoxin • LPS is toxic and highly reactive to humans

causing fever and vasodilation

• Some bacteria have a polysaccharide capsule which surrounds the bacteria

• Function – Protection against moisture loss– To adhere to surfaces for growth– Agent of pathogenicity – protects bacteria against

phagocytosis by host cells

• How do bacterial cells enlarge?• They produce enzymes called autolysins that

break the cross linking peptide bonds• New peptidoglycan units attach and enzymes

called transpeptidases reseal the breaks

• Why is this important??• Penicillin binds to transpeptidase enzymes

preventing resealing of the peptidoglycan during growth. The cell wall never reforms. Penicillin is effective against actively growing bacteria.

Bacterial appendagesPili made of proteins called pilin

Function: adhesion sex pilus- attaches during bacterial

sexresponsible for the specificity of

some pathogenic bacteria to certain host cells

if pili are destroyed, bacterial are no longer pathogenic

All Gram negative bacteria have pili, many gram positive bacteria do not

Bacterial appendageFlagella

function: locomotion by rotationstructure: 3 parts

filament hookBasal body

Arrangements of flagella:

Monotrichous

Lophotrichous

Amphitrichous

Peritrichous

• Flagella allow for movement in response to a stimulus

chemotaxisaerotaxisphototaxismagnetotaxis

• Spirochetes have axial filaments – do not extend outside of their body

– Allows movement like a corkscrew– Move best in viscous fluids