Structure and identification of the bacterial cell

Eukaryotic cells

numerous membrane bound organelles and simple plasma membrane structure

Prokaryotic cells

few membrane bound organelles and extremely complex membrane/cell wall structure

The nucleoid composition

approximately 60% DNA, 30% RNA 10% protein

The nucleoid location of chromosome

• often central, but DNA is attached at points to the plasma membrane

• Usually 1 per cell (can be more if reproducing rapidly)

How can bacteria access the genes it needs

Nucleoid projections

Nucleoid projections

done in rapidly growing cells; DNA is uncoiled and stretched

How is bacterial DNA coiled and recoiled

DNA gyrase and Topoisomerase IV

DNA gyrase

Introduces negative supercoils with double strand this relaxes positive supercoils

Topoisomerase IV

also relaxes supercoils and separates chromosomes during replication

Plasmids

• small, closed, circular DNA molecules

• exist and replicate independently of chromosome

• Not required for growth and reproduction

• May carry genes that confer selective advantage

• Can be laterally transferred

Bacterial cytosol

-no bacteria or ER

-inclusion bodies: storage for organic and inorganic materials

-proteins highly organized

-granular appearance

Where does oxidative phosphorylation, DNA transcription, and translation all occur near the

Plasma membrane

Ribosomes

-sites of protein synthesis

-Translate mRNA protein (export proteins and cellular proteins)

Ribosomes are comprised of 2 subunits

-large (50S) subunit: 5S rRNA+ 23S rRNA+ proteins

-small (30S) subunit: 16S rRNA+ proteins

Prokaryotic membranes use

hopanoids

Eukaryotic membranes use cholesterol

Cell Wall

provides shape, protects the cell from osmotic lysis, may contribute to pathogenicity, may protect the bacteria from toxic substances, consists of peptidoglycan (synthesis inhibited by penicillin and other antibiotics)

Peptidoglycan structure

polysaccharide formed from peptidoglycan subunits, backbone alternating sugars (NAG and NAM), muramic acid residues covalently crosslink with each other

Grm + cell wall picture

Grm- cell wall picture

Grm + cell wall

composed primarily of peptidoglycan and contains large amounts of teichonic acids

Grm - cell wall

-thin layer of peptidoglycan surrounded by an outer membrane

-outer membrane is more permeable than plasma due to porins and transporters

outer membrane of a grm - cell wall

lipids, lipoproteins, and lipopolysaccharide; no teichoic acids

porins

water soluble channels; nutrients can’t pass; water soluble antibiotics can pass

LPS

-embedded in the outer membrane

-three parts: lipid A, core polysaccharide, O side chain

-involved in resisting the immune response

-extremely toxic

O antigen

-protection against host defenses

-blocks lyzozyme activity

-interferes with antibody response

-lots of variability

-adheres to host tissues

core polysaccharide

contributes to negative charge on cell surface, harder for immune cells to phagocytose

Lipid A

pro inflammatory; helps stabilize outer membrane structure, can act as an endotoxin

Periplasmic Space

-plasma membrane and cell wall (Gm+) or plasma membrane and outer membrane (Gm-)

-filled with periplasm

Periplasmic enzymes

nutrient acquisition, bind sugars and amino acids, electron transport, peptidoglycan synthesis, modification of toxic compounds, inactivation of antibiotics

cocci

spheres

Diplococci

pairs

Streptococci

chains

Staphylococci

grape like clusters

bacilli

rods

coccobacilli

very short rods

vibrios

curved rods

mycelium

network of long, multinucleate filaments

spirilla

rigid helices

spirochetes

flexible helices

pleomorphic

organisms that are variable in shape

Gram staining

-most widely used differential staining procedure

-divides bacteria into two groups

Atypicals on a gram stain

-usually colorless at the end

-unique cell wall

Why gram positive is purple

-involve the constriction of the thick peptidoglycan layer

-constriction prevents loss of crystal violet/ iodine complexes during decolorization step

why gram negative is pink

-thinner peptidoglycan layer of gram negative bacteria does not prevent loss of crystal violet