Microbiology Chapter 3

Gram + vs gram -

Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.

Ether Link (Archaea)

All archaeal phospholipids replace the ester link between glycerol and fatty acid with an ether link. Ethers are much more stable than esters, which hydrolyze easily in water.

Flagellum

A helical protein filament whose rotary motor propels the cell in search of a more favorable environment.

Lipopolysaccharide (LPS)

Molecule that makes up the outer layer of the outer membrane of Gram-negative bacteria. a class of lipids attached to long polysaccharides (sugar chains).

Chemotaxis

Most flagellated cells have an elaborate sensory system for taxis, the ability to swim toward favorable environments (attractant signals, such as nutrients) and away from inferior environments (repellent signals, such as waste products).

Hoponoids (Bacteria)

Like cholesterol, hopanoids fit between the fatty acid side chains of membranes and limit their motion, thus stiffening the membrane.

Gram negative cell envelope (E. Coli)

(cell) Inner Membrane-composed of phospholipids, transporter proteins, and other molecules. Cell wall- in periplasm a fortress-like structure composed of sugar chains linked covalently by peptides (peptidoglycan). The cell wall forms a single molecule that surrounds the cell. Outer membrane- made of phospholipids and LPS

Polar aging

Bacterial cell poles differ in their origin and "age". One pole arises from the septum of the parental cell, whereas the other pole arises from a parental pole.

peptidoglycan

Cell wall of prokaryotes, but NOT ARCHAEA. Made of a sugar polymer and polypeptide. The bacterial cell wall consists of peptidoglycan. Peptidoglycan is synonymous with murein ("wall molecule"). The molecule consists of parallel polymers of disaccharides called glycan chains crosslinked with peptides of four amino acids. long chains of peptidoglycan consist of repeating units of a disaccharide composed of N-acetylglucosamine (an amino sugar derivative) and N-acetylmuramic acid.

Flagella

Flagella are helical propellers that drive the cell forward like the motor of a boat. A motor driven by the cell's transmembrane proton current—the same proton potential that drives the membrane-embedded ATP synthase. The flagellar motor is embedded in the layers of the cell envelope. The motor possesses an axle and rotary parts, all composed of specific proteins.

Firmicutes (Gram-positive)

Have a thick cell wall with 3-20 layers of peptidoglycan, interpenetrated by teichoic acids. The phylum Firmicutes consists of Gram-positive species such as Bacillus thuringiensis and Streptococcus pyogenes, the cause of strep throat.

Proteobacteria (Gram-negative)

Have a thin cell wall with one or two layers of peptidoglycan, enclosed by an outer membrane. The phylum Proteobacteria consists of Gram-negative species such as Escherichia coli and nitrogen-fixing Sinorhizobium meliloti.

Domains

In a bacterial cell the DNA is organized in loops called domains. The DNA domains extend throughout the cytoplasm.

Mycobacteria

Of the phylum Actinomycetes have a complex multilayered envelope that includes defensive structures such as mycolic acids. Examples include Mycobacterium tuberculosis, the cause of tuberculosis, and M. leprae, the cause of leprosy

septation

Replication of the DNA termination site triggers growth of the dividing partition of the envelope, called the septum. The septum grows inward from the sides of the cell, at last constricting and sealing off the two daughter cells.

Pilli

Short, hair-like protein structures used to help bacteria adhere to host cells; also used to transfer genetic material from one bacterium to another

Firmicute Cell Envelope—Gram-Positive

TEICHOIC Acids- The multiple layers of peptidoglycan are reinforced by teichoic acids threaded through its multiple layers. Teichoic acids are chains of phosphodiester-linked glycerol or ribitol, with sugars or amino acids linked to the middle -OH groups.

Proteobacterial Cell Envelope— Gram-Negative

The envelope includes one or two layers of peptidoglycan covered by an outer membrane. The Gram-negative outer membrane confers defensive abilities and toxigenic properties on many pathogens, such as Salmonella species and enterohemorrhagic E. coli (strains that cause hemorrhaging of the colon).

lipid A (gram -)

The membrane-embedded anchor of LPS. It extends to an O antigen or O polysaccharide, a chain of as many as 200 sugars. The O polysaccharide may be longer than the cell itself. These chains of sugars form a layer that helps bacteria resist phagocytosis by white blood cells.

Murein lipoprotein (gram -)

The outer membrane's inward-facing leaflet includes lipoproteins that connect the outer membrane to the peptide bridges of the cell wall.

lipopolysaccharide (LPS) gram -

The outward-facing leaflet of the outer membrane has very different lipids from the inner leaflet. LPS is of crucial medical importance because it acts as an endotoxin. An endotoxin is a cell component that is harmless as long as the pathogen remains intact; but when released by a lysed cell, endotoxin overstimulates host defenses.

Periplasm (gram -)

The region between the inner and outer membranes of Gram-negative cells, including the cell wall, defines a separate membrane-enclosed compartment of the cell known as the periplasm. The periplasm contains specific enzymes and nutrient transporters not found within the cytoplasm, such as periplasmic transporters for sugars, amino acids, or other nutrients. Periplasmic proteins are subjected to fluctuations in pH and salt concentration,

Shared Traits among most bacteria

Thick, complex outer envelope. Compact genome. Tightly coordinated functions.

Counter- Clockwise direction (CCW)

When a cell is swimming toward an attractant chemical, the flagella rotate counterclockwise (CCW), enabling the cell to swim smoothly for a long stretch.

Clockwise direction (CW)

When the cell veers away from the attractant, receptors send a signal that allows one or more flagella to switch, against the twist of the helix. The cell to tumble briefly and end up pointed in a RANDOM direction.

DNA replication (binary fission)

Within the cell, replication proceeds outward in both directions around the genome. Thus, bidirectional replication requires two replisomes, one for each replicating fork. Fluorescent probes show that two replisomes are located near the middle of the growing cell. Each replisome forms a replicating fork that directs two daughter strands of DNA toward opposite poles.

Periplasm

a water-filled space containing nutrientbinding proteins and secretion machines

Capsule

composed of polysaccharide and glycoprotein filaments, protects cells from phagocytosis. Either Gram-positive or Gram-negative cells may possess a capsule.

Bacterial cytoskeleton

includes proteins that regulate cell size, play a role in determining the rod shape of bacilli, and generate curvature in vibrios.

S-layer

is highly porous but can prevent phagocytosis and protect cells in extreme environments. In archaea, the S-layer serves the structural function of a cell wall.