Microbiology: an evolving science Chapter 3

holdfasts

Secreted by the tip of stalks for adhesion

Chemotaxis

the movement of a bacterium in response to chemical gradients.

In bacteria that appear superficially symmetrical, polar differences may appear at cell division

-Bacillus species can undergo an asymmetrical cell division to form an endospore at one end. -Other bacteria expand their cells by extending one pole only

Attractants cause CCW rotation

-Flagella bundle together - Push cell forward - "Run"

Repellents cause CW rotation

-Flagellar bundle falls apart - "Tumble" = bacterium briefly stops, then changes direction

flagellin

Each flagellum is a spiral filament of protein monomers

Storage granules

Glycogen, PHB, and PHA, for energy Sulfur, for oxidation

lipoprotein

Inward-facing leaflet

Cell wall

covers the cell membrane

RNA polymerase transcribes DNA into a single strand of RNA. For most genes, it is messenger RNA. mRNA immediately binds to a ribosome for translation into a polypeptide.

This is aided by transfer RNA (tRNA), which brings the amino acids to the ribosome. In prokaryotes, translation is tightly coupled to transcription.

Eukaryotic microbes possess their own structures to avoid osmotic shock examples being:

-Algae form cell walls of cellulose -Fungi form cell walls of chitin -Diatoms form exoskeletons of silicate

How do prokaryotes protect their cell membrane?

-For most species, the cell envelope includes at least one structural supporting layer -The most common structural support is the cell wall -bacteria has peptidoglycan -Nevertheless, a few prokaryotes, such as the mycoplasmas, have a cell membrane with no outer layers

Shape-determining proteins

-FtsZ = forms a "Z-ring" in spherical cells, cocci -MreB = forms a coil inside rod-shaped cells, baccili -CreS "crescentin" = forms a polymer along the inner side of crescent-shaped bacteria, crescent

Capsule

-Made of polysaccharide and glycoprotein -Protects cells from phagocytosis -Found also in Gram-negative cells

Magnetosomes

-Membrane-embedded crystals of magnetite, Fe3O4 -Orient the swimming of magnetotactic bacteria -Work like compasses, orients them on a plane so they know which way is up and which way is down

Different types of strains can be used for genetic analysis:

-Mutant strains that are selected for loss of a given function -Strains that are intentionally mutated as to lose or alter a gene -Strains that are constructed with "reporter genes" fused to a gene encoding a protein of interest -The phenotype of the mutant cell may yield clues about the function of the altered part

Membrane proteins serve numerous functions, including:

-Structural support -Detection of environmental signals -Secretion of virulence factors and communication signals -Ion transport and energy storage

Chemotaxis

-The alternating runs and tumbles cause a "random walk." -Receptors detect attractant concentrations -Sugars, amino acids -Attractant concentration increases and prolongs run -This is termed a "biased random walk" -Causes a net movement of bacteria toward attractants (or away from repellents)

ultracentrifuge

-The high rotation rate produces centrifugal forces strong enough to separate particles by size. -Parts are then subjected for structural and biochemical analysis.

cell membrane

-The structure that defines the existence of a cell -(fixed) proteins embedded in phospholipid bilayer, make up about 50% of the cell membrane

peptidoglycan is unique to bacteria

-Thus, the enzymes responsible for its biosynthesis make excellent targets for antibiotics -Penicillin inhibits the transpeptidase that cross-links the peptides -Unfortunately, the widespread use of such antibiotics selects for evolution of resistant strains

replisome

At each fork, DNA is synthesized by DNA polymerase with the help of accessory proteins

Polar aging

Bacterial cell poles differ in their origin and "age"

Cell fractionation (isolation technique)

Cells must be broken up by techniques that allow subcellular parts to remain intact. Examples of such techniques include: -Mild detergent analysis -Sonication -Enzymes (lysozyme) -Mechanical disruption (harshest)

S-layer

FORCEFIELD AROUND CELL -An additional protective layer commonly found in free-living bacteria and archaea -Crystalline layer of thick subunits consisting of protein or glycoprotein -May contribute to cell shape and help protect the cellfrom osmotic stress

Archaea, like bacteria, are prokaryotes

Have unique membrane and envelope structures No Nucleus!

Flagella

How prokaryotes that are motile generally swim

peptidoglycan consists of:

Long polymers of TWO DISACCHARIDES called N-acetylglucosamine and N-acetylmuramic acid, bound to a peptide of FOUR TO SIX AMINO ACIDS The peptides can form cross-bridges connecting the parallel glycan strands

The filament is rotated by a motor driven by the proton motive force.

Note: flagella rotate either clockwise (CW) or counterclockwise (CCW) relative to the cell.

The spatial orientation of septation has a key role in determining the shape and arrangement of cocci.

Parallel planes Streptococci Random planes Staphylococci Perpendicular planes Tetrads

diffusion

Small uncharged molecules, such as O2 and CO2, easily permeate the membrane

What locks the protein in the membrane

The hydrophilic and hydrophobic regions

Replication of the termination site triggers growth of the dividing partition, or septum.

The septum grows inward, at last constricting and sealing off the two daughter cells.

Gram negative outer membrane

The thin peptidoglycan layer consists of one or two sheets -confers defensive abilities and toxigenic properties on many pathogens

leaflets

The two layers of phospholipids in the bilayer

Most bacteria share fundamental traits:

Thick, complex outer envelope Compact genome Tightly coordinated cell functions (gene expression)

In prokaryotes, a circular chromosome begins to replicate at its origin, or ori site.

Two replications forks are generated, which proceed outward in both directions.

Osmosis

Water tends to diffuse across the membrane in this process

Cytoplasm

consists of a gel-like network, the inside of the cell

A phospholipid

consists of glycerol with ester links to two fatty acids and a phosphoryl head group -May have side chain

two types of selective transport

diffusion and osmosis

Cell membrane

encloses the cytoplasm, phospholipid bilayer

Membranes have approximately _______ parts (by weight) of phospholipids and proteins.

equal

Thylakoids

extensively folded intracellular membranes

Flagellum

external helical filament whose rotary motor propels the cell

An approach that is complementary to cell fractionation is

genetic analysis

Bacteria

has peptidoglycan

Nanotubes

intercellular connections that pass material from one cell to the next.

Stalks

membrane-embedded extensions of the cytoplasm.

Active transport

molecules move against their concentration gradient, from low concentration gradient to high, -REQUIRES ENERGY

Passive transport

molecules move along their concentration gradient, from high concentration gradient to low

Nucleoid

non-membrane-bound area of the cytoplasm that contains the chromosome in the form of looped coils

lipopolysaccharides

outward-facing leaflet

Most bacterial cell walls are made up _______

peptidoglycan (or murein)

Carboxysomes

polyhedral bodies packed with the enzyme Rubisco for CO2 fixation

Cell division, or cell fission, requires highly coordinated growth and expansion of all the cell's parts. Unlike eukaryotes, prokaryotes synthesize RNA and proteins continually while the cell's DNA undergoes replication.

prokaryotes synthesize RNA and proteins continually while the cell's DNA undergoes replication.

Paramecia possess a to contractile vacuole to:

pump water out of the cell

Pili or fimbriae

straight filaments of pilin protein. Used in attachment

Has multiple layers of peptidoglycan Threaded by

teichoic acids (Keeps peptidoglycan together)

Gram-positive bacteria

thick cell wall Example: the phylum Firmicutes

Gram-negative bacteria

thin cell wall Example: the phylum Proteobacteria

Gas vesicles

to increase buoyancy

Polar molecules and charged molecules require transport through ________

transporters

A key tool of subcellular fractionation is

ultracentrifuge

sex pili

used for conjugation