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