Exam 1: Bacterial Cell Structures Flashcards
What are the 2 classes of cell envelope?
Gram-positive and gram-negative
What is the classification of the cell envelope based on?
The ability of a species to retain a crystal violet-iodine stain when treated with organic solvents
What does the staining property of the cell envelope depend on?
The morphology and composition of the bacterial envelope
What is the gram-positive envelope structure?
Cell membrane: phospholipid bilayer similar to eukaryotic membranes
Cell wall: located outside cell membrane. Thick peptidoglycan layer
What is the gram-negative envelope structure?
Inner membrane: phospholipid bilayer similar to gram-positive cell membrane and eukaryotic membranes
Cell wall: peptidoglycan layer that is much thinner that gram-positive cell wall
Outer membrane: inner leaflet is phospholipid, but outer leaflet is a unique bacterial structure- lipopolysaccharide
Look at photo with differences between gram negative and gram positive
Look at photo with differences between gram negative and gram positive
What occurs due to gram-positive bacteria having a thicker cell wall?
They have an increased resistance to mechanical, heat or drying damage
What occurs due to gram-negative bacteria having the presence of the outer membrane?
The envelope is more impermeable, especially to hydrophilic compounds
What does the more impermeable membrane of gram-negative do?
Makes the bacteria less susceptible to many toxic compounds
What is periplasm?
An extra compartment between the inner and outer membranes of gram-negative bacteria
How much of the cell volume is periplasmic compartment?
20-40%
What does the periplasmic compartment contain?
The cell wall and a gel-like solution of proteins that facilitate nutrition and inactivate toxic compounds
What does the periplasmic space allow?
Concentration of detoxifying enzymes
In gram-positive bacteria, where are the detoxifying antibodies secreted?
Into surrounding membrane
What is the cell membrane?
An osmotic barrier modified by the presence of specific transport systems
What makes up the cell membrane?
Phospholipid bilayers that lacks sterols
Embedded membrane proteins
What are the embedded membrane proteins?
Specific transport systems for secretion and uptake
Macromolecular synthesis/secretion proteins, such as cell wall Metabolic proteins: electron transport system
What is the cell membrane the site of?
Action of some disinfectants and detergents
What does peptidoglycan (cell wall) do?
Imparts cell shape and allows bacteria to survive in hypotonic solution
What is peptidoglycan?
The basic layer just outside the cell membrane in all eubcteria except Mycoplasma
What is peptidoglycan composed of?
A complex polymer forming concentric sheets
Is peptidoglycan thicker in gram-positive or gram-negative?
Gram-positive
What is peptidoglycan the site of action for?
Lysozyme and lysostaphin
What is a special component of gram-positive cell walls?
Teichoic/lipoteichoic acids
Describe teichoic/lipoteichoic acids
Attached to peptidoglycan or anchored in the cytoplasmic membrane
Can account for up to half of cell wall mass
Species-specific structure
Composed of sugar backbone with side groups
Highly antigenic and useful as taxonomic markers
What are the 3 parts to peptidoglycan?
Backbone: alternating NAG and NAM monomers
Side chains: tetrapeptides attached to NAM
Crosslinkages: Linked side chains from peptides from different backbone units
What are the tetrapeptides attached to NAM?
D-alanine, L-alanine, D-glutamic acid, and L-lysine
What are crosslinkages the site of?
Penicillin action
How are gram-negative side chains linked?
Directly by interpeptide bonds
What are side chains like in many gram-positive bacteria?
They are crosslinked by an interpeptide bridge of amino acids
What do lipoproteins do?
Attach cell wall to outer membrane of gram-negative bacteria
What do the outer membrane proteins include of gram-negative bacteria?
Porins that allow nutrients to pass through
Many proteins involved in host-pathogen interaction
What is the inner leaflet of gram-negative bacteria made of?
Phospholipids
What is lipopolysaccharide?
Highly antigenic, species-specific and sometimes subspecies-specific structure
What does LPS induce?
A toxic response in mammals when release from lysed cells; hence it is also referred to as endotoxin
What are the 3 components of the unique bacterial structure of LPS?
Lipid A Core oligosaccharide O polysaccharide (O side chain or O antigen)
What is lipid A?
Hydrophobic portion that interacts with phospholipids inner leaflet
This is the toxic portion of LPS
What is core oligosaccharide?
Short CHO chain attached to lipid A
What is O polysaccharide?
Long hydrophilic CHO chain attached to core oligosaccharide that covers the bacterial surface
This is thee antigenic and serotype-specific structure of LPS
Where are capsules or slime layers?
Located outside the cell wall or outer membrane
What are capsules or slime layers?
Amorphous CHO polymers that vary widely from species to species in sugar composition and structure; often highly species or subspecies specific
What is the slime layer, more specifically?
The polymer that is loosely associated and continuously shed
What is the antigen involved with capsules?
K antigen
What are capsules and slime layers useful in? Why?
Serotyping and as vaccine antigens
They are immunogenic
What do capsules proivde?
An extra layer of protection for some bacteria by preventing lysosomal enzyme hydrolysis or complement-mediated lysis
In some bacteria, what can capsules serve as?
Adhesins, allowing adherence to epithelial surfaces
How are some capsules produced?
Only under certain conditions including in vivo
In some bacteria, what are capsules highly similar to?
The O polysaccharide
Describe the structure of Mycobacterium spp.
Gram-positive cell envelope structure, but cell wall contains mycolic acid and a large amount of lipids, which are complex, long-chain hydrocarbons substituted with sugars and other modifying groups
What does the acid-fast bacterial cell wall serve as?
A waxy, protective cover making them nearly impervious to many harsh chemicals
What do acid-fast bacterial cell walls prevent?
Penetration of gram stain reagents unless bacteria are pretreated with heat or a detergent
Why are acid-fast bacteria very slow growing?
The waxy coat causes slow uptake of nutrients
What is S layer?
Present on some fish pathogens
Located outside the cell wall or outer membrane
Describe S layer
Outer layer of protein subunits arranged in a crystalline array; usually a single king of protein molecule capable of self assembly
Resistant to proteolystic enxymes and protein-denaturing agents
Helps protect against phagocytosis and may participate in adherence to surfaces
What does the chlamydia cell envelope resemble?
The gram-negative envelope except they have no peptidoglycan layer
What does Chlamydia have instead of peptide crosslinkages?
A network of disulfied bonds among envelope proteins imparts rigidity to the chlamydial cell envelope
Describe Mycoplasma
Lack peptidoglycan cells wall; therefore, they are susceptible to osmotic lysis
What does the cytoplasm consist of?
A basic-staining, densely packed granular region surrounding an amorphous, less dense nuclear region
What is a chromosome?
Naked DNA
What is DNA of bacteria like?
Usually a circular, covalently closed double-stranded molecule
How many base pairs are in an E. coli chromosome? Protein coding genes?
4.6 million
4288
How does a chromosome fit inside the bacteria cell?
It is highly supercoiled
What is a plasmid?
Smaller, accessory DNA molecules that replicated independently of the chromosome
What can plasmids sometimes be transferred between?
Bacterial cells
What do plasmids often carry?
Genes that confer a selective advantage under certain conditions (antibiotic resistance genes)
What are ribosomes?
Protein translation machinery
What gives the cytosol the granular appearance?
Dense packing of ribosomes
What is the structure of prokaryotic ribosomes?
70S, which can be dissociated into 50S and 30S subunits
What is used for classification of ribosomes?
16S
What is a polysome?
More than one ribosome can attach to a single mRNA strand
What is the target of several antibiotic classes?
Ribosomes
What allows ribosomes to be the target of several antibiotic classes?
The structural differences between prokaryotic and eukaryotic ribosomes
What is flagellum?
Organ of bacterial locomotion
Helical filament that is driven by a motor at its base
How does flagella rotate?
Relative to the bacterial surface to propel bacteria through the medium
What is the bacterial flagella like compared to eukaryotic flagella?
Bacteria is more rigid. Motion is by rotation only
What is monotrichous flagellum?
Has a single, polar flagellum (Vibrio cholerae)
What is peritrichous flagellum?
Has multiple flagella over their surface (E. coli)
What are the 3 parts of flagellum?
Filament
Hook
Basal body
What is the filament of flagellum?
Long, helical outermost structure extending into medium
Composed of several thousand copies of a single protein called flagellin
What are flagellins?
Highly antigenic proteins that have high immunologic specificity for H antigens
What does the hook do?
Connects filament to basal body
What does the basal body do?
Anchors in membrane, flagellar motor
What is the basal body driven by?
Protonmotive force (membrane potential)
What are attachment pili or fimbriae?
Organelles of attachment to surfaces
Hair-like projections extending from cell membrane
How many attachment pili/fimbriae does typical E. coli have?
100 to 300
What is attachment pili/fimbriae composed of?
Structural proteins called pilins and adhesin proteins at tip
What do adhesin proteins do?
Mediate attachment and exhibit remarkable specificity
Often are important virulence factors mediating attachment to host cell or extracellular matrix
What are the fimbriae of different bacteria like?
Antigenically distinct, so specific host antibodies can block attachment
What is conjugative pili?
Specialized organelles of plasmid DNA during conjugation (bacterial mating)
Hollow tube connective 2 bacteria through which DNA is transferred
What can happen with antimicrobial resistance with a conjugative pili?
It can move from one bacteria to another
Describe endospores
Resting stag with high resistance to heat
They are dehydrated cells composed of 5-15% calcium dipicolinate covered by keratin-like protein
Extremely low metabolic activity, can survive for years in this state
What is the most resistance form of life known?
Endospores
What are L-forms?
A bacteria that lack a cell was the occurs spontaneously
Where may L-forms occur?
In vivo
What may L-forms be associated with?
Antibiotic resistance
What can induce formation of L-forms?
Special media with high osmolarity
