Microbiology - Bacterial Structure, Function, Growth Flashcards
Bacteria do not have:
a nuclear membrane, mitochondria, lysosomes, ERs
Bacterial cell wall:
rigid cell wall external to the cytoplasmic membrane that contains PEPTIDOGLYCAN. Gram+ and Gram- bacteria have different cell wall structures and react differenclty to the gram staining procedure. (+)=Blue, (-)=Red. The rigidity of the cell wall is essential for resisting osmotic lysis (-=5atmospheres, and +=20)
Bacterial shapes.
Coccus, Bacillus/Rod, Spirillum, vibrio (curved), spirochete
cytoskeletal elements:
FtsZ, MreB, CreS
FtsZ= tubulin like
MreB- Actin Like
CreS = Intermediate filament like. contributes to curvature
Peptidoglycan layer
Forms a rigid mesh that surrounds the cytoplasmic membrane. Peptidoglycan consists of a polymer with repeating units of 2 hexose sugars (N-acetylglucosamine and N-acetlymuramic acid (MurNAC).
N-acetlymuramic acid (MurNAC). residues
Linked to tetrapeptide chains that contain amino acids found only in bacterial cell wells. Tetrapeptides are cross-linked from one chain (via DAP in gram-negative bacteria or L-lys in gram-positive bacteria) to D-ala on another chain, and cross-linking in gram-positive bacteria occurs via an intervening peptide such as pentaglycine.
Cross-linking in peptidoglycan chains
Greater in gram-positive bacteria than in gram-negative bacteria.
Gram-Negative bacteria
have a thin, sparsely cross-linked peptidoglycan layer and other major components that are located exterior to the peptidoglycan.
Gram-Negative bacteria
have a thick, extensively cross-linked peptidoglycan layer that also contains teichoic acids.
outer membrane (OM) of gram-negative bacteria
a lipid bilayer that contains lipopolysaccharide (LPS), lipoproteins (which are linked covalently to the peptidoglycan), and porins (which form transmembrane channels permitting diffusion across the membrane of hydrophilic molecules <600 MW), other membrane proteins, and phospholipids. The OM is a barrier to entry of some antibiotics and also protects the cell against the action of detergents and other toxic compounds.
LPS of gram-negative bacteria
is located exclusively in the outer leaflet of the outer membrane, and the inner leaflet consists of phospholipids. LPS contains Lipid A (the toxic component of endotoxin), core polysaccharide, and O side chain oligosaccharides that function as somatic antigens (O antigen)
Teichoic acids of gram-positive bacteria
have a repeating polyglycerol-P or polyribitol-P backbone substituted with other molecules (sugars, aminosugars, D-alanine), and they are covalently attached to the peptidoglycan layer
Lipoteichoic acids
are attached to the underlying cytoplasmic membrane and help anchor the cell wall to the membrane.
Capsules
Loose, gelatinous outer surface layers that usually consist of complex polysaccharides. Capsules often enhance virulence by enabling the encapsulated bacteria to resist phagocytosis. Most capsular polysaccharies are antigenic, and some are used as components of vaccines to prevent specific bacterial infections
Flagella
are appendages originating in the cytoplasmic membrane that function as organs of motility. Some bacteria have flagella distributed over their surface
(peritrichous); others may have one or several flagella at one end of the cell (polar). Bacterial chemotaxis (movement toward attractive nutrients or away from toxic substances) involves the control of flagellar rotation (counterclockwise results in swimming; clockwise results in tumbling).
Pili
Are long, slender, proteinaceous, antigenic, hair-like structures on the surface of many bacteria. Pili often play a role in bacterial adherence to surfaces and tissues, and antibodies against pili may block adherence and confer

resistance to infection. Sex pili that play a role in bacterial conjugation are found in small numbers on some bacterial cells.
Cytoplasmic membrane
is the anatomical and physiological barrier between the inside and outside of the bacterial cell. exhibits selective permeability. It is essentially impermeable to all charged substances, even H+. Only hydrophobic molecules or uncharged molecules no larger than glycerol can diffuse through it. Contains the electron transport system which is the principal source for generating proton motive force during respiration in bacteria
Ribosomes
bacterial are 70S vs the 80S seen in eukaroytes
nucleoid
The DNA of bacteria is located within a distinct region of the cytoplasm known as the nucleoid or nuclear body. Translation and transcription occur as a coupled process!
Plasmids
are extra-chromosomal, self-replicating DNA molecules, much smaller than bacterial chromosomes, and they are usually not essential for bacterial
viability. Plasmids in pathogenic bacteria often encode virulence factors. Plasmids called R factors carry genes that determine resistance to antibiotics in many pathogenic bacteria.
Bacteriophages
are viruses that infect bacteria. The DNA genomes of temperate bacteriophages can integrate into bacterial chromosomes and replicate as part of those chromosome. Temperate bacteriophages often carry genes that encode bacterial toxins, other bacterial virulence factors or resistance to antibiotics
Bacterial growth lag phase
An initial lag phase is a period of physiologic adjustment for the starting cells, or inoculum, involving the induction of new enzymes and the establishment of a proper intracellular environment for optimal growth in the new medium.
Bacterial growth exponential phase
the rate of increase in cell number/cell mass is proportional to the cell number/cell mass already present. A constant interval of time (ranging from about 20 minutes up to about 1 day) is required for doubling of cell number/cell mass, and this interval is termed the generation time
Bacterial growth stationary phase
occurs as essential nutrients are consumed and toxic products of metabolism accumulate. Such non-growing or slow-growing cells may exhibit markedly increased resistance to antibiotics such as penicillin or other
Death phase
the number of viable bacteria will decrease over time. If spontaneous cell lysis (autolysis) occurs, the mass of intact bacteria in the culture will also decrease.
Bacterial nutrition
This includes factors such as nutrients, pH, temperature, aeration (O2 tension), salt concentration, and osmotic pressure.
Heterotrophic bacteria
Bacteria that require an organic carbon source (including most bacterial pathogens)
Autotrophic bacteria
bacteria that obtain their carbon exclusively from CO2
Aerobe
requires oxygen, cannot ferment.
bacteria that can grow in the presence of oxygen usually produce catalas (or peroxidase) and superoxide dismutase (SOD) that protect them against toxic reactive oxygen species.
anaerobe
killed by oxygen, fermentative metabolism
indifferent bacterial response
ferments in the presence or absence of O2
facultative
respires with )2, ferments in absence of )2
energy currency
ATP and electrochemical gradients (the proton motive force). ATP drives many biosynthetic reactions, and electrochemical gradients drive other functions like flagellar rotation and certain substrate transport systems. These two types of potential energy are interconvertible by the membrane ATPase. Bacteria also require reducing power in the form of NADH and NADPH to drive various metabolic interconversions. Heterotrophic bacteria obtain both energy and reducing power by subjecting nutrients to fermentation or respiration.
fermentation
organic compounds serve as both electron donors and electron acceptors, and no net oxidation of substrates occurs.
respiration
many bacterial species, like the mitochondria of higher organisms, generate ATP through electron transport and use molecular oxygen as the final electron acceptor. In anaerobic respiration, certain bacteria may use inorganic substrates such as nitrate or nitrite as terminal electron acceptors instead of O2.
Sporulation
Spores are specialized cells that are produced by certain bacteria, such as Clostridium sp. and Bacillus sp., when the nutritional supply of carbon, nitrogen or phosphorus is limited. During sporulation, these bacteria differentiate to form highly resistant, dehydrated forms (spores) that have no metabolic activity. Spores are adapted for prolonged survival under adverse conditions such as heat, drying, freezing, the presence of toxic chemicals, and radiation.
antimicrobial agents
work on the principle of selective toxicity, namely the selective inhibition of microbial growth at drug concentrations tolerated by the host. Many aspects of microbial metabolism are very similar to those of eukaryotic organisms (including humans). However, there are some components of bacteria that are not present in eukaryotes or are sufficiently different from their counterparts in eukaryotes be effective as targets for antimicrobial agents.
Cell wall-active antimicrobials
Selective toxicity due to the lack of peptodoglycan in mammalian cells. Examples: B-lactams, Vancomycin, Cycloserine
Outer and cytoplasmic membrane-active antimicrobials
Polymyxins are cationic surfactants that disrupt bacterial outer and cytoplasmic membranes They are less active on mammalian cell membrans.
Inhibitors of protein synthesis at the ribosomal level
Selective toxicity is due to differences between bacterial and mammalian ribosomes.. Ex) Aminoglycosides, tetracyclines, chloramphenicol, macrolides,and lincomycins
Inhibitors of nucleic acid synthesis
Quinolones - inhibit DNA gyrase and topoisomerase and therefor interfere with DNA replication
Rifampicin - Inhibits RNA polymerase and interferes with initiaion of transcription
Metabolic inhibitory antimicrobials
ex) sulfonamides, trimethoprim, Isoniazid, Metronidazole.
mRNA in bacteria
can be mono or poly for coding of proteins. In human cells mRNA only codes for one protein.
Bacteria use multiple secretion systems to:
1) deliver proteins to the cell surface. 2) assemble organelles on the cell surface. 3) export proteins to the extracellular milieu. 4) inject proteins or DNA into other cells
