exam 1-2 Flashcards
Spontaneous Generation
Microbes could arise spontaneously
Do microbes cause disease?
Germ theory say disease are caused by microbes
Robert Koch
Demonstrate anthrax chain of infection Determined the bacterium that causes tuberculosis Koch’s postulates are criteria to establish a link b/w a microbe and disease Microbe must be absent in healthy people Microbe must be isolated from host and purely grown When introduced to healthy host, the same disease is seen Microbe must be isolated from knew host and be the same strain
Kochs postulate
Criteria for establishing a causative link between an infectious agent and a disease
- The microbe is found in all cases of the disease but is absent from healthy individuals
- The microbe is isolated from the diseased host and grown in pure culture.
- When the microbe is introduced into a healthy, susceptible host (or animal model), the host shows the same disease.
- The same strain of microbe is obtained from the newly diseased host. When cultured, the strain shows the same characteristics as before.
Louis Pasteur
Discover that weaken strains can cause immunity of the disease Weakening strains differs, for instance rabies required complex heat treatment and inoculations
- Showed that microbes do not grow in liquid until introduced from the outside
- Developed the ”swan neck” flask – allowed airflow, but prevented entry of dust that carried microbes
- Remained free of growth for many years
Geochemical cycling:
interconversion of inorganic and organic forms of N, S, P etc.
Winogradsky and others showed that bacteria perform unique roles in geochemical cycling the global interconversion of inorganic and organic forms of nitrogen, sulfur, phosphorus, etc.
Domains of life evolution
Microbes were seen as neither plants nor animals Monera were divided into two groups Fungi was added as another eukaryotic kingdom Endosymbiosis theory Carl Woese Proposed 16s rRNA gene sequencing which is found in all life Found that archaea ribosomes were more similar to euk
•Describe cell membrane structure and what affects membrane fluidity
Structure that defines the existence of the cell Proteins embedded anchor membranes to envelop
Cell Wall
Aka the sacculus consists of single interlinked molecule Withstands intracellular turgor and maintains shape Composed of Peptidoglycan -Parallel (disaccharides) glycan chain crossed linked with peptides of four aa -Peptides contains two aa in D form
gram-positive
- Gram-positive – thick cell wall (e.g. firmicutes)
- S-layer • Made of protein (contains large pores)
- Thick cell wall • 3-20 layers of peptidoglycan • Interpenetrated by teichoic acids for strength
• Gram-negative
– thin cell wall (e.g. proteobacteria)
- Outer membrane (OM)
- Covers peptidoglycan layer
- Confers defensive abilities and toxigenic properties on many pathogens
- Thin peptidoglycan layer • 1-2 sheets
- Periplasm – area between membranes
Recall the structure of the bacterial nucleoid
region that extends throughout the cytoplasm Excludes ribosomes DNA forms 50 domains/loops and each domain is supercoiled
Cell Division
- Replication begins at the origin of replication
- The DNA double helix unzips and forms two replication forks
- At each fork DNA is synthesized by DNA polymerase with the help of accessory proteins (replisome)
- As the termination site is replicated, the two replisomes separate from the DNA
POLAR AGING
old poles degrade slightly increasing chances of lysis different poles might differ in resistance to antibiotics
Chemotaxis
- Chemotaxis is the movement of a bacterium in response to a chemical gradient
- Attractants cause CCW rotation “Run”
- Repellants cause CW rotation “Tumble”
The alternating runs and tumbles cause a “random walk”
• Receptors detect attractant concentrations
archaeal membrane
Uses L-glycerol ether linkages: more stable isoprenoid chains branches at 4th C fatty acid chains linked covalently (tetraether) fatty acids have cyclopentane rings
Some do have a cell wall – composed of pseudomurein or pseudopeptidoglycan
Heterotrophs:
break down organic compounds
autotrophs:
fix CO2 into complex molecules
phototrophs
: absorb light
chemotrophs:
electron donor are oxidized
• List the various kinds of differentiated cells that bacteria can produce
Bacteria faced with environmental stress undergo complex molecular reprogramming that includes changes in cell structure
- Examples include:
- Endospores of gram-positive bacteria
- Heterocysts of cyanobacteria
- Fruiting bodies of Myxococcus xanthus
biofilms:
surface attached, collaborative communities
•Explain how temperature affects growth
temperature + growth temperature denatures enzymes or decrease fluidity and enzymatic activity
psychrophiles
(0-20C), proteins are flexible, mem are fluid, antifreeze proteins
mesophiles:
(15-45C) lab strains
thermophiles:
(40-80C) enzymes have low [glycine] chaperone refold proteins stabilize DNA rigid membranes
barophiles:
high pressure growth
osmolarity
aquaporins allow water to traverse faster
viroids
infects plants and RNA genome if the infectious particle
Differentiate between sterilization, disinfection, antisepsis, and sanitation
- Sterilization – killing of all living organisms
- Disinfection – killing or removal of pathogens from inanimate objects
- Antisepsis – killing or removal of pathogens from the surface of living tissues
- Sanitation – reducing the microbial population to safe levels
Growth and oxygen
Strict aerobes – only grow in oxygen
- Microaerophiles – grow only at lower oxygen levels
- Strict anaerobes – die in the least bit of oxygen
- Facultative anaerobes – can live with or without oxygen
- Aerotolerant anaerobes – grow in oxygen while retaining anaerobic metabolism
filamentous:
helical tube around the genome
ICTV
genome composition, capsid symmetry, envelope, size and host range
lytic cycle
immediate reproduction of phage after infection early genes- produces phage components late genes - capsid is first assembled lysis/burst
lysogenic cycle
both genomes combine same type virions can’t infect the bacteria DNA is replicated with host reactivation of prophage can be trigger by stress transduction can accur
slow-release
phage reproduce without killing host slow assembly of phage extrude through envelope without lysing
viral life cycle
host recognition and attachment entry either through genome injection, endocytosis, or envelope fuse genome replication –+ssRNA can be translated by host ribosomes —ssRNA create mRNA and progeny genomes Exit through lysis or budding (host membrane surround capsid)
Differentiate gene, operon, and regulon
Gene; units of information composed of a sequence of DNA nucleotides
Operon : gens existing in tandem with other genes in a unit
Promoter : DNA control sequence that launch RNA synthesis
Regulon – collection of genes and operons at different positions in the chromosome that have a unified biochemical purpose
Recall the structure of DNA
4 nucleotides linked by a phosphodiester backbone Deoxyribose 2’carbon position Nucleobase attatched to carbon 1 Phosphodiester bond links 3’ carbon of one ribose to 5’ carbon of next ribose
Explain how bacterial chromosomes are compacted to fit into the cell •
- Boundaries of each loop are defined by anchoring proteins called histone-like proteins
- DNA ends must be tethered to form supercoils
- Supercoils are introduced by • Cleaving both strands at one site in the molecule
- Enzymes that change DNA supercoiling are called topoisomerases
- Type I – typically single proteins that cleave only one strand of a double helix • Relieve or unwind supercoils
- Type II – have multiple subunits that cleave both strands of the DNA molecule • Introduce negative supercoils • DNA gyrase
replication initiation
– melting (unwinding) of the helix and loading the DNA polymerase enzyme complex
• In E. coli initiation is activated by the protein DnaA and inhibited by the protein SeqA
DNA methylation controls timing of SeqA binding
• A DNA helicase (DnaB) and a DNA helicase loader (DnaC) bind to the DnaA-bound region
Clamp loading complex loads DNA polymerase to the ssDNA
• Replisome • Two DNA polymerase III, DNA primase (DnaG), and helicase (DnaB )