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EXAM 1- Prokaryotes, eukaryotes, and viruses- 1, Microbial growth- 2, Antibiotics and resistance- 3, Control of microbial growth- 4, 5- DNA
Lecture 1: chapters 1, 3, 12 & 13
Terms in this set (222)
Microbial world: prokaryotes, eukaryotes, and viruses
Sizes of the domains
smallest --> largest
bacteria, archaea, eucarya
Nuclear membranes of the domains
eucarya is the only one that has this
cell walls of the domains
bacteria is the only one with peptidoglycan present
membrane bound organelles of the domains
eucarya is the only one that has this
where are domains found?
bacteria and archaea in all environments (archaea can be in extreme environments)
eucarya in all environments that are not extreme
compare bacteria and archaea
both reproduce using binary fission
have different cellular composition
have different niches in which to grow (archaea like extreme environments)
scientific nomenclature: first and last name
first name- genus
second name- species name, specific epithet
what are the three infectious agents? (nonliving)
viruses, viroids, prions
Viruses (3 things)
obligate intracellular parasite
named by species name
are not alive but must replicate in a living cell
genetic material of viruses
either RNA OR DNA- never both
genome may be linear or circular, double-stranded or single-stranded
architecture of viruses (+ 3 shapes)
nucleic acid + protein coat + sometimes spikes
- icosahedral, helical, complex
In the simplest of terms, viruses can be viewed as
genetic info (DNA or RNA) contained within a protective coat. they are inert particles, incapable of metabolism replication, or motility outside of a cell
that does not contain genetic material, but replicates by changing a normal protein into an infectious form. transmitted by ingestion.
size of organisms
atoms-->small molecules-->lipids-->proteins-->ribosomes-->viruses--> mitochondria-->bacteria-->nucleus-->eukaryotic cells
what determines bacteria shape and organization
how bacteria divide by binary fission
7 bacteria shapes
coccobacillus- short rod/long sphere
spirochete-helical rod, corckscrew
pleomorphic- many different shapes
4 groups of how bacteria grow/divide
typical prokaryotic (bacterial) cell: cytoplasmic membrane
- has a phospholipid bilayer but does not contain cholesterol
- selectively permeable (water, o2, co2- simple diffusion)
- electron transport chain creates proton motive force (energy in prokaryotes)
- has transport proteins embedded in membrane
- protein secretion (proteins allow bacteria to excrete things into environment or cell)
typical prokaryotic (bacterial) cell: cell wall
Gram +/- cell wall
composition of peptidoglycan
(sugars and proteins)
2 sugars and 5 amino acids
2 sugars of peptidoglycan
NAM and NAG
transports the monomer through the plasma membrane to the periplasmic space in Gram +/- cell walls
process of inserting a peptidoglycan monomer into growing cell wall
1. autolysins cut the cell wall
2. transglycosidases link new sugars
3. transpeptidases crosslink peptide side chain
4. transpeptidase removes 1 amino acid from each sidechain when linking peptides together
what connects the glycan chains and in peptidoglycan?
tetrapeptide chain (contains D-amino acids and diaminopimlemic acid)
Gram positive cell wall
- thick peptidoglycan layer that is linked via peptide interbridges
- contains teichoic/lipoteichoic acid
- helps stabilize Gram + cell wall and linked to NAM
- lipoteichoic acid helps to anchor the cell wall to the bacterial plasma membrane
- gives cell negative charge
Gram negative cell wall
thin layer of peptidoglycan, then has outer membrane (joined together by lipoproteins)
Periplasmic space between cytoplasmic membrane and outer membrane
Peptide side chains linked directly
outer membrane of G- cell wall
1. lipid bilayer with embedded porin proteins
2. LPS- lipopolysaccharide= lipid A + polysaccharides
Lipid A: conserved
core polysaccharides: conserved in related specides
O-side chain: variable within species
body recognizes this as invasion
Why is LPS medically important?
signals defense system
contains peptidoglycan layer and enzymes
Lipoproteins connect outer membrane to peptidoglycan
typical prokaryotic (bacterial) cell: glycocalyx
goo layer made of polysaccharides and is used for adherence and evasion of host defenses
typical prokaryotic (bacterial) cell:Flagellummmm
Allows bacteria motility
Used for chemotaxis-directed movement
Chemotaxis directed movement
movement toward beneficial chemicals in the environment
What drives rotation of flagella
proton motive force
flagellum is composed of
- basal body rings inserted into plasma membrane and peptidoglycan
- hook attaches filament to body
- filament-flagellin composes the hollow tube
typical prokaryotic (bacterial) cell: fimbriae/pili
- terms used to identify bacterial appendages
- may be used for attachment, movement, or some are specialized for conjugation
typical prokaryotic (bacterial) cell: nucleoid
- contains bacterial chromosome
- must be replicated prior to or during cell division
typical prokaryotic (bacterial) cell: Plasmid
1. small circular extrachromosomal DNA
2. self replicating (
3. important in getting genetic codes
4. has own origin of replication
- 70s: 30 + 50
- found in cytoplasm of bacterium and can be directly associated with mRNA that is being transcribed
- formed when environmental conditions are poor
- primarily made by G+ bacteria
- very resistant to drying, heat, and toxic chemicals/disinfectants
How are endospores formed
1. chromosome is replicated, septum divides cell. plasma membrane engulfs smaller section (makes forespore)
2. interior forespore contains chromosome, ribosomes, protectants from environmental assults
3. cortex and core wall created from layers of peptidoglycan
4. spore coat is layered over cortex
- contain membrane bound organelles
- mights have cilia or flagella
- have cell wall (plants) but no peptidoglycan
80s: (40 + 60)
used to identify genetic similarity and differences: strains, etc
- supply energy for the cell
- divide by binary fission, contain 70s ribosomes, have own circular DNA
- resemble rickettsias
Eukaryotic pathogens (4)
Fungi, protozoans, helminths, arthropods
- multicellular eukaryotic organism
- cell walls do not contain peptidoglycan (they do chitin)
- plasma membrane contains ergosterol
how is fungi reproduced and what produces spores
binary fission or budding, molds
grow as either molds or yeasts depending on environment
- very few are pathogenic
- unicellular, eukaryotic, found in water and soil
- may reproduce asexually or sexually
- may have cilia, flagella, or pseudopodia
What do protozoans feed on
bacteria and particulate nutrients
- digestion occurs in vacuole and waste eliminated via plasma membrane or anal pore
2 types of protozoans
trophozoite (feeding form)
cyst (dormant form)
- multicellular eukaryotic organisms
- parasitic ones are not free living
- complex reproductive system (dioecious vs hermaphroditic)
3 groups of helminths
-insects, ticks, lice, mites
- some are vectors that transfer microorganism to humans and they themselves are not pathogenic (mechanical)
-biological vectors play a critical role in life cycle of infectious organism
- do not have envelope
- mostly all phages are naked
-lipid bilayer outside the capsid
-more susceptible to disinfectants because these chemicals damage the envelope, making the viruses non-infectious
- one single infectious viral particle
- nucleocapsid: capsid + nucleic acid it encloses
- genetic material: RNA or DNA
- viral spikes: stick out to attach to specific receptor sites on host cells
Prokaryotic binary fission
- one cell divides into 2 daughter cells (must replicate its chromosome during division)
Generation or doubling time
time it takes for a cell to reproduce under optimal conditions
Growth of organisms in a biofilm
- free floating organisms attach to surface. uses glycocalyx, fimbriae, EPS
- highly structured with anaerobic, aerobic organisms growing in same structure
-more resistant to effects of antibiotics and body defenses
what is biofilm
polymer-encased community of microorganisms
obtaining a pure culture
a population descended from a single cell
-streak plate method
in experimental conditions with nutrient broth cultures where nutrients aren't added or waste products removed
- lag, log, stationary, death, prolonged
cells begin synthesizing enzymes required for growth
cells synthesize primary metabolites that allows them to grow exponentially (amino acids, peptidoglycan, nucleic acids).
bacteria is most sensitive during this phase
nutrient levels too low to sustain growth. produce most secondary metabolites during this phase.
cells die off
prolonged decline phase
survival of the fittest
all microorganisms require _____ for growth. where there is no _____ available, a bacterium cannot replicate
psychrophile, psychrotroph, mesophile, thermophile, hyperthermophile
grow best between 20-30 celcius
primarily body temp (25-45 celcius)
heeeat: 45-70 celcius, mostly archaea
heat lovers-70 celcius or greater
oxygen requirements for prokaryotes
require oxygen, can produce bth catalase and superoxide dismutase
cannot tolerate the presence of oxygen- can grow only in the absence of oxygen. cannot produce either catalase or superoxide dismutase
use oxygen when present, but can grow by fermentation or anaerobic respiration when oxygen is absent
-can produce both catalase and superoxide dismutase
can tolerate only low levels of oxygen
-can only produce small amounts of catalase and superoxide dismutase
do not care if oxygen is present, always use fermentation
neutrophils, acidophiles, alkaliphiles
grow at neutral pH of 7
grow optimally at low pH of <6.5
grow best in high pH of >8.5
loss of water due to osmosis of water out of an organism. causes plasma membrane to shrink from the cell wall
capable of growing in high salt concentration. can control the loss of water from the cytoplasm in highly osmostic circumstances
organisms need what 3 things for growth
carbon source, energy source, electron/hydrogen source
what breaks down hydrogen peroxide into water and oxygen
carbon from inorganic source (CO2)
carbon from organic source (other organisms)
energy source is chemicals
energy source is light
organisms that get electrons from same source as their carbon
organisms that get electrons from inorganic molecules such as H2S and Fe2+
how a virus can impact the cell they infect
lytic phage infection, temperate phage infection, filamentous phages
lytic phage infections
- lytic phages exit the host at the end of the infection cycle by lysing the cell, host cell dies
- productive infection
temperate phage infections
-have option of a lytic phage infection or integrating the phage DNA into a hose cell chromosome at specific sites
- host cell multiples- continuous release of virons
- productive infection
Lytic viral replication
attachment, genome entry, synthesis, assembly, release
Lytic replication: attachment
must bind to a receptor on a cell to attach. if the receptor is not present, the virus will not be able to attach, affords tropism to the virus
lytic replication: genome entry
tail contracts and phage DNA is injected into the bacterial cell, leaving the phage coat outside.
lytic replication: synthesis
phage genome is transcribed and phage proteins synthesized. phage DNA is replicated, other virion components are made, and host DNA is degraded
lytic replication: assembly
phage components are assembled into mature virions
lytic replication: release
the bacterial cell lyses and many new infectious virions are released
reproductive cycle of temperate (lysogenic) bacteriophages
attachment, insertion of genome, depending on environmental circumstances, virus can do a lytic infection or lysogenic infection
Lysogenic infection reproductive cycle
1. insertion of viral DNA into bacterial chromosome at specific sites generating a propage
2. bacterial replication
4. progression into lytic cycle
5. lysogenic conversion (can change the phenotype of a bacterium containing a prophage)
1. Adsorption /attachment
a.Enveloped- can enter in one of two ways
b.Naked- endocytosis only
4. Biosynthesis of genetic material- DNA vs RNA Viruses (Fig. 13.14)
a. DNA virus-usually replicate in the nucleus. Requires DNA Dependent DNA polymerase, few mutations occur.
b. RNA virus- usually replicate in the cytoplasm. Requires production of a RNA dependent RNA Polymerase (RDRP).
5. Maturation-viral components self-assemble
a. Enveloped viruses bud (Fig. 13.15) to acquire a lipid envelope from living cell plasma membrane or ER/golgi.
b. Naked viruses burst and lyse the cell.
animal virus: attachment
animal virus surfaces are studded with attachmentproteins or spikes. the receptors to which these proteins bind are usually glycoproteins located on the host cell plasma membrane
animal virus: penetration: enveloped
fusion with host membrane or endocytosis
animal virus: penetration: naked
animal virus: uncoating
in all viruses, the nucleic acid separates from its protein coat prior to the start of replication by uncoating. protective coats are disassembled by virus-specific mechanisms to release the viral genome and any accompanying proteins
biosynthesis of genetic material:DNA
DNA virus usually replicates in the nucleus
- requires DNA dependent DNA polymerase
- may be double stranded, single stranded- negative or positive stranded
biosynthesis of genetic material: RNA
usually replicates in cytoplasm
-requires production of a RNA dependent RNA polymerase
- if the genome is like mRNA it is termed positive stranded, and can be directly translated like mRNA is
- if negative, it is a template. needs to bring in a viral RNA dependent RNA polymerase so that it can make viral mRNA to create viral proteins
requires reverse transcriptase which creates DNA from a RNA template
animal virus: maturation
-viral components self assemble
- some viruses create polycistronic messages that get translated into a polyprotein
- requires the polyprotein to be cleaved into functional proteins
-requires a virally encoded protease to be processed
animal virus: release: envelope
-must aquire envelope from living cell plasma membrane or ER.
-can modify envelope by inserting viral proteins (receptor/ligands) into the plasma membrane before budding
animal virus: release:naked virus
generally burst and kill the infected cell and virions are released in a viral burst
viral generation time
differs from bacterial growth patterns in that instead of one viru making two viruses; in one generation time, one virus can make 100s of progeny
viral mutation and mutation rate
RNA polymerase incorporates many mutations into RNA
-can quickly mutate a viral genome
ways viruses can cause changes in host cells
1. integration of viral/cellular genetic material can change cell morphology, insertional inactivation or change the way the cell divides
2. viral oncogenes-gene whos activity is involved in turning a normal cell into a cancer cell
-termed viral transformation
-ex: HeLa cells (transformed cells from Henrietta Lacks)
viruses associated with cancer in humans
mainly DNA viruses
wanted to find magic bullet (kills microbes and not us)
-discovered salvarsan (first anti-microbial agent)
discovered the first antibiotic (naturally occurring) penicillin in 1928. became discouraged when trying to purify and abandoned his research.
Ernst Chain and Howard Florey
isolated and produced penicillin. saved thousands of lives in WWII.
antibiotics should cause greater harm to microorganisms than to human host
toxicity of drug
-minimum toxic dose is minimum effective therapeutic dose
- high therapeutic index=less toxic to patient
targets of antibacterial medications
-cell wall (peptidoglycan)
-nucleic acid synthesis
-cell membrane integrity
cell wall drugs
nucleic acid synthesis drugs
1. Fluoroquinolones (Cidal): Ciprofloxacin
2. Rifamycins (Cidal): Rifampin
3. Metronidazole (Cidal): Only works against anaerobic organisms
cell membrane integrity drugs
metabolic pathways drugs
protein synthesis drugs
bacteriostatic drugs rely on host immunity to eliminate pathogen- action is reversible
bactericidal drugs are useful in situations when host defenses cannot be relied upon to control pathogen
drug combination can result in
antagonistic effects (interferes)
synergistic effects (enhances)
additive effects (neither)
tissue distribution/metabolism/rate of elimination
consider blood brain barrier
plasma half life
rate of elimination of drug from body
-short half life, more frequent
suppression of the normal microbiota
innate or intrinsic resistance
organism cannot be acted upon because of inherent resistance
minimum inhibitory concentration
lowest concentration of a specific antimicrobial drug needed to prevent visible growth of a given organism in vitro, without killing it.
-determined using serial dilutions of one antimicrobial drug
-in vivo, differences in absorption and distribution of the antibiotic will influence the dose/route/frequency of administration
minimum bactericidal concentration
lowest concentration of an antimicrobial that kills 99.9% of a given organism.
-have to have survived MIC
-concentration: short course, high concentration
-time dependent: the MIC must be achieved for a specific amount of time to get the antimicrobial effect
tests a specific bacteria against an array of antibiotics. can determine whether an organism is sensitive or resistant.
can tell MIC to an array of antibiotics
Antibiotic resistance: how do organisms become resistant?
1. Innate resistance- due to basic metabolism or structure that enables resistance.
2. Sensitive- MIC can be reached in blood or body fluids.
3. Resistant-MIC is not attainable at the site of infection.
4. Intermediate-range between the two, organism can be acquiring the ability to resist via small mutations.
direct selection- based on the direct action of an antimicrobial which then multiply
indirect- commensals become resistant to antibiotics then transfer resistance to pathogenic organism
mechanisms of acquired antimicrobial resistance
-alteration in target molecule
-decreased uptake of drug
-increased elimination of drug
-use diff pathway (sulfa)
drug inactivating enzymes
chemically modify drug (penicillinase breaking b-lactam ring of penicillin antibiotics)
alteration of target molecule
minor structural changes that prevent binding
changes in rRNA prevent macrolides from binding to ribosomal subunits
changes in porin proteins change what can/cannot access interior of G- cell
--> vancomycin is too big to enter through porin proteins, so it cannot act on G- peptidoglycan synthesis- innate resistant
increased elimination of the drug
some organisms produce efflux pumps
increase capacity to eliminate drug
allows organism to resist higher concentrations
use alternate metabolic pathway
sulfanimide resistances occur when microbes use different pathways for folic acid synthesis
no naturally occurring
use hosts metabolic machinery to replicate, giving very few targets for antiviral therapy
antiviral drugs target areas
nucleic acid synthesis
assembly and release of viral particles
plasma membrane synthesis
cell wall synthesis
nucleic acid synthesis
removal or destruction of all microorganisms and viruses on or in a product
what is a sterile item
one that is free of microbes, including endospores and viruses. does not consider prions
elimination of most or all pathogens on or in a material
antimicrobial chemicals used for disinfecting inanimate objects
antimicrobial chemicals non-toxic enough to be used on skin or other body tissue
a brief heat treatment that reduces the number of spoilage organisms and destroys pathogens
process used to reduce the number of pathogens to a level considered safe to handle
implies a process that substantially reduces the microbial population to meets accepted health standards
process of delaying spoilage of foods or other perishable products
highly resistant microbes include
- protozoan cysts and oocysts
- pseudomonas species
- naked viruses
bacterial endospores: what kills them
most resistant form of life
- only extreme heat or chemical treatment destroys them
protozoan cysts and oocysts
cysts and oocysts are stages in the life cycle of protozoan pathogens. excreted in feces.
- destroyed by boiling
waxy cell walls make them resistant to many chemical treatments. toxic chemicals must be used.
can actually grow in the presence of disinfectants
polio virus is more resistant than the envelope virus HIV
bacterial death rates are influenced by
1. ability of microbe to resist treatment
2. number of bacteria present at time of treatment and time of exposure to treatment
3. environmental conditions (pH and temperature)
4. risk for infection
5. composition of items to be disinfected
time it takes to reduce a bacterial population by 90% under specific conditions
temperature and pH can change the rate of killing.
-increase temperature of disinfectant/lower the pH, increase how effective it is and decrease time it takes to kill organism
risk for infection: critical instruments
come into direct contact with body tissues. must be sterile.
risk for infection: semi-critical instruments
come into contact with mucous membranes. must be free of viruses and vegetative bacteria
risk for infection: non-critical instruments
come into contact only with unbroken skin
Physical control: Dry heat
- flaming inoculating loop
- baking items at 160-170 c for 2-3 hrs
Physical control: Moist heat: boiling
-boiling water (100c) for 5 min
-destroys most microorganisms and viruses
- not effective means of sterilization (more than 30 min for endospores)
Physical control: moist heat: pasteurization
reduces number of organisms, does not sterilize
- HTST: 72c for 15 sec
- UHT: 140-150c for 2-3 sec
Physical control: Moist heat: autoclave
add pressure to wet heat
-15 min at 121c @15 psi sterilizes most objects
- allow steam into item being sterilized
-Loius Pasteur and swan neck flask
Physical control: Filtration (remember .3 size)
membrane filters are for fluids
HEPA filters are for air (hospital rooms)
-sterilizes fairly rapidly
-causes protein, DNA damage, free radicals as well as membrane damage. penetrates well. can be used on heat sensitive material, electronics, food, spices
-Gram - are most sensitive, spores are most resistant
- due to lower energy waves, need longer time to sterilize. does not penetrate.
-can sterilize spores, just takes longer
- works best on actively multiplying organisms while DNA is dividing to cause mutations
heats water with waves. water inside organisms heat up, destroying organisms nearby. uneven 'cooking'
High pressure (130,000psi)
pasteurizes food by denaturing proteins and permeability of bacteria (guacamole)
Chemical control of microbes
alcohols, aldehydes, biguanides, ethylene oxide gas, halogens, metals, ozone, peroxygens, phenolic compounds, quats
- diluted solutions are most effective
- antiseptic- coagulates enzymes, disrupts lipid membranes, does not reliably eliminate endospores or some naked viruses
- evaporates rapidly
dissolved in alcohol= tinture
disinfectant/sterilizes (toxic to humans)
- formaldehyde: preservation of biological samples
- gluteraldehyde: sterilize medical instruments (both are suspected to be carcinogenic)
-OPA- stains skin gray
chlorhexidine- used in antiseptics, low toxicity.
adheres to skin and mucous membranes. not good against spores or naked viruses
STAYS ON SKIN
ethylene oxide gas
1) Penetrates well because it is a gas.
2) Can be used to treat heat sensitive, electronics, pillows, mattresses, fabrics
3) Explosive, carcinogenic, toxic
Chlorine: effective against most things
-except for oocysts and cysts of protozoans
a. sodium hypochlorite (household bleach)
-NOT STERILANT as it is ineffective against protozoan cysts.
-Must be diluted in water to form hypochlorous acid.
-Evaporates quickly, must be made fresh (1:10 or 1:100 solutions)
-Inactivated by organic material
b. chlorine dioxide- STERILANT
Toxic, explosive, but not inhibited by organic material. Must be generated on site, degrades rapidly.
Iodine- disinfectant /antiseptic
a. Used as a tincture (but evaporates rapidly)
b. Useds as iodophores (linked to carrier molecule to be released slowly) but stains.
c. Cannot kill endospores.
toxic to humans, but can be used as disinfectants.
disinfectant, breaks down rapidly, must be generated on site
sterilant, effective in the presence of organic compounds.
1)Hydrogen peroxide- disinfectant, but breaks down when used on skin and tissue. Leaves no residue, non-toxic and vaporous form can be used on food containers.
2) Peracetic acid-stronger and faster than hydrogen peroxide, but irritating to skin and eye
disinfectant, not sterilant.
Active ingredient in Lysol and will leave RESIDUE
1) Hexachlorophene- has been found to be neurotoxic
2) Triclosan- because it was deemed non-toxic, is found in most "antibacterial" products.
endocrine disruptor and breaks down into dioxin in water and chloroform when combined with chlorine.
detergents which act to primarily disrupt cell membrane
anionic detergents: soaps, good wetting agent, removes dirt
positively charged compound detergent that react with the negative charge at bacterial membrane.
Kills vegetative bacteria and enveloped viruses.
Also, reduces surface tension, is a wetting agent.
Non-chemical food preservation techniques.
D. pH-acetic acid (vinegar)
1. DNA is always synthesized in the 5' to 3' direction
2. 5' and 3' indicate which base of the sugar molecule being used
3. DNA nucleotides, Deoxyribose sugar/phosphate backbone.
a. C---G base pair
b. T--A base pair
4. Replication fork starts at the origin of replication HOWEVER!!!! DNA polymerase CANNOT START REPLICATION ON ITS OWN. DNA polymerase can only ADD DNA nucleotides to the 3' OH of a nucleotide.
5. DNA polymerase requires Primase to make an RNA sequence to allow DNA polymerase to start replication.
6. Helicase unwinds double strand. DNA gyrase allows the resulting tension in the double helix to be released.
a. Leading strand-continuous synthesis.
b. Lagging strand-discontinuous synthesis requiring many RNA primers. Okazaki fragments formed.
c. DNA ligase joins all fragments into on long continuous strand.
What is made when a cell wants to make a specific protein?
differences from DNA
1. ribose sugar group
2. No thymine --> instead uracil
3. And RNA polymerase does NOT need a primer to start. Binds and recognizes a sequence in the DNA strand called a promoter
similarities to DNA
1. RNA polymerase can only make mRNA in the 5' to 3' direction.
2. Must use DNA as a template to create the proper sequence.
3 types of RNA
1. ribosomal (rRNA)
2. transfer (tRNA)
3. messenger (mRNA)
1. The negative strand is the template strand and is used to create a copy of the positive strand (which contains the gene).
2. RNA polymerase binds promoter with help from sigma factor (this recognizes promoter regions). Other transcription factors aid in ribosomal binding (yes, bacteria DO have transcription factors).
3. RNA polymerase melts open a stretch of DNA and reads the negative strand of DNA (it has to read in the 3' to 5' direction in order to synthesize mRNA in the 5' to 3' direction-just like with DNA).
4. Transcription ends when a terminator is encountered. The terminator occurs when the RNA forms a hairpin structure, which allows the RNA polymerase to dissociate from the DNA.
5. mRNA released
- genes can be located on either strand of DNA, so it is the promoter that indicates where the gene is
- the promoter is always upstream from the gene and the gene is in the 5' to 3' direction from the promoter
- a three nucleotide sequence that determines the amino acid needed in protein
- Start Codon sets the reading frame for translation
means that more than one codon can encode a specific amino acid
*However, each codon will always only specify ONE amino acid
- AUG (ATG in DNA), is always the first codon in a protein following a ribosomal binding site sequence
- If AUG is internal in protein, will also code for methionine
- three stop codons indicate the end of the coding sequence which terminates translation
- these do NOT code for an amino acid.
**process of decoding info carried on mRNA to synthesize a specific protein
a. All three RNAs come together: ribosome (rRNA)/mRNA/ tRNA
b. Initiating tRNA with fMet amino acid moves into P site on ribosome. This is the only amino acid that enters at the P site.
c. Next tRNA fills A site.
d. Peptide bond formation occurs and the 1st tRNA released via the E site.
e. Ribosome shifts and amino acids are added by reading codons until a stop codon is encountered.
1) Termination of protein synthesis at stop codon.
2) Translation machinery falls off.
f. Translation in Bacteria - can occur simultaneously with transcription.
major differences between prokaryotic and eukaryotic transcription/translation
4. Humans only make monocistronic mRNA whereas bacteria are capable of making polycistronic mRNA
major differences - processing
prokaryotes - mRNA not processed
eukaryotes - cap is added to 5' end of mRNA and poly A tail added to 3' end
major differences - introns
prokaryotes - no introns
eukaryotes - introns which are removed by splicing
major differences - translation
prokaryotes - translation of mRNA begins as being transcribed
eukaryotes - mRNA transcript transported out of nucleus to be translated in the cytoplasm
quorum sensing/ antigenic
A. Specific genes are activated only when critical mass is achieved
B. Antigenic/phase variation uses different transcripts which allows organisms to evade host responses.
*can "sense" and "talk" to each other
1. Operons consist of promoter, operator region, and set of regulated genes.
2. Control of transcription of the operon is regulated by DNA binding proteins known as repressors or activators.
a. Repressors stop transcription.
(a) An inducer blocks the ability of a repressor to bind to DNA.
(b) A co-repressor will block transcription by enhancing binding of DNA by a repressor.
b. Activators induce transcription. When an inducer binds to an activator, it causes the activator to bind to DNA and induces transcription.
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EXAM 1- Prokaryotes, eukaryotes, and vir…