Bacterial Genetics (Lecture 13)
What is an mRNA that can code for more than one polypeptide and are usually found in prokaryotes?
Polycistronic mRNA
What catalyzes metabolic reactions that constantly occur and give an example?
Constitutive enzyme; ex: Pyruvate decarboxylase (Krebs Cycle)
Name the four characteristics of an antibiotic.
Low molecular weight compounds
Produced by bacteria or fungi
Kill or inhibit growth of bacteria
Minimal side effects
What is a strain in which original phenotype is restored by means of a suppressor mutation?
Revertant
What are the implications of overuse of antibiotics?
Overuse of antibiotics on livestock has led to the rise of drug-resistant microbes. This is a major threat to human health, because the drugs become ineffective for people (and animals too).
What is McCarthy and McLeod's Experiment?
DNA is the transforming principle behind Griffith's experiment (not RNA nor protein); be able to explain in detail
What is catabolite repression and how does it result in diauxic growth?
Inhibition of the synthesis of several catabolic enzymes by a preferred carbon and energy source;
Ex: If E. coli grows in medium with glucose and lactose, it will preferentially use glucose until the sugar is exhausted. Then after a short lag, growth will resume with lactose (at a slower rate).
Who was the first person to discover penicillin? Who rediscovered it?
Ernest Duchesne (1896); Alexander Fleming (1928)
What is the difference between induced mutations and spontaneous mutations?
Induced: Made environmentally or deliberately; can result from exposure to natural radiation or oxygen radicals
Spontaneous: Occur without external intervention
What is the 'third type of symbiosis' mentioned with angler fish and their bioluminescent symbionts?
Bacteria can move from anglerfish bulb to water; bacteria actually not stuck with host (has genes for flagella) but still have to get nutrients from anglerfish (undergoing evolution)
What binds to -35 and -10 promoter region of prokaryotic DNA and positions RNA polymerase for transcription?
sigma factors
How does quorum sensing work?
Mechanism by which bacteria assess their population density; Ensures sufficient cell density to have an effect (e.g. toxin production in pathogenic bacterium)
Internal cascade effect (Kinase or Phosphatase)
What are some mechanisms used to inhibit cell wall synthesis?
B-LACTAM RING!!!
Penicillin (PBPs) resembles two amino acids at end of sidechain in peptidoglycan units-->blocks transpeptidation; Cephalosporins similar
Glycopeptides- inhibit side chain and main chain (blocks transglycosylation and transpeptidation)
Vancomycin and Teicoplanin-blocks transpeptidation too by binding to enzyme substrate rather than enzyme itself
What is the type of mutation that leads to frameshifts which changes the reading frame and results in incorrect amino acids?
Indel (insertion or deletion)
What arguments do pharmaceutical executives use to argue for the use of antibiotics?
Jeffrey Simmons (chief executive of Elanco) argues that he’s on a mission to fight hunger--want to help make protein affordable for everyone
Ted McKinney (former executive at Elanco) argues- food regulators are too focused on consumers, at the expense of pharmaceutical companies and research scientists working to meet growing global demand for food
How do Peanuts fit into the nitrogen cycle?
Peanuts are legumes. Legumes form nodules on their roots with soil bacteria (rhizobia) that can fix nitrogen, converting atmospheric n2 to ammonia (NH3). Peanuts / leguminous plants give bacteria energy and carbon while the bacteria give bioavailable nitrogen. symbiotic relationship
Explain Induction and Repression.
INDUCTION: repressor normally binds to operon (cannot make mRNA); inducer binds to repressor and tells it to back off and let RNA polymerase transcribe mRNA. Example: B-galactosidase enzyme digests lactose when lactose is only AVAILABLE
REPRESSION: Normally, repressor isn’t binded to the operator, transcription proceeds unless turned off. Corepressor (ex. arginine) binds to repressor and stops RNA polymerase from transcribing mRNA
What are some mechanisms used to inhibit protein synthesis?
Inhibit:
formation of ribosome complex
binding of 30S or 50S (Tetracycline, Aminoglycosides, Macrolides)
aminoacyl-tRNA binding
Peptide bond formation
mRNA reading
translocation
What is a change in one DNA base pair that is read as a stop codon and results in an incomplete protein?
What is a change in one DNA base pair that has no effect on the protein being made?
What is a change in one DNA base pair that substitutes an amino acid and results in a faulty protein?
Nonsense mutation; Silent mutation; Missense mutation
What are the key characteristics of the adaptive immune response?
Specificity- immune cells recognize and react with individual molecules (antigens) via direct molecular interactions.
Memory- immune response to a specific antigen is faster and stronger upon subsequent exposure because the initial antigen exposure induced growth and division of antigen-reactive cells (B cells), resulting in multiple copies of antigen-reactive cells.
Tolerance- immune cells not able to react with self cells/self-antigens. Those that do, are destroyed.
What are some similarities between bacterial and archaeal genomes/transcription/translation?
Chromosomes are circular, single chromosome, Introns rare, polycistronic mRNA, DNA gyrase, restriction enzymes, 70s ribosomes, 16s and 23s rRNA
How are signals passed from outside the cell to inside the cell and how is this related to cellular porosity?
Signals passed through Two Component Signal Transduction Systems-
histidine kinase on inner membrane transmits environmental signals
transfers phosphate from ATP->ADP to response regulator
Response regulator acts as DNA binding protein to activate or repress transcription
If under low osmolarity (low solute []), low kinase activity->Response regulator says more synthesis of OmpF than OmpC because needs larger porins to scavenge scarce nutrients
If under high osmolarity (high solute []), high kinase activity->Response regulator says more synthesis of OmpC than OmpF because has smaller porins (lower diffusion rate) to keep nutrients
How are viruses targeted by chemotherapeutic agents?
Protease Inhibitor- viruses translate multiple proteins together and then chop them up with a protease to make them functional (HIV cannot break down proteins to make new viruses)
Fusion Inhibitors – stops virus from entering the cell; Blocks HIV envelope from fusing with CD4 cell membrane
Nucleoside analogs- Retroviruses with reverse transcriptase RNA -> DNA, make them use a synthetic nucleotide-SHUT DOWN
Non-nuclease reverse transcriptase inhibitors – targeting the enzyme HIV reverse transcriptase itself (used in RNA→ DNA); prevents replication
What is an auxotroph and how do we use replica plating to find them?
Auxotroph: An organism with a mutation that causes it to lose the ability to synthesize an essential nutrient; auxotroph must obtain the nutrient or a precursor from surroundings
Replica plating distinguishes between auxotrophic mutants and the wild-type strain based on their ability to grow in the absence of a particular biosynthetic end product.
What are the different types of vaccines mentioned in class?
Inactive- killed version of pathogen, unable to cause disease (INFLUENZA)
Attenuated- living, weakened version of pathogen unable to cause disease (MMR-linked to autism?)
Toxoid- contain no pathogens, only the inactivated toxoid that they produce (TETANUS)
Recombinant- vector vaccines (RABIES)
Recombinant-antigen vaccine (subunit) (HEPATITIS B)