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gene expression
microbiology
| Question | Answer |
|---|---|
| Constitutive (house keeping) | –60-80% –Expressed constantly •Glycolysis enzymes |
| Controlled genes are : | Expressed only if needed Inducible or Repressible |
| Inducible | –lac (lactose) operon |
| Repressible | trp(tryptophan) operon |
| Inducible operon (lac operon) has an ______________ protein | Active repressor protein |
| Inducible | –Induces synthesis of enzymes involved in lactose utilization –Responds to presence of lactose |
| Repressible has an _______ protein. | Inactiverepressor protein |
| Repressible operon (trp operon) | –Represses tryptophan synthesis –Responds to presence of tryptophan |
| Regulatory gene (constitutive) | –Codes for a repressor protein |
| Promoter | –Site where RNA polymerase starts transcription |
| Operator | –Binding site of active repressor protein –Allows or interferes with the binding of RNA polymerase to promoter |
| Structural genes | –Genes under control of the operon |
| Lactose operon is influenced | by glucose concentration |
| Low cyclic adenosine monophosphate (cAMP)production | High glucose concentration |
| Low glucose concentration | High cAMP production |
| cAMP binds to a | catabolic activator protein (caP) |
| CAP facilitates binding of | RNA polymerase to promoter |
| Mutations are: | Permanent” change in the base sequence of DNA |
| Variable effect of Mutations: | •Disadvantageous (most often) •Advantageous •Neutral |
| Base substitution or point mutation (most common) : | Silent mutation Missense mutation Nonsense mutation |
| Different codon, still same amino acid | Silent mutation |
| Amino acid substitution, different amino acid | Missense mutation |
| Nonsense mutation | Nonsense (stop) codon, early termination of translation |
| Frameshift mutation | Insertion or deletion of nucleotide pairs –Long stretch of wrong amino acids |
| Chemical mutagens Nitrous acid (HNO2) | Adenine (A) change •Pairs with citosine (C) •Some AT pairs in parent DNA change to CG in granddaughter cells |
| Similar to normal nucleosides, but with different base-pairing properties | Nucleoside analogs |
| Ionizing radiation | X rays and gamma rays •Generates highly reactive free radicals •Damage of DNA •May break covalent bonds |
| Nonionizing radiation | –Ultraviolet (UV) light •Formation of thymine dimers –Interferes with transcription and replication |
| Eukaryotes (vertical) | –Formation of reproductive cells |
| Mediated by bacterial viruses | Bacteriophages (phages) |
| Prokaryotes (vertical and horizontal) | –Transformation –Conjugation –Transduction |
| Transformation | Transfer “naked” DNA in solution (from dead cells) among closely related organisms •Natural process only in a few types of bacteria •Major technique in genetic engineering |
| Cell processes phage DNA | –Replication –Transcription –Translation |
| Phage injects its DNA | into host bacterial cell |
| Generalized | •Transfer of any bacterial gene •Lysis of host |
| Specialized | •Transfer of an specific gene •Normal reproduction until the lytic cycle is triggered |
| Natural selection | –Survival of the fittest |
| Diversity | –Mutation –Recombination –Transposition |
| –Transposase | •Cutting and resealing DNA •Recognizes recombination sites |
| Movable genetic elements | –Carry information for own transposition –Move within DNA molecule –Move to a different DNA molecule –May carry antibiotic resistance genes |
| Extrachromosomal genetic material | Self-replicating –1 to 5% the size of bacterial chromosome –Usually not indispensable |
| Phage DNA and coat proteins are | are assembled into new phages |
| Usually not indispensable |
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