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gene expression


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
Created by: 1155187441193384



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