Microbial Genetic/ Biotech Flashcards
What are mutations ?
Random, inheritable alterations in the sequence of the genome
They can change the phenotype
What are selectable mutations ?
Could be selected after placing organisms under conditions where their growth will be favoured (eg: mutations of resistance
Mutations converting an auxotrophy to phototrophy (inability/ability to synthesise metabolites)
What are non selectable mutations ?
Can only be identified after testing the whole population of an organism (eg- mutations of auxotrophy, mutations of sensitivity like temp sensitive mutants
What are mutagens?
Physical or chemical factors that increase the rate of mutations
The most important processes contributing to genetic variation include ?
Mutations
Recombination
Transpositions
What is a point mutation?
It involves a single base pair change
What types of point mutations are there?
-base pair substitution: a single base pair/nucleotide is substituted with another
Base pair insertion/deletion: nucleotide is added or deleted
What May base pair substitutions lead to?
Silent, missense or nonsense mutations
What do insertions and deletions cause ?
Have a more dramatic effect: getting rid of a base pair changes the amino acid therfore can result in a non functional protein
What is a silent mutation?
Something that has no effect on the encoded protein (as genetic code is redundant: different triplets can code for the same amino acid)
What is a missense mutation?
If the altered codon causes encoding for a different amino acid (doesn’t really make sense)
What is a nonsense mutation?
If a codon for an amino acid is converted into a stop codon.
How do you detect mutagenic compounds ?
By an ames test.
Explain an Ames Test
Plate (his-) strain of salmonella typhimurium ( a mutant that requires the amino acid histidine for growth) in the medium without histidine
- The mutant (his-) cells don’t grow on the medium. The only (his+) cells could grow
- If the testes compound (soaked into the disk) is a mutagen it causes reversion of many his- cells into his+ cells due to mutations. The mutants grow around the disk.
- The more colonies grow, the more strong the mutagen is. Many strong mutagens are also carcinogens
What’s recombination ?
The process by which parts or all of the DNA molecules from 2 seperate sources are exchanged or brought together into a single DNA molecule
What’s homologous recombination ?
Exchanging DNA fragments from 2 different DNA molecules that have identity in some regions
This process involves an endonuclease, single strand binding protein and RecA protein
Examples of plasmid born resistance to metals?
Enterobacteria
Pseudomonas
Ralstonia metallidurans
What is enterobacteria resistant to?
Ions of arsenic, copper mercury zinc
What is pseudomonas resistant to?
Chromium Mercury tellurium
What is ralstonia metallidurans resistant to?
High content of heavy metals, possesses 2 large plasmids: pMOL28 and pMOL30
What is the main tool for genetic engineering ?
Bacterial plasmids
What kind of adaptive mechanisms do bacterial plasmids include ?
Antibiotic resistance Toxin production Metal resistance Degradation of organic compounds Utilisation of metabolic pathways
What’s transduction ?
Gene transfer in bacteria mediated by phages (bacterial viruses)
What’s generalised transduction ?
Potentially any donor bacterial gene could be transferred
