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Definition
| Heritable change in DNA sequence that can lead to a change in phenotype |
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| A strain of any cell or virus differing from parental strain in genotype |
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| Typically refers to strain isolated from nature |
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| A mutation that occurs without external intervention |
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Made environmentally or deliberately
Can result from exposure to natural radiation or oxygen radicals |
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Term
| Point mutations (base substitutions) |
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Definition
Mutations that change only one base pair
Can lead to a single amino acid change in a protein (missense), an incomplete protein (nonsense), or no change at all (silent) |
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| Amino acid is changed; polypeptide is altered |
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| Codon becomes stop codon; polypeptide is incomplete |
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| Does not affect amino acid sequence |
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Definition
- Deletions or insertions that result in a shift in the reading frame
- Often result in complete loss of gene function |
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- Give the mutant a growth advantage under certain conditions
- Useful in genetic research |
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Definition
- Neither an advantage nor a disadvantage over the parent
- Detection of such mutations require examining a large number of colonies and looking for differences (screening)
- Screening is always more tedious than selection |
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| Methods to facilitate screening |
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Definition
| Replica plating; useful for identification of cells with a nutritional requirement for growth (auxotroph) |
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| Direct reversal DNA repair |
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Definition
| Mutated base is still recognizable and can be repaired without referring to other strand |
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Term
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Definition
| Damaged DNA is removed and repaired using opposite strand as a template |
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| Repair of double strand DNA damage |
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Definition
| A break in the DNA requires more error-prone mechanisms, such as an SOS regulatory system |
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Definition
| Physical exchange of DNA between genetic elements |
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Definition
Exchange of homologous DNA from different sources
- Crossing over occurs whe two chromosomes break and rejoin |
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Definition
| Passage of genes to offspring |
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Definition
| Transfer of genes between cells of the same generation |
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| Different types of horizontal gene transfer |
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Definition
Transformation
Transduction
Conjugation |
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Term
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Definition
Genetic transfer process by which DNA is incorporated into a recipient cell and brings about genetic change
- Discovered by Fredrick Griffith in the late 1920s; worked with Streptococcus pneumonia |
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Term
| Competent cells (transformation) |
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Definition
Cells capable of taking up DNA and being transformed
- Natural competence
- Induced competence: CaCl2 and heat shock; electroporation – electricity is used to force cells to take up DNA |
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Term
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Definition
Transfer of DNA from one cell to another by a bacteriophage
Two modes:
- Generalized transduction
- Specialized transduction |
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Term
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Definition
DNA derived from virtually any portion of the host genome is packaged inside the mature virion
- Defective virus particle incorporates fragment of the cell’s chromosome randomly
- Virus can be temperate or virulent
- Low efficiency |
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Term
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Definition
DNA from a specific region of the host chromosome is integrated directly into the virus genome
- DNA of temperate virus excises incorrectly and takes adjacent host genes along with it
- Transducing efficiency can be high |
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Term
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Definition
Cell-to-cell contact
- plasmid-encoded mechanism
- Donor cell: contains conjugative plasmid
- Recipient cell |
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Term
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Definition
F plasmid is an episome; can integrate into host chromosome
Cells possessing a non-integrated plasmid are called F+
Cells possessing an integrated F plasmid are called Hfr (high frequency of recombination)
- High rates of genetic recombination between genes on the donor chromosomes and those of the recipient |
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Term
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Definition
- Discrete segments of DNA that move as a unit from one location to another within other DNA molecules are transposable elements
- Transposable elements can be found in all three domains of life
- Moves by a process called transposition; frequency of transposition is 1 in 1,000 to 1 in 10,000,000; first observed by Barbara McClintock |
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Term
| Two main types of transposable elements in bacteria |
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Definition
Transposons
Insertion sequences
- Both carry genes encoding for transposase; both have inverted repeats at their ends |
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Term
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Definition
| Transcription of gene into mRNA followed by translation of mRNA into protein |
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Term
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Definition
Two major levels of regulation in the cell:
Post-translational
- Controls the activity of preexisting enzymes
- Very rapid process (seconds) |
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Term
| What mechanisms control gene expression in bacteria? |
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Definition
The environment in which the organism is growing
Presence of absence of specific small molecules
Interactions between small molecules and DNA-binding proteins result in control of transcription or translation |
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Term
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Definition
| A regulatory mechanism that stops transcription |
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| Types of negative control |
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Definition
Repression
Induction
Operon |
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Term
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Definition
Preventing the synthesis of an enzyme in response to a signal
- Enzymes affected by repression make up a small fraction of total proteins
- Typically affects anabolic enzymes (arginine biosynthesis) |
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Term
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Definition
Production of an enzyme in response to a signal
- Typically affects catabolic enzymes (e.g., lac operon)
- Enzymes are synthesized only when they are needed (no wasted energy) |
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Term
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Definition
Cluster of genes arranged in a linear fashion and whose expression is under the control of a single operator
- the operator is located downstream of the promoter
- transcription is physically blocked when repressor binds to operator |
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Term
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Definition
regulator protein activates transcription by the binding of RNA polymerase to DNA
- Malstose catabolism in E. coli
-- Maltose activator protein cannot bind to DNA unless it first binds to maltose
- Activator proteins bind specifically to certain DNA sequence
-- called activator-binding site...not operator |
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Definition
| Systems that regulate expression of many different genes simultaneously |
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Term
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Definition
An example of a global control system.
- synthesis of unrelated catabolic enzymes is repressed if glucose is present in growth medium
- lac operon is under control of catabolite repression
- ensures the "best" carbon and energy source is used first |
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Term
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Definition
| Two exponential growth phases |
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Term
| Cyclic AMP receptor protein (CRP) |
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Definition
| Activator protein that controls transcription in catabolite repression |
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Term
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Definition
Key molecule in many metabolic control systems
- It is derived from a nucleic acid precursor
- It is a regulatory nucleotide |
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