Microbial Genetics Flashcards
(36 cards)
Explain spontaneous mutation
Naturally caused mutation, generally via mistakes in replication. Mutation rate is low 1 in 1 billion.
Explain induced mutation
Mutation caused by mutagens (ionizing radiation, UV Irradiation, base analogs, reactive chemicals, intercepting agents)
Can be caused deliberately or may occur from the environment. Mutation rate is 1 in 1 million.
Explain point mutation, differentiating between missense and nonsense mutations
Substitution of one nucleotide in the DNA molecule. Changes one amino acid in a protein, resulting in an altered protein.
Missense- substitution in DNA results in mRNA codon that codes for different AA, which can make a protein that is less functional than the originally coded for protein.
Nonsense- substitution in DNA that results in mRNA codon that codes for stop or termination resulting in protein fragments
What are some specific results of bacterial mutations?
Pigmentation- loss of ability to produce pigment
Change in colonial appearance- S colonies vs. R colonies
Antimicrobic resistance
Pro-phage
Loss of ability to produce flagella or other structures
Altered metabolic pathway does not equal usual end product
Auxotrophs- fastidious bacteria
What are recombinations?
Any process by which DNA from two different organisms get in the same cell or DNA molecule. More usual in prokaryotes because of asexual reproduction. Can happen via: Transformation Conjugation Lysogenic conversion Transposons Bio technological methods
Explain transformation
A COMPETENT cell (receptors/binding sites) ADSORP to DNA fragments of dead cell of same or related species. .3% of the dead cell DNA PENETRATES the competent cell. The host cell RECOGNIZES the fragments base sequence and either destroys it or RECOMBINATES it. APPEARANCE of a MARKER will be expressed by new cell (phenotypic expression)
Explain conjugation
Transfer of DNA from donor to a recipient via F Pilus and conjugable plasmid (contains f Factor= fertility /F+)
Donor and recipient bump into each other. F Pilus is triggered and links to receptor site, pulling recipient cell close. An endonucleous nicks the plasmid, making it linear and replicates via DNA polymerase. Once copied, plasmids become circular via DNA ligase. The copy is sent through F Pilus to recipient. Will either become integrated (recombination) or will act independently as plasmid. Recombination rate is low: 1 in 10,000
F- + F+ =
And
Hfr + F- cell =
100% F+ progeny
And
Hfr (high frequency recombination)
99% F- progeny b/c F factor is part of a plasmid and the bacterial chromosome. Takes 90 minutes, can result in spontaneous breakdown of replicated DNA or F Pilus
Greater chance of integration 1 in 1,000-100. Recipient cell usually remains F- because the F Factor rarely is transferred. But, chromosomal genes are transferred.
Transduction
The transfer of DNA from one bacterium to another via bacteriophage capsid.
Generalized- occurs during lyric cycle. Any piece of bacterial DNA is replicated by accident and incorporated in phage capsid
Specialized (restricted)- occurs during lysogenic cycle. Piece of bacterial DNA adjacent to prophase is incorporated into page capsid and transduced.
Explain lysogenic conversion
When bacterial cells express new traits due to a prophage.
What are transposons?
DNA sequence containing one or more genes, that have insertion sequences at both ends, which allow DNA to integrate into the bacterial chromosome or plasmid or phage DNA. Insertion sequences consist of palindromes (inverted repeats), and when transposons are integrated in DNA they interrupt a gene, which leads to a mutation. They can also confer resistance.
Called “jumping genes”
What are conjugative transposons
Discovered in enterococci, these confer on their hosts the ability to conjugate and transfer antibiotic resistance
What is biotechnology?
The use of living organisms and their components to do practical tasks.
Recombinant DNA, gene splicing, gene cloning,
What is a mutation?
Any alteration in the sequence of nucleotides. Can happen via substitution (point mutation: missense/ nonsense) or deletion/insertion (frameshift).
Explain the Lac Operon
See notes
Explain the SRc genes and its contribution to virology
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Explain the Lyric cycle and its phases
Cycle where host bacterium is lysed.
1) adsorption/ penetration/initiation
2) eclipse phase
3) biochemical replication
4) assembly and maturation
5) release/lysis
Explain the lysogenic cycle
Bacterial replication where host cell DNA is not immediately destroyed.
Occurs in temperate phage, which can replicate via both cycles, and contains repress or protein to prevent phage DNA from being transcribed and translated (no eclipse phase)
Bacterial DNA is cut ONCE and phage DNA s recombinated, creating a prophage.
Prophage replicates via binary fission.
Eventually, the repressive protein will fall off of prophage DNA or degrade and the cell will enter the eclipse phase and finish the lyric cycle
Explain translocation
See notes
What are common viral structural proteins?
Hemagglutinins (h spikes) found on influenza virus. Aggregates erythrocytes around virus
Neuraminidase (n spikes) found on surface of influenza to break down mucous, allowing virus to spread to respiratory epithelial cells
GP120- peplomers that allow HIV to attach to CD4 receptors on helper T cells and macrophages
Describe inclusion bodies
Areas of viral destruction or aggregates of virus particles in virus infected cells
What is a viruon?
Fully infectious particle. A nucleus acid core surrounded by a protein coat capsid composed of protein subunits called capsomeres
What is a naked virus?
A virus without an envelope?
What is an enveloped virus?
An animal virus with an outer envelope of lipid or lipoprotein that surrounds a virus as it it budded out.
