z-MicroBio Final – Ch. 7,9,10

Central Dogma of MicroBio
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GENE
the nucleotide sequence coding for a single polypeptide chain, or a ribosomal RNA, or a t-RNA.

anti-sense strand of DNA is transcribed into a mRNA

Prokaryote vs Eukaryotes (RNA)
Prokaryote. A single mRNA often contains more than one coding region (such mRNAs are called polycistronic). In Eukaryotes, the DNA contains introns and exons. The Primary RNA transcript must undergo processing which means the introns must be removed and the exons are spliced back together to make mature mRNA that is transported to the cytoplasm. The mRNAs of eu are almost always monocistronic (only code for one polypeptide chain).
Structure of DNA
Polymer of deoxyribonucleotides held together by 3’5’ phosho-diester bonds.
DNA is double stranded & anit-parallel with the two strands held together by hydrogen bonding between the bases.
The hydrogen bonds between the bases will break as temperature is raised, but not the covalent bonds.
This will separate the strands and DNA is said to melt.
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DNA in eukaryotes
associates with basic proteins called histones to form nucleosome
DNA in Prokaryotes
the DNA is also double stranded but the ends are closed to make a circle. In both cases the DNA is highly coiled.
Nonchromosomal genetic elements include
Viruses – either DNA or RNA viroids: small pieces of RNA Plasmids – small genetic elements that exist and replicate separately from the major bacterial “chromosome”. Most are circular polynucleotides that do not usually cause cell damage and they do not have extra cellular forms. (Some can integrate into host DNA.)
Circular DNA Reproduction
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tRNA Production
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Mutations
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Comparison of naked and enveloped virus
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Plaque Count Assay
Top agar contains phage dilution and is seeded with bacterial host cells. Where a single virion is present it replicates and lysis the host cells in the vicinity and forms a plaque.
Animal viruses
penetration involves the entrance of both the protein coat & the nucleic acid, but then an uncoating enzyme removes the protein coat.
Hershey-Chase
experiment with bacteriophage supported DNA as genetic material. They labeled DNA with P32 and the protein with S35 and observed that the phosphorous label went into the host cell. Most of the sulfur stayed on the outside. But if they had used an animal virus, they would have both labels go in.
Lytic Cycle
Lytic or virulent cycle – virus replication occurs and the host is lysed
Lysogenic cycle
Lysogenic cycle – the viral nucleic acid integrates into the host chromosome and replicates when the host DNA replicates

In the integrated state it is called a prophage, which can be induced and when it is it undergoes a lytic cycle and produces mature viruses that lyse the cell.

Lysogenic versus Lytic
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Possible effects that an animal virus may have on the cell it infects
1. Latent infection
virus present but not causing harm to cell, but later emerges in virulent
(lytic) infection.

2. Persistent infection
slow release of virus without cell death.
3. Virulent (lytic)
death of cell and release of virions.

4. Transformation into Tumor cells
Transformation into tumor cell and replication to form more tumor cells.
In transformation, the virus infects the animal cell and is then integrated into host DNA where it is later transcribed into tumor virus mRNA to produce proteins that alter the cell to tumor state.

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Replication of Retrovirus
It is a single strand RNA virus that penetrates into animal cell and is uncoated. It has a reverse transcriptase enzyme that converts single strand RNA into a complementary DNA that is converted to double strand DNA. The double strand DNA is integrated into host DNA. When it is transcribed, it produces viral single strand RNA and protein coat subunits that are assembled into the virion which is released by a budding process that places host membrane
Transformation
genetic transfer mediated by small pieces of double stranded extracellular DNA
Transduction
genetic transfer mediated by virus.
Conjugation
DNA transfer from donar to recipient cell mediated by cell to cell contact and sometimes bridge formation.
(3 – plasmid 4 chromosome)
Categories: Microbiology