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DNA Structure and Function
- DNA and RNA are macromolecules called nucleic acids
- The function of nucleic acids is to store and retrieve genetic information
- DNA is a polymer of nucleotides
- DNA has 2 polynucleotide chains held together by complementary base pairs
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The four nitrogenous bases in DNA
- Thymine and Cytosine
- Adenine and Guanine
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The scientists who discovered DNA’s structure
Rosalind Franklin, James Watson & Francis Crick
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Information flow in a cell (Gene Expression)
DNA --> Transcription --> RNA --> Translation --> Protein
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Ingredients for Translation
- DNA, mRNA and Protein
- 1. The ribosome and initiator tRNA bind to mRNA to begin translation.
- 2. On the assembled ribosome, a tRNA carries the first amino acid and it is paired with the start codon on the mRNA. A tRNA carrying the second amino acid approaches.
- 3. The place on the ribosome where the first tRNA sits is the P site and A sits right next to it. The 2nd codon of the mRNA pairs with a tRNA carrying the second amino acid.
- 4. The first amino acid joins to the second by a peptide bond and the first mRNA is released.
- 5. The ribosome moves along the mRNA until the second tRNA is in the P site and the process continues.
- 6. When the ribosome reaches a stop codon, the polypeptide is release.
- 7. Finally, the last tRNA is released and the ribosome comes apart. The released polypeptide forms a new protein.
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Transcription
- 1. Initiation
- 2. Elongation
- 3. Termination
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DNA Replication
- Copies chromosomes for cell division.
- Starts off with a parental molecule of DNA. Then both parental strands serve as templates and nucleotides fill in. Finally, there are 2 identical daughter molecules of DNA.
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FIltration Method
The sample is filtered. The filter is transferred to a petri dish and colonies grow on filter.
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Counting Methods
- Grid Counting
- Metabolic activity: measure appearance or disappearance of metabolic products
- Dry weight: used for filamentous organisms where an accurate plate count cannot be done.
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Bacterial Growth Curve
- Lag phase: bacteria start to grow
- Exponential phase: population doubles every 20 minutes.
- Stationary Phase: Growth stops
- Death phase: Bacteria die faster than they multiply.
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Bacteria Control
- How quickly bacteria are killed depends upon:
- Initial number of bacteria present
- Presence of lipids or proteins in media
- Time of exposure to the chemical agent
- Which microbes are present
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Sterilization
Destruction or removal of all forms of microbial life including endospores
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Commercial Sterilization
Sufficient heat treatment to kill endospores of Clostridium Botulinum in canned food
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Disinfection
Destruction of vegetative pathogens
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Antisepsis
Destruction of vegetative pathogens on living tissue
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Degerming
Removal of microbes from a limited area such as the skin around an injection site
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Sanitization
Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels.
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Chemical Agents used to Control Microbial Growth
Disruption of plasma membrane, denaturation of proteins (phenol, phenolics like vesphene) denaturation of enzymes, mechanical removal of microbes through scrubbing (soap)
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Evaluation of Chemical Agents
- Disk-diffusions method
- Dilution test
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Physical Control of Microbial Growth
- Pasteurization
- -Phosphatase test
- Moist heat
- -autoclaving
- Dry heat
- -Flaming, incineration, hot-air sterilization
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Physical Control of Microbial Growth (Low Temperature)
- Bacteriostatic effect
- Slow freezing: causes ice crystals to form
- Freezing
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Physical Control of Microbial Growth (Filtration)
- Important for heat sensitive materials
- Works by exclusion
- Different pore sizes
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Other Physical Controls
- High Pressure
- Dessication
- Osmotic Pressure
- Radiation
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