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
The four nitrogenous bases in DNA
- Thymine and Cytosine
- Adenine and Guanine
The scientists who discovered DNA’s structure
Rosalind Franklin, James Watson & Francis Crick
Information flow in a cell (Gene Expression)
DNA --> Transcription --> RNA --> Translation --> Protein
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.
- 1. Initiation
- 2. Elongation
- 3. Termination
- 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.
The sample is filtered. The filter is transferred to a petri dish and colonies grow on filter.
- 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.
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.
- 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
Destruction or removal of all forms of microbial life including endospores
Sufficient heat treatment to kill endospores of Clostridium Botulinum in canned food
Destruction of vegetative pathogens
Destruction of vegetative pathogens on living tissue
Removal of microbes from a limited area such as the skin around an injection site
Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels.
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)
Evaluation of Chemical Agents
- Disk-diffusions method
- Dilution test
Physical Control of Microbial Growth
- -Phosphatase test
- Moist heat
- Dry heat
- -Flaming, incineration, hot-air sterilization
Physical Control of Microbial Growth (Low Temperature)
- Bacteriostatic effect
- Slow freezing: causes ice crystals to form
Physical Control of Microbial Growth (Filtration)
- Important for heat sensitive materials
- Works by exclusion
- Different pore sizes
Other Physical Controls
- High Pressure
- Osmotic Pressure