6.0 Notes
Dilution Techniques
A series of dilutions using a 1 ml original culture to create various concentrations.
1:10 Dilution (10⁻¹): Mix of 1 ml original culture with 9 ml broth.
1:100 Dilution (10⁻²): Mix of 1 ml from the 1:10 dilution with 99 ml broth.
1:1000 Dilution (10⁻³): Mix of 1 ml from the 1:100 dilution with 999 ml broth.
1:10,000 Dilution (10⁻⁴): Mix of 1 ml from the 1:1000 dilution with 9999 ml broth.
1:100,000 Dilution (10⁻⁵): Mix of 0.1 ml from the 1:10,000 dilution.
Quantifying results:
TNTC: Too numerous to count indicates high colony counts on plates.
Example counts from different dilutions show varying levels of growth:
1:10,000 dilution: TNTC
1:100,000 dilution: 65 colonies
1:1000 dilution: 6 colonies
1:10 dilution: 0 colonies.
Importance of Serial Dilutions
Saves solvent/broth by allowing for effective dilution without wasting resources.
Provides a controlled method to reduce concentration to manageable levels for enumeration.
Example calculations provided in context:
1 ml bacteria mixed with 9 ml broth results in larger dilutions rather than excess broth usage.
Microbial Genetics Overview (Chapter 7)
Gene: A linear sequence of nucleotides encoding proteins.
E.g., ATGGGCTCAA…
Gene locus: Specific location on a chromosome.
Genome: Total DNA from a species.
Genetic code: Nucleotide triplets in DNA that dictate transitions from DNA to protein.
Genotype and Phenotype
Genotype: The genetic constitution of an organism.
Phenotype: The observable physical characteristics determined by genotype.
Characteristics include:
Transmission of traits from parent to offspring.
Variation and expression of traits based on genetic material, mutations, or transformations.
Example: Fitness or appearance based on DNA variations.
Applications of Microbial Genetics
Utilization of microbial genetics for practical applications such as:
Production of insulin and vaccines like Hepatitis B.
Understanding the role of genetic differences in diseases.
Easier study compared to complex human genetics.
Genome Size and Organism Complexity
Genome size does not necessarily indicate organism complexity:
Smallest viruses: 5 genes
E. coli: 4,288 genes
Roundworm: 19,000 genes
Humans: 25,000 genes
Water Flea: 31,000 genes
Corn: 50,000 genes
Genetic Material Packaging
Differences in genetic material packaging across organisms:
Prokaryotes: Circular genomes, plasmids, no nucleus.
Eukaryotes: Linear chromosomes, packaged in a nucleus (including organelles).
Viruses: Varying structures, can be DNA or RNA.
Nucleic Acids
Nucleotides consist of:
A phosphate group, a pentose sugar, and a nitrogenous base.
DNA Structure:
Two complementary strands running antiparallel.
Hydrogen bonds between base pairs:
Three bonds between guanine (G) and cytosine (C).
Two bonds between adenine (A) and thymine (T).
DNA Replication
Semiconservative process requiring multiple enzymes:
Helicase: Unzips DNA by breaking hydrogen bonds.
Polymerase: Synthesizes new strands by adding nucleotides in the 5' to 3' direction.
Leading strand synthesized continuously; lagging strand synthesized in fragments (Okazaki fragments).
Key points:
DNA replication process is fast (approximately 1 hour).
Accurate synthesis is critical for organism's integrity.
Transcription and Translation
Transcription: Process of synthesizing RNA using DNA.
Occurs in the nucleoid (prokaryotes) or nucleus (eukaryotes).
Different types of RNA produced:
mRNA: Translated into polypeptides.
rRNA: Forms ribosomes.
tRNA: Transfers amino acids to ribosome.
Translation: Synthesis of proteins based on mRNA.
Events include promoter recognition, elongation, termination.
Eukaryotic vs. Prokaryotic Gene Regulation
Prokaryote genes often grouped into operons; eukaryotic genes independently transcribed.
Eukaryotic genes contain introns (non-coding) and exons (coding).
Splicing: Mechanism to join exons and remove introns during RNA processing.
Gene Expression
Despite identical genetic codes, diverse cell types arise due to differential gene expression methods.