Microbiology Lab Concepts and Core Topics: Metabolism, Genetics, and Biotechnology

Lab Concepts

Streak Plating

Streak plating is a fundamental microbiological technique used to isolate pure colonies from a mixed culture. It involves spreading bacteria across the surface of an agar plate in a pattern that thins out the sample and separates individual cells.

• Purpose: To obtain isolated colonies for further study or identification.

• Common Errors: Not flaming the loop between quadrants, using too much inoculum, or not streaking enough can result in poor isolation.

• Troubleshooting: Ensure proper sterilization of the loop, use a gentle touch, and streak in a systematic pattern.

DNA Extraction

DNA extraction is the process of isolating DNA from cells or tissues for analysis. Safety and proper technique are essential, especially when using a centrifuge.

• Centrifuge Safety and Balancing: Always balance tubes with equal volumes opposite each other to prevent damage or accidents.

• Centrifuge Purpose: To separate components based on density by spinning samples at high speed.

• Supernatant vs Pellet: The supernatant is the liquid above the solid material (pellet) after centrifugation. The pellet contains the denser material collected at the bottom.

Key Materials and Functions in Strawberry DNA Extraction

• Strawberries: High DNA yield due to being octoploid (eight sets of chromosomes).

• Dish Soap (Detergent): Breaks down cell and nuclear membranes by dissolving phospholipids.

• Salt (NaCl): Neutralizes DNA's negative charge, allowing it to clump and separate from proteins.

• Ice-Cold Ethanol/Isopropyl Alcohol: Precipitates DNA, making it visible as white fibers.

• Plastic Bag/Mash: Mechanically disrupts cell walls.

• Filter (Coffee filter/cheesecloth): Removes cell debris, leaving DNA in the filtrate.

• Stirrer (Wooden skewer/hook): Used to spool and collect DNA.

Comparison of DNA Extraction Methods

• Bead Bashing: Uses beads to physically break cells open.

• DNA Wash: Removes contaminants from DNA.

• Column Filtration: DNA binds to a column matrix and is washed and eluted for purity.

CH 5: Microbial Metabolism

Catabolism and Anabolism

Microbial metabolism consists of all chemical reactions within a microorganism. These reactions are divided into two main types:

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy. These are exergonic and often involve hydrolytic reactions (addition of water to break bonds).

• Anabolism: The synthesis of complex molecules from simpler ones, consuming energy. These are endergonic and involve dehydration synthesis (removal of water to form bonds).

ATP Release and Consumption:

• Catabolic reactions release ATP.

• Anabolic reactions consume ATP.

Enzymes

Enzymes are biological catalysts, usually proteins ending in -ase, that speed up chemical reactions without being consumed.

• Role in Pathways: Enzymes lower activation energy and are essential for metabolic pathways, converting substrates to products.

• Substrate: The molecule upon which an enzyme acts.

• Active Site: The region on the enzyme where the substrate binds.

• Products: Common products include ATP, acids, alcohols, and gases.

Factors Affecting Enzyme Activity

• pH: Each enzyme has an optimal pH; deviations can denature the enzyme.

• Temperature: High temperatures can denature enzymes; low temperatures slow activity.

• Substrate Concentration: Increased substrate increases reaction rate until saturation.

• Inhibitors: Chemicals that decrease enzyme activity (competitive or noncompetitive).

CH 8: Microbial Genetics

Central Dogma and -Omics Analyses

The central dogma describes the flow of genetic information: DNA → RNA → Protein.

• Genomics: Study of the entire genome (DNA).

• Transcriptomics: Study of RNA transcripts.

• Proteomics: Study of the protein complement.

• Mutations: Changes at any step can affect subsequent steps and overall phenotype.

Gene Expression and Regulation

• Transcription: Synthesis of RNA from DNA; gene expression.

• Constitutively Expressed: Genes that are always active.

• Repressible Operon: Normally on; can be turned off by a repressor (e.g., trp operon).

• Inducible Operon: Normally off; can be turned on by an inducer (e.g., lac operon).

• Role of Enzymes and Substrates: Inducers activate enzymes; repressors inhibit them.

• Operon: A cluster of genes under control of a single promoter and operator.

• Operator: DNA segment where a repressor binds.

• Promoter: DNA sequence where RNA polymerase binds to initiate transcription.

Enzymes in Genetic Processes

• Enzymes are essential for DNA replication, transcription, and translation.

RNA Differences: Prokaryotes vs Eukaryotes

• Prokaryotic RNA: Often polycistronic (multiple genes per mRNA), no introns, transcription and translation are coupled.

• Eukaryotic RNA: Monocistronic, contains introns (spliced out), transcription in nucleus, translation in cytoplasm.

Ribosomes and Amino Acids

• Ribosomes: Sites of protein synthesis; differ in size between prokaryotes (70S) and eukaryotes (80S).

• Amino Acids: Building blocks of proteins.

Codons

• Codon: A sequence of three nucleotides in mRNA that codes for a specific amino acid.

• Not all codons are the same; some code for the same amino acid (degeneracy), and some are stop codons.

Gene Transfer and Mobile Genetic Elements

• Vertical Gene Transfer: Parent to offspring.

• Horizontal Gene Transfer: Between organisms of the same generation.

• Mobile Genetic Elements (MGEs): DNA segments that can move within or between genomes (e.g., plasmids, transposons).

Plasmids

• Conjugative Plasmids: Carry genes for transfer between cells (e.g., F factor).

• R Factors: Plasmids carrying antibiotic resistance genes.

Transposons

• DNA sequences that can change position within the genome.

• Pros: Genetic diversity, adaptation.

• Cons: Can disrupt genes, cause mutations.

Bacteriophages (Phages)

• Lytic Cycle: Phage replicates and lyses host cell.

• Lysogenic Cycle: Phage DNA integrates into host genome and replicates with it.

Mechanisms of Horizontal Gene Transfer

• Conjugation: Direct transfer of DNA via cell-to-cell contact.

• Transformation: Uptake of free DNA from the environment (e.g., Griffith's experiment).

• Transduction: Transfer of DNA by bacteriophages.

CH 9: Biotechnology and DNA Technology

Key Concepts

• Vector: A DNA molecule used to carry foreign genetic material into a host cell (e.g., plasmids, viruses).

• Biotechnology: The use of living organisms or their products to modify or improve human health and the environment.

• rDNA Technology: Techniques for combining DNA from different sources (genetic modification).

• Common Products: Insulin, growth hormones, vaccines, genetically modified crops.

• Recombination: Exchange of genetic material between different DNA molecules, resulting in new combinations.

PCR (Polymerase Chain Reaction)

• A technique to amplify specific DNA sequences.

• Heating: Denatures DNA (separates strands).

• Cooling: Allows primers to anneal and DNA polymerase to extend new strands.

Cloning

• Production of identical copies of DNA, cells, or organisms.

• Applications: Gene function studies, protein production, transgenic organisms.

DNA Insertion Methods

• Transformation: Uptake of naked DNA by cells.

• Electroporation: Use of electric pulses to introduce DNA into cells.

• Protoplast Fusion: Fusion of cells without cell walls to combine genetic material.

• Microinjection: Direct injection of DNA into cells.

Sequencing Methods

• Amplicon Sequencing: Targets specific DNA regions for sequencing (e.g., 16S rRNA gene).

• Shotgun Sequencing: Randomly sequences all DNA in a sample; useful for whole-genome analysis.

• Nanotechnology: Used to enhance sequencing accuracy and throughput.

Method	Main Purpose	Key Features
Streak Plating	Isolate pure colonies	Sequential dilution on agar plate
DNA Extraction	Isolate DNA from cells	Uses detergent, salt, alcohol
PCR	Amplify DNA	Cycles of heating and cooling
Transformation	Introduce foreign DNA	Natural or artificial uptake
Electroporation	Introduce foreign DNA	Electric pulses create pores
Protoplast Fusion	Combine genetic material	Fusion of cell membranes
Microinjection	Introduce foreign DNA	Direct injection into cell

Example: The production of human insulin using recombinant DNA technology involves inserting the human insulin gene into a bacterial plasmid vector, transforming bacteria, and harvesting the insulin produced.

Additional info: The notes above expand on brief points with academic context, definitions, and examples to ensure completeness and clarity for exam preparation.