DNA Structure & Base Pairing

Base Pairing Rules and DNA Composition

Understanding the structure of DNA and the rules of base pairing is fundamental in microbiology, as it underpins genetic inheritance and molecular biology techniques.

• DNA (Deoxyribonucleic Acid): The molecule that carries genetic information in all living organisms.

• Base Pairing Rules: In DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

• Example: If 30% of the bases are adenine (A), then thymine (T) must also be 30%. The remaining 40% is divided equally between cytosine (C) and guanine (G), so each is 20%.

Equation:

Central Dogma of Molecular Biology

Transcription and Translation

The central dogma describes the flow of genetic information from DNA to RNA to protein. Disruptions in this process can affect cell survival and function.

• Transcription: The process by which DNA is copied into messenger RNA (mRNA) by RNA polymerase.

• Translation: The process by which ribosomes synthesize proteins using mRNA as a template.

• Example: A drug that prevents mRNA from being translated into proteins targets the translation step, potentially inhibiting bacterial growth.

DNA Replication & Antibiotics

Antibiotic Mechanisms and DNA Polymerase

Some antibiotics target bacterial DNA replication by inhibiting DNA polymerase, the enzyme responsible for synthesizing new DNA strands.

• DNA Polymerase: Enzyme that synthesizes DNA molecules from nucleotides.

• Antibiotic Resistance: Bacteria may develop resistance to antibiotics that target DNA replication, impacting treatment effectiveness.

Genetic Mutations

Leading vs. Lagging Strand & Okazaki Fragments

During DNA replication, the leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments called Okazaki fragments.

• Okazaki Fragments: Short DNA fragments synthesized on the lagging strand during DNA replication.

• Mutation Example: A mutation that prevents Okazaki fragment formation would disrupt lagging strand synthesis, impairing DNA replication.

Types of Mutations

• Point Mutation: A single nucleotide change; may have minor or no effect.

• Frameshift Mutation: Insertion or deletion of a nucleotide shifts the reading frame, often causing more severe effects on protein function.

• Example: Deleting one nucleotide from a gene causes a frameshift, likely resulting in a nonfunctional protein.

Transcription, Translation, and Antibiotic Resistance

RNA Polymerase and Ribosomes as Drug Targets

Antibiotics can target bacterial RNA polymerase (blocking transcription) or ribosomes (blocking translation), inhibiting bacterial growth.

• RNA Polymerase Inhibitors: Block mRNA synthesis, affecting only bacteria if the drug is specific.

• Ribosome Inhibitors: Prevent protein synthesis by blocking ribosome function.

Predicting Amino Acid Sequences & Genetic Diseases

Genetic Code and Protein Synthesis

The genetic code translates nucleotide sequences into amino acid sequences. Mutations can alter protein structure and function.

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

• Example: The DNA sequence 5'-ATG GGC TTT TAA-3' codes for the amino acids methionine, glycine, phenylalanine, and a stop signal.

Conjugation, Transformation & Public Health

Horizontal Gene Transfer in Bacteria

Bacteria can acquire new genetic traits, such as antibiotic resistance, through horizontal gene transfer mechanisms like conjugation and transformation.

• Conjugation: Transfer of genetic material between bacteria via direct contact, often involving plasmids.

• Transformation: Uptake of free DNA from the environment by a bacterium.

• Plasmids: Small, circular DNA molecules that can carry antibiotic resistance genes.

Anabolic Reactions & Bacterial Growth

Macromolecule Synthesis and Energy Requirements

Anabolic reactions build complex molecules like proteins and DNA, requiring energy input, usually in the form of ATP.

• Anabolism: Biosynthetic processes that require energy to build cellular components.

• Example: Rapid bacterial growth during infection involves increased anabolic activity and ATP consumption.

ATP & Metabolic Energy

ATP Production and Utilization

ATP (adenosine triphosphate) is the primary energy currency in cells, produced mainly through cellular respiration.

• ATP: Molecule that stores and transfers energy for cellular processes.

• Equation:

Enzyme Activation Energy & Industrial Applications

Enzyme Function and Industrial Use

Enzymes lower the activation energy required for biochemical reactions, making them useful in industrial processes, especially when engineered for heat resistance.

• Activation Energy: The minimum energy required to start a chemical reaction.

• Heat-Resistant Enzymes: Useful in high-temperature cleaning and industrial applications.

Cellular Respiration Overview & Oxygen Use in Bacteria

Aerobic vs. Anaerobic Respiration

Bacteria can use oxygen (aerobic respiration) or other molecules (anaerobic respiration) as final electron acceptors in cellular respiration, affecting ATP yield.

• Aerobic Respiration: Uses oxygen, produces more ATP per glucose molecule.

• Anaerobic Respiration: Uses alternative electron acceptors, produces less ATP.

Citric Acid Cycle & Bacterial Metabolism

Role of Acetyl-CoA and Alternative Pathways

The citric acid cycle (Krebs cycle) is a key metabolic pathway for energy production. Bacteria lacking pyruvate into Acetyl-CoA must use alternative pathways to generate energy.

• Citric Acid Cycle: Series of reactions that generate ATP, NADH, and FADH2 from Acetyl-CoA.

• Alternative Pathways: Fermentation or other metabolic routes may be used if the citric acid cycle is blocked.

Electron Transport Chain & Drug Development

Proton Pumping and ATP Synthesis

The electron transport chain (ETC) pumps protons across the bacterial inner membrane, creating a proton gradient that drives ATP synthesis.

• ETC Inhibitors: Drugs that block proton pumping reduce ATP production and can inhibit bacterial growth.

• Equation:

Labeling Enzymes and Replication Steps

Major Enzymes in DNA Replication

Key enzymes involved in DNA replication include:

• Helicase: Unwinds the DNA double helix.

• Primase: Synthesizes RNA primers.

• DNA Polymerase: Synthesizes new DNA strands.

• Ligase: Joins Okazaki fragments on the lagging strand.

• Single-Strand Binding Proteins: Stabilize unwound DNA.

Most ATP is produced during the electron transport chain step of cellular respiration.

Summary Table: DNA Replication Enzymes

Additional info: These study notes expand on the exam review questions by providing definitions, explanations, and context for each major microbiology topic covered in the provided materials.