Microbial Metabolism Lecture 5

Microbiology Exam 3 MICROBIAL METABOLISM (Lecture Topic 5) Metabolism: Refers to all chemical reactions in a cell, including those that build up (anabolism) and break down (catabolism) molecules to produce energy. Redox reactions: These involve the transfer of electrons. ● Oxidized means a substance loses electrons. ● Reduced means a substance gains electrons. Enzymes: Proteins that speed up biochemical reactions. ● Apoenzyme: The protein part of an enzyme, without any cofactors. ● Cofactor: A non-protein component required by some enzymes to function (e.g., metal ions). ● Holoenzyme: The complete enzyme, consisting of the apoenzyme and its cofactor. ● Enzymes are crucial because they lower activation energy for reactions and are named often by adding “-ase” to the substrate or the type of reaction they catalyze. Impact of pH and temperature on enzymes: ● Enzymes work best at optimal pH and temperature. ● Extremes in either can denature enzymes (alter their structure), making them ineffective. Enzyme inhibition: ● Competitive inhibition: A substance competes with the substrate for binding to the active site. ● Allosteric inhibition: A substance binds elsewhere on the enzyme, changing its shape and reducing activity. NAD and FAD: These are electron carriers. ● NAD is reduced to NADH and FAD is reduced to FADH2 during metabolic reactions. They carry electrons to the electron transport chain for ATP production. Stages of aerobic respiration: ● Glycolysis, Krebs cycle, and Electron Transport Chain (ETC). They occur in this order. ATP production: ● ● ● ● Glycolysis: 2 ATP Krebs cycle: 2 ATP ETC: About 34 ATP Total: ~38 ATP for prokaryotes, ~36 ATP for eukaryotes. Cellular respiration steps: ● Glycolysis starts with glucose, producing pyruvate. ● Krebs cycle starts with acetyl-CoA, producing CO2. ● ETC starts with NADH and FADH2, producing ATP and water. Location of respiration: ● Prokaryotes: Glycolysis in the cytoplasm, Krebs in the cytoplasm, and ETC in the cell membrane. ● Eukaryotes: Glycolysis in the cytoplasm, Krebs in the mitochondrial matrix, and ETC in the inner mitochondrial membrane. ATP synthase: This enzyme creates ATP from ADP and inorganic phosphate, driven by a flow of protons (H+) across a membrane during oxidative phosphorylation. Metabolic pathways: ● EMP (Embden-Meyerhof-Parnas): The most common glycolytic pathway, produces 2 pyruvate and 2 ATP and 2 NADH ● PPP (Pentose Phosphate Pathway): Produces NADPH and ribose-5-phosphate for nucleotide synthesis. ● ED (Entner-Doudoroff): Alternative glycolytic pathway, produces pyruvate, used by some bacteria. produces 1 ATP 1NADPH Fermentation: Occurs when oxygen is not available, allowing cells to regenerate NAD+ by converting pyruvate into products like lactic acid or ethanol. Lipid and protein catabolism: These molecules are broken down during the Krebs cycle. Types of organisms: ● Photoautotrophs: Use light energy and CO2 (e.g., plants, cyanobacteria). ● Chemoautotrophs: Use chemical energy and CO2 (e.g., some bacteria). ● Photoheterotrophs: Use light for energy but organic compounds for carbon (e.g., purple non-sulfur bacteria). ● Chemoheterotrophs: Use organic compounds for both energy and carbon (e.g., animals, fungi). MICROBIAL GROWTH (Lecture Topic 6) Temperature groups of bacteria: Bacteria are classified into five groups based on their optimum growth temperatures: ○ Psychrophiles: Thrive at cold temperatures (below 15°C, optimal around 10°C). ○ Psychrotrophs: Grow between 0–30°C, optimal around 20–30°C (spoil food in refrigerators). ○ Mesophiles: Optimal growth at moderate temperatures, around 25–40°C (most human pathogens). ○ Thermophiles: Thrive at warmer temperatures, 50–60°C. ○ Hyperthermophiles: Can grow at extremely\ high temperatures, above 80°C, often found in hot springs. ● Physical and chemical requirements for microbial growth: ○ Physical requirements: Temperature, pH (most bacteria grow best between pH 6.5 and 7.5), and osmotic pressure (salt concentration). ○ Chemical requirements: Carbon, nitrogen, sulfur, phosphorus, trace elements (e.g., iron, magnesium), and in some cases, oxygen. ● Oxygen requirements for microbes: ○ Obligate aerobes: Require oxygen. ○ Obligate anaerobes: Cannot tolerate oxygen. ○ Facultative anaerobes: Can grow with or without oxygen, but prefer oxygen. ○ Aerotolerant anaerobes: Do not use oxygen but can tolerate its presence. ● Microaerophiles: Require lower levels of oxygen than present in the atmosphere. Thioglycolate broth is often used to determine oxygen preferences, as it allows an oxygen gradient, where bacteria grow based on their oxygen needs. Chemically defined vs. complex culture media: ○ Chemically defined media: The exact chemical composition is known. Used when precise nutrient requirements of microbes are known (e.g., in research settings). ○ Complex media: Contains a variety of ingredients like meat extracts or yeast extract, and the exact composition is not known. Often used in routine lab culture work (e.g., nutrient broth, tryptic soy agar). Selective, enrichment, and differential media: ○ Selective media: Suppresses the growth of unwanted bacteria while encouraging the growth of the desired microbe (e.g., MacConkey agar for Gram-negative bacteria). ○ Enrichment media: Provides conditions that favor the growth of a particular microbe but doesn’t suppress others (e.g., blood agar for growing fastidious organisms). ○ Differential media: Allows differentiation between species based on observable changes (e.g., blood agar differentiates organisms based on hemolysis). Biosafety levels (BSLs): ○ BSL-1: Low-risk microbes (e.g., non-pathogenic strains of E. coli). ○ BSL-2: Moderate-risk pathogens (e.g., Staphylococcus aureus). ○ BSL-3: High-risk microbes that can cause serious or potentially lethal diseases (e.g., Mycobacterium tuberculosis). ○ BSL-4: High-risk microbes with no available treatments or vaccines (e.g., Ebola virus). Prokaryote and eukaryote reproduction: ○ Prokaryotes: Replicate via binary fission, a simple division process. ○ Eukaryotes: Replicate via mitosis (somatic cells) or meiosis (sex cells). ○ Yeast: Use mitosis with budding, where a new cell forms as a bulge. ○ ● ● ● ● ●