Micro1_QA2_HIGHLIGHTED.pptx

1. Which of the following is CORRECT regarding anabolic or catabolic reactions: a.Catabolism and biosynthesis are synonymous b.Anabolism results in energy, nutrients, waste products c.Catabolism results in the synthesis of cell components from nutrients d.At a given moment in time, a bacterial cell...

1. Which of the following is CORRECT regarding anabolic or catabolic reactions: a.Catabolism and biosynthesis are synonymous b.Anabolism results in energy, nutrients, waste products c.Catabolism results in the synthesis of cell components from nutrients d.At a given moment in time, a bacterial cell is executing either only anabolic or catabolic reactions e.Anabolic and catabolic reactions are occurring in parallel within all bacterial cells in a microbial population Anabolism and catabolism Anabolism (anabolic reactions) The processes by which these substances are transformed into new cellular components Biosynthesis Catabolism (catabolic reactions) Biosynthesis requires energy, which is also required for motility and transport. Most obtained from the oxidation of chemical compounds which are broken down into simpler forms The released energy is conserved 3 Catabolic and anabolic reactions Catabolism results in energy + nutrients + waste products Anabolism - synthesis of cell components from nutrients Different bacterial cells have different nutritional requirements and this provides a method for classification 4 1. Which of following classifications of microelements or macroelements is INCORRECT: a.Macroelement : Potassium b.Macroelement : Magensium c.Microelement : Iron d.Microelement : Copper e.Microelement : Manganese Macroelements / macronutrients Potassium, calcium, magnesium and iron exist as cations and have a variety of roles: Potassium required for activity of enzymes including those involved in protein synthesis Calcium Heat resistance of spores Magnesium enzyme co-factor, complexes with ATP, stabilizes ribosomes and cell membranes Iron (Fe²⁺ and Fe³⁺) in cytochromes and a cofactor for enzymes and electron carrying proteins 7 Micronutrients / trace elements Trace elements needed by most cells: Manganese Zinc Cobalt Molybdenum Nickel Copper Part of enzymes and cofactors, aid in the catalysis of reactions and maintenance of protein structure 8 1. Which of the following does NOT require nitrogen during biosynthesis: a.Amino acids b.Lipids c.Carbohydrates d.Nucleic acids e.All of the ABOVE require nitrogen N / P / S metabolism Microorganisms need to incorporate large quantities of these to grow May be available from same sources as carbon etc, but often use inorganic source as well Nitrogen needed for synthesis of: Amino acids Purines Pyrimidines Carbohydrates Lipids Enzyme co-factors Other substances Many use the nitrogen in amino acids. Also reduce nitrate to ammonia and incorporate by assimilatory nitrate reduction 11 N / P / S metabolism Phosphorous present in nucleic acids, phospholipids, ATP, cofactors, proteins and other cell components. Use inorganic phosphate sources and incorporate directly Sulphur needed for synthesis of amino acids, cysteine and methionine, some carbohydrates, biotin and thiamine 12 1. Which of the following statements is INCORRECT regarding bacterial nutrient transport: a. The bacterial cell needs to transport substances into the cell b. Compounds transported into the cell have to pass through fully permeable membranes c. A wide variety of compounds are required, which necessitates a wide variety of different transport systems d. Several different categories of nutrient transport exist e. Both passive and active transport function in parallel within bacterial cells Nutrient uptake Need to be able to transport necessary substances into the cell Have to pass through selectively permeable plasma membrane Many different nutrient molecules needed, complex task using several different transport systems Facilitated diffusion, active transport and group translocation 15 1. Which of the following statements describes facilitated diffusion: a.It is driven by a concentration gradient across a membrane, therefore, it is reversible. b.It is promiscuous, thus, widely variable solutes can be transported by the same transport proteins c.It only allows lipid-soluble molecules to enter into the cell d.Permeases function by decreasing the rate of diffusion e.All of the above are CORRECT Facilitated diffusion Rate of diffusion increased by use of carrier proteins, permeases, embedded in membrane Selective for particular solute Driven by concentration gradient across membrane, so is reversible Allows lipid insoluble molecules to enter the cell e.g. glycerol transport in E. coli, S. typhimurium, Pseudomonas, Bacillus and many others. 18 Facilitated diffusion 19 1. Which of the following is INCORRECT about active transport: a.It allows uptake against a concentration gradient b.It can involve substrate-binding periplasmic binding proteins (PBPs) c.The energy source is ATP d.E. coli transports a variety of sugars in this manner, including arabinose, maltose, ribose, etc…) e.All of the above are CORRECT Active transport Allows uptake against a concentration gradient and therefore allows concentration of solutes inside the cell Substrate-binding proteins in the periplasmic space (PBPs) of Gram-negative bacteria bind the molecule to be transported and interact with membrane transport proteins to move the solute inside the cell Energy source is ATP E. coli transports a variety of sugars (arabinose, maltose, galactose, ribose) via PBPs 22 Active transport (w/PBP) 23 Active Transport Proton motive force (PMF) can also be used to drive active transport. The following examples function as a single protein. Lactose permease of E. coli is a good example: Single protein transports lactose inward as proton enters cell at same time, symport. E. coli also uses proton symport to take up amino acids and organic acids Antiport when, e.g. E. coli pumps sodium outward and protons inward. Sodium gradient drives uptake of sugars and amino acids. 24 Active transport (syn/antiporters) 25 1.Which of the following is INCORRECT about group translocation: a.The molecule is transported into the cell while being chemically altered (phosphorylation) b.It is also referred to as the phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS) c.E. coli uses these systems to take up fructose, glucose, mannitol and sucrose. d.Phosphorylation allows the sugars to directly enter into the ETC e.Obligate aerobes lack these systems but Group translocation (PTS) Molecule transported into cell while being chemically altered, e.g. by phosphorylation Called phosphoenolpyruvate: sugar phosphotransferase system (PTS) Aerobic bacteria lack these systems, but found in facultative anaerobes and some obligate anaerobes E. coli uses PTS to take up glucose, fructose, mannitol and sucrose. 28 Group translocation (PTS) 29 1. Which of the following phases of growth is IMPROPERLY described with respect to the growth curve: a.lag phase : upon inoculation into new medium, the cells require time to prepare before they start growing again b.log phase : microorganisms are dividing at the fastest rate possible for their genetic potential, culture medium and conditions c.stationary phase : this phase is logarithmic with cells dividing and dying d.death phase : cell death remains logarithmic but with a slower rate than the lag phase e.all descriptions are CORRECT 1. Lag phase When a microbial population is inoculated into a fresh medium, growth does not usually begin immediately - lag phase - during which they may need to: resynthesise essential constituents cells need time to recover from damage transfer from rich to poor medium requires synthesis of new enzymes Length of lag phase varies considerably with conditions of bacteria and nature of the medium 32 2. Exponential (Log) phase Exponential phase (log phase): Influenced by temperature, culture medium and genetic characteristics Microorganisms are growing and dividing at the maximal rate possible for their genetic potential, culture medium and conditions. Constant rate of growth Used in biochemical and physiological studies 33 3. Stationary phase Stationary phase - essential nutrient used up, waste products accumulate to unacceptable levels NO net increase or decrease in cell number Usually at a population level of 10⁹ /ml Dependent on level of nutrient availability, physical conditions: oxygen availability if aerobic, build up of toxic waste products e.g. Streptococci producing lactic and other organic acids from sugar fermentation Several genes necessary for survival sur genes 34 4. Death phase Death phase Cell death slower than exponential growth. Also logarithmic Growth curve characteristics reflect events in a population of cells Bacterial growth can be demonstrated on solid culture media with the formation of colonies or in liquid samples via cell counts Viable cell count better with solid media 35 Bacterial growth curve 36 1. Which of the following pairs of environmental conditions and their effect on bacterial growth is MISMATCHED: a.Water : during growth, nutrient and waste products enter and leave in solution, so freely available is a necessity b.Salt : excess salt may modify the threedimensional structure of proteins c.pH : bacteria have an internal buffering systems, thus ancillary buffers are not required in bacterial growth media d.temperature : enzymes (and proteins in general) have an optimal temperature for activity (and stability) e.oxygen : products from reaction with oxygen are toxic to most cells, so most cells have enzymes that protect them Water 80% or more of the cell mass is water During growth, nutrients and waste products enter and leave in solution and so free available water (Aw) is a necessity Mostly the cytoplasm of the cell has higher solute concentration and so water tends to diffuse into the cell Positive water balance 39 Salt (osmolarity) Some bacteria have adapted to higher salt levels (seawater has 3% salt) Halophiles Halophiles require salt levels of 2.8M to saturation of 6.2M Modify structure of proteins and membranes Extreme halophiles accumulate levels of potassium to remain hypertonic, 4-7M Halotolerant bacteria can tolerate some reduction in Aw 40 Effect of pH Most environments have a pH of between 5 and 8-9 and most organisms are able to grow within these parameters Acidophiles grow optimally between pH 0 and 5.5 Neutrophiles between 5.5 and 8 Alkalophiles 8.5-11 With extreme alkalophiles at 10 or above Most bacteria and protozoa are neutrophiles Most fungi require prefer slightly acid conditions, pH4-6. Algae also favour acidity. 41 Effect of pH When obligate acidophiles are placed in neutral pH: cytoplasmic membrane melts (dissolves) cells lyse Obviously need high levels of hydrogen ions for stability Need for buffers when bacteria grown in artificial media to maintain optimum pH 42 Temperature Bacteria and archaea survive over a wide temperature range from -22 to >1000C Extremophiles can tolerate extreme cold or heat Related to structure and enzymes Because they are unicellular, temp surrounding the microorganism has a direct effect upon it and may influence enzyme catalysed reactions High temperatures denaturing enzymes, affect the lipid bilayer etc. 43 Classification by O2 Strict anaerobes are killed by oxygen but can be found in otherwise aerobic environments. e.g. Mouth where aerobes use up the oxygen and enable them to survive Products of oxygen are extremely toxic and so many bacteria have enzymes that protect them (aerotolerant): Superoxide dismutase and catalase 44 1. Which of the following pairs of stages of metabolism and pathways are MISMATCHED: a. First stage : proteins being broken down into amino acids b. Second stage : glycolysis (Embden-Meyerhof-Parnas EMP) c. Third stage : bacterial fermentation d. Fourth stage : flagellar rotation from the H+ being pumped via ETC e. All pairs are CORRECT Overview 47 Three stages of catabolism First stage Proteins, polysaccharides and lipids – first stage catabolism Proteins to amino acids Lipids to glycerol Polysaccharides to monosaccharides 48 Feeding pathways ex. monosaccharides 49 Glucose to pyruvate Second stage: Further breakdown to pyruvate or acetyl-CoA Glycolytic pathway – Embden-Meyerhof-Parnas (EMP pathway) Pentose phosphate pathway Entner-Doudoroff pathway Most common is the glycolytic pathway Takes place in cytoplasm of bacteria 50 Glycolysis / Embden-Meyerhof-Parnas (EMP) pathway 51 Pentose phosphate pathway 52 Entner-Doudoroff pathway 53 Glucose to pyruvate Pentose phospshate pathway may be used at the same time as the glycolytic and Entner-Doudoroff Can operate either aerobically or anaerobically and is also important in biosynthesis Entner-Doudoroff pathway: Only used in a few bacteria, e.g. Pseudomonas spp. and very few Gram-positives (exception is Enterococcus faecalis) EMP / PPP / ED all have pyruvate as end product 54 Maximising energetic return Third stage Aerobic, anaerobic respiration and fermentation Pyruvate can be oxidised by pyruvate dehydrogenase to carbon dioxide and acetyl-CoA Which can enter the TCA cycle Fermentation can take place in the absence of aerobic or anaerobic respiration 55 Replenishment of NAD+ / FAD+ Without replenishment glycolysis will stop 56