In chemical structure procariotic cell don't differ from eucariotic. Substances required for survival are essential nutrients - usually containing the elements (C,H,N,O,P,S,Na, Cl, K,Ca, Fe, Mg). Essential nutrients are considered as macronutrients (required in larger amounts).
Micronutrients are trace elements required in smaller amounts - Zn, Mn, Cu. A growth factors are organic nutrient (amino acid and vitamn) that cannot be synthesized and must be provided.
As a general rule, the optimum temperature for growth, defined as the temperature at which the organism devedes most rapidly, is close to the upper limit of its range. This phenomenon is due to the fact that the speed of enzymatic reactions in the cel approximately doubles for each 100C rise in temperature, and this the cells grow more rapidly as the temperature rises. However, if the temperature becomes too high, enzymes required for the life of the cell are denatured and can no longer function, resulting in the slower growth or death of cells.
Most eucaryotic forms cannot survive above 60 C. but a few thermopilic bacteria called hyperthermophiles, grow between 80 and 100 C .
The majority of organisms do not sive ir grow in high or low pH habitats, because acids and bases can be highly demeging to enzymes and other cellular substances.
The cell wall structures of bacteria make them relatively resistent to changes in osmotic pressure, however, extreme osmotic pressures can result in the death of bacteria. In hypertonic solutions, bacteria may shrind and vecome desiccated. In hypotonic solutions the cell may burst.
Bacteria can be classified into some divisions based upon their requirments for gaseous oxygen or air, which contain 20% oxygen.
Most fungi and protozoas, as well as many bacteria (genera Micrococcus and Pseudononas) have strict requirements for oxygen in their metabolism
Why are some anaerobes killed in the presence of O2, but others can tolerate in even though they cannot use it? Oxygen can be converted into a number of forms that are highly toxic. Some of these toxic forms, such as hydrogen peroxide (H2O2), are formed by metabolic processes onvolning O2. Other toxic compounds, such as superoxide ()2-), are produced as a chamical reaction on light. Cells that are not killed in the presence of oxygen contain enzymes that can convert these toxic compounds to nontoxic forms.
As you can see, aerobic respiration is a series of reactions (glycolysis, the TCA cycle, and the respiration chain) that converst glulose to CO2 and gives off energy. It relies in free oxygen as the final acceptor for electrons and hydrogens and produces a relatively large amount of ATP. Facultative and aerotolerant anaerobes may ile only the glycolysis scheme to incompletely oxidize of ferment glucose. In this case, oxygen is not required, organic compounds are the final electron acceptors, and a relatively small amount of ATP is produced. anaerobic respiration involves the same three pathways as aerobic respiration, but it does not use molecular oxygen as the final electron acceptor. So, to obtain the same amount of energy, a cell growing under anaerobic conditions must degrade about 20 times more glucose than a cell growing under aerobic conditions. Because the amount of work a cell can perform depends on its supply of ATP, a facultatives can synthesize more cell material per unit of time (and therefore can multiply more rapidly) in presence of oxygen than without it.
Anabolism sometimes also called biosynthesis. From simle substrates, cells synthesize the various types of macromolecules needed to allow the cells to live and to grow. The substrates may be the inorganic compounds such as CO2 used by autotrophs or the organic compounds such as glucose used by heterotrophs. The compounds formed from these substrates include proteins (which act as enzymes, structural proteins, membrane carriers, receptors), lipids (components of membrane), carbohydrates (which firm much of the structure of cell walls) and nucleic acids.
There are 3 classification of enzymes. They are found on different principles: genetical cl., biochemical cl., microbiological cl. Many bacterial pathogens secrete inuque exoenzymes that help them avoid host defenses or promote their multiplication in tissue. Because these enzymes contribute to pathogebicity, they are referred to as virulence factors. But we will meet with them later.
After initial synthesis in the cell, exoenzymes are transported extracellularly, where they break down large food molecules of harmful chemicals (examples of exoenzymes are cellulase, amylase, penicillinase). By contrast, endoenzymes are retained intracellularly and function there.
Constitutive enz. are always present and in relatively constant amounts, regardless of the amount of substrate. The enz. involved in utilizing glucose are very important in metabolism and thus are constitutive. Induced enz. are not constatntly present and are produced only when their substrate is present. They are normally presrnt in trace amounts, but their quantity can be increased by the addition of substrate. This property of selective synthesis of enz. prevents a cell from wasting energy by making enzymes that will not be used immediately.
Microbes with rigid cell walls as bacteria are incapable engulfing large food particles. To compensate, they release ebzymes to the extracellular environment and digest the food particles into smaller molecules that can pass freely into the cell.
In Gram+ bacteria, such enzymes as proteases and nusleases, terced exoebzymes, are secreted by the cell into the medium, where they act. In Gram - bacteria, degradative enzymes are generally located in the periplasm. thus, any large molecules that pass through the porous cell wall sill come in contact with these enzymes, which will break them down into smaller molecules that will then pass through the cytoplasmic membrane.
Bulk transport is endocytosis (phagocytosis or pinocytosis) and can be used only by microbes with flexible cell membrane like amebas.
Bohomolets Microbiology Lecture #2
Chemical structure and metabolism of bacteria
Principal elements of the cell and their physiological functions (1) Important inorganic cation and cofactor for some enzymatic reactions. It stabilizes ribosomes 1 Potassium (K) Constituent of some amino acids in proteins and some coenzymes 1 Sulfur (S) Constituent of nucleic acids, phospholipids, coenzymes 3 Phosphorus (P) Constituent of cellular water and organic cell components 8 Hydrogen (H) Constituent of proteins, nucleic acids, coenzymes 14 Nitrogen (N) Constituent of cellular water and most organic cell components; molecular oxygen serves as an electron acceptor in aerobic respiration 20 Oxygen (O) Constituent of all organic cell components 50 Carbon (C) Physiological functions Cell dry weight Element
Principal elements of the cell and their physiological functions (2) The elements are required in very small amounts. Part of enzymes, required for enzyme activity 0,3 Trace elements: Cobalt, Zinc, Molybdenum, Manganese (Mn) Constituent of cytochromes and some proteins 0,2 Iron (Fe) Important inorganic cation 0,5 Chlorine (Cl) Important inorganic cation and cofactor for many enzymatic reactions 0,5 Magnesium (Mg) Important inorganic cation and cofactor for some enzymatic reactions 0,5 Calcium (Ca) One of the principal inorganic cations in eukaryotic cells and important in membrane transport 1 Sodium (Na) Physiological functions Cell dry weight Element
Bacteria biopolimers Constituent of fats, phospholipids . Functions : toxicity , pyrogenic properties , resistance to environment factors and antibiotics 1,5-38% Lipids Constituent of capsule or slime layer. Functions : antigen properties, virulence ( Vi - antigen ). Nutrient substrate 10-30% Carbohydrates Enzymatic activity , antigen properties , toxicity and virulence До 50% Proteins Transmission of genetic information, protein synthesis , stored nutrient substrate 4-15% RNA Heredity , variability 3-4% DNA Functions Content in cell Biopolimer
Environmental factors that influence microbes <ul><li>Temperature </li></ul><ul><li>Oxygen </li></ul><ul><li>pH </li></ul><ul><li>Osmotic pressure </li></ul>Environment factors fundamentally affect the function of metabolic enzymes.
Psychrophiles are microorganisms that have an optimum temperature below 15 0 C and is capable of growth at 0 0 C. These organisms are usually found in such environments as the Arctic and Antarctic regions.
Mesophiles are microorganisms that grow at intermediate temperature and have their optimum within the range of 20 0 C to about 50 0 C. This grope includes the majority of disease-causing bacteria. Their optimum temperature for growth is according to temperature of human body (35-40 0 C)
Thermophiles are microbes that grow optimally at temperatures greater than 450C, and can exist with temperature between 500C and 800C. Heat-loving microbes live in soil and water associated with volcanic activity and in habitats directly exposed to the sun. Extreme thermophiles are microorganisms whole optumum growth temperature is above 80 0 C.
Effects of pH Optimum pH for most mictobes ranges approximately from 6 to 8. Most human pathogens grow optimally at a pH of 6,5 to 7,5. Acidophiles are microorganisms which prefer lower pH (yeasts and molds) Alkalinophiles prefer higher pH
Osmotic pressure and salinity Osmotolerant (halotolerant) are microorganisms that can grow in solutions with high solute concentrate (salinity). Osmophiles (halophiles) are microorganisms that require a high solute concentration (salinity).
General gropes of bacteria with respect to oxygen requirements <ul><li>Obligate (strict) aerobes </li></ul><ul><li>Obligate (strict) anaerobes </li></ul><ul><li>Facultative anaerobes </li></ul><ul><li>Microaerophiles </li></ul><ul><li>Aerotolerant microorganisms </li></ul><ul><li>Capnophiles </li></ul>
Obligate aerobes There are microorganisms that cannot grow without oxygen because they metabolize sugars through a pathway that requires oxygen.
Obligate anaerobes There are microorganisms that cannot multiply is any oxygen is present. Some members are actually killed by traces of oxygen because they cannot modify the toxic forms of oxygen produced in metabolism. Some of their enzymes are denatured by oxygen. Among the more important anaerobic pathogens are some species of Clostridium, Bacteroides
Facultative anaerobes There are microorganisms that does not require oxygen for their metabolism and capable of growth in the absence of oxygen. This type of organism metabolizes by aerobic respiration when oxygen is present, but, in its absence, it adopts an anaerobic mode of metabolism such as fermentation. A large member of bacterial pathogens fall into this group (Enterobacteriaceae, Staphylococcus).
Microaerophiles These microorganisms require small amounts of oxygen (2% to 10%), but higher concentration are toxic. Disease-causing microaerophilic microorganisms are Helicobacter pylori (the agent of gastrointestinal ulcers), Actinomyces israelii.
Aerotolerant anaerobes These microorganisms grow in the presence or absence of oxygen, but unlike facultative anaerobes, they derive no benefit from oxygen. Medically important member of this grope is Streptococcus pyogenes (agent of strep throat).
Capnophiles There are microorganisms that grow better at a higher CO 2 tension than is normally present in the atmosphere. Special CO 2 incubators are used for cultivation of capnophile bacteria. Medically important member of this grope is Streptococcus pneumonia (agent of pneumonia), Neisseria (agents of gonorrhea and meningitis), Brucella (agent of undulant fever).
Enzyme content of bacteria with different requirement for oxygen Neither catalase nor superoxide dismutase Strict anaerobe Superoxide dismutase Aerotolerant Small amount of catalase and superoxide dismutase Microaerophile Catalase Superoxide dismutase Facultative anaerobe Catalase – H 2 O 2 H 2 O + O 2 Superoxide dismutase O 2 - +2H+ O 2 + H 2 O 2 H 2 O + O 2 Strict aerobe Enzyme content for O 2 detoxification Name
Metabolic strategies among heterotrophic microorganisms Facultative, aerotolerant, strict anaerobes 2 ATP, CO2, ethanol, lactic acid Organic molecules Glycolysis Fermentative Anaerobes, some facultatives CO 2 , ATP, organic acids, H 2 O, CH 4 , N 2 Various inorganic salts Glycolysis, TCA cycle, electron transport Respiration Anaerobe metabolism Aerobes, facultative anaerobes 38 ATP, CO 2 , H 2 O O 2 Glycolysis, TCA cycle, electron transport Aeronic restiration Chief microbe type Net products Final elect-ron acceptor Pathways involved Scheme
Metabolism is the sum of cellular chemical changes; it involves scores of reactions that interlink in linear or branched pathways. Metabolism is a complementary process consisting of anabolism and catabolism
Features of bacterial metabolism <ul><li>High enzyme activity </li></ul><ul><li>Different pathways of metabolism </li></ul><ul><li>Metabolism is supple and efficient </li></ul>
Anabolism is any process that results in synthesis of cell molecules and structures. It is a building and bond-making process that forms larger molecules from smaller ones, and it usually requires the input of energy. Catabolism is the inverse process in which large molecules are degraded. During the catabolism energy is released and can be stored in form of adenosine triphosphate (ATP).
Some enzymes and their function Catalyzes the reduction (addition of electrons and hydrogen) to O 2 Molecular oxygen Oxido-reductase Oxidase Catalyzes the conversion of pyruvic acid to lactic acid Pyruvic acid Oxido-reductase Lactate de-hydrogenase Catalyzes the conversion of the substrate to two 3-carbon fragments Fructose diphosphate Lyase Aldolase Synthesizes a strand of DNA using the complementary strand as a model DNA nucleosides Transfe-rase DNA polymerase Hydrolyzes beta-lactam ring Penicillin Hydrolase Penicillinase Breaks lactose down into glucose and galactose Lactose Hydrolase Lactase Action Substrate Enzyme class Name
Nutritional categories of microbes by carbon and energy source Only certain bacteria, such as methanogens Simple inorganic chemicals CO 2 Chemo-autotroph Photosynthetic organism, such as algae, plants, cyanobacteria Sunlight CO 2 Photo-autotroph Nonliving environment CO 2 Autotroph Examples Energy source Carbon source Category
Nutritional categories of microbes by carbon and energy source Various parasites and pathogens; can be bacteria, fungi, protozoa Utilizing the tissues, fluids of a live host Organic Parasite Fungi, bacteria Metabolizing the organic matter of dead organisms Organic Saprobe Protozoa, fungi, many bacteria Metabolic conversion of the nutrients from other organisms Organic Chemo-heterotroph Other organisms Organic Heterotroph Examples Energy source Carbon source Category
Substrate degradation in Gram-positive and Gram-negative bacteria Gram-positive Gram-negative
How microbes take in molecules <ul><li>In passive transport, nutrient exist in a gradient from a high concentration outside the cell to a low concentration inside the cell. The molecules diffuse into the cell without consumption of energy </li></ul><ul><li>In active transport, the cell actively picks up nutrients from a solution in which the nutrients are not in a gradient (it requires of energy) </li></ul><ul><li>In bulk transport, large solids or mass of liquids enter the cell intact by engulfment. It type of active transport. </li></ul>
Features of diffusion and active transport Binds to protein in periplasmic space, which then interacts with a receptor protein in the cytoplasmic membrane Higher on inside Yes Active transport Permeases in cytoplasmic membrane involved Same No Facilitated diffusion Diffuses through cytoplasmic membrane Same No Passive diffusion Mechanisms of transport Concentration on outside and inside of cell Energy required Type of transport
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