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Microbial metabolism lecture 3, Oxygen requirements, Glycolysis,…
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Oxygen requirements
Aerobic microbes.
- can grow in presence of atmospheric oxygen. (21%)
Anaerobic.
- some microbes grow in the absence of oxygen.
Facultative anaerobes
- do not require oxygen for growth, but grow faster in its presence.
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Oxygen is highly toxic to some anaerobic bacteria, this is due to toxic products called reactive oxygen species (ROS)
- Hydrogen peroxide (H202).
-Superoxide radical (02)
Hydroxyl radical (OH-)
Aerobes have enzymes ( e.g. Superoxide dismutase & catalase) to decompose these products anaerobes do not.
Other** aerobic microbes use pigments, such as carotenoids, to detoxify the ROS.**
Some anaerobes, with low levels of enzymes/ pigments are killed by the exposure of oxygen- if your wanting to grow these in a lab, a anaerobic chamber is required.
Glycolysis
conversion of 1 molecule of glucose (6C) to 2 molecules of pyruvate (3C ). Net production of 2 molecules of ATP & 2 molecules of NADH an energy requiring phase followed by a energy releasing phase.
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during glycolysis a continuous supply of NAD+ is required to remove hydrocarbons from immediate, NADH is a biproduct of this, Must then be oxidised.
if oxygen is not present, an alternative pathway is required. Microbes have developed anaerobic pathways.
Pyruvate (3C) which is a biproduct of glycolysis must then be converted to acetyl CoA (2C + coenzyme A) to enter the tricarboxylic acid TCA cycle. aka kreb cycle.
oxidative process, the biproduct is NADH.
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Energy cycle
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Photosynthetic organism "fix" this energy by anabolic reactions which synthesize energy-rich molecules such as sugar.
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Catabolism produces adenosine triphosphate (ATP) sometimes via reduced nicotinamide adenine dinucleotide (NADH)
Fermentation
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Alot of microbes survive in environments that are deficient in oxygen, alternative metabolisms such as fermentation is common.
fermentation
- uses the NADH that is a biproduct of glycolysis, to reduce intermediate compounds.
Net yield of 2 ATP per glucose ( glycolysis)- very inefficient compared to aerobic respiration.. an example is alcoholic fermentation. (Ethanol) homolactic fermentation ( lactic acid)
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Fermentation application
microbes product a vast range of metabolites, some are unwanted bi products of catabolic reactions e.g. ethanol.
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‒ Foods - cheese, bread, yoghurt
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‒ Chemical production - acetone, ethanol
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Primary metabolism
major metabolic pathways involve energy production and release (catabolism) others involved in synthesizing cell components- including enzymes (anabolism)
Secondary metabolism, subsidiary pathway that may produce none essential ( but useful producer) materials ( anabolism.
Oxidative catabolism
as well as extracting energy from organic compounds, some types of micro organisms can also oxidise inorganic ions, allowing them to extract energy. known as chemolithotrophs, none pathogenic microbe. each species is specific in the ions it can oxidise. an example is Sulphate and ammonia , nitrite can also be further oxidised to nitrate.
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