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Examples of biosynthetic pathways include those for the production of amino acids, lipid membrane components, and nucleotides, but also for the production of all classes of biological macromolecules, and of acetyl-coenzyme A, adenosine triphosphate, nicotinamide adenine dinucleotide and other key intermediate and transactional molecules needed ...
[123] [124] Furthermore, different research focuses have given the word "pathway" different meanings. For example, 'pathway' can denote a metabolic pathway involving a sequence of enzyme-catalyzed reactions of small molecules, or a signaling pathway involving a set of protein phosphorylation reactions and gene regulation events.
Response to stimuli: a response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun ( phototropism ), and chemotaxis .
An example progress curve for an enzyme assay is shown above. The enzyme produces product at an initial rate that is approximately linear for a short period after the start of the reaction. As the reaction proceeds and substrate is consumed, the rate continuously slows (so long as the substrate is not still at saturating levels).
Examples of mechanoreceptors include baroreceptors which detect changes in blood pressure, Merkel's discs which can detect sustained touch and pressure, and hair cells which detect sound stimuli. Homeostatic imbalances that can serve as internal stimuli include nutrient and ion levels in the blood, oxygen levels, and water levels.
For example, the most widely studied bacterium, E. coli strain K-12, is able to produce about 2,338 metabolic enzymes. [1] These enzymes collectively form a complex web of reactions comprising pathways by which substrates (including nutients and intermediates) are converted to products (other intermediates and end-products).
Hypersensitive response (HR) is a mechanism used by plants to prevent the spread of infection by microbial pathogens.HR is characterized by the rapid death of cells in the local region surrounding an infection and it serves to restrict the growth and spread of pathogens to other parts of the plant.
In biochemistry, the committed step (also known as the first committed step) is an effectively irreversible, enzyme-catalyzed reaction that occurs at a branch point during the biosynthesis of some molecules. [1] [2] As the name implies, after this step, the molecules are "committed" to the pathway and will ultimately end up in the pathway's ...