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Metabolic Pathways

Metabolic Pathways. Metabolism. All the enzyme catalysed reactions occuring in a cell. Metabolic pathway. An intracellular series of enzyme-controlled sequential biochemical reactions – one enzyme takes the product of another enzyme as a substrate. The product passes to another enzyme.

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Metabolic Pathways

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  1. Metabolic Pathways

  2. Metabolism • All the enzyme catalysed reactions occuring in a cell

  3. Metabolic pathway • An intracellular series of enzyme-controlled sequential biochemical reactions – • one enzyme takes the product of another enzyme as a substrate. • The product passes to another enzyme. • Different pathways are linked through shared substrates

  4. Role of gene • Each reaction in a pathway is controlled by a specific enzyme, which is the product of an expressed gene. • If a mutation creates a gene that prevents the enzyme forming, the final product of the pathway will not appear and intermediate substances will accumulate, affecting the phenotype.

  5. Example Gene C/c Gene B/b Gene O/o Tyrosine  intermediate  black (eumelanin)  orange (phaeomelanin) substance Tryosinase enzyme 2 enzyme 3

  6. Question practice • In poodles, white and black coat colours are controlled by a metabolic pathway. This pathway is controlled by two genes. • Discuss how the two genes control this pathway to produce both black poodles and white poodles. Gene A Gene B Substrate  intermediate  black substrate

  7. Answer (next 3 slides) • In a metabolic pathway a series of genes act in turn to change a substrate into an intermediate substrate and then a final product. If a gene is faulty this final product will not be reached.

  8. To produce a black poodle there needs to be at least one dominant allele at each of gene A and gene B, A_B_. This is because it is the presence of the dominant allele that produces the functional enzyme to work on the substrate. Genotypes that will produce a black poodle include AABB, AABb, AaBB, AaBb.

  9. To produce a white poodle there is a homozygous recessive genotype at one or more of the genes (aa or bb or both). This means that the enzyme produced is nonfunctional and so the substrate cannot be acted on past this point. Therefore the final product is not reached and there can be a build up of the substrate. Genotypes that produce this are aaBB, aaBb, AAbb, Aabb, aabb.

  10. Extra genetic practice • Give the difference between: • Gene mutation and chromosomal mutation • Inversion and translocation • Aneuploidy and polyploidy • Autopolyploidy and allopolyploidy

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