Biochemical Pathways Biosynthetic pathway: purpose is to produce a compound that
ID: 252477 • Letter: B
Question
Biochemical Pathways Biosynthetic pathway: purpose is to produce a compound that the organism needs. If the path is blocked, that compound is not produced. Degradative pathway: Purpose is to break down a product. If there is a blocked step in the path, the chemical is not broken down completely. Determining the order of compounds in a biochemical pathway: You have several strains that cannot grow without supplementation of compounds A through D You obtain the data below(+"sign indicates growth;sign indicates no growth). Determine th biochemical pathway and indicate the step at which each strain is deficient. Note: If a compound is added that is after the block in the pathway, it will allow the mutant to grow, but if a compound is added that is before the block in the pathway it will have no effect. Remember that compounds/metabolites/intermediates go between arrows and that strain names/mutation group names go over arrows at the step at which they are deficient. . Compound Strain AB C D S1 ++ S4 Biochemical pathway practice problem You isolated several mutant bacterial strains of B. subtillis that are defective in the biosynthetic pathway for biotin and cannot grow on minimal media. Biotin is a water-soluble B vitamin (B7) that is required as a cofactor for many enzymes and thus required for survival of the organism. You attempted to grow each strain on minimal media with one compound added at a time. A +"indicates that the strain grew when provided with the compound. A-indicates that the strain still did not grow when the compound was present. Determine the biosynthetic pathway for biotin. Indicate which strain is defective at which step by pla are numbered S1- S5 and compounds are indicated by name in this table. cing the strain name over the arrow at the defective step. Note that strains Compound Strain DAPA Pimeloyl-CoA DTB KAPA Biotin S1 S2 S3 S4 S5Explanation / Answer
Biotin biosynthetic pathway.
S2 S1 S4 S3
Pimeloyl CoA-------->KAPA---------->DAPA---------->DTB----------> Biotin
A mutant that has a defect in a particular enzyme will not be able to synthesise a particular compound and therefore compounds that come afterwards in the pathway. So if we add either the blocked compound or any compound that comes after the block in the pathway, the mutant will grow. But If we add a compound that is synthesized before the block, the mutant will not be to grow. So the compounds that come towards the end of the pathway will support the growth of the most mutants (biotin), and compounds that come earliest in the pathway will support the growth of the fewest mutants (pimeloyl CoA). Based on this we can tell the order of the compounds in the pathway.
So for example if a strain cannot synthesise DAPA (block between KAPA and DAPA), adding DAPA,DTB or Biotin will help the strain to grow. But adding KAPA (or Pimeloyl CoA) will not help as the enxyme that needs to convert KAPA to DAPA is not working.
Strain 3 can grow only when biotin is provided. it doesnt grow when any of the other compounds are provided, meaning that biotin is the last compund in the pathway. Strain 5 on the other hand, can grow in all the compounds, showing that it has no defective enzymes in the pathway. Strain 2 can grow in all the compounds except Pimeloyl coA showing that there is a block between Pimeloyl CoA and KAPA.
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