ribulose

(noun)

A ketopentose whose phosphate derivatives participate in photosynthesis.

Related Terms

Examples of ribulose in the following topics:

  • Regulation of the Calvin Cycle

    • The carbon dioxide is combined with ribulose 1,5-bisphosphate to form two 3-phosphoglycerate molecules (3-PG).
    • The enzyme that catalyzes this specific reaction is ribulose bisphosphate carboxylase (RuBisCO).
    • RuBisCO is only active during the day as its substrate, ribulose 1,5-bisphosphate, is not generated in the dark.
    • This phase is characterized by the conversion of G3P, which was produced in earlier phase, back to ribulose 1,5-bisphosphate.
    • Outline the three major phases of the Calvin cycle: carbon fixation, reduction, and regeneration of ribulose

  • The Pentose Phosphate Shunt

    • The first is the oxidative phase in which glucose-6-phosphate is converted to ribulose-5-phosphate.
    • Glucose 6-phosphate + 2 NADP+ + H2O → ribulose-5-phosphate + 2 NADPH + 2 H+ + CO2
    • Depending on the body's state, ribulose-5-phosphate can reversibly isomerize to ribose-5-phosphate.
    • Ribulose-5-phosphate can alternatively undergo a series of isomerizations as well as transaldolations and transketolations that result in the production of other pentose phosphates including fructose-6-phosphate, erythrose-4-phosphate, and glyceraldehyde-3-phosphate (both intermediates in glycolysis).
    • It produces ribulose-5-phosphate, used in the synthesis of nucleotides.

  • Study of Photosynthesis

    • C3 carbon fixation is a metabolic pathway that converts carbon dioxide and ribulose bisphosphate into 3-phosphoglycerate.

  • Intermediates Produced During the Calvin Cycle

    • The Calvin cycle can be divided into three major phases which include: Phase 1: carbon fixation; Phase 2: reduction; and Phase 3: regeneration of ribulose .
    • However, additional GAP molecules that are formed will be converted to ribulose-1,5-bisphosphate (RuBP), which is responsible for the conversion of CO2 to 3-PGA in phase 1, via numerous steps.

  • Carboxysomes

    • These compartments are thought to concentrate carbon dioxide to overcome the inefficiency of RuBisCo (ribulose bisphosphate carboxylase/oxygenase) - the predominant enzyme in carbon fixation and the rate limiting enzyme in the Calvin cycle.

  • The Calvin Cycle

    • In the stroma, in addition to CO2,two other components are present to initiate the light-independent reactions: an enzyme called ribulose bisphosphate carboxylase (RuBisCO) and three molecules of ribulose bisphosphate (RuBP).