Advanced Botany

  The nif genes are genes encoding enzymes involved in the fixation of atmospheric nitrogen into a form of nitrogen available to living organisms. They are found in nitrogen-fixing bacteria.  They occur as an operon (a segment of DNA containing adjacent genes including structural genes, an operator gene and a regulatory gene; thus a functional unit of transcription and genetic regulation) in free-living anaerobic nitrogen-fixing bacteria such as  Klebsiella pneumoniae ,  Rhodospirillum rubrum , and  Rhodobacter capsulatus . These genes may also be found on plasmids in symbiotic bacteria, such as in Rhizobium inhabiting the roots of leguminous plants.  Functions nif genes encode an important enzyme, nitrogenase complex which is in charge of converting atmospheric nitrogen (N2 ) to usable form of nitrogen such as ammonia. Nitrogen fixation is important because many living organisms are unable to metabolize directly the atmospheric nitrogen and...

  Ribulose bisphosphate carboxylase/oxygenase ( Rubisco ) is a key enzyme in photosynthesis catalyzing corbon dioxide fixation. Rubisco is ubiquitus for photosynthetic organisms and is regarded as the most abundant protein on earth. More than 90% of the inorganic carbon that is converted into biomass is fixed by the enzyme RubisCO that catalyzes the carboxylation and cleavage of ribulose-1,5-bisphosphate (RuBP) into two molecules of 3-phosphoglycerate (3PG). RubisCO is found in all three domains of life: bacteria, archaea and eukaryotes. The enzyme makes up 30-50% of the soluble protein in plant leaf. Structure Rubisco enzymes are multimeric having two different types of subunits catalytic large (L, 50–55 kDa), and small (S, 12–18 kDa) subunits. Different molecular forms of Rubisco are distinguished by the presence or absence of the small subunit. The most common form (form I) of Rubisco is composed of large and small subunits in a hexadecameric structure, L8S8. This form is presen...