Unit-3

Anaplerotic reactions  Biochemical reactions that replenish (நிரப்புதல்) the intermediates (that are removed for other biosynthetic reactions, e.g. oxaloacetate of TCA cycle is removed for biosynthesis of methionine and aspartate) of a metabolic pathway. e.g. pyruvate carboxylase and pyruvate dehydrogenase are replinishing enzymes that supply oxaloacetate from pyruvate.

Archaellum  The archaeal functional equivalent of the bacterial flagellum.

Assimilation  The incorporation of an environmental element, such as phosphorus, into precursor metabolites. 

Bacterial cell inclusions - They are intracellular granules or storage bodies that serve as energy reserves, structural components, or protective mechanisms. They are typically not membrane-bound  (non Unit membrane) and help bacteria survive under fluctuating environmental conditions. e.g. poly beta hydroxy butyrate  (PHB) granules stores lipids for energy production.

Capsule  A well-organized, tightly bound layer surrounding the bacterial cell. It protects against desiccation, phagocytosis, and antibiotics. Capsules contribute to bacterial virulence (e.g., Streptococcus pneumoniae).

Carboxysomes BBacteria that obligately grow on CO2 as their sole or major source of carbon (strict autotrophs) sometimes have large (100 nm) polyhedral protein-walled microcompartments called carboxysomes. These  inclusions  have  been observed in nitrifying bacteria, sulfur oxidizers, and cyanobacteria.

Chlorosomes - Photosynthetic  green sulfur bacteria  (e.g., Chlorobium)  have  ellipsoid  inclusions  called chlorosomes  (formerly  called  chlorobium vesicles)  that  lie  immediately  underneath  the  cytoplasmic  membrane. During photosynthesis in these organisms, light is absorbed by pigments present in the chlorosomes and energy is transmitted to the reaction centers in the cell membrane where photosynthesis takes place.

Diazotrophs  A nitrogen fixing bacteria e.g. Rhizobium and Azospirillum. 

Flagellin  It is a globular protein that makes up the filament of bacterial flagella. It is the primary structural component of the flagellar filament, which enables motility in many bacteria. 

Gas vesicles  They are  hollow,  spindle-shaped  structures  about  100  nm  long,  filled with gas in equilibrium with the gases dissolved in  the  cytoplasm. Aquatic bacteria such as cyanobacteria, certain  photosynthetic  bacteria,  some  nonphotosynthetic  bacteria.

Magnetosomes Certain  marine  and  freshwater  bacteria  belongs to class α-Proteobacteria,  β-Proteobacteria,  δ-Proteobacteria, and phylum Nitrospira have chains  of  membrane-bound  organelles  called magnetosomes,  which  originate  as  invaginations  of  the  cell  membrane. The  bacteria  are referred to as magnetotactic bacteria (MB) or (MTB) because the magnetosomes influence the direction of swimming with respect to the earth’s magnetic field. 

Nitrogen assimilation  Refers to the process by which inorganic nitrogen (N₂, NO₃⁻, NH₄⁺) is converted into organic compounds like amino acids and nucleotides. This process is essential for cellular metabolism and is catalyzed by specific enzymes.

Slime Layer  A loosely attached, unorganized extracellular layer that can be easily washed away. It helps in adhesion to surfaces (biofilm formation) and protects against dehydration (e.g., Pseudomonas aeruginosa).