Question

RUBP is present in
(a) Grana thylakoid
(b) Stroma
(c) Inner Chloroplast membrane
(d) Outer chloroplast Membrane

Answer 1

Hint: RUBP or ribulose bisphosphate carboxylase is an enzyme present in chloroplast. They are believed to be involved in carbohydrate synthesis. RUBP is present in the metabolic center of the chloroplast, where Carbon dioxide fixation and synthesis of nucleic acids, sugars, starch, fatty acids, and some chloroplast proteins take place.

Complete answer:
RUBP is present in the stroma. It is the metabolic center where Carbon dioxide fixation and synthesis of nucleic acids, sugars, starch, fatty acids, and some chloroplast proteins take place. It contains a lamellar membrane system, ribosomes, circular DNA, messenger, and transfer RNAs, starch grains, lipid globules, and the enzymes for DNA duplication, genetic transcription, genetic translation, and the dark reaction of photosynthesis. The stroma contains nearly 50% of the chloroplast proteins most of which are of the soluble type. Most algal chloroplasts contain pyrenoids, in association with starch grains. Pyrenoids contain active enzyme ribulose bisphosphate carboxylase.

Additional Information:
- Chloroplast is a double-walled and fluid-filled bag. It has a gelatinous core, called matrix or stroma, covered by two concentric membranes.
- Across these membranes, the molecular exchange takes place between stroma and cytosol. The outer membrane is highly permeable and the inner membrane is less permeable.
- In between these membranes is the intermembrane space or periplastudial space. The membranes have a lipoprotein composition, lamellar structure, and fluid mosaic organization.
So, the correct answer is '(b) Stroma'.

Note:
- In lower organization chloroplasts are primitive. They are bounded by two-layered membranes and contain pigment coated plates in the matrix.
- Such chloroplasts are called lamellar chloroplasts. The extensive stromal membrane system is called the thylakoid system or lamellar system.
- Chlorophyll molecules and light-absorbing accessory pigments are embedded in it. It mainly consists of several cylindrical discs called grana.