Skip to content
Login Register

#chloroplasts

11 public questions tagged with this topic.

Cell Organelles

The light-dependent reactions of photosynthesis occur in:

Photosynthetic light reactions convert photon energy into chemical energy through vectorial electron and proton transport generating ATP and reducing power. This machinery is embedded exclusively in the thylakoid membrane system of chloroplasts, forming flattened sac-like discs that stack into grana interconnected by unstacked stroma lamellae, vastly increasing surface area for photon capture. Integral complexes include Photosystem II with Mn4CaO5 oxygen-evolving complex, plastoquinone pool, cytochrome b6f dimer, plastocyanin luminal electron shuttle, Photosystem I, ferredoxin and ferredoxin-N

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 14: Chloroplasts and Light-Dependent Reactions.

View Details
Cell Organelles

The site of CO₂ fixation in chloroplasts is:

Chloroplasts compartmentalize photosynthesis into light harvesting and carbon assimilation stages across membrane systems. Thylakoid membranes, intricate network of flattened discs stacking into grana interconnected by stroma lamellae, house photosystems II and I, cytochrome b6f complex and ATP synthase that convert light energy into ATP and NADPH through non-cyclic and cyclic electron transport, proton pumping and water splitting at oxygen-evolving complex. Those products are consumed in the aqueous phase surrounding thylakoids, the stroma, where the Calvin-Benson-Bassham cycle operates. Stro

Ref: Taiz et al., Plant Physiology and Development, 6th ed., Chapter 8: Photosynthesis – The Calvin Cycle in Stroma.

View Details
Protein Sorting and Trafficking

What signal is required for targeting proteins to the thylakoid lumen?

Final intra-chloroplast sorting thylakoid lumen after stroma entry requires crossing thylakoid membrane barrier maintaining proton gradient ATP synthesis. Lumenal precursors plastocyanin copper OE16 OE23 photosystem II oxygen evolving complex Rieske iron-sulfur PetC transport stroma lumen. Precursors carry bipartite targeting sequences N-terminal chloroplast transit peptide TOC-TIC entry second thylakoid transfer domain 30-70 residues positively charged N-region hydrophobic core C-region cleavage thylakoid processing peptidase. Two distinct pathways recognize transfer domain: Sec pathway trans

Ref: Cline & Theg, Mol Membr Biol 2007: Twin-arginine RR motif for Tat pathway to thylakoid lumen.

View Details
Protein Sorting and Trafficking

Which pathway is involved in the targeting of thylakoid proteins?

Thylakoid membrane harbors photosynthetic machinery requiring insertion light-harvesting polytopic proteins after chloroplast envelope import stroma. Four conserved pathways inherited cyanobacterial ancestor: Sec pathway unfolded proteins SecYEG translocase SecA ATPase, SRP pathway specialized highly hydrophobic light-harvesting chlorophyll a/b binding proteins LHCPs pigments. Stromal chloroplast SRP cpSRP54 GTPase homologous bacterial SRP54 NG M domains binding signal sequence GTP, unique cpSRP43 chaperone absent bacteria three chromodomains four ankyrin repeats specifically binding L18 motif

Ref: Schuenemann, Annu Rev Plant Biol 2007: cpSRP pathway targets proteins to thylakoid membrane.

View Details
Protein Sorting and Trafficking

What is the main function of the TIC complex in chloroplasts?

Chloroplast envelope encloses two translocon systems tandem importing majority organelle proteome 3000 proteins despite plastid genome about 100. Precursors synthesized cytosol N-terminal transit peptide enriched hydroxylated serine threonine positively charged amphipathic not hydrophobic distinct mitochondrial presequence. First receptor TOC outer envelope: Toc159 large 159 kDa GTPase selectivity filter photosynthetic versus housekeeping via acidic A-domain, Toc34 small 34 kDa regulatory, Toc75 Omp85 beta-barrel superfamily 14-strand channel 3 nm pore translocating polypeptide. After outer me

Ref: Soll & Schleiff, Nat Rev Mol Cell Biol 2004: TIC imports proteins across chloroplast inner envelope.

View Details
Mitochondria Plastids Ribosomes and Other Organelles

A green leaf cell contains approximately 20–40 double-membrane organelles. Each contains chlorophyll and carotenoid pigm

Most chloroplasts of green plants occur in leaf mesophyll cells, where approximately 20–40 may occur per cell. Chloroplasts contain chlorophyll and carotenoids that trap light energy required for photosynthesis.

Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles

View Details
Mitochondria Plastids Ribosomes and Other Organelles

During cell fractionation, a researcher identifies: Fraction X: a semi-fluid material in which numerous reactions needed

The cytoplasm is the semi-fluid matrix and principal arena of cellular reactions. Ribosomes are non-membrane-bound RNA–protein particles occurring freely in the cytoplasm, on rough ER, and within mitochondria and chloroplasts.

Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles

View Details