Membrane-Bound Organelles and Compartmentalization (2A) - Bio & Biochem

Which organelle performs photosynthesis in plants and algae?

Chloroplast. It converts light energy into chemical energy using pigments and enzyme systems in its membranes and stroma.
Which process brings extracellular material into endosomes and often to lysosomes?

Endocytosis. This mechanism internalizes extracellular substances into vesicles that fuse with endosomes, leading to lysosomal degradation.
Which organelle modifies, sorts, and packages proteins for secretion or delivery?

Golgi apparatus. It processes proteins from the ER, adding modifications like glycosylation before directing them to their destinations.
Which structure is responsible for intracellular protein degradation via ubiquitin tagging?

Proteasome. It targets misfolded or unnecessary proteins marked with ubiquitin for proteolysis in the cytosol.
Which trafficking route delivers newly synthesized lysosomal enzymes from the Golgi?

Trans-Golgi to endosome to lysosome. Enzymes are tagged with mannose-6-phosphate in the Golgi for vesicular transport to endosomal compartments that form lysosomes.
What is the main role of vacuoles in plant cells?

Storage and maintenance of turgor pressure. Central vacuoles store nutrients, waste, and water, providing structural support through osmotic pressure.
Which face of the Golgi receives ER vesicles, and which face ships products?

Cis receives; trans ships. The cis face accepts incoming vesicles, while the trans face dispatches processed molecules, reflecting the organelle's polarized structure.
Which organelle carries out $H_2O_2$ -producing oxidation and contains catalase?

Peroxisome. It detoxifies harmful substances by oxidizing them and neutralizing resulting peroxides with catalase.
In chloroplasts, where do the light reactions occur?

Thylakoid membrane. Photosystems and electron transport chains in these membranes capture light and generate ATP and NADPH.
Which mitochondrial membrane contains the electron transport chain complexes?

Inner mitochondrial membrane. This membrane houses proteins for electron transfer and proton pumping during cellular respiration.
What is the main function of lysosomes in animal cells?

Acidic degradation of macromolecules and organelles. These organelles contain hydrolytic enzymes that break down waste and engulfed materials in an acidic environment.
What is the mitochondrial intermembrane space used for during respiration?

Proton accumulation to create a gradient. Protons are pumped here during electron transport, establishing an electrochemical gradient that drives ATP synthesis.
What is the primary function of the nucleus in a eukaryotic cell?

Stores DNA and regulates gene expression. It acts as the cell's control center by housing genetic material and directing transcription to manage cellular activities.
What is the key advantage of organelle compartmentalization in eukaryotic cells?

Separates incompatible reactions and concentrates enzymes/substrates. Compartmentalization enhances efficiency by isolating processes and optimizing local conditions for specific reactions.
Identify the organelle: ATP production, double membrane, and its own circular DNA.

Mitochondrion. These features enable aerobic respiration and reflect its endosymbiotic origin with independent replication.
Identify the organelle: hydrolytic enzymes, acidic lumen, and autophagy function.

Lysosome. These characteristics allow it to digest cellular debris and recycle components through degradation processes.
Identify the organelle: lipid synthesis and detoxification; lacks ribosomes on its surface.

Smooth endoplasmic reticulum. Its smooth surface and functions distinguish it from the rough ER, focusing on non-protein metabolic roles.
What is the primary function of the rough endoplasmic reticulum (RER)?

Synthesis of secreted and membrane proteins. Studded with ribosomes, it facilitates translation of proteins destined for export or insertion into membranes.
Which organelle is non-membrane-bound but essential for protein synthesis?

Ribosome. Composed of rRNA and proteins, it translates mRNA into polypeptides in both cytosol and on ER.
What is the primary function of mitochondria in eukaryotic cells?

ATP production via oxidative phosphorylation. These organelles harness energy from nutrients through the electron transport chain and ATP synthase.
What is the function of the nucleolus?

rRNA synthesis and ribosomal subunit assembly. Located within the nucleus, it specializes in producing ribosomal components essential for protein synthesis.
What is the primary function of the smooth endoplasmic reticulum (SER)?

Lipid synthesis, detoxification, and $Ca^{2+}$ storage. Lacking ribosomes, it performs metabolic functions crucial for cellular homeostasis and signaling.
What is the nuclear envelope composed of, and what is its key transport feature?

Double membrane with nuclear pore complexes. This structure encloses the nucleus, with pores allowing selective transport of molecules like RNA and proteins between nucleus and cytoplasm.
What is the approximate pH inside a lysosome?

About $5$ . The low pH optimizes the activity of acid hydrolases for efficient macromolecule breakdown.
In chloroplasts, where does the Calvin cycle occur?

Stroma. This fluid matrix contains enzymes for carbon fixation, using products from light reactions to synthesize sugars.

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