CLEP Biology Cell Organelle Structure/Function 4 — Questions and Answers
Question 1: A researcher discovers a protein with a signal sequence targeting it to the mitochondrial matrix. Through which structure(s) must this protein pass after synthesis on cytoplasmic ribosomes?
- The outer mitochondrial membrane only
- Both the outer and inner mitochondrial membranes via translocases (Correct answer)
- The smooth ER and then the mitochondria
- The Golgi apparatus and then the outer membrane
Correct answer: Both the outer and inner mitochondrial membranes via translocases
Cytoplasmic proteins destined for the mitochondrial matrix must cross both the outer membrane (via TOM complex) and the inner membrane (via TIM23 complex) using translocase complexes.
Question 2: Plasmodesmata in plant cells are functionally analogous to which structure in animal cells?
- Tight junctions
- Gap junctions (Correct answer)
- Desmosomes
- Adherens junctions
Correct answer: Gap junctions
Both plasmodesmata and gap junctions allow direct cytoplasmic communication between adjacent cells, enabling the passage of small molecules and ions.
Question 3: Which organelle would be most abundant in a cell that secretes large amounts of digestive enzymes, such as a pancreatic acinar cell?
- Smooth ER and mitochondria
- Rough ER and Golgi apparatus (Correct answer)
- Chloroplasts and ribosomes
- Lysosomes and peroxisomes
Correct answer: Rough ER and Golgi apparatus
Secretory proteins like digestive enzymes are synthesized on rough ER ribosomes, then processed and packaged in the Golgi for exocytosis.
Question 4: The mitochondrial matrix contains all enzymes needed for which metabolic pathway?
- Glycolysis
- The citric acid (Krebs) cycle (Correct answer)
- The electron transport chain
- Fatty acid synthesis
Correct answer: The citric acid (Krebs) cycle
The enzymes of the citric acid cycle are located in the mitochondrial matrix, where they oxidize acetyl-CoA and generate NADH, FADH2, and CO2.
Question 5: Which of the following is a key difference between prokaryotic and eukaryotic ribosomes?
- Prokaryotes have 80S ribosomes; eukaryotes have 70S ribosomes
- Prokaryotes have 70S ribosomes; eukaryotes have 80S ribosomes (Correct answer)
- Both have 80S ribosomes but differ in subunit composition
- Only eukaryotes use ribosomes for protein synthesis
Correct answer: Prokaryotes have 70S ribosomes; eukaryotes have 80S ribosomes
Prokaryotic ribosomes are 70S (50S + 30S subunits) while eukaryotic cytoplasmic ribosomes are 80S (60S + 40S subunits); this difference is exploited by many antibiotics.
Question 6: A mutation destroys the proton gradient across the inner mitochondrial membrane. What would be the direct consequence?
- The citric acid cycle would stop
- ATP synthase could not produce ATP (Correct answer)
- Glycolysis would be inhibited
- The outer membrane would rupture
Correct answer: ATP synthase could not produce ATP
ATP synthase uses the proton gradient (proton-motive force) as the driving force to synthesize ATP; without the gradient, ATP synthesis via oxidative phosphorylation would cease.
Question 7: In the endomembrane system, vesicles traveling from the Golgi to the plasma membrane for exocytosis are called what?
- Endosomes
- Secretory vesicles (Correct answer)
- Autophagosomes
- Coated pits
Correct answer: Secretory vesicles
Secretory vesicles bud from the trans face of the Golgi apparatus and transport their cargo to the plasma membrane, where they fuse and release contents outside the cell.
CLEP Biology Cell Organelle Structure/Function 4
A researcher discovers a protein with a signal sequence targeting it to the mitochondrial matrix.
Through which structure(s) must this protein pass after synthesis on cytoplasmic ribosomes?