AP Biology · Unit 2: Cell Structure & Function

2.1 Cell Structure: Subcellular Components

The organelles

Eukaryotic cells contain organelles, each with a job. The nucleus holds DNA. Ribosomes build proteins. The rough ER (studded with ribosomes) processes proteins; the smooth ER makes lipids and detoxifies. The Golgi apparatus modifies, packages, and ships molecules.

Powerhouses and recyclers

Mitochondria make ATP through cellular respiration (double membrane, inner folds called cristae). Lysosomes hold digestive (hydrolytic) enzymes that break down waste. Vacuoles store materials — the large central vacuole gives plant cells support. Chloroplasts carry out photosynthesis in plants and algae.

Key terms

Nucleus: The organelle that stores the cell's DNA, enclosed by a nuclear envelope.
Ribosome: The site of protein synthesis; can be free or attached to the rough ER.
Rough ER: Ribosome-studded ER that processes and folds proteins.
Golgi apparatus: Modifies, packages, and ships proteins and lipids in vesicles.
Lysosome: Contains hydrolytic (digestive) enzymes that break down waste and worn parts.

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Experiment

Cells are given radioactive amino acids for 3 minutes, then unlabeled amino acids. Label appears first in the rough ER, then the Golgi, then vesicles near the plasma membrane, and finally outside the cell.

Which conclusion is best supported by this pulse-chase experiment?

Proteins made on free ribosomes are secreted directly across the membrane
Secreted proteins are made in the Golgi and then modified by the rough ER
The label moves randomly between organelles until it leaves the cell
Secreted proteins are made at the rough ER and pass through the Golgi before exocytosis

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D. The ordered movement ER → Golgi → vesicles → exterior traces the secretory (endomembrane) pathway.

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