Eukaryotic Organelles
- Identify the major eukaryotic organelles and state the function of each
- Trace the path of a secreted protein through the endomembrane system
- Compare organelles unique to plant cells with those unique to animal cells
The control center and the power plants
The nucleus is the cell’s information hub: it stores the DNA, is wrapped in a double membrane (the nuclear envelope) studded with pores, and contains the nucleolus, where ribosomes are assembled. Mitochondria are the sites of cellular respiration, using oxygen to convert the energy in food into ATP; they have a double membrane whose highly folded inner membrane (cristae) adds surface area for the reactions. In plants and algae, chloroplasts carry out photosynthesis, capturing light energy to build sugar. Both mitochondria and chloroplasts have their own DNA and double membranes — evidence they arose from ancient engulfed prokaryotes (endosymbiosis).
The endomembrane system: a molecular assembly line
Several organelles work together as the endomembrane system. Ribosomes read mRNA and build proteins. The rough endoplasmic reticulum (ER), studded with ribosomes, folds and packages proteins destined for membranes or export; the smooth ER (no ribosomes) synthesizes lipids and detoxifies. The Golgi apparatus is the "post office": it receives molecules from the ER, modifies and sorts them, and ships them in vesicles to their destinations. Lysosomes are the "recycling centers" — acidic sacs of digestive enzymes that break down worn-out organelles and engulfed material.
Plant vs. animal: who has what
Most organelles are shared, but a few set the kingdoms apart. Plant cells have three structures animal cells lack: a rigid cell wall of cellulose outside the membrane, chloroplasts for photosynthesis, and a large central vacuole that stores water and props the cell up with turgor pressure. Animal cells typically have centrioles (which help organize cell division) and lysosomes that are prominent and abundant. Both share the nucleus, mitochondria, ER, Golgi, and ribosomes.
A pancreatic cell manufactures the protein insulin and secretes it into the bloodstream. Put the organelles it passes through in the correct order.
- 1.The protein is synthesized by ribosomes attached to the rough ER, entering the ER interior as it is built.
- 2.The rough ER folds and packages it, then buds off a transport vesicle that carries it to the Golgi apparatus.
- 3.The Golgi modifies, tags, and sorts the finished insulin, packing it into a secretory vesicle.
- 4.The secretory vesicle travels to the plasma membrane and fuses with it (exocytosis), releasing insulin outside the cell.
A cell is highly specialized to secrete large amounts of protein. Which organelle would you expect to be especially abundant?
Match each organelle to a workplace metaphor: nucleus = library/control room, mitochondrion = power plant, ribosome = factory machine, rough ER = production line, Golgi = post office, lysosome = recycling center. The metaphor recalls the function.
Mitochondria and chloroplasts both have their own DNA and a double membrane. What does this evidence best support?
Know the three plant-only structures cold: cell wall, chloroplast, and central vacuole. A frequent exam prompt gives an unlabeled cell and asks you to identify it as plant or animal — the wall and chloroplasts are the giveaways.
Answer the 2 checkpoints as you read.
Sign in to save your progress