AP Biology 2.9-2.10: Cell Compartmentalization

What is cellular compartmentalization?

The division of a eukaryotic cell into membrane-bound organelles and other specialized regions, each with conditions and contents suited to particular functions.

What is a major advantage of cellular compartmentalization?

It allows different, sometimes incompatible, chemical reactions to occur simultaneously under specialized conditions while concentrating enzymes and substrates where they are needed.

How does the endomembrane system support cellular compartmentalization?

The endoplasmic reticulum, Golgi apparatus, vesicles, lysosomes, and related membranes create separate spaces for synthesizing, modifying, sorting, transporting, and digesting cellular materials.

What specialized functions do the endoplasmic reticulum and Golgi apparatus perform?

The endoplasmic reticulum synthesizes lipids and modifies newly made proteins, while the Golgi apparatus further modifies, sorts, tags, packages, and distributes proteins and lipids.

How do lysosomes and peroxisomes provide specialized cellular environments?

Lysosomes provide an acidic compartment for digesting macromolecules and recycling worn-out organelles. Peroxisomes contain enzymes that break down fatty acids and amino acids and detoxify harmful substances.

How do mitochondria and chloroplasts compartmentalize energy-converting reactions?

Mitochondria provide specialized compartments for cellular respiration and ATP production, while chloroplasts provide compartments for photosynthesis.

How do vacuoles contribute to cellular organization?

Vacuoles provide membrane-bound spaces for storage and transport; in plant cells, the central vacuole also supports turgor pressure and can have digestive functions.

Endosymbiotic theory

The theory that mitochondria, chloroplasts, and other plastids originated from formerly free-living prokaryotes that entered ancestral host cells and formed stable symbiotic relationships.

What evidence supports the endosymbiotic theory for mitochondria and chloroplasts?

These organelles contain their own DNA, replicate by binary fission-like division, and have features resembling bacteria, including circular chromosomes, bacterial-type porins, and cardiolipin in their membranes.

Which prokaryotic groups are considered likely evolutionary relatives of mitochondria and chloroplasts?

Mitochondria are most closely associated with alphaproteobacteria, while chloroplasts are derived from cyanobacteria.

Why did mitochondria and chloroplasts retain small genomes if they originated from free-living prokaryotes?

During evolution as endosymbionts, many genes were transferred from the organelle to the host-cell nucleus. The organelles therefore became dependent on host-produced proteins and retained only a reduced genome.

How does organelle replication provide evidence for an endosymbiotic origin?

Mitochondria and chloroplasts reproduce by splitting, similar to bacterial binary fission, rather than being assembled from scratch by the endomembrane system.

What membrane-composition evidence supports a bacterial origin for mitochondria and chloroplasts?

Porins occur in the outer membranes of mitochondria and chloroplasts as well as in bacterial membranes, and cardiolipin is characteristic of bacterial membranes and the inner mitochondrial membrane.

What is the main evolutionary significance of endosymbiosis?

It provides a mechanism by which major evolutionary innovations, especially the eukaryotic cell's energy-producing and photosynthetic organelles, arose through symbiotic mergers rather than only through gradual mutation within one lineage.