A typical plant cell (e.g., in the palisade layer of a leaf) might contain as many as 50 chloroplasts.

The chloroplast is made up of 3 types of membrane:

  1. A smooth outer membrane which is freely permeable to molecules.
  2. A smooth inner membrane which contains many transporters: integral membrane proteins that regulate the passage in an out of the chloroplast of
    • small molecules like sugars
    • proteins synthesized in the cytoplasm of the cell but used within the chloroplast
  3. A system of thylakoid membranes


  • The thylakoid membranes enclose a lumen: a system of vesicles (that may all be interconnected).
  • At various places within the chloroplast these are stacked in arrays called grana (resembling a stack of coins).
  • Four types of protein assemblies are embedded in the thylakoid membranes:
    1. Photosystem I which includes chlorophyll and carotenoid molecules
    2. Photosystem II which also contains chlorophyll and carotenoid molecules
    3. Cytochromes b and f
    4. ATP synthase
    These carry out the so-called light reactions of photosynthesis.
    Links to (1) a discussion of the "light" reactions
    and (2) a graphic showing the 4 complexes in the thylakoid membrane.
  • The thylakoid membranes are surrounded by a fluid stroma.
    The stroma contains:

The electron micrograph above on the right (courtesy of Dr. L. K. Shumway) shows the chloroplast from the cell of a corn leaf.

The electron micrograph on the left (courtesy of Kenneth R. Miller) shows the inner surface of a thylakoid membrane. Each particle may represent one photosystem II complex. In the functioning chloroplast, these particles may not be as highly ordered as seen here.