Semi-autonomous organelles are named as such because they function independently within a cell, but cannot exist on their own outside a cell. These organelles grow and reproduce themselves, but they rely on other parts of the cell for certain products.
Structure:
- Similar in size to bacteria.
- Outer membrane & inner membrane are separated by the intermembrane space.
- Folds in the inner membrane space are called cristae.
- The compartment inside the inner membrane is called the mitochondrial matrix.
Function:
- ATP is made on the surface of the inner membrane; mitochondria converts chemical energy by breaking bonds in molecules such as sugars, fats, and amino acids, and converting the smaller molecules into ATP.
- Mitochondria is involved in the synthesis, modification, and breakdown of many molecules, such as hormones.
- Mitochondria generates heat in brown fat cells that are involved in hibernation and protecting some young animals from cold environmental conditions.
Chloroplasts/Plastids
Structure:
- Has an inner and outer membrane that are separated by an intermembrane space.
- A third membrane, called a thylakoid membrane, is composed of many flat tubules that are filled with liquid. A stack of thylakoid membranes is called a grana. The plural of grana is granum.
- The inside of a thylakoid membrane is called the thylakoid lumen.
- Inside the inner membrane but outside the thylakoid membrane is stroma, which is the plant equivalent of cytoplasm.
Function:
- The thylakoid lumen facilitates photosynthesis.
- Chloroplasts use light energy to synthesize organic molecules.
- Chloroplasts contain a green pigment which gives the color to green plants.
- Chloroplasts are one type of plastid; other plastids have different pigments and functions. Some examples are chromoplasts, leucoplasts, and amyloplasts.
Structure:
- Peroxisomes are relatively small organelles.
- Composed of a single membrane with a fluid-filled lumen.
Function:
- Catalyst of chemical reactions.
- Breaks down hydrogen peroxide (H2O2), which is a byproduct of chemical reactions that involve removing hydrogen or adding oxygen, by using the enzyme catalase to break down the hydrogen peroxide to make water and oxygen gas.
- May contain other enzymes to detoxify other molecules.
- Usually contain enzymes that aid in the metabolism of fats and amino acids.
Origins of Semi-Autonomous Organelles
The origin of semi-autonomous organelles is elusive and somewhat controversial, but the prevailing theory is the endosymbiotic theory, which I describe in this blog post.
Related posts:
Top Articles