Cellular Organelles: Structure and Function
Golgi Apparatus
Functions:
- Finalizes the protein glycosylation process underway in the Rough Endoplasmic Reticulum (RER). This process occurs sequentially from the cis face to the trans face of each dictyosome.
- Synthesizes glycolipids and sphingomyelins.
- Synthesizes complex polysaccharides of the cell wall in plant cells, which will be transported in vesicles for distribution and export.
- Directs proteins.
- Forms the acrosome in spermatozoa.
Chloroplast
Functions:
- Photosynthesis
- Fatty acid biosynthesis
- Reduction of nitrate to nitrite
Lysosome
A lysosome is a vesicle containing hydrolytic enzymes that are used in intracellular and extracellular digestion. The majority of acid hydrolases require an acidic pH. The lysosome membrane contains proton pumps to maintain a pH around 5, and it also contains transport proteins.
There are three types of lysosomes:
- Primary (which have not yet started the digestive process)
- Secondary (which have started the process)
- Residual bodies (which have already completed the digestive process)
Cellular digestion is considered a function of the digestive system in the cell because both intracellular digestion of materials collected from outside (heterophagy) and from the same cell (autophagy) take place.
Mitochondria
Functions:
- Cellular respiration
- Krebs cycle
- Respiratory chain
- Oxidative phosphorylation
- Beta-oxidation
Mitochondria accumulate substances in their internal chamber, such as proteins and lipids.
Ribulose-1,5-bisphosphate carboxylase/oxygenase
This enzyme, also called RuBisCO, is involved in fixing CO2 during the dark phase of photosynthesis. It is found in the chloroplast stroma. It is a multi-subunit enzyme and is the most abundant on the planet. It is only capable of fixing 3 molecules of CO2 per second, compared to 1000 for other enzymes. This is why it abounds in the chloroplast, reaching 20% of the total protein.
Cytochrome f
Cytochrome f forms part of the transport chain involved in the light phase of photosynthesis, forming a complex with cytochrome b. It functions as a proton pump. It is found in photosystem II, where water is the donor and quinone, plastoquinone, and cytochrome b3 are the acceptors.
Centrosome
The centrosome is a structure without a membrane, present in all animal cells susceptible to division. It has a central rod surrounded by centrioles formed by pericentriolar material with hundreds of ring-shaped structures composed of a special type of tubulin that serves as a nucleation site for microtubule formation. These rings are attached to the anchor, and growth takes place on the other side. These microtubules are called Aster.
In animal cells, the centrosome and the nucleus are close, and microtubules radiate from there. The centrioles are arranged perpendicularly. Each centriole has walls formed by nine groups of three microtubules, forming the 9×3 + 0 structure.
Chloroplast
The chloroplast is a membranous organelle of plant cells, surrounded by a double membrane with an internal space. Between both membranes exists the intermembrane space. The inner membrane of the chloroplast encloses a space called the stroma, which contains ribosomes, DNA, enzymes, and thylakoids (flattened structures). The thylakoid membrane contains chlorophyll. These are connected to each other and enclose a compartment: the thylakoid space. Sometimes they form small stacked groups called grana. The main function of the chloroplast is photosynthesis.