In the past installments in this series on the Simple Cell, I have mentioned the cytoplasm on many occasions. I have discussed many of the organelles and structures that are found in the cytoplasm, but have never talked in any detail about the cytoplasm and its function, that is until today.
The cytoplasm is a thick jelly-like fluid that fills the space between the cell membrane and the nucleus and accounts for nearly 70% of the total cell volume. It is comprised of a transparent substance known as hyaloplasm or cytosol. The cytoplasm is made up of cell organelles, cytoskeleton, protein filaments, soluble proteins, enzymes, fatty acids, sugars, amino acids, salts and up to 90% water. In many cells, there is an inner granular area of the cytoplasm called the endoplasm and an outer section called the ectoplasm which contains fewer particles and organelles.
Functions of the Cytoplasm
- Cell shape. The gelatinous nature of the cytoplasm helps to maintain the cell shape.
- Supports cytoskeleton. The cytoplasm contains protein filaments that are used for the formation of the various cytoskeletal structures. For instance, when a microtubule is building and extending, it pulls the protein filaments from the cytoplasm. As the microtubule reverses it process and begins to breakdown and shorten, the protein filaments are returned to the cytoplasm.
- Supports organelles. The various organelles are suspended in the cytoplasm and are then moved around as needed via the cytoskeleton.
- Storage. The cytoplasm stores a number of vital substances necessary for cell metabolism and survival. These substances include protein filaments, soluble proteins, enzymes, fatty acids, sugars, amino acids, and salts.
- Molecular Processing. There are a number of macromolecules located in the cytoplasm. Cytoplasmic enzymes work to break down many of these huge molecules into smaller molecules that are more usable by the various organelles.
- Glycolysis. The cytoplasm contains glucose molecules. Mitochondria are incapable of using glucose. Enzymes in the cytoplasm break down the glucose into pyruvate molecules which the mitochondria are able to use.
- Protein Synthesis. Protein synthesis takes place in the cytoplasm with the aid of three forms of RNA. Messenger RNA (mRNA) is coded for the production of a specific protein by the DNA located in the nucleus. The mRNA than passed through pores in the nuclear membrane and enters the cytoplasm. It is then transported to a ribosome in the cytoplasm. Ribosomes are ultramicroscopic strands of ribosomal RNA (rRNA) and a protein. We discussed earlier that the rough endoplasmic reticulum contains ribosomes whose primary function is the synthesis of proteins. Like their counterparts in the endoplasmic reticulum, the cytoplasmic ribosomes also synthesize a number of proteins vital to cell metabolism. Transfer RNA (tRNA) which also exists in the cytoplasm carries specific amino acids to the rRNA or ribosomes for the synthesis of specific proteins.
- Chemical Exchange. Not all compounds are carried through the cell via vacuoles. Sometimes, they are released into the cytoplasm from one organelle and directed to another. These usually consist of proteins, enzymes and amino acids.
While the cytoplasm may look like nothing more than a thick jam or jelly, it is far more complex than that. It supports, contains and processes many of the other structures and functions that have been discussed in previous installments of this series. Once again we see that there is nothing simple in the cell, not even the fluid that fills it. And once again, we see the impossibility of the evolution of the cell and the handiwork of an all knowing Creator God.