protein and cytoplasm

Cytoplasm refers to the entire part of the cell outside the nucleus and bound by cell membrane (plasma membrane). Cytosol is the fluid part of cytoplasm and organelles are embedded in cytosol, forming cytoplasm. Proteins have various functions in cytoplasm and the following is the discussion.

Structural significance:

1. Protein is responsible for the formation of cytoskeleton in cytoplasm which supports the cell and maintains shape of cells.Adsorption of organelles on cytoskeleton offers structural support.
2. Cytosol, the fluid part of cytoplasm, is composed of matrix made up of proteins.
3. Proteins are structural components of organelles in the cytoplasm. For instance, endoplasmic reticula and mitochondria are structurally composed of proteins.
4. Proteins make up the two subunits in ribosomes, which are locations of
translation of protein synthesis.

Functional significance:

1. Proteins are constituents of enzymes which serve important roles in metabolism. Globular proteins make up enzymes which catalyse metabolic reactions by speeding up reaction rate through providing alternative reaction pathway of lower activation energy.
2. Proteins are usually constituents of intracellular receptors which detect intracellular signals and trigger corresponding cellular responses. For instance, protein channels embedded in endoplasmicc reticulum provide paths for calcium ions movement upon detection of rise in level of IP3 (inositol triphosphate).
3. Proteins provide buffering function inside the cell. Amphoteric amino acids neutralize excess acid or alkali, thereby forming zwitterion to maintain a constant pH range inside the cell (in cytoplasm). This contributes to the cell stable internal environment for metabolic reactions.

In conclusion, proteins have important structural and functional roles in cytoplasm as mentioned above.

細胞質是一種膠狀基質，也就是蛋白質溶液。如果細胞質中的蛋白質太少，細胞質將化為水滴狀態。

Proteins act as enzymes to transfer signals for metabolism reactions.