Cooperation Among Cellular Organelles

Section 2: Cooperation Among Cellular Organelles

Cells undergo complex changes in substances and energy during their life activities. Inside the cell is like a busy factory, with many bustling "departments" in the cytoplasm, each having a specific structure such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, ribosomes, etc., collectively known as organelles. The cytoplasm also contains a colloidal cytoplasmic matrix, where organelles are distributed.

Organelles in the cytoplasm are not floating freely; they are supported by structures called the cytoskeleton (Figure 3-7). The cytoskeleton is a meshwork structure composed of protein fibers that maintain cell shape, anchor and support many organelles, and are closely involved in cell movements, division, differentiation, as well as substance transport, energy conversion, and information transfer.

Coordination Among Organelles The cell has many "assembly lines," each requiring the coordinated efforts of several organelles. The synthesis and transport of secretory proteins serve as an example.

The process of synthesizing secretory proteins is roughly as follows: First, peptide chain synthesis begins with amino acids as raw materials in free ribosomes. Once a peptide chain segment is synthesized, it moves with the ribosome to the rough endoplasmic reticulum (ER) where it continues its synthesis. As it is synthesized, it moves into the lumen of the ER, undergoes processing and folding to form a protein with a specific spatial structure. The ER membrane buds to form vesicles that envelop the proteins and transport them out of the ER, reaching the Golgi apparatus where they fuse with the Golgi membrane; the vesicle membrane becomes part of the Golgi membrane. The Golgi apparatus further modifies and processes the proteins, which are then packaged into vesicles by the Golgi membrane. These vesicles are transported to the cell membrane where they fuse, releasing the proteins into the extracellular space (Figure 3-8). The synthesis, processing, and transport of secretory proteins consume energy primarily supplied by mitochondria. Within the cell, many vesicles composed of membranes act like submarines in the deep sea, shuttling back and forth, busy transporting "cargo," with the Golgi apparatus playing a crucial role as a major transport hub.

Cellular Biomembrane System In cells, many organelles are membrane-bound, such as the endoplasmic reticulum, Golgi apparatus, mitochondria, chloroplasts, and lysosomes. These organelle membranes, along with the cell membrane and nuclear membrane, collectively constitute the cellular biomembrane system. The components and structures of these biomembranes are very similar, closely linked in structure and function, further demonstrating the coordination and cooperation among various structures within the cell.

The biomembrane system plays a crucial role in the life activities of cells. First, the cell membrane not only maintains a relatively stable internal environment but also plays a decisive role in the transport of substances, energy conversion, and information transfer between the cell and the external environment. Second, many important chemical reactions require the involvement of enzymes, and the extensive membrane surface provides attachment sites for various enzymes. Third, the cellular biomembrane segregates various organelles within the cell like small compartments, enabling multiple chemical reactions to proceed simultaneously without interference, ensuring efficient and orderly cellular activities.