Chapter 04. Systems within the Cell

We've examined how protein synthesis started, and came about but for it to come about, the most important need is for raw materials. And in order to participate in protein synthesis, these raw materials need to go through certain processes, to be refined to bring them to a usable state. For example, plastic and many other products are made from oil, but first the oil must go to the refinery, and through many chemical processes, in order to bring it to a state that can be used for production.

The same sort of technology, though much more highly developed, is found in the cell.

The Laboratory in the Cell

Nutrients entering the cell are broken down as a result of a series of extensive chemical reactions, resulting in their becoming raw materials that can then participate in new syntheses. In this way they can be used in totally new ways-not just as amino acids to form proteins, but many other chemical substances that the cell will use in many ways.

1-Exocytic Vesicles The budding vesicles of the Golgi body carry the substances they contain towards the cell membrane. The substances that the cell doesn't want or for which the body has no need are ejected from the cell. 2-Golgi Body Transported proteins and lipids are stored here, and classed according to their duties. Substances are then stored in cell organelles as needed. 3-Transport Vesicles Vesicles deliver proteins and lipids to the Golgi body, where they will be stored. 4-Endoplasmic Reticulum (ER) Many proteins are produced by ribosomes found on the surface of the rough ER. Lipids, on the other hand, are synthesized on smooth ER. Both substances are either secreted out of the cell or stored. 5-Endocytic Vesicles Forming as buds on the cell membrane, they import substances from outside the cell. When they arrive at the lysosomes, digestive enzymes break them down, along with their contents. 6-Lysosomes Containing digestive enzymes, they produce basic raw materials the cell needs by digesting macromolecules arriving from outside the cell. The vesicle that enters the cell transports substances to the lysosomes. 7-Microbodies Just like lysosomes, they contain digestive enzymes that break down substances such as fats and hydrogen peroxide.
	a. Cell Membrane b. Rough ER c. ER
Figure 4.3 Proteins are built according to DNA instructions. In the nucleus, synthesized RNA receives from the DNA the relevant instructions needed for protein synthesis. It takes these instructions to the ribosomes and carries out protein synthesis on these organelles. Proteins synthesized on ribosomes found on the surface of the endoplasmic reticulum are deposited at the endoplasmic reticulum for transport.

One organelle within which these processes are carried out, and which resembles a highly developed chemical laboratory, is the lysosome. Approximately 36 different enzymes in the lysosome have the duty of digesting different nutrients. For example five enzymes take part in protein digestion, four participate in the digestion of nucleic acids, 15 in the digestion of polysaccharides, six have a role in the digestion of lipids, two in the digestion of organic sulphates, and four different enzymes take part in the digestion of organic phosphates. Consider just one enzyme's chemical structure, physical characteristics, complex processes and incredible speed with which these processes are carried out, and then realize that there are 36 different enzymes that have duties in an organelle only 1 micron (a thousandth of a millimeter) in size, and it becomes clear how great a miracle this all is. Such powerful digesters cooperate with each other in such harmony without harming each other or the cell as a whole.

Transport Within the Cell

Products made in the cell and their raw materials are transported through channels called endoplasmic reticula (see Figure 4.1). The ribosomes that carry out protein synthesis are generally placed near this transport line, just as factories are built close to the highway and docks for easier delivery of raw materials.

1. Smooth ER tubes 2. Vesicle 3. Newly formed vesicle 4. Budding vesicle	5. Ribosomes on the endoplasmic reticulum 6. Cisternal spaces between the rough endoplasmic reticulum 7. Cross section of rough ER tubes
Figure 4.1 A) The endoplasmic reticulum, which facilitates transport of substances within the cell B) Rough endoplasmic reticulum (with ribosomes) C) Cross section of rough endoplasmic reticulum (with ribosomes)

The Cells' Packaging System

Clearly, every detail in the cell has been especially created by a superior intelligence. For another example of this, look at the packaging facilities within the cell.

One of the most important aspects in manufacturing any product is packaging and transporting it to the consumer. Food especially must be packaged in such a way to keep it from spoiling for as long as possible. While modern technology has found solutions to this problem only in the last few decades, every one of the trillions of cells contains a superior packaging, transportation, and storage system that has been around for thousands of years, ever since man was first created.

1. Budding vesicle 2. Cisternal spaces Figure 4.2 Electron micrograph of Golgi body This packaging system is carried out within an organelle called the Golgi body (see Figure 4.2). It accumulates secreted substances, then packages them into small vesicles where they are either stored as needed, or exported out of the cell.

Figure 4.4 1. Plasma membrane: control of material exchanges, regulation of cell-environment interactions 2. Golgi complex: modification, distribution and storage of substances 3. Lysosome: digestion, breakdown 4. Endoplasmic reticulum: isolation, modification, and transport of proteins and other substances 5. DNA and genetic control 6. Mitochondrion: energy production 7. Nuclear membrane 8. Nucleus