FUNCTIONS OF CELLS
Our body is synthesized from the food we eat. It is made of a complex structure of cells, tissues and organs. How does this change from food to our body structure occur? All the changes that occur in the food from the time we eat it, to its use in the body and discarding of the waste matter are known as metabolism. One can describe metabolism of each nutrient separately to ensure ease of understanding. But actually it occurs in a correlated systematic manner.
Basic concepts of biology and chemistry need to be understood in the study of nutrition. Let us review these.
Concepts of biology: This study of nutrition begins with the cell, the basic unit of body. All the nutrition processes, which we refer to as metabolism, take place in the cell. Metabolism includes both anabolism and catabolism. Anabolism involves synthesis of compounds needed for use in the body. Breakdown of complex substances to simpler ones is known as catabolism. Thus cells are able to take up nutrients, synthesize substances they need and climate wastes. The energy release and its utilization occur in the cell.
There are many kinds of cells in the body, each type specializes in carrying out certain functions required by the body.
Cells are grouped together to form a tissue. Muscle, nerve, epithelial and connective tissue are examples of various tissues.
Two or more tissues are combined to form a an organ, which carries out a specific function. Heart , lungs and kidneys are examples of organs.
Cells are made up of several parts. Each part has an appropriate structure and a specific function. Two main parts of the cell are the nucleus and the protoplasm, which surrounds the nucleus and is called cytoplasm.
The nucleus controls the functions of the cell; the metabolic activities of the cell are carried out by the cytoplasm. The deoxyribonucleic acid (DNA) in the cell nucleus contains the pattern for each of the different proteins body. The ribonucleic acid (RNA) directs the actual protein synthesis in the ribosome, using the information stored in the DNA. This process, which is directed and controlled by DNA, is the key to nutrition.
All the components, which form nutrients, come from food. Our genes determine the nutrients that can be synthesized in the body and those which need to be provided preformed in the food. The small channels in the cytoplasm, called endoplasmic reticulum, transport nutrients and their metabolites throughout the cytoplasm. The enzymes, which function in metabolism, are found in the membranes surrounding the channels.
The mitochondria and lysosomes are also present in the cytoplasm. Mitochondria release the energy provided by the carbohydrates, fats and proteins and transfer it to an energy acceptor (ATP). The ATP transfers the energy as needed wherever work is being done. Therefore the mitochondria are known as the ‘power plants’ of the cell.
Lysosomes contain enzymes, which function in the breakdown of protein and other compounds. Lysosomes help to digest foreign matter that may have entered the cell and thus protect the body from their harmful effects.
Chemistry: Our body and the food that nourishes it are made of chemical elements. Therefore knowledge of the chemical elements and their behavior is basic to the study of nutrition. Chemical analysis enables one to obtain useful data regarding the approximate content of carbohydrates, fats, proteins, minerals, vitamins and water in any given food. It also enables us to determine with fair accuracy, the amounts of mineral elements, such as iron, calcium, phosphorus, sulfur, sodium and chlorine present in different foods. Vitamins can also be determined by chemical analysis, but other methods such as physical methods which measure absorption spectra, fluorescence, turbidity, etc. or microbiological assay (influence of a particular vitamin on growth of bacteria) can be used.