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.
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