There are five major groups of compounds that compose the human body. They are carbohydrates, lipids, proteins, nucleotides, and water. These are all very important to humans and without them we would not be able to survive. They have many functions that encourage a human cell and a human body to function.

Carbohydrates include sugars and starches, contain carbon, hydrogen, and oxygen which appears in a ratio of 1:2:1. Carbohydrates are classified according to size as monosaccharides, disaccharides, and polysaccharides. The primary function of carbohydrates is to serve as sources of energy. Carbohydrates are some of the most numerous molecules in living organisms. They play a major role as food molecules in the cell, being broken down to produce energy. Polysaccharides play an important role serving as energy reserves also. It provides a quick-release energy source that keeps us going between meals. Small amounts of carbohydrates are also used for structural purposes and others are attached to outer surfaces of cell membranes to guide cellular interactions. For many cells, sugars are the most important source of energy.

Lipids are important because they function as structu

ral components of cell membranes, sources of insulation, and a mean of energy storage. The lipid molecules are most well known as forming basic structures of cell membranes and as energy storage molecules as well. In this group of lipids, there are about three main types: true fats (triglycerides), phospholipids, and steroids. True fats represent the body's most abundant and concentrated source of usable energy. When they are oxidized, they yield large amounts of energy. They are stored chiefly in fat deposits beneath the skin and around body organs, where they help insulate the body and protect deeper body tissues from heat loss and bumps. True fats are a storage form for excess food, they are stored energy. Any type of food consumed in excess need to be converted to fat and stored. Phospholipids although similar in structure to the true fats, are not stored energy but rather structural components of cells. Lecithin is a phospholipid that is part of our cell membranes and myelin provides electrical insulation for nerve impulse transmission. The third group is steroids and cholesterol is an important steroid. Cholesterol is another component of cell membranes and a form of cholesterol in the skin is changed to vitamin D on exposure to sunlight. All of the sex hormones like estrogen and testosterone are also steroids. So despite the links to bad effects, cholesterol is an essential substance for human beings.

Proteins are very important in biological systems as control and structural elements. Proteins do almost everything in the body, from catalyzing reactions, fighting off foreign things, storing and transporting oxygen, to forming muscle, skin, hair, and a variety of other structural tissues. They exist in a multitude of forms, but almost all are constructed from a basic

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Approximate Word count = 1215
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