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Important Organic Compounds in the Body
Organic compounds are compounds that have the el-ements carbon, hydrogen and, usually, oxygen. Many of the compounds have the carbon atoms in chains, linked by covalent bonds. There are four important organic compounds in the body—carbohydrates;proteins; fats or lipids; and nucleic acids. The firstthree are vital sources of energy in the body. The structure of the body is mostly made up of proteins. Lipids are needed for building certain structures, such as cell membranes. Lipids are also stored and used as a reserve. Nucleic acids are used to form ge-netic material.
Carbohydrates are organic compounds that have car-bon, hydrogen, and oxygen in a ratio of 1:2:1. Sugars and starches are typical examples. Carbohydrates are typical sources of energy for the cell and can be eas- ily broken down by the cells of the body. Carbohy-drates may be simple or complex.
Simple sugars or monosaccharides contain 2–7 carbon atoms. Glucose, for example, has six carbon atoms. Fructose, found in fruits, is another example. Simple sugars dissolve easily in water and are easily transported in the blood. Complex sugars are formed by the combination of two or more simple sugars. They are broken down by the digestive tract into its simplest form before being absorbed into the body.
Simple sugars that are absorbed are reconverted by chemical reactions in the presence of enzymes into various complex forms by the liver, muscle, and other tissues. Glycogen is one form of complex car-bohydrate. This form of carbohydrate is insoluble in body fluids. When the demand for energy goes up, glycogen is broken down into its simple form and transported by blood to the needed areas.
Lipids are organic compounds that have carbon, hydrogen, and oxygen atoms, however, in a different ra-tio than carbohydrates. These compounds are insolu-ble in water and must be transported in the blood by special mechanisms. For example, in blood, lipids combine with proteins and are carried as lipoproteins. Lipids are used to form important structures,such as cell membranes and certain hormones, and are an important source of energy. When there is more lipid supply than needed, it is stored in various regions for future use. The properties of lipids make them important body insulators. Fatty acids, glyc-erides, steroids, and phospholipids are some of the important lipids found in the body.
Proteins are the organic compounds that are most abundant in the body. All proteins contain carbon, hydrogen, oxygen, and nitrogen. In addition, some proteins may contain sulfur. There are about 100,000 different kinds of proteins in the body.
Proteins form the structural framework for the body. The bulk of our muscles are made of proteins.
The enzymes that facilitate chemical reactions are proteins, as are the buffers. The blood contains pro-tein in the plasma. Hemoglobin is a plasma protein used to transport gases. The antibodies are plasma proteins used in defense. Many of the hormones are made of proteins.
Proteins consist of organic molecules chains known as amino acids. There are about 20 significant amino acids in the human body. Different proteins in the body are formed by combining amino acids, using covalent bonds in different sequences. A protein chain may have any number of amino acids and is known as a polypep-tide. Some proteins may have 100,000 or more aminoacids. Each amino acid has a different chemical struc-ture and this, in turn, alters its properties.
The shape of a protein is one property that may be altered. Certain proteins may be flat and appear as a long chain; certain proteins are more complex and form spirals. Others may be folded or coiled to form complex three-dimensional structures (e.g., hemoglo-bin). The structural properties are determined by the sequence in which the amino acids are arranged. The alteration of just one amino acid sequence can alter the function of the protein drastically, as in the ex-ample of sickle cell anemia given earlier.
Nucleic acids are large organic molecules containing carbon, hydrogen, oxygen, nitrogen, and phosphorus. Found in the nucleus of the cell, they are important for storing and processing information in every cell. Nucleic acid is the major component of ova and sperm and conveys such information as shape, eye color, and sex. There are two types of nucleic acid—DNA (deoxyribonucleic acid) and RNA (ribonu-cleic acid).
DNA is in the form of a double helix (i.e., two spi-rals, parallel to each other). The two strands are held together by hydrogen bonds. A small segment of DNA molecule forms a gene. Each gene deter-mines the traits we inherit from our parents. They also control protein synthesis in each cell. The RNA conveys the message from the gene to the cell and determines the amino acids sequence when proteins are synthesized.
All cells require energy to carry out their functions. This energy is derived by catabolism of organic sub-stances in the presence of enzymes. The energy liber-ated is stored as potential energy in the form of high-energy bonds. High-energy bonds are covalentbonds created in specific organic substrates in the presence of enzymes. When the cell needs energy, these bonds are broken and the energy harnessed.
AMP is the most important organic substrate used by the cells to form covalent bonds. The cells use the energy liberated by nutrient breakdown to convert AMP to ADP, which is then converted to ATP. Both ADP and ATP are formed by attaching phosphate groups by covalent bonds.
ADP + phosphate group + energy → ATP + H2O
ATP → ADP + phosphate group + energy
As the body needs energy, ATP is broken down. Other compounds with high-energy bonds exist, but ATP is the most abundant.
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