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Until as recently as the 1940s, scientists thought that genetic information was carried in the proteins of the body. They thought nucleic acids, a new discovery at the time, were too small to be significant. That all changed in 1953 when James Watson and Francis Crick figured out the structure of a nucleic acid, proving things were the other way around: Nucleic acids created the proteins! Nucleic acids are large molecules that carry tons of small details, specifically all the genetic information for an organism. Nucleic acids are found in every living thing — plants, animals, bacteria, and fungi. Just think about that fact for a moment. People may look different than fungi, and plants may behave differently than bacteria, but deep down all living things contain the same chemical “ingredients” making up very similar genetic material. Nucleic acids are made up of strands of nucleotides. Each nucleotide has three components of its own: ✓ A nitrogen-containing base called a nitrogenous base ✓ A sugar that contains five-carbon molecules ✓ A phosphate group That’s it. Your entire genetic composition, personality, and maybe even your intelligence hinge on molecules containing a nitrogen compound, some sugar, and a phosphate. The following sections introduce you to the two types of nucleic acids.
Deoxyribonucleic acid (DNA) You may have heard DNA (short for deoxyribonucleic acid) referred to as “the double helix.” That’s because DNA contains two strands of nucleotides arranged in a way that makes it look like a twisted ladder. See for yourself in the drawing below.
The twisted ladder model of DNA double helix :
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The sides of the ladder are made up of sugar and phosphate molecules, hence the nickname “sugar-phosphate backbone.” (The name of the sugar in DNA is deoxyribose.) The “rungs” on the ladder of DNA are made from pairs of nitrogenous bases from the two strands. The nitrogenous bases that DNA builds its double helix upon are adenine (A), guanine (G), cytosine (C), and thymine (T). The order of these chemical letters spells out your genetic code. Oddly enough, the bases always pair in a certain way: Adenine always goes with thymine (A-T), and guanine always links up with cytosine (G-C). These particular base pairs line up just right chemically so that hydrogen bonds can form between them. Certain sections of nitrogenous bases along a strand of DNA form a gene. A gene is a unit that contains the genetic information or codes for a particular
protein and transmits hereditary information to the next generation. Whenever a new cell is made in an organism, the genetic material is reproduced and put into the new cell. The new cell can then create proteins and also pass on the genetic information to the next new cell. But genes aren’t found only in reproductive cells. Every cell in an organism contains DNA (and therefore genes) because every cell needs to make proteins. Proteins control function and provide structure. Therefore, the blueprints of life are stored in each and every cell. The order of the nitrogenous bases on a strand of DNA (or in a section of the DNA that makes up a gene) determines the order in which amino acids are strung together to make a protein. Which protein is produced determines which structural element is produced within your body (such as muscle tissue, skin, or hair) or what function can be performed (such as the transportation of oxygen to all the cells). Every cellular process and every aspect of metabolism is based on genetic information stored in DNA and thus the production of the proper proteins. If the wrong protein is produced (as in the case of cancer), then disease occurs. Ribonucleic acid (RNA) RNA, short for ribonucleic acid, is a chain of nucleotides that serves as an important information molecule. It plays an important role in the creation of new proteins. The structure of RNA is slightly different from that of DNA. ✓ RNA molecules have only one strand of nucleotides. ✓ The nitrogenous bases used are adenine, guanine, cytosine, and uracil (rather than thymine). ✓ The sugar in RNA is ribose (not deoxyribose).
