What is DNA?

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What is DNA?

• A cell uses a code that is stored in hereditary material. The code is a chemical called DNA (deoxyribonucleic acid). DNA contains information for an organism’s growth and function.
• When a cell divides, the DNA code is copied and passed to the new cells. New cells receive the same coded information as the original cell.

Discovering DNA

• By 1950, chemists had learned what the nucleic acid DNA was made of, but they didn’t understand how the parts of DNA were arranged.
• In 1952, scientist Rosalind Franklin discovered that DNA is two chains of molecules in a spiral form. In 1953, James Watson and Francis Crick made a DNA model

A DNA Model

• Each side ladder is made up of sugar-phosphate molecules.
• The rungs of the ladder are made up of other molecules called nitrogen bases.
• Four kinds of nitrogen bases are found in DNA: adenine, guanine, cytosine, and thymine (A, G, C, and T).

DNA Model

• Adenine always pairs with thymine, and guanine always pairs with cytosine.
• Like interlocking pieces of a puzzle, each base bonds only with its correct partner.

Copying DNA

• When chromosomes are duplicated before mitosis, the amount of DNA in the nucleus is doubled. The two sides of DNA unwind and separate. Each side then becomes a pattern of which a new side forms.
• The new DNA has bases that are identical to those of the original DNA and are in the same order.

RNA

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Ribonucleic Acid

• RNA is different from DNA.
• If DNA is like a ladder, RNA is like a ladder that has all its rungs sawed in half.
• RNA has the bases A, G, and C like DNA but has the base uracil (U) instead of thymine (T).
• The sugar-phosphate molecules in RNA contain the sugar ribose, not deoxyribose.

DNA and RNA: A Tag Team

• DNA uses RNA to communicate its instructions to the rest of the cell. Most of these instructions involve the creation of proteins (molecules that cells use for all kinds of different jobs).
• DNA contains the recipes for making all those proteins, but it needs RNA to deliver and interpret them for the rest of the cell.

Three Main Kinds of RNA

1. Messenger RNA (mRNA)-carries the protein recipes from the DNA to the ribosomes (organelles that manufacture proteins).
2. Transfer RNA (tRNA)-decodes the instructions from the mRNA since the ribosomes can’t read the recipes encoded in the mRNA

Three Main Types of RNA

3. Ribosomal RNA (rRNA)-Ribosomes are themselves partly made up of rRNA. This is the most common type of RNA in a cell.