What is DNA?

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  • 0:02 What is DNA?
  • 3:29 Characteristics
  • 3:55 Functions
  • 4:21 Creating the Helix
  • 5:18 Lesson Summary
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Lesson Transcript
Instructor: Jayne Yenko

Jayne has taught health/nutrition and education at the college level and has a master's degree in education.

In this lesson, we will learn what DNA is, what its characteristics and functions are, even where it is located and what information it contains. We'll also learn how the double helix is created. Find out more.

What Is DNA?

Why do people look and act like people, cats look and act like cats, or frogs look and act like frogs? All of us have what is called DNA in every one of our cells. This is the genetic information we get from our parents, half from our mother, half from our father. Every time one of our cells divides, this information is passed on to the new cells to make sure the new cells look and behave like the original ones.

DNA stands for deoxyribonucleic acid - that's a mouthful, isn't it? DNA is the master molecule in every cell. In eukaryotic organisms, such as animals, plants and fungi, the DNA is stored inside the cell nucleus and in the chromosomes. Prokaryotes (bacteria) store their DNA only in the cytoplasm within their cells. This master molecule, the DNA, is the perfect hiding place for biological or genetic information. This information is the instruction for the making of the DNA itself, as well as other proteins, somewhat like a cookbook. If the recipe is changed even slightly, mutations will occur. DNA belongs to a class of molecules called nucleic acids (the other nucleic acid is RNA or ribonucleic acid).

DNA looks very complex, but it is really pretty simple. It is just a pattern made out of four different shapes, or an alphabet with only four letters. Each side of the double helix is a long string of these shapes or letters in a specific pattern. Each of these shapes is a nucleotide.

A nucleotide is made of a sugar and a phosphate on the outsides, and in the middle, contains the nitrogenous bases, either purine or pyrimidine. The bases pair up, purine with pyrimidine, and are held together with hydrogen bonds.

Cells are pretty small, so how does the DNA fit inside? DNA is, after all, a very long molecule. To fit inside the cell, DNA is coiled and twisted around proteins called histones. The histones are also coiled to form chromosomes, which are located in the nucleus of the cell. The DNA contains instructions for making proteins, which determine our physical characteristics. Each protein, or recipe, is contained within a specific gene. The pattern made by the nucleotides lists the order of ingredients or amino acids to be put together to create a protein.

Plants and animals have 50,000 to 100,000 genes on many different chromosomes. Humans have 46 chromosomes. A bacteria, like E. coli, only has about 3,000 genes in one DNA molecule, which would be about one millimeter long. The bacteria is only three microns long, or three one-hundredths of a millimeter. That's really small. No wonder DNA has to twist and coil up to fit into a cell.

Let's find out what the characteristics of DNA are.


The characteristics of DNA include:

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