2.3) Cells and DNA
In this section we will discuss the cells that make up your body and the DNA inside of each of those cells.
Cells are the building blocks of life
Cells are the basic building blocks of all living things, including you. Your body is composed of an estimated 30 trillion cells. Cells provide structure for your body, take in nutrients, convert nutrients into energy and contain your body’s hereditary material, DNA.
Figure 2-1 Your body is made up of approximately 50 trillion cells. The nucleus of the cell contains the chromosomes. Chromosomes are made up of DNA.
Chromosomes are the DNA packaging
In the nucleus of each of your cells, there are thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. Each cell in your body contains 23 pairs of chromosomes. One chromosome from each pair is inherited from your mother and one is inherited from your father.
Figure 2-2 In the nucleus of each of your cells there are 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of
DNA is the blueprint for life
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Human DNA consists of about 3 billion bases, and more than 99.8 percent of those bases are the same in all people. This is significant as it allows researchers to focus on the 0.2% that is different.
Characteristics of Human DNA
There are roughly 30 trillion cells in the human body.
There are approximately 3,000,000,000 (3 billion bases) in each human cell.
These bases make up roughly 25,000-30,000 genes.
The 3,000,000,000 bases are organized into 23 pairs of chromosomes.
The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. DNA carries the instructions used for growth, development, function and reproduction.
DNA bases pair up with each other, A with T, and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
Nearly every cell in your body has the same DNA. An important property of DNA is that it can replicate or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when your cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
Figure 2-3 The structure of the DNA double helix, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces.
Nucleotide: The basic structural unit of DNA and RNA; a nitrogen-containing base plus a phosphate and sugar molecule (such as deoxyribose or ribose).
Double helix: Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.