1.2 DNA Introduction
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The nucleus of cells contains chromosomes. Chromosomes consist of long strands of a substance called deoxyribonucleic acid (DNA). A short section of DNA is called a gene. A chromosome may have several thousand genes in it. Each gene carries a code that determines our characteristics. The codes determine the activities that the cells undertake. Some genes determine what proteins to produce and the type of protein produced leads to the development of certain features. We inherit these chromosomes from our parents (the egg of our mother and sperm from our father. We will be looking at reproduction in more detail later in the course).
How is DNA Composed?
A DNA molecule is two strands of nucleotides coiled together to form a double helix (or a polynucleotide). The two strands are linked through a series of paired bases. Each strand contains a nitrogenous base, a sugar molecule and a phosphate group.
A DNA molecule is two strands of nucleotides coiled together to form a double helix (or a polynucleotide). The two strands are linked through a series of paired bases. Each strand contains a nitrogenous base, a sugar molecule and a phosphate group.
There are four different types of nitrogenous bases. These are adenine (A), thymine (T), cytosine (C) and guanine (G). Nucleotides with adenine (A) are always opposed to nucleotides with thymine (T). Also, nucleotides with guanine (G) are always opposed to cytosine (C). We can say that adenine (A) and thymine (T) are complementary bases, and so are cytosine (C) and guanine (G). A complementary base means that the bases will only bind with other and never any other bases. We call this the base pairing rule.
From the diagram above, we can see that the four different nitrogenous bases have different shaped ends. The ends of the bases will only fit into certain other bases like jigsaw puzzle pieces. For example, we see that adenine (A) will only fit into thymine (T). Also, cytosine (C) will only fit into guanine (G).
From the diagram above, we can see that the four different nitrogenous bases have different shaped ends. The ends of the bases will only fit into certain other bases like jigsaw puzzle pieces. For example, we see that adenine (A) will only fit into thymine (T). Also, cytosine (C) will only fit into guanine (G).