In sexual reproduction, organisms inherit half of their nuclear DNA from the male parent and half from the female parent. However, organisms inherit all of their mitochondrial DNA from the female parent. This occurs because only egg cells, and not sperm cells, keep their mitochondria during fertilization.
DNA is made of chemical building blocks called nucleotides. These building blocks are made of three parts: a phosphate group, a sugar group and one of four types of nitrogen bases. To form a strand of DNA, nucleotides are linked into chains, with the phosphate and sugar groups alternating. The four types of nitrogen bases found in nucleotides are: adenine A , thymine T , guanine G and cytosine C. The order, or sequence, of these bases determines what biological instructions are contained in a strand of DNA.
The complete DNA instruction book, or genome, for a human contains about 3 billion bases and about 20, genes on 23 pairs of chromosomes. DNA contains the instructions needed for an organism to develop, survive and reproduce. To carry out these functions, DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies.
Each DNA sequence that contains instructions to make a protein is known as a gene. The size of a gene may vary greatly, ranging from about 1, bases to 1 million bases in humans. Genes only make up about 1 percent of the DNA sequence. It is often compared to a blueprint, since it contains the instructions to construct other components of the cell, such as proteins and RNA molecules.
The DNA segments that carry genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the expression of genetic information.
In eukaryotes such as animals and plants, DNA is stored inside the cell nucleus, while in prokaryotes such as bacteria and archaea, the DNA is in the cell's cytoplasm.
Other proteins such as histones are involved in the packaging of DNA or repairing the damage to DNA that causes mutations. DNA is a long polymer of simple units called nucleotides, which are held together by a backbone made of sugars and phosphate groups. This backbone carries four types of molecules called bases and it is the sequence of these four bases that encodes information.
The major function of DNA is to encode the sequence of amino acid residues in proteins, using the genetic code. DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone. What is a gene? What is a chromosome? How many chromosomes do people have? What is noncoding DNA?
This page appears in the following eBook. Aa Aa Aa. Deoxyribonucleic acid , more commonly known as DNA , is a complex molecule that contains all of the information necessary to build and maintain an organism. All living things have DNA within their cells. In fact, nearly every cell in a multicellular organism possesses the full set of DNA required for that organism.
Key Concepts DNA chromosomes. Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics.
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