Nucleotides are arranged in two long strands and are held together by the sugar-phosphate backbone. The nucleotide strands form a spiral double helix that looks similar to a ladder. The sides of the ladder consist of sugar and phosphate molecules. The middle rungs are formed by the base pairs and the hydrogen bond.
Nucleotides are the building blocks of nucleic acids. In each pair of autosomes, one was inherited from the mother and one was inherited from the father. Mitochondrial DNA has one chromosome that codes for the specific proteins needed for the metabolic processes that mitochondria perform. Mitochondrial DNA replicates separately from the rest of the cell and is passed down only from the mother. However, noncoding DNA does have a purpose. The regulatory function of this DNA is to determine when and where some genes are transcribed.
Noncoding DNA also provides chromosomal structure and binding sites for regulatory proteins. Much research is being conducted on noncoding DNA. Tell us what you think about Healio. What is a Genome? DNA sequences outside this 1 percent are involved in regulating when, how and how much of a protein is made.
DNA's instructions are used to make proteins in a two-step process. First, enzymes read the information in a DNA molecule and transcribe it into an intermediary molecule called messenger ribonucleic acid, or mRNA. Next, the information contained in the mRNA molecule is translated into the "language" of amino acids, which are the building blocks of proteins.
This language tells the cell's protein-making machinery the precise order in which to link the amino acids to produce a specific protein. This is a major task because there are 20 types of amino acids, which can be placed in many different orders to form a wide variety of proteins. But nearly a century passed from that discovery until researchers unraveled the structure of the DNA molecule and realized its central importance to biology. For many years, scientists debated which molecule carried life's biological instructions.
Most thought that DNA was too simple a molecule to play such a critical role. Instead, they argued that proteins were more likely to carry out this vital function because of their greater complexity and wider variety of forms.
By studying X-ray diffraction patterns and building models, the scientists figured out the double helix structure of DNA - a structure that enables it to carry biological information from one generation to the next. Despite his scientific achievements, Dr. Scientist use the term "double helix" to describe DNA's winding, two-stranded chemical structure.
This shape - which looks much like a twisted ladder - gives DNA the power to pass along biological instructions with great precision. To understand DNA's double helix from a chemical standpoint, picture the sides of the ladder as strands of alternating sugar and phosphate groups - strands that run in opposite directions.
Each "rung" of the ladder is made up of two nitrogen bases, paired together by hydrogen bonds. Because of the highly specific nature of this type of chemical pairing, base A always pairs with base T, and likewise C with G. So, if you know the sequence of the bases on one strand of a DNA double helix, it is a simple matter to figure out the sequence of bases on the other strand.
Compare the relative sizes of the double helix, histones, and chromosomes. Figure 8: In eukaryotic chromatin, double-stranded DNA gray is wrapped around histone proteins red. Figure 9: Supercoiled eukaryotic DNA. How do scientists visualize DNA? Figure This karyotype depicts all 23 pairs of chromosomes in a human cell, including the sex-determining X and Y chromosomes that together make up the twenty-third set lower right.
Watch this video for a closer look at the relationship between chromosomes and the DNA double helix. What are karyotypes used for? Who is James Watson? What do we know about Francis Crick? Topic rooms within Genetics Close. No topic rooms are there.
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