Deoxyribonucleic Acid

Respond to this Friday Faithfuls challenge by writing anything about DNA, RNA, chromosomes, or cells, or you can write about whatever else you think might fit.  The human body is made up of trillions of cells and each cell is a copy of a single cell that divided itself to make all of the cells in your body.  DNA is a self-replicating material that is passed down from parent to child.  Your cells need instructions to create who you are.  Your DNA, genes and chromosomes work together to tell your body how to form and function.  Deoxyribonucleic acid which is better known as DNA, is the hereditary material in humans and almost all other organisms.  Nearly every cell in a person’s body has the same DNA.  Most DNA is located in the cell nucleus, but a small amount of DNA can also be found in the mitochondria, an organelle found in the cells of most eukaryotes, such as animals, plants and fungi.  Mitochondria are structures within cells that convert the energy from food into a form that cells can use.  DNA is a fundamental molecule that carries the genetic instruction of all living organisms.  DNA is packed into chromosomes with the help of special proteins called histones.  A chromosome is a long chain of DNA molecules that contains part of all of the genetic material of an organism.  Chromosomes are structures within cells that contain a person’s genes.  Genes are contained in chromosomes, which are in the cell nucleus.  A chromosome contains hundreds to thousands of genes.

A nucleotide consists of a sugar molecule attached to a phosphate group and a nitrogen-containing base and they form the basic structural unit of nucleic acids such as DNA and RNA.  Ribonucleic acid RNA is present in all living cells.  Its principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins, although in some viruses RNA rather than DNA carries the genetic information.  DNA works by copying itself into the molecule called RNA.  If DNA is the blueprint, you can think of RNA as the translator of instructions written in the blueprint.  DNA is double-stranded, forming a double helix, while RNA is usually single-stranded.  The information in RNA, although copied into another chemical form, is still written in essentially the same language as it is in DNA, the language of a nucleotide sequence.  Portions of a DNA sequence are transcribed into RNA.  DNA is responsible for storing and transferring genetic information while RNA directly codes for amino acids and as acts as a messenger between DNA and ribosomes to make proteins.

Amino acids are molecules used by all living things to make proteins.  Proteins are complex molecules that do most of the work in cells.  A set of three nucleotides called a codon carries the information to make one subunit of a protein, an amino acid.  One codon codes or has the sequence for one amino acid.  DNA keeps the nucleotide sequence in each gene, which can direct the body to make each amino acid in a protein, using the RNA molecule to carry the codon to where amino acids are put together.  Each gene has several codons, therefore coding for the amino acids of a protein by directing the order of the amino acids.  The sugar in DNA is deoxyribose a monosaccharide sugar in living organisms, whereas RNA contains ribose that is naturally produced by the body from food.  DNA uses the bases adenine, thymine, cytosine, and guanine, while RNA uses adenine, uracil, cytosine, and guanine.  Uracil differs from thymine in that it lacks a methyl group on its ring.  The difference between ribose and deoxyribose is fairly subtle, as ribose has one more -OH group than deoxyribose has.  DNA is more stable under extreme conditions, because it is double stranded.

Complex structures are often composed of smaller components called building blocks.  Living organisms are built this way, with their molecules being comprised of many smaller molecules and atoms.  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 percent of those bases are the same in all people.  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 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.  You can think of DNA as being like a zipper where the nucleotides are like the teeth of that zipper.  The chains of nucleotides in human DNA are wound up and compacted into 46 chromosomes (two sets of 23) that are held together by proteins called histones which help to keep the shape of the chromosomes.  A histone is a protein that provides structural support for a chromosome.  Each chromosome contains a long molecule of DNA, which must fit into the cell nucleus.  To do that, the DNA wraps around complexes of histone proteins, giving the chromosome a more compact shape.

In 1866, Gregor Mendel was the first to suggest that characteristics are passed down from generation to generation.  DNA was discovered in 1869 by Swiss-born biochemist Fredrich Miescher, but it took more than 80 years for its importance to be fully realized.  Miescher isolated nuclein, a term that was later changed to nucleic acid and eventually to deoxyribonucleic acid.  He also hypothesized that it may serve as the material basis of heredity.  Miescher’s plan was to isolate and characterize not the nuclein (which nobody at that time realized existed), but instead the protein components of leukocytes (white blood cells).  Miescher made arrangements for a local surgical clinic to send him used, pus-coated patient bandages, which he would wash to filter out the leukocytes, and extract and identify the various proteins within the white blood cells.  During these experiments, he noticed a substance with unexpected properties that did not match those of proteins from the cell nuclei that had chemical properties unlike any protein, including a much higher phosphorous content and resistance to proteolysis (protein digestion), Miescher realized that he had discovered a new substance.  Despite there being many important and contributing discoveries both before and after the work done by James Watson and Francis Crick, who discovered the double helix, or spiraling, intertwined structure of DNA in 1953, this became fundamental to our current understanding of DNA as a whole.