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Most DNA is located in the cell nucleus (where it is called nuclear DNA).
A small amount of DNA can also be found in the mitochondria when it is called mitochondrial DNA or mtDNA.
- Human DNA, collectively called human genome, consists of about 3 billion bases.
- Over 99 percent of those bases are the same in all people.
- 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.
- 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 cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
- DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.
DNA and chromosomes
- During DNA replication, DNA unwinds so it can be copied.
- At other times in the cell cycle, DNA also unwinds so that its instructions can be used to make proteins and for other biological processes.
- During cell division, DNA is in its compact chromosome form to enable transfer to new cells.
Male and female contribution
- In sexual reproduction, organisms inherit half of their nuclear DNA from the male parent and half from the female parent.
- 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 and proteins
- 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.
- There are 20 types of amino acids, which can be placed in many different orders to form a wide variety of proteins.
History and discovery
- The Swiss biochemist Frederich Miescher first observed DNA in the late 1800s.
- But nearly a century passed from that discovery until researchers unraveled the structure of the DNA molecule and realized its central importance to biology.
James Watson et al
- The importance of DNA became clear in 1953 thanks to the work of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin.
- 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.
Recombinant DNA molecules are DNA molecules formed by laboratory methods of genetic recombination to bring together genetic material from multiple sources, thereby creating sequences that would not otherwise be found in the genome.
- Genetic engineering is the process of using recombinant DNA (rDNA) technology to alter the genetic makeup of an organism.
- Traditionally, humans have manipulated genomes indirectly by controlling breeding and selecting offspring with desired traits.
- Genetic engineering involves the direct manipulation of one or more genes.
- Most often, a gene from another species is added to an organism's genome to give it a desired phenotype.
Latest research - DNA