The double-helix model explains Chargaff's rule of base pairing and how the two strands of DNA are held together. The two strands of DNA held together by hydrogen bonds between the nitrogenous bases adenine and thymine, and between guanine and cytosine.
Is DNA really a double helix?
DNA is a double-stranded helix, with the two strands connected by hydrogen bonds. Why is DNA a helix? The double comes from the fact that the helix is made of two long strands of DNA that are intertwined—sort of like a twisted ladder.
What does it mean that DNA is a double helix?
The double helix describes the appearance of double-stranded DNA, which is composed of two linear strands that run opposite to each other, or anti-parallel, and twist together. Each DNA strand within the double helix is a long, linear molecule made of smaller units called nucleotides that form a chain.
Who deduced that DNA is shaped like a double helix?
The DNA of all species has the same four nitrogen bases. After DNA was found to be the genetic material, scientists wanted to learn more about it. James Watson and Francis Crick are usually given credit for discovering that DNA has a double helix shape, like a spiral staircase (see Figure below ).
Why is the DNA called a double helix?
Some of the most important reasons are:
- A double helix is very stable in comparison to a single strand.
- A single strand is not as geometrically constrained as a double helix and this prevents unwanted molecular movements that may disrupt the DNA structure.
- Having a second strand means that if there is some DNA damage is one strand, the other strand can be used to repair it. ...
What is double helix?
Updated February 07, 2020. In biology, "double helix" is a term used to describe the structure of DNA . A DNA double helix consists of two spiral chains of deoxyribonucleic acid. The shape is similar to that of a spiral staircase. DNA is a nucleic acid composed of nitrogenous bases (adenine, cytosine, guanine, and thymine), ...
Who discovered the double helical structure of DNA?
Credit for the discovery of the double-helical structure of DNA has been given to James Watson and Francis Crick, awarded a Nobel Prize for their work. Determining the structure of DNA was based in part on the work of many other scientists, including Rosalind Franklin.
Why Is DNA Twisted?
The twisting aspect of DNA is a result of interactions between the molecules that make up DNA and water. The nitrogenous bases that comprise the steps of the twisted staircase are held together by hydrogen bonds. Adenine is bonded with thymine (A-T) and guanine pairs with cytosine (G-C). These nitrogenous bases are hydrophobic, meaning that they lack an affinity for water. Since the cell cytoplasm and cytosol contain water-based liquids, the nitrogenous bases want to avoid contact with cell fluids. The sugar and phosphate molecules that form the sugar-phosphate backbone of the molecule are hydrophilic, which means they are water-loving and have an affinity for water.
Why do DNA strands twist?
The fact that the two DNA strands that form the double helix are anti-parallel helps to twist the molecule as well.
How does DNA replication work?
In DNA replication, the double helix unwinds and each separated strand is used to synthesize a new strand. As the new strands form, bases are paired together until two double-helix DNA molecules are formed from a single double-helix DNA molecule.
What are the bases of DNA?
DNA is a nucleic acid composed of nitrogenous bases (adenine, cytosine, guanine, and thymine), a five-carbon sugar (deoxyribose), and phosphate molecules. The nucleotide bases of DNA represent the stair steps of the staircase, and the deoxyribose and phosphate molecules form the sides of the staircase.
Why do nitrogenous bases want to avoid contact with cell fluids?
Since the cell cytoplasm and cytosol contain water-based liquids, the nitrogenous bases want to avoid contact with cell fluids. The sugar and phosphate molecules that form the sugar-phosphate backbone of the molecule are hydrophilic, which means they are water-loving and have an affinity for water.
What is the double helix?
The discovery in 1953 of the double helix, the twisted-ladder structure of deoxyribonucleic acid (DNA), by James Watson and Francis Crick marked a milestone in the history of science and gave rise to modern molecular biology, which is largely concerned with understanding how genes control the chemical processes within cells. In short order, their discovery yielded ground-breaking insights into the genetic code and protein synthesis. During the 1970s and 1980s, it helped to produce new and powerful scientific techniques, specifically recombinant DNA research, genetic engineering, rapid gene sequencing, and monoclonal antibodies, techniques on which today's multi-billion dollar biotechnology industry is founded. Major current advances in science, namely genetic fingerprinting and modern forensics, the mapping of the human genome, and the promise, yet unfulfilled, of gene therapy, all have their origins in Watson and Crick's inspired work. The double helix has not only reshaped biology, it has become a cultural icon, represented in sculpture, visual art, jewelry, and toys.
Who discovered the structure of DNA?
Moreover, he had pioneered the method of model building in chemistry by which Watson and Crick were to uncover the structure of DNA.
What did Franklin prove about the backbones of sugar phosphate?
Her evidence demonstrated that the two sugar-phosphate backbones lay on the outside of the molecule, confirmed Watson and Crick's conjecture that the backbones formed a double helix, and revealed to Crick that they were antiparallel. Franklin's superb experimental work thus proved crucial in Watson and Crick's discovery.
What evidence did Watson and Crick use?
A more enduring controversy has been generated by Watson and Crick's use of Rosalind Franklin's crystallographic evidence of the structure of DNA , which was shown to them, without her knowledge, by her estranged colleague, Maurice Wilkins, and by Max Perutz. Her evidence demonstrated that the two sugar-phosphate backbones lay on the outside of the molecule, confirmed Watson and Crick's conjecture that the backbones formed a double helix, and revealed to Crick that they were antiparallel. Franklin's superb experimental work thus proved crucial in Watson and Crick's discovery. Yet, they gave her scant acknowledgment. Even so, Franklin bore no resentment towards them. She had presented her findings at a public seminar to which she had invited the two. She soon left DNA research to study tobacco mosaic virus. She became friends with both Watson and Crick, and spent her last period of remission from ovarian cancer in Crick's house (Franklin died in 1958). Crick believed that he and Watson used her evidence appropriately, while admitting that their patronizing attitude towards her, so apparent in The Double Helix, reflected contemporary conventions of gender in science.
What are the four types of bases in DNA?
The biochemist Erwin Chargaff had found that while the amount of DNA and of its four types of bases--the purine bases adenine (A) and guanine (G), and the pyrimidine bases cytosine (C) and thymine (T)--varied widely from species to species, A and T always appeared in ratios of one-to-one, as did G and C. Maurice Wilkins and Rosalind Franklin had obtained high-resolution X-ray images of DNA fibers that suggested a helical, corkscrew-like shape. Linus Pauling, then the world's leading physical chemist, had recently discovered the single-stranded alpha helix, the structure found in many proteins, prompting biologists to think of helical forms. Moreover, he had pioneered the method of model building in chemistry by which Watson and Crick were to uncover the structure of DNA. Indeed, Crick and Watson feared that they would be upstaged by Pauling, who proposed his own model of DNA in February 1953, although his three-stranded helical structure quickly proved erroneous.
What is the smallest unit of genetic information?
Researchers working on DNA in the early 1950s used the term "gene" to mean the smallest unit of genetic information, but they did not know what a gene actually looked like structurally and chemically, or how it was copied, with very few errors, generation after generation. In 1944, Oswald Avery had shown that DNA was the "transforming principle," the carrier of hereditary information, in pneumococcal bacteria. Nevertheless, many scientists continued to believe that DNA had a structure too uniform and simple to store genetic information for making complex living organisms. The genetic material, they reasoned, must consist of proteins, much more diverse and intricate molecules known to perform a multitude of biological functions in the cell.
What is the function of DNA?
The two had shown that in DNA, form is function: the double-stranded molecule could both produce exact copies of itself and carry genetic instructions. During the following years, Crick elaborated on the implications of the double-helical model, advancing the hypothesis, revolutionary then but widely-accepted since, that the sequence of the bases in DNA forms a code by which genetic information can be stored and transmitted.
What is a Double Helix?
The dna double helix is the demonstration of the structure of one molecule of DNA (Deoxyribonucleic).
What is the Difference Between a Helix and a Double Helix?
While speaking of a double helix, we assume two strands intertwined or coiled around each other to look like a twisted staircase. On the other hand, we don't know what is a helix. A single helix consists of a single strand that is coiled around itself. Such types of the single helix are seen while reading the structure of RNA.
Who created the first DNA double helix model?
The first accurate DNA double helix structure model was unveiled in 1962 and credited to two scientists, James Watson and Francis Crick. Their work was based on the x-ray crystallography structures collected and analyzed by another scientist, Rosalind Franklin .
Who discovered the double helix structure of DNA?
The work done by these earlier scientists formed the foundation for the discovery of the double helix structure of the DNA molecule by Watson and Crick.
What is the shape of DNA?
DNA molecules have two strands that coil around an axis, forming a twisted ladder shape, commonly known as a double helix . The rungs on the ladder are the nitrogenous base pairs connected by a hydrogen bond (bases adenine and thymine or guanine and cytosine) while the sides are alternating sugar molecules and phosphate groups bonded together. The sides are commonly known as the sugar phosphate backbone. You can get a feel for how the two strands are woven together by twisting two pipe cleaners.
What did Watson and Crick discover about DNA?
By analyzing the results of Franklin’s X-ray crystallography, Watson and Crick got vital indications of DNA structure. This crystallography technique uses x-rays to form a diffraction pattern which indicates a molecule’s structure. This technique was used to examine a DNA molecule, and it produced an X-shaped diffraction image which suggested to Watson and Crick that DNA had a two-stranded helical structure.
What is the structure of DNA?
The structure of DNA is a double-stranded helix. The strands are bound with hydrogen bonds. Adenine bases are always joined with thymine bases, and cytosine bases are always joined with guanine bases. This is in accordance with Chargaff’s rules.
What did Miescher discover?
Interestingly, Miescher wasn’t trying to discover DNA. He was trying to identify the proteins that make up the white blood cells. During his experiments, he discovered a substance that was different from any other protein. This substance had an unusually high amount of phosphorus and was resistant to protein digestion.
Why are the outer edges of the DNA ladder important?
While a hydrogen bond links the base pairs inside the ladder, the exposed outer edges are important for binding other molecules such as proteins for DNA maintenance.
Why Is DNA Twisted?
DNA Replication and Protein Synthesis
- The double-helix shape allows for DNA replication and protein synthesis to occur. In these processes, the twisted DNA unwinds and opens to allow a copy of the DNA to be made. In DNA replication, the double helix unwinds and each separated strand is used to synthesize a new strand. As the new strands form, bases are paired together until two double-...
DNA Structure Discovery
- Credit for the discovery of the double-helical structure of DNA has been given to James Watson and Francis Crick, awarded a Nobel Prize for their work. Determining the structure of DNA was based in part on the work of many other scientists, including Rosalind Franklin. Franklin and Maurice Wilkins used X-ray diffraction to ascertain clues about the structure of DNA. The X-ray d…
Sources
- “The Discovery of the Molecular Structure of DNA—The Double Helix.” Nobelprize.org, www.nobelprize.org/educational/medicine/dna_double_helix/readmore.html.