Simone Lawson
DNA is a molecule that carries the genetic instructions for the development, function, growth, and reproduction of all known living organisms. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). These bases are joined via a sugar (deoxyribose) phosphate backbone to form specific sequences, and assembled into discrete packages called chromosomes. 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.
| Characteristics | Values |
|---|---|
| Number of bases | 4 |
| Names of bases | Adenine (A), Cytosine (C), Guanine (G), Thymine (T) |
| Bases that pair together | Adenine and Thymine, Cytosine and Guanine |
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What You'll Learn
DNA is made up of four chemical bases
DNA is a molecule that carries the genetic code and instructions for building and maintaining an organism. It is made up of two strands wound around each other, forming a spiral shape called a double helix. Each strand is composed of four types of chemical bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These bases are joined by hydrogen bonds, with adenine pairing with thymine and cytosine pairing with guanine. This complementary base pairing allows for efficient packing within the double helix structure.
The four bases are also known as nucleotide bases or subunits, and they are linked together to form polynucleotide chains, or DNA strands. Each base is attached to a sugar molecule, deoxyribose, and a phosphate group, forming a "backbone" of alternating sugar and phosphate molecules. This structure, with the bases extending from the backbone, gives DNA its chemical polarity. The sequence of these bases determines the information available for building and maintaining an organism, similar to how letters of the alphabet form words and sentences.
The discovery that DNA is made up of two strands was a crucial finding in understanding its potential for replication and information encoding. Early x-ray diffraction analyses in the 1950s first revealed this double-stranded structure, leading to the Watson-Crick model of DNA. The ability of DNA to replicate is essential for cell division, as each new cell requires an exact copy of the DNA from the old cell.
The four bases play a critical role in storing and transmitting genetic information. They form specific sequences that are assembled into chromosomes. These sequences are read in groups of three nucleotides, called triplets, which specify a particular amino acid. This genetic code is interpreted by the cellular machinery, allowing for the creation of proteins necessary for the development and functioning of an organism.
The four chemical bases of DNA, adenine, cytosine, guanine, and thymine, are fundamental to the structure and function of DNA. They provide the building blocks for the genetic code and enable DNA to carry out its essential role in storing and transmitting hereditary information.
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Adenine (A) pairs with Thymine (T)
DNA is a molecule that carries the genetic instructions for assembling proteins in all free-living organisms. It is made up of two strands wound around each other, with each strand held together by bonds between the bases. There are four types of bases found in a DNA molecule: adenine (A), cytosine (C), guanine (G), and thymine (T). Adenine always pairs with thymine, and cytosine pairs with guanine. This is known as Chargaff's rule, which states that the amount of adenine in an organism's DNA is always equal to the amount of thymine, and the same goes for guanine and cytosine.
The pairing of adenine (A) and thymine (T) is essential to the structure and function of DNA. Adenine and thymine are nitrogenous bases found in DNA. They are joined by a hydrogen bond, which forms a base pair. This base pairing is crucial for maintaining the stability and integrity of the DNA molecule. The hydrogen bond between adenine and thymine is strong due to the difference in their acidity levels—thymine has the lowest acidity, while adenine has the highest. This complementary pairing allows the bases to stack neatly and facilitates the base pairing of the other nucleotides in the DNA strand.
The sequence of bases in a portion of a DNA molecule, known as a gene, carries the instructions for assembling proteins. This sequence of bases is read in groups of three, called triplets, and each triplet codes for a specific amino acid. The genetic code refers to the way these four bases are arranged in a sequence that can be read by the cellular machinery, the ribosome, to produce proteins. Mutations can occur when there are alterations in these bases, leading to changes in the genetic information encoded by DNA.
One type of mutation is a base substitution mutation, where a single base is changed for another. For example, if adenine is substituted for guanine or vice versa, it is called a transversion. This can lead to a change in the amino acid specified by the triplet, resulting in a new or altered protein structure. Another type of mutation is a frameshift mutation, which occurs when one or two bases are inserted or deleted from the DNA sequence, shifting the reading frame and "scrambling" the encoded protein from the site of mutation onwards.
In summary, the pairing of adenine (A) with thymine (T) is fundamental to the structure and function of DNA. The hydrogen bond between them ensures the stability of the DNA molecule, and their complementary pairing allows for the accurate encoding and transmission of genetic information, which is essential for the creation of proteins and the functioning of all known free-living organisms.
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Cytosine (C) pairs with Guanine (G)
DNA is made up of four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These bases pair up to form the DNA sequence, with adenine pairing with thymine, and cytosine pairing with guanine. This is known as complementary base pairing.
The structure of DNA is that of a double helix, formed by two polynucleotide chains that wind around each other. This was discovered in the 1950s through x-ray diffraction analysis. The chains are held together by hydrogen bonds between the bases on the different strands, with the bases on the inside of the helix and the sugar-phosphate backbones on the outside. This arrangement ensures that the two backbones are held an equal distance apart.
The cytosine (C) base pairs with the guanine (G) base through interstrand hydrogen bonds. In the Watson-Crick model, the DNA double helix is formed from the coiling of two strands of purine and pyrimidine bases. Guanine is a purine base, while cytosine is a pyrimidine base. This means that cytosine is a smaller base than guanine. The larger purines pair with the smaller pyrimidines, ensuring that the base pairs are of similar widths.
The G-C base pair has been studied using carefully calibrated theoretical methods, such as the B3LYP gradient-corrected density functional in conjunction with the DZP++ basis set. This research has investigated the structural perturbations and energy relaxation due to radical formation. The energies of the isolated guanine and cytosine radicals and the G-C radicals have also been studied.
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Mutations can occur through base alterations
DNA is a long polymer made up of four types of nucleotide bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The four bases are joined via a sugar (deoxyribose) phosphate backbone to form specific sequences, and assembled into chromosomes. The genetic code is the term used to describe the way these four bases are strung together and read by the cellular machinery, the ribosome, to be turned into a protein.
Mutations can occur when one or more bases are altered, removed, or added to DNA. These base alterations can be caused by environmental influences, certain chemicals, spontaneous mutations, and errors that occur during the replication process. For example, ultraviolet (UV) light from the Sun can induce mutations in skin cells, causing a C-to-T mutation that has been linked to basal cell carcinoma, a form of skin cancer. Oxidizing agents, or free radicals, can also cause mutations by chemically modifying nucleotides and altering their base-pairing capacities.
Single base changes are called point mutations and can occur when one base is substituted for another. For example, a purine may be substituted for another purine, such as A to G, or a pyrimidine may be changed to another pyrimidine, such as T to C. This is called a transition. If a purine is substituted for a pyrimidine, or vice versa, it is called a transversion. Point mutations can also occur due to deamination of bases, which changes their base-pairing properties.
Frameshift mutations occur when one or two bases are deleted or inserted into a DNA sequence, shifting the reading frame and altering the entire protein produced. This type of mutation can also occur due to homologous chromosomes misaligning during meiosis, resulting in the deletion or insertion of a DNA sequence.
Base alterations can have significant impacts on the structure and function of proteins, highlighting the critical role of maintaining the integrity of the DNA code.
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Base substitutions can lead to new amino acids
DNA is composed of four types of nucleotide subunits or bases: adenine (A), cytosine (C), guanine (G), and thymine (A). These bases are joined via a sugar (deoxyribose) phosphate backbone to form specific sequences, and assembled into discrete packages called chromosomes. The genetic code is read in triplets, such that three nucleotides are read together to specify one specific amino acid.
Base substitutions, also known as point mutations, are a type of mutation in which one nucleotide is replaced by another. This means that one base is substituted for another, such as A changing to G. Base substitutions can lead to new amino acids because the substitution of a single nucleotide changes the amino acid sequence, which can impact how the protein it forms will look and act. For example, sickle cell anemia is caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced.
There are two types of base substitution mutation: transition and transversion. A transition occurs when a purine substitutes for another purine or a pyrimidine is substituted for another pyrimidine. A transversion, on the other hand, is when a purine is substituted for a pyrimidine or vice versa. Both types of base substitution mutations can occur, but they have a reasonably high chance of being silent, meaning they have no effect. This is due to the redundancy of the genetic code, and about one-quarter of all possible base substitutions in codons will not result in amino acid changes.
A frameshift mutation is a special type of mutation that occurs when one or two bases are deleted or inserted into a DNA sequence, causing the sequence of bases encoding amino acids to shift out of register. This results in a scrambled" protein with an altered structure and decreased or abolished enzymatic activity.
Base substitutions can have significant impacts on human health, as seen in the case of sickle cell anemia. By understanding how these small genetic changes work, scientists can develop new treatments for diseases.
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Frequently asked questions
There are four types of bases that constitute DNA code.
The four types of bases are adenine (A), cytosine (C), guanine (G), and thymine (T).
Adenine pairs with thymine, and cytosine pairs with guanine.
The DNA molecule is double-helix-shaped, resembling a twisted ladder.
