The minor groove, the major groove, and the recognition helix are labeled G m , G M , and RH, respectively. See Antennapedia, deoxyribonuclease. Subjects: Science and technology — Life Sciences. View all related items in Oxford Reference ». All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single entry from a reference work in OR for personal use for details see Privacy Policy and Legal Notice.
Oxford Reference. Publications Pages Publications Pages. Recently viewed 0 Save Search. Your current browser may not support copying via this button. Dear Sir: Is there a so called complex carbohidrate code glicosaminglicanes, etc. Hello Alejandro, You've put forward a very interesting question! As you likely know, our chromosomes are segregated in a compacted form during mitosis.
Impressively, the packing ratio of DNA in human metaphase chromosomes is typically 10, This high degree of compaction has been compared to compacting a rope the length of a football field down to less than half an inch.
How do our cells do this? Proteins called histones play an important role in the first level of DNA packaging. Negatively charged DNA binds tightly to the positively charged histones. A double-stranded DNA molecule is wrapped approximately 1. This histone octamer with approximately base pairs of DNA wrapped around it is called a nucleosome, and it is the basic building block for constructing higher-order DNA structures.
Nucleosomes are connected to each other via the histone H1 linker protein and another 20 base pairs of DNA. The nucleosomes, each around 10 nanometers nm in diameter, are further packaged to form the nm fiber. As its name suggests, the nm fiber is 30 nm in diameter, and it consists of around three nucleosomes stacked together.
The structural state of chromatin also affects how genes encoded by its DNA are expressed to make proteins. This is because the chromatin has to unwind enough to permit the transcription machinery to gain access to the DNA. The term epigenetics refers to changes in phenotypes or gene expression not associated with changes in gene sequences.
Epigenetic modifications i. As you can see, a fine balance must be maintained in our cells so that our DNA is properly packaged and yet still accessible when necessary!
The histone code hypothesis refers to the idea that different combinations of histone modifications may promote or inhibit the recruitment of certain proteins to chromosomal regions, thereby regulating the local environment, function, and activity of chromosomes in the cell.
So, how might a similar hypothesis apply to complex carbohydrates? Carbohydrates also called polysaccharides , which serve as fuel for our cells, are made up of monosaccharide monomers joined via glycosidic bonds.
Monosaccharides share the following general formula: CH 2 O n, with n corresponding to 3, 4, 5, 6, 7, or 8. They can occur in open forms or in ring forms. Monosaccharides are single sugars e. Monosaccharides and disaccharides are generally considered simple carbohydrates.
In contrast to simple carbohydrates, complex carbohydrates are built of three or more monosaccharides. Complex carbohydrates are also known as starchy foods, and they are found in bananas, lentils, oats, whole grain cereals, yams, chickpeas, pastries, pizza, pastas, white rice, and more.
The monosaccharides used to build complex carbohydrates contain multiple hydroxyl groups, allowing them to form a variety of glycosidic linkages between them. This wide variety of potential linkages, which often includes branching patterns, means that complex carbohydrates are considered information-rich molecules. You've already mentioned one type of complex carbohydrates: glycosaminoglycans.
Some of the most well known glycosaminoglycans include chondroitin sulfate, heparin, heparin sulfate, keratan sulfate, dermatan sulfate, and hyaluronate. Typically, glycosaminoglycans are comprised of unbranched repeated units of a disaccharide that contains a derivative of an amino sugar either glucosamine or galactosamine.
Glycosaminoglycans are often attached to a protein molecule to yield a proteoglycan. Glycosaminoglycans and proteoglycans carry out many key functions in our cells, and studies of their cellular roles are ongoing.
For example, heparin plays a vital role in the prevention of blood coagulation and clotting. And several lysosomal storage diseases are associated with the inappropriate accumulation of glycosaminoglycans in lysosomes.
You'll be interested to read that we have come across some articles that discuss the possibility of a complex carbohydrate code also referred to as a glycan code or sugar code associated with the wide variety of linkages that form between monosaccharides and their positions relative to each other.
Similar to the histone code hypothesis, a complex carbohydrate code hypothesis would predict that the overall structures of complex carbohydrates would dictate their cellular functions. Although it is relatively easy these days to determine the sequence of nucleotides that comprise a given DNA molecule or to determine the sequence of amino acids that make up a protein molecule of interest, the determination of the sequence of sugars that make up complex carbohydrates, especially those that are highly branched, is much more challenging.
A binds T with 2 hydrogen bounds. G binds C with 3 hydrogen bounds: more stable link: 5. One is the template of the other one, and reciprocally: this property will allow exact replication semi-conservative replication: one strand -the template- is conserved, another is newly synthesized, same with the second strand, conserved, allowing another one to be newly synthesized; see chapter ad hoc. Notes: Hydrogen bounds in base pairing are sometimes different from the model of Watson and Crick above described, using the N7 atom of the purine instead of the N1 Hoogsteen model.
The double helix is a quite rigid and viscous molecule of an immense length and a small diameter. It presents a major groove and a minor groove. The major groove is deep and wide, the minor groove is narrow and shallow. Proteins bind at the floor of the DNA grooves, using specific binding: hydrogen bounds, and non specific binding: van der Waals interactions, generalized electrostatic interactions; proteins recognize H-bond donnors, H-bond acceptors, metyl groups hydrophobic , the later being exclusively in the major groove; there are 4 possible patterns of recognition with the major groove, and only 2 with the minor groove see iconography.
Notes: - The 2 strands are called "plus" and "minus" strands, or "direct" and "reverse" strands. At a given location where one strand any of the two bears coding sequences, it is unlikely but not impossible that the other strand also bears coding sequences. The double helix as described above is the "B" form of the DNA; it is the form the most commonly found in vivo, but other forms exist in vivo see below or in vitro. DNA is a molecule which moves, fidgets, does gymnastics, dances. The structures below cited are being proved to have funtional roles; on the other hand, they may favour DNA breaks and further deletions, amplification, recombination, and mutations.
Glossary: Palindromes: these are names that read the same backwards and forwards e. DNA uses to play with palindromes: see below. Only one groove is observed, resembling the minor groove, the base pairs being set off to the side, far from the axis. The bases which form the major groove -close to the axis- in B-DNA are here at the outer surface.
Phosphates are closer together than in B-DNA.
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