Glycans
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US National Heart, Lung, and Blood Institute (NIH/NHLBI) has recognized the importance of training scientists and clinicians in glycoscience by establishing a National Career Development Consortium for Excellence. This Program for Career Development in Glycosciences (K12) focuses on immersive training of medical and research professionals in all aspects of glycoscience. For future Directions in Glycoscience, see chapter 60 in the Essentials of Glycobiology -
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For learning, we need to understand how the memory formation works in our brain. Memory formation centers around the hippocampus, a brain region central to learning. A new study reveals the contribution of dendrites of the hippocampus in learning and memory. READ MORE. Also, see this article for memory formation by the non-brain cells. -
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Learning Glycobiology
Glycan
This term is also used for carbohydrates or sugars that are ubiquitous in nature. Glycans consist of monosaccharides linked together by chemical bonds. These chain-like structures can vary widely, from simple linear forms to incredibly complex branched ones. In practice, the term glycan may refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan. Glycans can be homo- or heteropolymers of monosaccharide residues, and they can exist in linear or branched forms. READ MORE
The smallest monosaccharides found in nature are dihydroxyacetone and glyceraldehyde. These simple sugars consist of only three carbon atoms (3-C) each. Dihydroxyacetone is an aldotriose, meaning it has an aldehyde group (C=O) at the end of the carbon chain. Dihydroxyacetone is involved in various metabolic pathways, including glycolysis and gluconeogenesis. Glyceraldehyde is also an aldotriose. It has a single asymmetric carbon atom, resulting in two enantiomers: D-glyceraldehyde and L-glyceraldehyde. Glyceraldehydes serve as essential building blocks in various biochemical processes. READ MORE
The next larger monosaccharide found in nature contains four carbon (4-C) atoms and are known as tetrose. There are two such glycans: D-Erythrose and D-Threose. Each of these has an aldehyde functional group (C=O) at carbon number one. These tetroses play essential roles in various biochemical processes. Even though they are small, their significance is remarkable. READ MORE
Pentoses are monosaccharides composed of five carbon atoms (5-C). For living organisms The most important pentoses are ribose and deoxyribose, which are structural components of nucleic acids that govern every cellular functions in all three kingdoms (see here for an hypothesis why it has been chosen by Nature as the building block of 'Life'). Ribose is a constituent of RNA (also, see the publication on RNA), and deoxyribose is a constituent of DNA (follow the publications by the CSH). These molecules play essential roles in nucleotide synthesis, nucleic acids, and aromatic amino acids. D-Ribose, an aldopentose found in nature, are incorporated into larger biomolecules: RNA, a fundamental component of RNA, which plays a critical role in protein synthesis and gene expression. The other aldopentose is NAD+ (Nicotinamide adenine dinucleotide), an essential coenzyme involved in redox reactions and energy transfer. Arabinose, Xylose, Ribulose, and Xylulose are other examples of pentose sugars. These pentoses participate in various metabolic pathways and structural components within cells. Thus, pentoses are not only building blocks of nucleic acids but also essential for energy transfer and cellular functions. READ MORE
Hexoses are six-carbon monosaccharides, such as, glucose, fructose, galactose. These can exist in two forms: open-chain or cyclic. In aqueous solutions, they easily convert between these two forms. The cyclic forms play essential roles in biochemistry. In Nature, hexoses found in aldohexoses and ketohexoses. Aldohexoses have the carbonyl group (C=O) at carbon 1, forming an aldehyde derivative. The most important example is glucose. In its linear form, an aldohexose has four chiral centers, resulting in 16 possible stereoisomers (8 pairs of enantiomers). Ketohexoses have the carbonyl group at carbon 2 or carbon 3, forming a ketone derivative. The term “ketohexose” usually refers to 2-ketohexoses, as the 3-ketohexoses are rare. Examples include fructose. These hexoses can be found as “D-” or “L-” termed optical isomers or enantiomers, depending on whether the hydroxyl group in position 5 (in the Fischer projection) is to the right or left of the axis, respectively. Generally, only one of the two enantiomers occurs naturally (e.g., D-glucose) and can be metabolized by animals or fermented by yeasts. Glucose, fructose, and galactose serve as the building blocks of dietary sugars and carbohydrates, providing the main source of fuel for most living organisms. These are also essential building blocks of compounds like starch, cellulose, and glycosides. Another aldohexose series of carbohydrates is mannose, which is a C-2 epimer of glucose, meaning it differs from glucose only at the second carbon position. READ MORE
Heptoses are seven-carbon monosaccharide (C-7). These sugars can have either an aldehyde functional group in position 1 (called aldoheptoses) or a ketone functional group in position 2, 3, or 4 (known as ketoheptoses). Ketoheptoses have four chiral centers, whereas aldoheptoses have five. Examples of seven-carbon sugars found in nature include: Sedoheptulose or D-altro-heptulose (a ketose), which is an intermediate in the Calvin cycle and lipid A biosynthesis. Mannoheptulose (a ketose) is found in avocadoes. L-glycero-D-manno-heptose (an aldose) is found in nature as a late intermediate in lipid A biosynthesis.
An octose is an eight-carbon monosaccharide (C-8) and are relatively less common than their hexose or even nonose counterparts.
A nine-carbon monosaccharide (C-9) or nonose plays essential role in various biochemical processes. Among those, N-Acetyl-D-Neuraminic Acid, also known as sialic acid is commonly found in animals. Sialic acids are a diverse group of about eighty 9-carbon monosaccharide derivatives, all possessing a carboxyl group at the anomeric C-2 position, a glycerol side chain at the C-6 position, an amino-acyl group or hydroxyl group attached at the C-5 position, and a deoxygenerated C-3 position. Neu5AC, Neu5Gc, and KDN are the three basic forms. This family of monosaccharides plays critical roles in cell recognition and signaling. READ MORE
Interestingly, larger the monosaccharide rarer it becomes. Larger than C-9 monosaccharides are rarely found in nature. Monosaccharides are very diverse and their roles also vary. But, only ten monosaccharides (syn. Glycans) linking together in multiple combinations form the glycocode in humans. Know these ten glycans here.