ESSENTIALS OF CARBOHYDRATE CHEMISTRY AND BIOCHEMISTRY PDF
Essentials of Carbohydrate Chemistry and Biochemistry, 2nd Edition (Thisbe K. Lindhorst). David J. A. Schedler View: PDF | PDF w/ Links. Related Content. A molecule is only called a carbohydrate, when all ring−positions are hydroxylated. ▫ Aldohexoses can be reduced to alditols. ▫ There are two enantiomeric forms. Request PDF on ResearchGate | Essentials of Carbohydrate Chemistry and Biochemistry, 2nd Edition (Thisbe K. Lindhorst) | This book is a well organized, well.
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Reducing sugars are basically sugars with an aldehyde group in their open form or a hemiacetal group in their ring form at the anomeric carbon that is ready to oxidize. In other words, reducing sugars allow for chain formation and elongation.
Examples of reducing sugars are glucose, maltose, and lactose. Reducing sugars can form aldehyde or ketone groups under basic conditions as the carboxyl group is reduced to carbonyl group of aldehyde or ketone group and occurs when the anomeric carbon is not bonded to hemiacetal or hemiketal hydroxyl group. It has only been mentioned that aldoses can form reducing sugars.
What about ketoses? Mechanistically, when ketoses isomerize to their ring form, acetals are formed. So no, ketoses do not form reducing sugars. However, ketoses can tautomerize to aldoses, where a hemiacetal can then be formed upon ring closure. These type of sugar is basically an acetal in its ring form at the anomeric carbon. Since the anomeric carbon is fixed in a glycosidic linkage, the sugar chain cannot form or be elongated.
An example of a nonreducing sugar is sucrose. Glycoproteins[ edit ] Structure Glycoproteins, namely organic compounds of a mixture of carbohydrates and proteins bonded by covalent bonds, are formed in the process of glycosylation.
Carbohydrate groups may be covalently bonded to a protein to form a glycoprotein, which is an important part of the cell membrane in such processes as cell adhesion and the binding of sperm to eggs in fertilization. In glycoproteins, the carbohydrate weight percentage is much less than the weight of carbohydrates found in proteoglycans.
The sugar group of glycoproteins help protein folding and increase protein stability. Sugars within glycoproteins are found attached either to the amide nitrogen atom side chain of asparagine by N-linked glycosidic bond or to the oxygen atom in the side chain of serine or threonine by O-linked glycosidic bond.
The bond formed between carbohydrate and protein is by bonding to one of four amino acids of asparagine, hydroxylysine, serine, or threonine. Thus protein glycosylation sites can be predicted because an asparagine can only be glycosylated when found in the form: Asn-X-Ser, Asn-X-Thr, or Asn-X-Cys sequence, where X can be any amino acid but Proline.
But not all potential sites are glycosylated. Glycosylated sites have other factors such as the cell type in which the protein is expressed and protein structure. In N-linked oligosaccharides , it has a common pentasaccharide core with three mannose and two N-acetyglucosamine residues. To form a great variety of oligosaccharide pattern, additional sugars are attached to this core.
Integral membrane proteins of glycoproteins are important for interactions between one cell to the other. Glycosylation Glycosylation of the extracellular part of proteins takes place in the Endoplasmic Reticulum and in the Golgi complex. Golgi is the major sorting center of the cell. Protein proceed from Golgi to lysosomes, secretory granules, or plasma membrane.
Ribosomes on the cytoplasmic face of the rough ER synthesize the protein that is taken into the lumen of the ER. N-linked glycosylation starts in the ER and continues into the Golgi complex.
It begins with the addition of an oligosaccharide precursor made up of a chain of 14 sugar molecules.
However, the O-linked glycosylation site is exclusively in the Golgi complex. Also unlike N-linked glycosylation, O-linked glycosylation has the sugar molecules added one at a time, each by a different glycotransferase enzyme.
One example includes the addition of N-acetylgalactosamide GalNAc , in the cis-Golgi area, by N-acetylgalactosamide transferase. It should be noted that the Golgi complex is split into three areas the cis, trans, and medial. In the trans-Golgi, a galactose residue is attached to N-acetylgalacosamide by a galactosamide transferase specific to the this region of the Golgi complex. An oligosaccharide precursor that is to be attached to the amide side chain of an asparagine residue in a protein is first attached to dolichol phosphate.
Dolichol phosphate is a lipid molecule found in the ER lumen and is made of about twenty isoprene units. The terminal phosphate group of dolical phosphate is the site of attachment of the oligosaccharide.
With the help oligosaccharide-protein transferase, the oligosaccharide is transferred from dolichol phosphate to the asparagine molecule. Proteins from the lumen of the ER and the ER membrane are then transferred to the Golgi complex, where the carbohydrate part of the glycoprotein is altered.
Since the Golgi has three areas, each with its own set of enzymes, modifications to the precursor oligosaccharide allows for a range of oligosaccaride structures to form. After the Golgi complex, proteins proceed to either lysosomes, secretory granules, or the plasma membrane, depending on the signals embedded within the amino acid sequences and the three-dimensional structures.
Essentials of Carbohydrate Chemistry
Examples Erythropoietin EPO is a glycoprotein hormone that stimulate the production of red blood cells. The presence of three Asn residues and one Ser residues allow oligosaccharides to link the protein at the three N-linked glycosylation and one O-linked glycosylation sites. It is secreted by the kidney. Zona Pellucida The zona pellucida is a glycoprotein membrane, where it appears at multilaminar primary oocytes around the plasma membrane.
The zona pellucida structures must initiate the acrosome reaction, in order to binds with the spermatozoa. Therefore, scientists found four zona pellucidas that are responsible binding the spermatozoa and the acrosome reaction within the mouse. The most important zona glycoprotein is the ZP3, because ZP3 is responsible for sperm binding. The sperm protein is adhering with the plasma membrane of the oocyte.
Transformations Robyt, John F. Modifications Robyt, John F. Sweetness Robyt, John F. Polysaccharides I Robyt, John F. Cyclodextrins Robyt, John F. GIycoconjugates Robyt, John F. Biosynthesis Robyt, John F. Biodegradation Robyt, John F. Determinations Robyt, John F. Glycosidic bonds also called glycosidic linkages can be of the alpha or the beta type.
Sucrose is formed when a monomer of glucose and a monomer of fructose are joined in a dehydration reaction to form a glycosidic bond. In the process, a water molecule is lost. By convention, the carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group. In sucrose, a glycosidic linkage is formed between carbon 1 in glucose and carbon 2 in fructose.
Lactose is a disaccharide consisting of the monomers glucose and galactose. It is found naturally in milk. Maltose, or malt sugar, is a disaccharide formed by a dehydration reaction between two glucose molecules. The most common disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose. Common disaccharides include maltose grain sugar , lactose milk sugar , and sucrose table sugar. The chain may be branched or unbranched, and it may contain different types of monosaccharides.
The molecular weight may be , daltons or more depending on the number of monomers joined. Starch, glycogen, cellulose, and chitin are primary examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of a mixture of amylose and amylopectin both polymers of glucose. The starch in the seeds provides food for the embryo as it germinates and can also act as a source of food for humans and animals.
The starch that is consumed by humans is broken down by enzymes, such as salivary amylases, into smaller molecules, such as maltose and glucose. The cells can then absorb the glucose. The numbers and refer to the carbon number of the two residues that have joined to form the bond.
Amylose and amylopectin are two different forms of starch. Because of the way the subunits are joined, the glucose chains have a helical structure. Glycogen not shown is similar in structure to amylopectin but more highly branched. Glycogen is the storage form of glucose in humans and other vertebrates and is made up of monomers of glucose.
Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells.Some amino acids have functions by themselves or in a modified form; for instance, glutamate functions as an important neurotransmitter.
This makes them amphiphilic molecules having both hydrophobic and hydrophilic portions. Improper glycosylation of proteins can lead to inheritable human diseases called congenital disorders of glycosylation.
Wade, L. Because they contain at least one phosphate group, the compounds marked nucleoside monophosphate, nucleoside diphosphate and nucleoside triphosphate are all nucleotides not simply phosphate-lacking nucleosides.
Viruses can bind to certain residues on glycoproteins and once within the cell, release proteins which will break certain bonds within the glycoprotein to grant the virus free access. Diversity as a result of carbohydrate chemical properties Chemical structure. Sixth Ed. Nucleic acids , so called because of their prevalence in cellular nuclei , is the generic name of the family of biopolymers.