BCHM 3010 Carbohydrates
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This 5 page Class Notes was uploaded by Morgan Dimery on Monday February 1, 2016. The Class Notes belongs to 3010 at a university taught by Dr. Cheryl Ingram-Smith in Spring 2016. Since its upload, it has received 20 views.
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Date Created: 02/01/16
Carbohydrates • The standard formula is C (H O) n 2 n o They all have a certain amount of carbons and water • They’re produced in plants during photosynthesis • They’re the single most abundant biomolecule that is found in nature • They are very complex-‐ they serve in many different ways and can give a lot of information • There are three major classes of carbohydrates o Monosaccharides-‐ single carbohydrate molecule (glucose) o Oligosaccharides-‐ short chains of monosaccharides § Disaccharides are the most abundant type (sucrose aka glucose and fructose) o Polysaccharides-‐ polymers of simple monosaccharides • Monosaccharides have two or more hydroxyl (-‐OH) groups o 3 carbons-‐ triose o 4 carbons-‐ tetrose o 5 carbons-‐ pentose o 6 carbons-‐ hexose • Aldoses “aldehydes”-‐ the carbonyl group is located at the end of the carbon chain • Ketoses “ketones”-‐ carbonyl group is located within the carbon chain All monosaccharides except for dihydroxyacetone are chiral!!!! Some terms to know: • Stereoisomer-‐ molecules that have the same basic chemical formula but different molecular arrangements • Enantiomers-‐ stereoisomers that are nonsuperimposable mirror images of each other • Diasteromers-‐ stereoisomers that are not mirror images of each other • Epimers-‐ sugars that are diasteromers that only differ in one configuration around a carbon bond Monosaccharides are either D or L form (isomer) • D-‐ -‐OH group is on the right • L-‐ -‐OH group is on the left This is determined by the chiral center that is the most distant from the carbonyl carbon • For Fischer Projections the horizontal lines mean the atom or group is coming towards you and the vertical lines mean the atom or group is going away from you • Make sure you know the structure of glucose!!!! • To netermine the number of different forms for a specific carbohydrate you do 2 o n= number of chiral carbons • Pentose and hexose sugars occur as cyclic structures in a solution o There is covalent bond formed between the carbonyl group of one molecule to the oxygen from the hydroxyl group of the other molecule • Anomeric carbons are carbons that are linked to the oxygen that is by itself in the molecule-‐ it used to be the carbonyl carbon • Haworth projections (chair conformation) do not give as much information about the molecule When looking at a ring structure of a molecule… • α-‐ -‐OH located on the anomeric carbon is on the opposite side of the CH OH 2 • β-‐ -‐OH located on the anomeric carbon is on the same side 2as the CH OH These different forms are different configurations • There are pyrans (aldose) that are hexagons, and furans (ketose) that are pentagons • A glycosidic bond is between an anomeric carbon and a hydroxyl carbon of another anomeric carbon o This gives you two carbons linked by an oxygen o This is how disaccharides are formed • Sugars that have a free (not bound by anything) are called reducing sugars o Reduce oxidizing agents o Convent sugar to sugar acid • In nonreducing sugars both of the anomeric carbons are involved in a bond o These are more stable towards oxidation How to Name Carbohydrates • If there is a nonreducing sugar, that name goes on the left • α and β configuration joins the first monosaccharide to the second • D/L isomer must be indicated • Pyran/furan much be indicated • Carbons that are in the glycosidic bond are shown using an arrow (# -‐-‐> #) • Name of the second residue is included • Glycogen is a branched homopolysaccharide of glucose o Stores glucose for the cell to use later-‐ main storage polysaccharide in animals o Molecular weight can be high • Starch is used for energy storage in plants o Polymer of amylose (unbranched) and amylopectin (branched) o Forms something like a helix-‐ it has a lot of hydrogen bonding that adds to its strength • Amylose and amylopectin both have many nonreducing ends-‐ these ends can be added on to, and also many enzymes can remove glucose from these ends at once and get large amounts of glucose very quickly Glucose is not stored as a monomer, and for a good reason! • The concentration of glucose is ~0.4 M, the concentration of glycogen is ~0.01 uM o Glucose contributes to the osmolarity of the cell because it is soluble, but glycogen does not because it is insoluble o If glucose were stored inside of the cell then eventually the high concentration would cause the cell to rupture § Since glycogen does not have as high of a concentration glucose can be stored here without disrupting the osmolarity of the cell • A chain of glucose (glycogen or starch) is not the same thing as one glucose molecule!!!! • Cellulose is the main structural component of plants-‐ most abundant natural polymer on Earth o Very extended structure, the long chains are held together by hydrogen bonding and this gives it added strength. There are many chances for hydrogen bonding o Insoluble in water o C-‐2 has a hydroxyl group o Only certain organisms are able to digest cellulose o Fungi, bacteria, protozoa, and termites have cellulases o Cattle and other ruminants can degrade cellulose because they have a special stomach called a rumen that has microbial symbionts-‐ it breaks down the grass they eat and they get glucose out of it • Chitin is the second most abundant organic polymer on Earth o Makes up the exoskeletons of insects and crustaceans and most cell walls of plants and fungi o Different monomeric structure than cellulose-‐ still has added strength from hydrogen bonding § C-‐2 has an acetylated group • Peptidoglycan is the rigid component of bacterial cell walls o Cross linking from peptides gives it added strength-‐ glycine connects them o Lysozymes prevent the crosslinking and break them apart-‐ cells tend to burst because of lysozymes § They are found in tears, some viruses, and some antibiotics • Agar makes up the cell wall of marine algae and is also used in labs o Structural function o When it is put into solution and heated it melts o Algarose is the component of agar that has the fewest charged groups and it also has gel-‐forming properties • The extracellular matrix (ECM) is known as the ground substance-‐ it is the gel-‐like stuff that is between cells and holds them together o Has 3 major functions-‐ anchor cells to matrix, provide paths that direct migration of cells, and convey information o Composed of glycosaminoglycan-‐ a lot of carbohydrates • Glycosaminoglycan is not found in plants, but it is found in bacteria and animals o Gives recognition by decorating the outside of the cell and attaching to extracellular proteins o There are a lot of different functions that these can do-‐ it is very important!! • Proteoglycans bind carbohydrates to membrane proteins or secreted proteins o They are bound by electrostatic interactions o Big component of extracellular matrices o Can be huge-‐ gives the protein added strength o Usually they can only add to certain structures-‐ not very diverse o Bound to core protein at a serine reside (Ser-‐Gly-‐X-‐Gly) • Glycoproteins bind oligosaccharides to proteins o Covalently attached, may be simple or complex o Smaller than proteoglycans, but they are usually branched and more diverse o Sugars can be linked to proteins in this way o Half of all proteins have this o Proteins can have huge amounts of carbohydrates added on at different places o There are two types: § O-‐linked: attached to OH group of Ser or Thr § N-‐linked: attached to amide nitrogen group of Asp • Glycolipids are membrane lipids with their hydrophilic head group being an oligosaccharide o These have roles in signal transduction All of these things above add on information to other kinds of molecules!!!! • Glycosylation (things talked about above) can change how proteins behave by altering the polarity or solubility of the protein o They can tell the protein where to go o Check to make sure the protein is made properly o Cause changes in protein structure that allow for the formation of rod like structures o Protect proteins from degradation, or say that the protein needs to be degraded Cells use oligosaccharides to encode important information! • Cell-‐cell interactions • Cell differentiation • Tissue development • Extracellular signals • Intracellular targeting of proteins These are just as important if not more important than any other biomolecule! • The structural diversity of carbohydrates makes them give even more information o Can be branched and have many linkages o 20 monosaccharides give billions of different hexameric combinations • Lectins are proteins that read the sugar code to obtain information o Bind very specifically and tightly to different oligosaccharides o Have cell-‐cell recognition, signaling, and adhesion processes o They give information on how sugars are arranged o They have multiple carbohydrate binding domains-‐ they can recognize a certain structure in many different ways because they have so many of these sites, this increases their strength
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