7: Sugars & Glycobiology

Aldoses and Ketoses

Each consecutive connecting carbon within the backbone contains a hydroxyl group. There is also a carbonyl group present as well. An aldose (ald-ehyde) has the carbonyl at the end (top) of the Fischer projection. A ketose (ket-one) has the carbonyl sandwiched between backbone carbons.

Highly soluble. Polyhydroxyl aldehydes/ketones 3-7 carbons

Using a Fischer projection, select the carbon furthest from the carbonyl to be the reference carbon. Then, observe the position of that carbon's hydroxyl relative to the backbone. L: if the -OH of the reference carbon is to the left. D: if the -OH of the reference carbon is to the right.

Epimers are two sugars that differ only in configuration about one carbon.

Note: they may have differing names, as the difference in configuration may not be on the reference carbon. Therefore, it is not reliable to delineate epimers from D/L distinctions.

Relative to the CH2-OH group, α: the C1 -OH group is OPPOSITE SIDE β: the C1 -OH group is SAME SIDE

Isomeric monosaccharides varying only in configuration about hemiacetal or hemiketal carbon. Makes more sense if you draw a Fischer projection and Haworth projection for a sugar.

Anomers are sugars that vary only in α/β configuration.

Pyranose: 6-membered sugar ring Furanose: 5-membered sugar ring.

Neither of these are planar.

Amine-substituted sugars Deoxy-sugars Acidic-sugars Sugar-phosphates

A sugar able to have its aldehyde undergo redox with a Cu2+ ion, under basic conditions. The sugar is oxidized into a carboxylic acid. Reduces the Cu2+ to Cu+

An O-glycosidic bond links to monosaccharides into a disaccharide.

Readily hydrolyzed by acid. Resist cleavage by base.

Sugars usually can easily interconvert between linear and cyclic forms, or between chair conformations. However, within disaccharides and bigger sugars, the O-glycosidic bond prevents this interconversion from happening.

Sucrose

Monosaccharide component sequence Glycosidic linkages Chain length Degree of branching

Plants: chitin, cellulose, used for structure; starch used as energy storage Animals: glycogen, used as energy storage

Amylose: unbranched glucose polymer with α(1-4) linkages Amylopectin: highly branched glucose polymer, with α(1-6) branch point linkages.

Glucose, α(1-4) linkages, highly branched, more compact than starch.

n+1

Reducing sugars have hemiacetals. Nonreducing sugars have acetals that are "locked" within the ring and are thereby inactive.

A homopolysaccharide that makes up cell walls of plants. Linear and unbranched, its key difference from amylose is that cellulose has β(1-4) linkages.

A helix, stabilized by inter-chain H-bonding

A straight, extended chain, stabilized by intrachain and interchain hydrogen bonding. (They exist in flat planes of many chains) Kinda like b sheets

A heteropolysaccharide comprised of β(1-4) linked N-acetylglucosamine and N-acetylmuramic acid.

Makes up bacterial cell walls and creates stability in structure.

A family of linear polysaccharides found in animals and bacteria, but not plants. It is made up of repeating disaccharide subunits, typically comprised of N-acetyglucosamine and a uronic acid. It has a high density of negative charge.

An information-carrying carbohydrate (sugar) that is covalently linked to either a protein or lipid.

A proteoglycan is a glucosaminoglycan chain that is covalently linked to a core protein via a serine residue.

It attaches via a tetrasaccharide linker.

Syndecans and glypicans

These proteins can be "shed" from the cell's membrane surface; the cell's surface features plays a role in cell-to-cell communication, recognition, adhesion, proliferation, and differentiation.

Form from many core proteins that attach to a single long strand of hyaluronan. Have multiple chains of sulfates. Contribute strongly to tensile strength and resilience of connective tissue.

A glycoprotein is a protein that has multiple oligosaccharides covalently bound. The glycans are branched and very structurally diverse. N-linkages involve asparagine residues covalently linked to an oligosaccharide.

O-linkages involve serine or threonine residues covalently linked to an oligosaccharide.

50%

Glycolipids are components of the plasma membrane that have oligosaccharides as the hydrophobic head component.

It is a type of glycoprotein containing many o-glycosidic bonds. They are present in most bodily secretions (i.e. mucus)

Antibodies, certain hormones, mucins.

Eukaryotic membrane lipids containing a polar head group composed of a complex oligosaccharide with a sialic acid.

Sugar-lipid membrane molecules that interact with antibodies.

Compared with amino acids and nucleic acids, there are several orders of magnitude more of different permutations of a given amount of oligosaccharide subunits than of amino acid sequences or nucleic acid sequences of the same amount of subunits.

This is due to the prevalence of branched structures, nonexistent in nucleic or amino acids. Further, oligosaccharides have many more bond types and therefore variations of bound groups.

Lectins are molecules essential to cell signaling. They are able to separate and detect glycans and glycoproteins with different oligosaccharide groups.

Selectins are lectins specific to the plasma membrane. They commonly mediate the movement of immune cells to infection sites.

They are the main players of the inflammatory response.

This is done via the interaction of selectins with surface oligosaccharides on the leukocytes; this slows the leukocytes to allow them to bind to the infection site. The second step is where integrin actually stops the leukocyte and mediates its cross over the capillary wall and to the infection site.

This process is known as "lymphocyte homing"

E-selectin: Binds endothelial oligosaccharide L-selectin: Binds leukocyte oligosaccharide

Both during the process of lymphocyte homing.