北大生化4-3

Haworth projection
A Haworth projection is a conventional planar representation of a cyclized mono saccharide molecule. The hydroxyls that are represented to the right of the chain in a Fischer projection are shown below the plane in a Haworth projection. Plane of the ring is perpendicular to that of the paper and the heavy line projects towards the reader
Stereoisomers that are not mirror images of each other are called diastereomers D-glyceraldehyde and L-glyceraldehyde are mirror images of each other, called enantiomers, and stereoisomers at the same time, and cannot be superimposed on each other
Stereoisomers, diastereomers, enantiomers
For a chiral or asymmetric carbon, there are 2 forms. In general a molecule with m chiral centers will have 2(m) stereoisomers. The multiple stereoisomeric forms means that not all stereoisomers will be mirror images of each other.
•Monosaccharides containing an aldehyde group are called aldoses.
ቤተ መጻሕፍቲ ባይዱ
•Monosaccharides containing a ketone group are called ketoses. •Monosaccharides that form five member rings are called furanoses. •Monosaccharides that form six member rings are called pyranoses.
The simplest member of the carbohydrate family is glyceraldehyde. Since glyceraldehyde contains an asymmetric or chiral carbon, it can be found in two stereoisomeric forms designated as Dor L-. Almost every sugar found in animals is related to D glyceraldehyde, although there are a few rare exceptions such as L- Fucose, found in glycoproteins, etc.
Saccharides play a variety of roles in living organisms, including energy storage, structural roles (RNA and DNA, cell wall, exoskeleton) , and cell identity.
Saccharides
Saccharide is another name for a carbohydrate. Simple saccharides are the monosaccharides, commonly called sugars. Glucose is an example of a monosaccharide. We use terms monosaccharide, oligosaccharide, or polysaccharide to refer to compounds composed of a single sugar, several sugars linked together, or many sugars linked together, respectively.
Anomers
When sugars cyclize, they typically form furanose or pyranose structures. These are molecules with fivemembered or six-membered rings, respectively. Cyclization creates a carbon with two possible orientations of the hydroxyl around it. We refer to this carbon as the anomeric carbon and the two possible forms as anomers. The two possible configurations of the hydroxyl group are called alpha and beta, which correspond to the hydroxyl being in the "down" and "up" positions, respectively, in standard projections
Stereoisomers = Diastereomers + enantiomers
Ketose-aldose pairs of sugars frequently are named by inserting the letters 'ul' in the name of the corresponding aldose to derive the name of the ketose. An example is erythrose - erythrulose.
The enantiomers of glyceraldehyde
Fischer projection
A Fischer projection is a convention for representing stereoisomers in a plane. The tetrahedron of bonds on a carbon is represented as a plane cross, where the bonds to the right and left are assumed to be pointing toward the viewer and the bonds to the top and bottom are assumed to be pointing away from the viewer. Projections of monosaccharides are oriented with the carbonyl group at the top; the chiral carbon farthest from the carbonyl group (which is the one that determines whether the sugar is the D or the L form) is then drawn with its hydroxyl to the right for the D form and to the left for the L form.
This figure shows the structure of alpha, Dglucose in what is know as the Haworth Projection format. In solution, glucose is an equilibrium mixture between the free aldehyde or open chain form and the cyclized form shown here in which an internal hemiacetal is formed between carbons 1 and 5.
Carbohydrates
(Several descriptive slides are added as notes. They are not slides for real lecture)
Carbohydrates are polyhydroxy aldehydes and ketones which have chemical formulae which resemble hydrated carbons, hence the name carbohydrate. All of the common sugars found in living systems contain either a free or potentially free aldehyde or ketone.
Glucose Fructose Galactose
Mannose Ribose Erythrose
Monosaccharide nomenclature


are the simplest sugars, having the formula (CH2O)n. The smallest molecules usually considered to be monosaccharides are those with n = 3 Category 3-------------Triose 4-------------Tetrose 5------------- Pentose 6--------------Hexose 7--------------Heptose 8--------------Octose
Carbons in a monosaccharide are numbered such that the aldehyde group is carbon number one or the ketone group is carbon number two
Sucrose is composed of a pyranose and a furanose
The term carbohydrate derives from the fact that many of them have a formula that can be simplified to (CH2O)n. Some of these compounds are chemically modified, however, and do not fit the formula due to the modification.
Monosaccharide
Monosaccharide is another term for a simple sugar, such as glucose, which is not linked to any other sugars. Common monosaccharides include: