 Types of Carbohydrates  Classification of Monosaccharides  D and L Notations from Fischer Projections  Structures of Some Important Monosaccharides Carbohydrates

Carbohydrates Carbohydrates are: A major source of energy from our diet. Composed of the elements C, H and O. Also called saccharides, which means “sugars”. Produced by photosynthesis in plants.

Photosynthesis in plants requires CO2, H2O, and energy from the sun and produces carbohydrates, such as glucose [C 6 H 12 O 6 = C(H 2 O) 6 ]. In respiration, glucose is oxidized in living cells to produce CO 2, H 2 O, and energy. Photosynthesis and Respiration

Types of Carbohydrates  Monosaccharides are the simplest carbohydrates.  Disaccharides consist of two monosaccharides.  Polysaccharides contain many monosaccharides.

Most of the names of carbohydrates end in -ose Glucose-What plants make Maltose- used in making beer (disaccharide) Fructose – found in fruit (monosaccharide) Sucrose- Table sugar (disaccharide) Lactose – In milk (disaccharide)

Classification of Monosaccharides Aldoses are monosaccharides with an aldehyde group and many hydroxyl (-OH) groups. Ketoses are monosaccharides with a ketone group and many hydroxyl (-OH) groups. AldoseAldoseKetose

Monosaccharides Monosaccharides are also classified according to the number of carbon atoms. A triose has three carbons; a tetrose has four carbons; a pentose has five carbons; and a hexose has six carbons. TrioseTetroseHexose

The two simplest sugars 2 | 1—C—3 | 4 2 | 3—C—1 | 4 Note Numerous Chiral Carbons

Fischer Projection a two-dimensional representation of the three- dimensional structure of organic molecules. usually used to represent the molecular structures of monosaccharides and amino acids. devised by Hermann Emil Fischer in Haworth Projection a common way of representing the cyclic structure of monosaccharides with a simple three-dimensional perspective. a common way of representing the cyclic structure of monosaccharides with a simple three-dimensional perspective. was named after the English chemist Sir Walter N. Haworth. was named after the English chemist Sir Walter N. Haworth.

Fischer Projections Is used to represent carbohydrates. Places the most oxidized group at the top. Uses horizontal lines for bonds that come forward. Uses vertical lines for bonds that go back.

D and L Notations By convention, the letter L is assigned to the structure with the —OH on the left. The letter D is assigned to the structure with —OH on the right.

D and L Monosaccharides The —OH on the chiral atom farthest from the carbonyl group is used to assign the D or L configuration. The D form is usually the isomer found in nature.

D-Glucose Found in fruits, corn syrup, and honey. An aldohexose with the formula C 6 H 12 O 6 Known as blood sugar in the body.

Blood Glucose Level In the body, glucose has a normal concentration of mg/dL. In a glucose tolerance test, blood glucose is measured for several hours after ingesting glucose.

D-Fructose Is a ketohexose with formula of C 6 H 12 O 6. Is the sweetest carbohydrate. Is found in fruit, juices and honey. Converts to glucose in the body.

D-Galactose Is not found free in nature. Is obtained from lactose, a disaccharide. Is important in cellular membranes.

Cyclic Structures  Monosaccharides with 5-6 carbon atoms form cyclic structures  The hydroxyl group on C-5 reacts with the aldehyde group or ketone group

Sugars Prefer To Be Cyclic

Haworth Structure for D-Isomers The cyclic structure of a D-isomer has the final CH 2 OH group located above the ring.

Numbered carbons C CC C C C 1' 2'3' 4' 5' 6' O

Haworth Structure for D-Glucose  The new –OH on C1 has two possibilites: down for  anomer, up for  anomer Isomers that differ only in their configuration about the new asymmetric carbon are called anomers, the carbonyl carbon is called anomeric carbon. α-anomer β-anomer

Cyclic Haworth Structures  Stable cyclic hemiacetals form when the C=O group and the  -OH are part of the same molecule.  For hexoses, the hydroxyl group on C-5 reacts with the aldehyde group or ketone group.  The cyclic structure of a D-isomer has the last CH 2 OH group located above the ring.

Formation of Cyclic Glucose  The Haworth structure can be written from the  Fischer Projection.  The –OH group on the left (C3) is drawn up.  The –OH groups on the right (C2, C4) are drawn down.

Haworth Structure for D-Glucose    -D-Glucose  -D-Glucose

Glucose Anomers

D-(+)-glucose UPUP DOWNDOWN on right = D CONVERTING TO HAWORTH PROJECTIONS -CH 2 OH up = D cis =  FISCHERPROJECTION trans =  HAWORTHPROJECTIONS BOTH ANOMERS OF A D-SUGAR (D-glucose)

Mutarotation A small amount of open chain is in equilibrium with the cyclic forms. The most stable form of glucose is β -D-glucose.  -D-glucoseD-glucose (open) β -D-glucose (36%)(trace) (64%) (36%)(trace) (64%)

 -D-Glucose  and  are “anomers” and differ in configuration at the new chiral center formed in the cycle In nature, open chain forms are rare. All 5 forms coexist with the pyranose forms occurring 99% of the time, furanose about 0.5% each and a trace of open chain