BIOCHEMISTRY TRANSES
Lecture/First Semester
CARBOHYDRATES
Carbohydrates
-provide energy through oxidation
- serve as a form of stored chemical energy
-supply carbon for the synthesis of cell components
- form part of the structures of some cells and tissues
- a molecule that contains the elements CHO in a 1:2:1
ratio
- sizes vary (simple and complex carbohydrates)
- building block is simple sugar or monosaccharide
- Carbohydrates or saccharides (saccharon) are
polyhydroxy aldehydes or ketones, or substances that
yield such compounds on hydrolysis
- An aldehyde is an organic compound in which
the carbonyl group is attached to a carbon
atom at the end of a carbon chain. A ketone is
an organic compound in which the carbonyl
group is attached to a carbon atom within the
carbon chain.
Stereochemistry of Carbohydrates
- Two Forms of Glyceraldehyde (enantiomers)—not
the same as each other; one enantiomer cannot be
superimposed on the other. Enantiomers are mirror
images of each other.
-D-glyceraldehyde
-L-glyceraldchyde
Chiral Carbons
- any carbon atom which is connected to four different
groups will be CHIRAL, and will have two
nonsuperimposable mirror images (The mirror images
are called enantiomers)
- An achiral object is identical with (superimposable on)
its mirror image.
2 raised to n Rule
- when a molecule has more than one chiral carbon,
each carbon can possibly be arranged in either the
right-hand or left-hand form, thus if there are n chiral
carbons, there are 2n possible stereoisomers
Fischer Projection
- are a convenient way to represent mirror images in two
dimensions
- Place the carbonyl group at or near the top and the last
achiral carbon at the bottom
Naming Stereoisomers
- look at the chiral carbon farthest from the carbonyl
group:
- if the hydroxyl group points to right when the
carbonyl is up, it is the D-isomer
- if the hydroxyl group points to left when the
carbonyl is up, it is the L-isomer
Chiral Carbon Atoms
Classes of Carbohydrates
A. Monosaccharides
- simplest of the carbohydrates,since they
contain only one polyhydroxy aldehyde or
ketone
- Monosaccharides are classified according to
the number of carbon atoms they contain:
- 3 carbon atoms - triose
- 4 carbon atoms - tetrose
- 5 carbon atoms - pentose
- 6 carbon atoms - hexose
- The presence of an aldehyde is indicated by
the prefix aldo- and an ketone by the prefix
keto-
- Properties of Monosaccharides
(Carbohydrates)
- monosaccharides & disaccharides
are white crystalline substance;
starches are amorphous powder;
cellulose is fibrous
- solubility to ordinary solvents is
inversely proportional to the
complexity of their structures
- monosaccharides & disaccharides
are sweet; starch and cellulose are
tasteless
-Reducing power - the potential or
power of any substance to reduce
1
