Biomolecules

Configuration of D-Aldose
- D-aldoheptose has seven carbon atoms.
- All the carbon atoms except the last one have a hydroxyl group attached to them.
- The last carbon atom is bonded to an aldehyde group.
- Example: D-Glyceraldehyde
Configuration of D-Ketose
- D-ketohexose has six carbon atoms.
- The first carbon atom is a ketone group.
- The remaining carbon atoms have a hydroxyl group attached to them.
- Example: D-Fructose
Fischer Projection Formula
- A method to represent the stereochemistry of a molecule using a flat, two-dimensional drawing.
- Vertical lines represent bonds coming out of the plane of the paper (wedges).
- Horizontal lines represent bonds going behind the plane of the paper (dashes).
- The carbon chain is depicted vertically in the middle of the projection.
- Example: Fischer Projection of Glucose
```
HOCH2−(CHOH)4−(CH2OH)
```
Haworth Projection Formula
- A method to represent cyclic structures of carbohydrates.
- The carbon chain is depicted as a polygon.
- The oxygen atom that forms the cyclic structure is enclosed within the polygon.
- Hydroxyl groups attached to carbon atoms are shown as lines coming out of or going into the plane of the paper.
- Example: Haworth Projection of Glucose
```
O
 \
  CH2OH
   |
HO−(CHOH)4−H
```
Anomers
- Stereoisomers that differ in their configuration at the anomeric carbon.
- α-anomer: The hydroxyl group attached to the anomeric carbon is trans to the terminal CH2OH group.
- β-anomer: The hydroxyl group attached to the anomeric carbon is cis to the terminal CH2OH group.
- Example: α-D-Glucose and β-D-Glucose

======= 11. Configuration of D-Ketose

D-ketose is a type of sugar molecule that contains a ketone group on the second carbon atom.
The remaining carbon atoms have a hydroxyl group attached to them.
Example: D-Fructose
Fischer Projection Formula:
- The ketone group is represented by a horizontal line.
- The hydroxyl groups are represented by vertical lines.
- Example: Fischer Projection of Fructose
```
        HO―C(=O)―CH2OH
         |
H―C―OH―C―OH―C―H
     |       |
    H       OH
```

Configuration of L-Aldose

L-aldoheptose is a seven-carbon sugar molecule.
All the carbon atoms except the last one have a hydroxyl group attached to them.
The last carbon atom is bonded to an aldehyde group.
Example: L-Glyceraldehyde
Fischer Projection Formula:
- The carbon chain is depicted vertically in the middle of the projection.
- The aldehyde group is represented by a horizontal line.
- The hydroxyl groups are represented by vertical lines.
- Example: Fischer Projection of L-Glyceraldehyde
```
          HO―C(=O)―H
           |
H―C―OH―C―OH―C―OH
     |       |
    H       H
```

Configuration of L-Ketose

L-ketohexose is a six-carbon sugar molecule.
The first carbon atom is a ketone group.
The remaining carbon atoms have a hydroxyl group attached to them.
Example: L-Fructose
Fischer Projection Formula:
- The carbon chain is depicted vertically in the middle of the projection.
- The ketone group is represented by a horizontal line.
- The hydroxyl groups are represented by vertical lines.
- Example: Fischer Projection of L-Fructose
```
            HO―C(=O)―CH2OH
             |
HO―CH―OH―C―OH―C―OH
     |       |
    H       H
```

Haworth Projection of D-Glucose

Haworth projection is used to represent cyclic forms of sugars.
The carbon chain is depicted as a polygon.
The oxygen atom that forms the cyclic structure is enclosed within the polygon.
Hydroxyl groups attached to carbon atoms are shown as lines coming out of or going into the plane of the paper.

Example: Haworth Projection of D-Glucose

        O       HO
         \     /
HO―CH2OH―C―OH
     |      | 
     H      H

Haworth Projection of D-Fructose

Example: Haworth Projection of D-Fructose

        O       HO
         \     / 
     HO―CH2OH―C―OH
            |   \
            HO   H

Anomers of D-Glucose

D-Glucose can exist in two anomeric forms: α and β.
α-D-Glucose: Hydroxyl group on C1 is trans to the -CH2OH group.
β-D-Glucose: Hydroxyl group on C1 is cis to the -CH2OH group.

Haworth Projection examples:

α-D-Glucose:

        O       HO
         \     / 
     HO―CH2OH―C―OH
            |   \
            HO   H

β-D-Glucose:

        O       HO
         \     / 
     OH―CH2OH―C―OH
            |   \
            HO   H

Anomers of D-Fructose

D-Fructose can also exist in α and β anomeric forms.
α-D-Fructose: Hydroxyl group on C2 is trans to the terminal CH2OH group.
β-D-Fructose: Hydroxyl group on C2 is cis to the terminal CH2OH group.

Haworth Projection examples:

α-D-Fructose:

        O       HO
         \     / 
     HO―CH2OH―C―OH
        |       |
        H       OH

β-D-Fructose:

        O       HO
         \     / 
     OH―CH2OH―C―OH
        |       |
        H       OH

Chirality in Biomolecules

Biomolecules, such as amino acids and sugars, often exhibit chirality.
A chiral molecule is one that cannot be superimposed on its mirror image.
Chirality arises from an asymmetric carbon atom, also known as a stereocenter.
A stereocenter is a carbon atom that is bonded to four different groups.
Chirality is important in biological processes, as different enantiomers can have different effects.
Example: L- and D-amino acids

Enantiomers

Enantiomers are chiral molecules that are mirror images of each other.
Enantiomers have the same physical properties (except for optical activity) but exhibit different biological activities.
Enantiomers rotate plane-polarized light in equal and opposite directions.
Enantiomers are denoted by prefixes L- and D- or (+) and (-) based on their optical activity.
Example: L-alanine and D-alanine

Optical Activity

Optical activity refers to the ability of a substance to rotate the plane of plane-polarized light.
Dextrorotatory (d-) substances rotate light clockwise (to the right) and have a positive rotation value.
Levorotatory (l-) substances rotate light counterclockwise (to the left) and have a negative rotation value.
Optical rotation is measured in degrees using a polarimeter.
Specific rotation (α) is a standardized value that represents the rotation per unit length.
Example: D-glucose has a specific rotation of +52.7°.

Haworth Projection of L-Glucose

Example: Haworth Projection of L-Glucose

        O       HO
         \     / 
     HO―CH2OH―C―OH
            |   \
            HO   H

Anomers of L-Glucose

L-Glucose can also exist in α and β anomeric forms.
α-L-Glucose: Hydroxyl group on C1 is trans to the -CH2OH group.
β-L-Glucose: Hydroxyl group on C1 is cis to the -CH2OH group.

Haworth Projection examples:

α-L-Glucose:

        O       HO
         \     / 
     HO―CH2OH―C―OH
            |   \
            HO   H

β-L-Glucose:

        O       HO
         \     / 
     OH―CH2OH―C―OH
            |   \
            HO   H

Epimers

Epimers are stereoisomers that differ in the configuration of only one stereogenic center.
Epimers are a type of diastereomers.
Example: D-glucose and D-mannose are epimers at the C2 carbon atom.

Fischer Projection examples:

D-Glucose:

            HO―CH2OH―C―OH
           |       |
    H―C―OH        H
         |
         H

D-Mannose:

            HO―CH2OH―C―OH
           |       |
    H―C―OH        OH
         |
         H

Anomerization

Anomerization is the interconversion between anomers.
It occurs due to the rotation of the hydroxyl group attached to the anomeric carbon.
Anomerization can be catalyzed by acids or enzymes.
Example: α-D-glucose can convert into β-D-glucose.

Haworth Projection examples:

α-D-Glucose:

        O       HO
         \     / 
     HO―CH2OH―C―OH
            |   \
            HO   H

β-D-Glucose:

        O       HO
         \     / 
     OH―CH2OH―C―OH
            |   \
            HO   H

Glycosidic Bond Formation

Glycosidic bond formation occurs when a hydroxyl group of one sugar reacts with the anomeric carbon of another sugar.
It is an example of a condensation reaction, resulting in the formation of a glycosidic bond and the release of a molecule of water.
Glycosidic bonds are typically formed between the anomeric carbon of one sugar and a hydroxyl group on the carbon atom of another sugar.
Example: Sucrose formation from glucose and fructose.
Equation: Glucose + Fructose → Sucrose + H2O

Classification of Carbohydrates

Carbohydrates can be classified into three main groups: monosaccharides, disaccharides, and polysaccharides.
Monosaccharides: Simple sugars that cannot be hydrolyzed into smaller units. Examples: glucose, fructose.
Disaccharides: Formed by the condensation of two monosaccharide units. Examples: sucrose, lactose.
Polysaccharides: Long chains of monosaccharide units. Examples: cellulose, starch.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates.
They are classified based on the number of carbon atoms they contain: trioses, tetroses, pentoses, hexoses, etc.
Examples of monosaccharides: glucose, fructose, ribose.
Monosaccharides are usually white, crystalline solids that are soluble in water.

Disaccharides

Disaccharides are formed by the condensation reaction between two monosaccharide units.
The glycosidic bond is formed between the anomeric carbon of one monosaccharide and a hydroxyl group on the carbon atom of another monosaccharide.
Examples of disaccharides: sucrose (glucose + fructose), lactose (glucose + galactose), maltose (glucose + glucose).
Disaccharides are usually crystalline solids that are soluble in water.

Polysaccharides

Polysaccharides are complex carbohydrates that consist of long chains of monosaccharide units.
They serve as energy storage molecules and structural components in organisms.
Examples of polysaccharides: cellulose, starch, glycogen.
Polysaccharides are usually amorphous solids that are insoluble in water.

Functions of Carbohydrates

Carbohydrates have multiple functions in living organisms, including:
- Energy storage: Carbohydrates serve as a primary source of energy for cellular processes.
- Structural support: Polysaccharides like cellulose provide structural support to plant cell walls.
- Cell recognition: Carbohydrates on the cell surface play a role in cell recognition and immune response.
- DNA and RNA synthesis: Carbohydrates are essential for the synthesis of nucleotides, the building blocks of DNA and RNA.
- Glycoproteins and glycolipids: Carbohydrates are present in glycoproteins and glycolipids, which are important for cell signaling and communication.