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Introduction to Bio-Molecules

Biomolecules are the most essential organic molecules, which are involved in the maintenance and metabolic processes of living organisms.
  • These non-living molecules are the actual foot-soldiers of the battle of sustenance of life. 

Different Classes of CarbohydratesDifferent Classes of Carbohydrates

  • They range from small molecules such as primary and secondary metabolites and hormones to large macromolecules like proteins, nucleic acids, carbohydrates, lipids, etc. 
  • These are certain complex organic molecules that form the basis of life. These build up living organisms and are also required for their growth and maintenance. 
  • The main classes of biomolecules are

1. Carbohydrates

2. Nucleic acids

3. Amino Acids

4. Peptides

5. Terpenes

6. Lipids

7. Alkaloids


Carbohydrates

Carbohydrates are macronutrients and are one of the three main ways by which our body obtains its energy. The carbohydrates may be defined as polyhydroxy aldehydes or ketones or substances which give such molecules on hydrolysis. 

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

  • Carbohydrates form a very large group of naturally occurring organic compounds which play a vital role in daily life. 
  • They are produced in plants by the process of photosynthesis. After eating plant foods, humans convert carbohydrates into glucose.
  • The most common carbohydrates are glucose, fructose, sucrose, starch, cellulose etc. 
  • Many carbohydrates are sweet in taste and all sweet carbohydrates are called as sugars. The chemical name of the most commonly used sugar in our homes is sucrose.

Functions of Carbohydrate

1. Provide energy

2. Maintain blood glucose

3. Spare protein

4. Prevents ketosis


Classification of Carbohydrates

A. Depending upon their behavior on Hydrolysis

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(1) Monosaccharides: 

  • Polyhydroxy aldehyde or ketone which cannot be hydrolyzed further to a smaller molecule containing these functional groups, is known as a monosaccharide. About 20 monosaccharides occur in nature and glucose is the most common amongst them.
  • Monosaccharides are further classified on the basis of the functional group present in them. If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group, it is known as a ketose.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(2) Disaccharides: 

Carbohydrates that give two monosaccharide molecules on hydrolysis are called disaccharides e.g. sucrose, maltose, lactose, etc.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(3) Polysaccharides: 

Carbohydrates yield a large number of monosaccharide units on hydrolysis e.g. starch, glycogen, cellulose etc.

Amylose: It is a component of starch.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Amylopectin: It is another polysaccharide component of starch that has a branched structure.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

The Comparison of Starch and Glycogen Molecules

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(4). Oligosaccharides: 

  • Similar in length to simple carbohydrates and in makeup to polysaccharides. Humans lack the enzymes necessary to digest them. 
  • Intestinal microflora digest and ferment them and cause bloating, discomfort, and flatulence. Food sources are Legumes, beans, cabbage, brussels sprouts, broccoli.

The Structure of an Oligosaccharide

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

B. Depending upon Functional Group

1. Aldoses: They are aldehyde-containing carbohydrates. At C1, the carbonyl is an aldehyde.

2. Ketoses: They are ketone-containing carbohydrates. At any other carbon, carbonyl present would be the ketonic group.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

C. Depending upon no. of Carbon Atoms

(a) Aldoses

(i) Three carbons: Aldotriose

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(ii) Four carbons: Aldotetrose

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(iii)Five carbons:Aldopentose

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(iv) Six carbons: Aldohexose

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

(b) Ketoses

Ketoses are less common than aldoses.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Fructofuranose and Fructopyranose

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

 Cyclic Forms of Carbohydrates: Furanose Forms

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Cyclic Structure of Monosaccharides Hemiacetal Formation

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Cyclization of carbohydrates to the hemiacetal creates a new chiral center. The hemiacetal or hemiketal carbon of the cyclic form of carbohydrates is the anomeric carbon. Carbohydrate isomers that differ only in the stereochemistry of the anomeric carbon are called anomers.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Haworth Projections

The structures of cyclic sugars are best represented by the Haworth projections. Haworth projections allow us to see the relative orientation of the OH groups in the ring.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Converting Fischer Projections to Haworth formulas

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Note: The pyranose forms of carbohydrates adopt chair conformations.


Mutarotation

The α- and β-anomers are in equilibrium, and interconvert through the open form. The pure anomers can be isolated by crystallization.

  • When the pure anomers are dissolved in water they undergo mutarotation, the process by which they return to an equilibrium mixture of the anomer.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Osazone Formation: 

Aldoses and ketoses react with three equivalents of phenylhydrazine.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

The C-2 epimers of aldoses form identical osazones.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Reaction of Ketoses with Phenylhydrazine.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Deoxy Sugars

Carbohydrates that do not contain hydroxy group.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Amino Sugars

Carbohydrates in which a hydroxyl group is replaced with an —NH2 or —NHAc group

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Oxidation of Monosaccharides

C1 of aldoses can be selectively oxidized to the carboxylic acid (aldonic acids) with Br2 or Ag(I) (Tollen’s test).

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Reducing Sugars

Carbohydrates that can be oxidized to aldonic acids. For example, oxidation of aldoses to aldaric acids with HNO3.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Reduction of Monosaccharides

C1 of aldoses are reduced with sodium borohydride to the 1° alcohol (alditols)

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Chain Elongation

The carbon chain of an aldose can be increased by one carbon by Kiliani–Fischer synthesis method.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Chain Shortening

The Ruff degradation shortens an aldose chain by one carbon.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

Preparation of the Calcium D-Gluconate for the Ruff Degradation

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Acylation of Monosaccharides: 

The OH groups of monosaccharides show the chemistry of typical alcohols.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Alkylation of the OH Groups

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Formation of Glycosides

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Mechanism:

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


Formation of an N-Glycoside

Introduction to Biomolecules & Carbohydrates | Organic Chemistry


The Anomeric Effect

The anomeric effect refers to the tendency of a group X at C(1) of a pyranose ring to assume the axial rather than the equatorial orientation. This phenomenon is important in carbohydrate chemistry since it influences the composition of isomeric mixtures and hence their reactivities. It has been suggested that the effect is caused mainly by a stabilizing interaction between the axial lone pair of electrons on the ring oxygen atom and the anti-periplanar, antibonding orbital of the C-X bond. This leads to a shortening of the bond between the ring oxygen and the anomeric carbon and a lengthening of the C-X bond. Alternatively, electrostatic repulsive forces between the dipoles due to the ring oxygen lone pairs and the exocyclic oxygen or halogen may account in part for the observed axial preferences.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

The anomeric effect is solvent and substituent dependent and decreases in the following order: C1> OAc > OMe > OH, as exemplified by the equilibrium concentrations of the alpha and beta anomers of substituted D-glucose in various protic solvents at 250C.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

The formation of a glycoside favors the α-glucoside product: the anomeric effect.

Introduction to Biomolecules & Carbohydrates | Organic Chemistry

The document Introduction to Biomolecules & Carbohydrates | Organic Chemistry is a part of the Chemistry Course Organic Chemistry.
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FAQs on Introduction to Biomolecules & Carbohydrates - Organic Chemistry

1. What are carbohydrates?
Carbohydrates are biomolecules that consist of carbon, hydrogen, and oxygen atoms. They serve as a major source of energy for living organisms and play essential roles in various cellular processes.
2. How are carbohydrates classified based on their behavior on hydrolysis?
Carbohydrates can be classified into three main groups based on their behavior on hydrolysis: monosaccharides, disaccharides, and polysaccharides. Monosaccharides are the simplest form of carbohydrates and cannot be further hydrolyzed into smaller sugar units. Disaccharides consist of two monosaccharide units joined together, while polysaccharides are composed of multiple monosaccharide units.
3. What is the significance of the functional group in classifying carbohydrates?
The functional group present in carbohydrates determines their chemical properties and reactivity. Based on the functional group, carbohydrates can be classified into aldoses (carbohydrates with an aldehyde functional group) and ketoses (carbohydrates with a ketone functional group). This classification helps in understanding the structure and behavior of different types of carbohydrates.
4. How is the number of carbon atoms used to classify carbohydrates?
Carbohydrates can also be classified based on the number of carbon atoms they contain. Monosaccharides can have three, four, five, six, or more carbon atoms. For example, trioses have three carbon atoms, pentoses have five carbon atoms, and hexoses have six carbon atoms. The number of carbon atoms affects the size and complexity of the carbohydrate molecule.
5. What is the significance of cyclic structures in monosaccharides?
Monosaccharides, such as fructose and glucose, can exist in both linear and cyclic forms. The cyclic structure is formed through a reaction called hemiacetal formation. The cyclic form is more stable and biologically active compared to the linear form. Cyclic structures play a crucial role in the three-dimensional arrangement of monosaccharides and their interactions with other molecules in biological systems.
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