Biomolecules: Introduction, Types and Sources

 Biomolecules:

    Biomolecules are organic macromolecules which are produced by living organisms, essential for life. Carbon and hydrogen are basic units of biomolecules. They are classified into following categories:

• Carbohydrates
• Lipids
• proteins 

Carbohydrates:

    Chemically, carbohydrates are polyhydroxy aldehydes or ketones. The general formula is 

Cn​(H2​O)n. The word carbohydrate means hydrated carbon. They are composed of carbon, hydrogen and oxygen as the same ratio in water. 

Classification of carbohydrates:

    Carbohydrates are classified into three groups.

• Monosaccharides
• Oligosaccharides
• polysaccharides

Monosaccharides:

   These are simple and sweet sugar. These are easily soluble in water. Chemically, they are polyhydroxy aldehydes or ketones. With aldehyde group these sugar are called aldo-sugar and with ketone group is called keto-sugar. They are called trioses, tetroses, pentoses, hexoses and heptoses according to their carbon number. The most abundant monosaccharide is glucose, fructose and ribose which are combined to form more complex sugar.

Oligosaccharides:

       These are much complex sugar because, two to ten monosaccharides combine to form oligosaccharides. The bond between two monosaccharides is called glycosidic bond. These are tasteless and less soluble in water. They give 2 to 10 units of monosaccharides on hydrolysis. Most  important oligosaccharides are maltose, lactose and sucrose. Sucrose is most familiar which is found in sugar cane which on hydrolysis give glucose and fructose. 

Polysaccharides:

    Polysaccharides are more complex compound. These are tasteless and are sparingly soluble in water. Thee are amorphous solid and are nonreducing agents. These are most abundant in nature. They have high molecular weight because several monosaccharides are combine to form a polysaccharides. Most common polysaccharides are glycogen, starch and cellulose. which are described below.

Starch:

    It is found in fruits and seeds and a main source of carbohydrates for animals. It yields glucose on hydrolysis. There are two types of starch: amylose and amylopectin.

Amylose are soluble in hot water. They have unbranched glucose.

Amylopectin are insoluble in water and give blue color with iodine.

Cellulose:

      Cellulose is most abundant in nature. It is a major part of plant cell wall. On hydrolysis it gives glucose. It is insoluble in water an could not digested in human. It can be digested in herbivores because they contain microorganisms in their digestive track. Cotton is a pure form of cellulose.

Glycogen:

    Glycogen is a chief form of carbohydrates which is also called animal starch. Because it is found in muscles and liver of animals. It is used for store energy in animal body. It is insoluble in water and give red color with iodine. 

 Sources and uses of carbohydrates:

• Seeds fruits and grains are common source of glucose and fructose. 
• Dairy products is the source of lactose.
• Cotton is pure form of cellulose.
• Sugarcane is a source of sucrose.

Uses:

•  Carbohydrates help in regulate our sugar level.
• It protect us from muscle cramp.
• It control blood pressure.
• It give nutrients to microorganisms which are found in digestive track.

Lipids:

    Chemically, lipids are triglycerides of fatty acids. 

Fatty acids:

    Fatty acids are basic unit of lipids. They contain even number of carbon atoms which have an acidic group.

They are insoluble in water but soluble in organic solvents such as ethers, benzene and alcohol. Lipids stored high concentration of energy as compared to carbohydrates because of high proportion of C-H bond and low proportion of C-O bond. Lipids  are classified into acylglycerols, waxes, phosopholipids and terpenoids. These are described below.

 Acylglycerols:

    Acylglycerols are composed of glycerol and fatty acids. Chemically, acylglycerol can be defined as esters of fatty acids and alcohol. An ester is the compound which is product of alcohol and acid. When three fatty acids react with one glycerol it produce triacyl glycerol which is widely spread acylglycerol. It is also called triglycerides or neutral lipids.

Saturated fatty acids are compound which don't have double bond. These are solid at room temperature.

Unsaturated fatty acids are compound containing double bond. These are liquid at room temperature.

Phospholipids:

    Phospholipids are derivatives of phosphatic acid. Phosphatic acids are composed of fatty acids, glycerol and phosphoric acid. Nitrogenous bases are also part of phospholipid. These are found in bacteria, animal and plant cell. Phophatidylcholine is one of the common phospholipid. 

Waxes:

    Chemically waxes are mixtures of long chain alkanes and alcohols, ketones and esters of long chain fatty acids. These are widespread lipids found on fruits and leaves as protective coating. Waxes protect plants from water loss. Some insects secrete waxes.

Terpenoids:

    Terpenoids are composed of simple units called isoprenoid units. Terpenoid give rise to rubber, steroids, terpenes and carotenoids.

Uses and sources of lipids:

• Secretions of insects are source of waxes
• Animal body contain fats.
• Oils are unsaturated fatty acids comes from plants.
• Cuticle of epidermis is also lipid.

 Uses:

• lipids are major source of energy as it stores high energy as compare to carbohydrates. 
• Lipids provide insulation and protection in animal body.
• It protect from abrasive damage and water loss. 
• It also play an important role in organelles and cell membrane.

Proteins: 

   Proteins are most abundant organic compounds. Proteins are found in all parts of cell. Approximately over 50% part of dry body composed of proteins. 

Amino acids:

    Amino acids are basic units which are building blocks of protein. There are 170 types of amino acids and of these 25 amino acids make protein. Amino acids contain an amino group, an alpha carbon with one hydroxyl group, a carboxyl group and an alkyl group. The linkage between hydroxyl group and carboxyl group of another amino acid release one molecule of water, such a linkage called peptide bond. 

Structure of proteins:  

    Specific properties of proteins are determined by specific sequence and structure of amino acids. There are four specific structures of proteins.

Primary structure:

    F.Sanger was a scientist who firstly determine the sequence of amino acids. He concluded that size and structure of protein is determined by type and size of amino acids. Haemoglobin has four chain two alpha and two beta chain. Each alpha chain have 141 amino acids and each beta chain have 146 amino acids.  

Secondary structure:

     Polypeptide chain usually coil into helix or other regular configuration. Alpha helix is most common structure in which chain form a spiral shape. 3.6 amino acids are kept in each turn of helix. Beta pleated sheet is is formed by folding back of polypeptide.

Tertiary structure:

    Usually a helical structure bends and fold into each other form complex globular shape. This is tertiary structure of protein. Its bond may be ionic hydrogen and disulfide.

Quaternary structure:

    Tertiary structure are combined to form more complex structure are called quaternary structure. They are held together by hydrophobic interactions, hydrogen and ionic bonds.