Organic Compounds Biological System.

Unit II

• 2.1 Definition of organic and inorganic compounds.

• 2.2 Importance of organic compounds – in Biological system.

• 2.3 Basic chemistry of carbohydrates, proteins, and lipids - Their nutritional effect in humans.

2.1 Definition of organic and inorganic compounds:

• Organic compounds are chemical compounds composed of carbon atoms bonded with hydrogen, oxygen, nitrogen, sulfur, and other elements. Organic compounds are mainly associated with living organisms. They are characterized by their covalent bonds.

• Inorganic compounds are chemical compounds derived from minerals, non-living sources, or synthetic processes. Inorganic compounds are not composed of carbon-hydrogen bonds (C-H bonds).

2.2 Importance of organic compounds – in Biological system.

Organic compounds play very important roles in the biological system. These are followings

1. Structure of biological system: Biological systems are composed of proteins, carbohydrates, lipids, and nucleic acids.

2. Cell membrane: Cell membranes are composed of phospholipids. These membranes act as barriers to separate the internal and external environment of cells. They control the movement of molecules into cells and out of cells.

3. Enzymes and hormones: Enzymes are hormones that stimulate chemical reactions inside the human body. These chemical reactions take place for the normal functioning of the biological system. These enzymes and hormones are chemically proteins.

4. Energy sources: Biochemical reactions require energy to perform normal functions. Carbohydrates are the main source of energy.

5. Metabolic reactions: Chemical reactions inside the biological system are called metabolism. Metabolic reactions require organic compounds to complete the chemical reactions inside the biological system.

6. Immunity: The power of the body to resist infection is called immunity. Antibodies develop immunity inside the biological system. Chemically, these antibodies are proteins.

7. Genetic information: The biological system stores genetic information inside DNA. Chemically, DNA is nucleic acid.

2.3 Basic chemistry of carbohydrates, proteins, and lipids - Their nutritional effect in humans.

Basic chemistry of Carbohydrates: Carbohydrates are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O) atoms. Examples: Glucose, Sucrose, Starch, etc.

Classification of carbohydrates: Carbohydrates are classified into the following three classes

1. Monosaccharide: Monosaccharides are the simplest carbohydrates. They cannot be further hydrolyzed to smaller sugars. The general formula of monosaccharide is (CH2O)n. “n” represents the number of carbon atoms in the monosaccharide. Examples of common monosaccharides are glucose, fructose, and galactose. Monosaccharide is the basic building block of complex carbohydrates.

2. Disaccharide: Disaccharide consists of two monosaccharide molecules. Both monosaccharide molecules are connected with glycosidic bonds. Examples are sucrose (glucose + fructose), maltose (glucose + glucose), and lactose (glucose + galactose). Hydrolysis of one molecule of disaccharide releases two molecules of monosaccharide.

3. Oligosaccharide: Oligosaccharide consists of three or more monosaccharide molecules. Hydrolysis of oligosaccharides produces three or more molecules of monosaccharide.

4. Polysaccharide: Polysaccharide consists of more than ten molecules of monosaccharide. Hydrolysis of polysaccharides produces more than ten molecules of monosaccharide. They are not sweet in taste and are also called non-sugar. Examples: Starch, cellulose, glycogen, etc.

5. Starch: Plants store glucose as starch as a source of energy. It consists of a long chain of glucose.

6. Glycogen: Animals store glucose as glycogen as a source of energy. It consists of a large number of glucose molecules.

7. Cellulose: Cellulose is a structural component of plant cell wall. It consists of a large number of glucose molecules. The arrangement of glucose molecules in cellulose is different from the arrangement of glucose molecules in starch and glycogen.

Basic chemistry of proteins: Proteins are complex organic molecules composed of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S). The basic chemistry of proteins includes structure, composition, and their interactions.

Structure and composition of proteins: Proteins are composed of amino acids. Amino acids are building blocks of protein molecules. Protein molecules consist of 20 different amino acids.

1. Amino acid: Each amino acid consists of one central carbon atom (alpha carbon) bonded to four different chemical groups:

   Amino group: (-NH2).

   Carboxyl group: (-COOH),

   Hydrogen group: (-H),

   Variable R group (Sidechain).

2. Peptide bond: Protein molecule consists of amino acids. Amino acids bind with each other by peptide bonds. The carboxyl group of one amino acid combines with an amino group of another amino acid. This combination develops peptide bonds. The Peptide bond is a covalent bond. The linkage of amino acids with each other develops a long chain structure called a Polypeptide chain.

3. Primary structure: The linear arrangement of amino acids in protein structure is called primary structure. The specific arrangement of amino acids determines the unique structure and function of that amino acid.

4. Secondary structure: The folding pattern of long chains of amino acids in protein structure is the secondary structure of proteins. The most common secondary structures are

   Alpha helical structure: Twist in long chain of amino acids in protein structure forms spiral or helical shape.

   Beta sheets: Protein chain folding backs develop shee-like structure.

5. The secondary structures are stabilized by the hydrogen bond between the carboxyl group of one polypeptide chain and with amino group of another polypeptide chain.

6. Tertiary structure: Three-dimensional folding of the polypeptide chain develops a globular shape. This is the tertiary structure of the protein. The tertiary structure is stabilized by several types of bonds. These are hydrogen bonds, ionic bonds (bonds between charged ions), disulfide bonds (covalent bonds between sulfur atoms), and hydrophobic interactions.

7. Quaternary structure: Some proteins consist of multiple polypeptide subunits. These polypeptide subunits come together to form a quaternary structure. Interaction between these polypeptide subunits decides the overall functions of the protein.

8. Denaturation: A change in the three-dimensional structure of protein molecules is called denaturation of protein. Heat, extreme pH levels, or exposure to certain chemicals cause protein denaturation. Protein loses its biological functions after denaturation. Example: Heating of raw egg causes coagulation of egg contents. This is due to the denaturation of protein in an egg. The denaturation of protein is an irreversible process.

Biological functions of protein: There are several types of protein inside the biological system. The proteins perform the following functions

1. Enzymes: Chemically, enzymes are proteins. They catalyze biochemical reactions.

2. Hormones: Chemically, hormones are proteins. They catalyze biochemical reactions,

3. Connective tissues: Collagen in connective tissues is protein. Collagen is a structural protein.

4. Hemoglobin: Chemically, Haemoglobin consists of globin and haem. Globin is a protein. Hemoglobin transports respiratory gasses.

5. Antibodies: Chemically, antibodies are proteins. Antibodies develop immunity.

Basic chemistry of lipids: Lipids are composed of carbon (C), hydrogen (H), and oxygen (H). Some lipids also contain phosphorus (P) and nitrogen (N). Lipids are organic molecules characterized by their hydrophobic (water-repellent) property. The following are some common chemical characteristics of lipids

1. Fatty acids: Fatty acids are building blocks of lipids. Each fatty acid is composed of hydrocarbon chains. Hydrocarbon chains of fatty acids are composed of long chains of carbon atoms with a carboxyl group at one end (-COOH). The nature of fatty acids in lipids decides the chemical properties of lipids. There are two types of fatty acids.

   Unsaturated fatty acids: Unsaturated fatty acids consist of an unsaturated hydrocarbon chain. Hydrocarbon chains containing one or more double bonds are called unsaturated hydrocarbons.

   Saturated fatty acids: Saturated fatty acids consist of a saturated hydrocarbon chain. Hydrocarbon chains containing only single bonds are called saturated hydrocarbon.

2. Triglycerides (Triacylglycerols): Triglycerides are the most common type of lipid in the biological body. Triglycerides are composed of three fatty acid molecules. These fatty acid molecules are bonded with the glycerol molecules through ester binds. Triglycerides store energy. They release energy if the biological system requires energy.

3. Phospholipids: The chemical structure of phospholipids and triglycerides are similar. Two fatty acids and one phosphor group are attached to a glycerol molecule in phospholipids. Phospholipids molecule has one polar end called the hydrophilic end or head of phospholipids molecule. Another end of the phospholipids molecule is the non-polar end called the hydrophobic end or tail of phospholipids molecules. Phospholipids form a lipid bilayer in the cell membrane.

4. Sterols: Sterols are lipids. They consist of four interconnected carbon rings. Example cholesterol.

5. Lipid bilayer

Author: Dr Pramila Singh