Biological Molecules - Session 2

As we know, disaccharides are made up of two monosaccharide units. These two monosaccharide units are joined together by glycosidic linkage. In order to utilize energy from disaccharides, they should be converted into individual monosaccharide units. For this purpose, the glycosidic linkage needs to be broken. But how can we break this glycosidic linkage between two monosaccharides?.

The glycosidic linkage between two monosaccharides can be broken by the process of hydrolysis. The term hydro means water and lysis means breakdown. So the term hydrolysis means breakdown of complex molecules by the addition of water. Hydrolysis of disaccharides involve breaking the disaccharide into two individual monosaccharide units by the addition of water.

Disaccharides are formed by the condensation reaction between two monosaccharides, which involves the removal of a water molecule. Hydrolysis is the reverse of this process. In hydrolysis the water molecule is added back, breaking the glycosidic bond between the two monosaccharides. For example, the hydrolysis of sucrose involves the addition of a water molecule to the glycosidic bond between glucose and fructose. This breaks it into its constituent monosaccharides. The enzyme sucrase facilitates this reaction.

Hydrolysis of polysaccharides refers to the breakdown of these large molecules into smaller subunits, through the addition of water molecules. For example, when starch is hydrolyzed, it is typically broken into maltose and glucose monomers. The hydrolysis of polysaccharides allows organisms to break complex carbohydrates into smaller, more easily digestible subunits.

Lipids are a group of organic biomolecules that have a crucial role in living organisms. They are insoluble in water but soluble in organic solvents. Lipids are used by the body for storing energy, keeping it warm, making cell walls, and sending signals between cells. Examples of lipids include fats, oils, and cholesterol.

Lipids are classified into different categories, including triglycerides, phospholipids, steroids, and waxes. Triglycerides are a type of fat found in our bodies and in foods. They are made up of a molecule called glycerol and three fatty acids. Triglycerides can be stored in our body's fat cells and used for energy when needed.

Let’s discuss the structure of triglycerides. As we know, triglycerides are made up of glycerol and fatty acids. Glycerol is a type of sugar alcohol that is made up of a propane backbone with three hydroxyl groups attached. This makes it a triol. It has a sweet taste. It is not as sweet as regular sugar.

Fatty acids are made up of a long chain of carbon atoms with a carboxyl group -COOH at one end and a methyl group -CH3 at the other end. The carbon atoms in the chain are linked by single or double bonds. The number of carbon atoms in the chain can vary. They usually range from four to twenty four. Some examples of fatty acids are palmitic acid and oleic acid.

Fatty acids are further classified into saturated fatty acids and unsaturated fatty acids. The term saturated refers to the fact that these fatty acids have no double bonds between their carbon atoms. This makes them saturated with hydrogen atoms. Saturated fatty acids are solid at room temperature. Palmitic acid is an example of a saturated fatty acid.

Unsaturated fatty acids have one or more double bonds between carbon atoms. This causes the molecule to bend and not pack as tightly as a saturated fatty acid. This makes unsaturated fatty acids liquid at room temperature. Oleic acid is an example of unsaturated fatty acid.

Unsaturated fatty acids are of two types. Monounsaturated fatty acids and Polyunsaturated fatty acids. Monounsaturated fatty acids contain one double bond in the carbon chain. Palmitic acid is an example of monounsaturated fatty acid. Foods high in Monounsaturated fatty acids include olive oil, avocado, nuts and seeds.

Polyunsaturated fatty acids contain more than one double bonds in carbon chain. Examples of foods high in Polyunsaturated fatty acids include fatty fish such as salmon, flaxseeds, walnuts, and vegetable oils such as soybean and sunflower. Unsaturated fatty acids are considered to be healthier than saturated fatty acids. This is because they can help reduce the risk of heart disease by lowering levels of cholesterol in the blood.

In triglycerides, glycerol is connected with three fatty acid molecules through ester bonds. An ester bond is a type of chemical bond that connects a carboxylic acid group -COOH with an alcohol group -OH . It is formed through a condensation reaction, which involves the removal of a molecule of water. The resulting molecule is a compound with an ester -COO- linkage between glycerol and fatty acids.

Phospholipids are a type of lipid molecule that make up the basic structure of all cell membranes. They are composed of a glycerol molecule, two fatty acid chains, and a phosphate group. The fatty acid chains are long chains of carbon and hydrogen atoms. These chains can vary in length. Phospholipids can be broken up by enzymes to release fatty acids. Fatty acids can then be used as a source of energy by cells.

The head of phospholipid contains a phosphate group. It is hydrophilic. Hydro means water and phillic means attract. So the term hydrophilic means water attracting. The head of phospholipid attracts water. The tail of phospholipid contains fatty acids. It is hydrophobic. Hydro means water and phobic means repelling. So the term hydrophobic means water repelling. The tail of pphospholipid repels water.

As we know that cell membrane of cells is made up of two layers of phospholipids. In cell membrane, these two layers are arranged in a way that the hydrophobic tails are facing each other. This makes the cell membrane selectively permeable. It allows passage of some molecules while blocking others.