Understanding Biomolecules: Carbohydrates, Lipids, and Proteins
Biomolecules: Carbohydrates, Lipids, and Proteins
Heteropolysaccharides and Heterosides
Heteropolysaccharides are formed by two or more classes of monosaccharides. Heterosides are formed by a carbohydrate and a non-carbohydrate part.
Lipids
Lipids are a very heterogeneous set of substances, both structurally and by the functions they perform. They are insoluble in water and soluble in organic solvents. Chemically, they are made of Carbon, Hydrogen, and Oxygen.
Properties of Lipids
- Oily to the touch
Biological Functions of Lipids
- Structural
- Energetic
- Vitamins and Hormones
Classification of Lipids
1) Saponifiable Lipids
Acylglycerides are the esterification of a molecule of glycerol with one, two, or three molecules of fatty acids, resulting in monoacylglycerides, diacylglycerides, or triacylglycerides, respectively.
Fatty Acids are organic acids characterized by the length of their hydrocarbon chain and the presence of double bonds. Some are called essential because we cannot synthesize them. They are amphiphilic, possessing an apolar zone in the aliphatic chain and a polar area in the carboxyl group. They react with alcohols, forming esters, and are hydrolyzed with alkali to form soaps. The length and degree of unsaturation of the aliphatic chain influence the melting point of fats.
Triglycerides are energy reserves stored in seeds and serve to conserve body heat.
Waxes result from the esterification of a long-chain fatty acid with a high molecular weight alcohol. Due to their strong water-repellent properties, they act as a protective layer on skin, hair, and feathers.
Phospholipids are components of biological membranes. They are made of glycerol esterified with a phosphate group, two fatty acids (one saturated and one unsaturated), and another group. They are amphipathic. In aqueous solutions, phospholipids tend to associate in micelles and bilayers.
Sphingolipids are similar in structure to phospholipids and are abundant in neurons. They possess an amino alcohol, a fatty acid, and a varied and complex polar group.
2) Unsaponifiable Lipids
Terpenes are a family of substances derived from the polymerization of isoprene.
Steroids are polycyclic compounds derived from sterane. For example, cholesterol is a structural component of animal cell membranes, located between phospholipids, acting as a stabilizer and a precursor of vitamin D.
Prostaglandins are derived from prostanoate and have functions in blood clotting.
Proteins
Proteins are central to vital activity. They are composed of Carbon, Hydrogen, Oxygen, and Nitrogen (CHON), are large, high molecular weight molecules that break down into their amino acid units, and their charge changes by varying the pH.
Isoelectric Point
The isoelectric point is the pH value at which the acidic and basic properties of an amino acid offset each other, and the amino acid is amphoteric.
Peptide Bond
Proteins consist of long chains of amino acids arranged in specific sequences and bound by a peptide bond between the amino group of one amino acid and the carboxyl group of another, with the detachment of a water molecule. It is a rigid covalent bond that does not allow rotation.
Levels of Structural Organization
The structure of proteins refers to the spatial arrangement of amino acids throughout the polypeptide chain. It adapts to the interactions that may occur between amino acids in the chain or with other chains. These interactions are generally weak but keep the molecule with a definite shape, although flexible. Strong interactions include disulfide bridges. There are four types of protein structure:
1) Primary Structure: This is the linear sequence of amino acids in the polypeptide chain, linked together by peptide bonds. Protein chains differ in the number, nature, and order of amino acids.
2) Secondary Structure: This configuration allows for the formation of hydrogen bonds between the NH and CO groups of the polypeptide. Two types are distinguished:
- Alpha-helix: Intrastrand hydrogen bonds form between amino acids located every four residues. Characteristic of globular proteins.
- Beta-sheet or folded sheet: Formed when the chain folds back on itself, joining in opposite directions.
3) Tertiary Structure: This is the final spatial conformation adopted by different regions of the polypeptide chain, each with its corresponding secondary structure, as a result of various interactions between points on the chain.