Biomolecules

Biomolecules are very large molecules of many atoms covalently bonded together. All biomolecules contain carbon ( C ). Biomolecules are substances which are present exclusively in the living organisms. These include carbohydrates, proteins, fats and nucleic acid.

 Each biomolecule is essential for body functions and manufacture within the body. They can vary in nature, type, and structure where some may be straight chains, some may be cyclic rings or both. Also, they can vary in physical properties such as water solubility and melting points.

Characteristics of Biomolecules:
• most of them are organic compounds
• they have specific shapes and dimensions
• functional group determines their chemical properties
• many of them are asymmetric
• macromolecules are large molecules and are constructed from small building block molecules
• building block molecules have simple structure

4 Major Types of Biomolecules
A. Carbohydrates
Carbohydrates are very important sources of energy for any physical body function. Carbohydrates are essential macromolecules that are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.

Classification of Carbohydrates
1. Monosaccharides
These are simple sugars made up of three to seven carbons They can exist as a linear chain or as ring-shaped molecules. Glucose ( C6H12O6 ) is a common monosaccharide. Glucose ( also known as dextrose ) and the final product of photosynthesis ), galactose ( found in milk sugar ), and fructose ( fruit sugar ) are monosaccharide isomers.

2. Disaccharides
Sugars formed when two monosaccharides undergo a dehydration reaction (a condensation reaction). They are held together by a covalent bond. Sucrose ( table sugar ) is the most common disaccharide, which is composed of the monomers glucose and fructose. Other disaccharides include lactose ( milk sugar ) and maltose ( malt sugar )

3. Polysaccharide

Also known as glycose, it is a long chain of monosaccharides linked by glycosidic bonds. The chain may be branched or unbranched and can contain many types of monosaccharides. Examples of polysaccharides are glycogen ( stored sugar in animals ), cellulose, and starch.

B. Lipids
Lipids are a group of water-insoluble compounds which include fats, glycerol, phospholipids, steroids, oils etc. Types of lipids vary according to their constituents . Fatty acids are simple lipids made up of carboxyl group and a variable group, R . Fats may be saturated ( having single bonds ) or unsaturated ( having double bonds ) and can be unhealthy but essential to plants and animals for important functions. Fats provide energy, insulation, and storage of fatty acids for many organisms.

Classification of Lipids
1. Triglyceride - a glycerol combined with fatty acids. It includes fats and oil. Triglycerides are abundant and constitute about 98 percent of all dietary lipids. The rest consists of cholesterol, its esters and phospholipids. Unlike carbohydrates, which can be stored only for a short time in the body, triglycerides are stored in the body in large amounts as body fat, which can last for years.

2. Phospholipids - lipids consisting of phosphorus group along with the organic chain. Phospholipids are major components of the plasma membrane, the outermost layer of animal cells. Phospholipids contain fatty acids, glycerol, nitrogen bases, phosphoric acid, and other substituents. They are most abundant in cell membranes and serve as structural components. They are not stored in large quantities. As their name implies, phospholipids contain phosphorus in the form of phosphoric acid groups. Their molecular structure is polar, consisting of one hydrophilic head group and two hydrophobic tails.

3. Steroids Steroids play roles in reproduction, absorption, metabolism regulation, and brain activity. Steroids are lipids because they are hydrophobic and insoluble in water, but they do not resemble lipids since they have a structure composed of four fused rings. Cholesterol is the most important steroid and is the precursor to vitamin D, testosterone, estrogen, progesterone, aldosterone, cortisol, and bile salts. Cholesterol is a component of the phospholipid bilayer and plays a role in the structure and function of membranes. Steroids are found in the brain and alter electrical activity in the brain.Because they can tone down receptors that communicate messages from neurotransmitters, steroids are often used in anesthetic medicines.

C. Protein
Proteins make up the majority of biomolecules present in a cell. Proteins are responsible for many enzymatic functions in the cell and play an important structural role. Proteins are composed of subunits called amino acids ( the building block of protein ). Amino acids are composed of a carboxyl group and an amino group bound to a central carbon atom. A hydrogen atom occupies the third bonding site on the carbon and a variable “R” group occupies the fourth. This R group gives the amino acid special properties that are responsible for making proteins functional. Long chains of amino acids, formed by peptide bonds between each amino acid, form a polypeptide. Proteins help in tissue and cell formation.

Structure of Amino Acid

D. Nucleic Acids
Nucleic acids are the genetic materials present in an organism which includes DNA and RNA. Nucleic acids are the combination materials of nitrogenous bases, sugar molecules and phosphate group linked by different bonds in a series of steps. Our body consists of heterocyclic compounds like pyrimidines and purines. These are nitrogenous compounds like adenine, guanine, cytosine, thymine, and uracil. When these bases bond with sugar chains, nucleosides are formed. Nucleosides in turn bond with a phosphate group to give nucleotides like DNA and RNA. DNA carries the hereditary information and RNA helps in protein formation for the body.
Nucleic acid enzymes catalyze biochemical reactions in both catabolism and anabolism of macromolecules. Catabolism is the breakdown of biomolecules in living organisms. Anabolism is the synthesis of complex biological macromolecules.

DNA Structure
Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code.
Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If the double helix structure is as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine. DNA molecules are so long that they can't fit into cells without the right packaging. To fit inside cells, DNA is coiled tightly to form structures we call chromosomes. Each chromosome contains a single DNA molecule. Humans have 3 pairs of chromosomes, which are found inside the cell's nucleus.

DNA Sequencing
DNA sequencing is technology that allows researchers to determine the order of bases in a DNA sequence. The technology can be used to determine the order of bases in genes, chromosomes, or an entire genome.

DNA Replication
DNA is replicated (duplicated) before a cell divides. Because the two strands of a DNA molecule have complementary base pairs, the nucleotide sequence of each strand automatically supplies the information needed to produce its partner. If the two strands of a DNA molecule are separated, each can be used as a pattern or template to produce a complementary strand. Each template and its new complement together then form a new DNA double helix, identical to the original.

Before replication can occur, the length of the DNA double helix about to be copied must be unwound. In addition, the two strands must be separated, by breaking the weak hydrogen bonds that link the paired bases. Once the DNA strands have been unwound, they must be held apart to expose the bases so that new nucleotide partners can hydrogen-bond to them.

The enzyme DNA polymerase then moves along the exposed DNA strand , joining newly arrived nucleotides into a new DNA strand that is complementary to the template.