MODULE 1: Basics of Biomolecules
Molecules of Life (MD-CHM-2.1)
B.Sc. Zoology – RTU Hojai University
Comprehensive Study Material
Introduction to Biomolecules
Living organisms are made up of a large number of chemical substances that perform various structural, physiological, and biochemical functions necessary for life. These chemical substances are known as biomolecules or molecules of life. Biomolecules are organic compounds produced by living organisms and are essential for growth, metabolism, reproduction, energy production, and maintenance of cellular activities. They form the structural and functional basis of all living cells and tissues.
Biomolecules are mainly composed of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Carbon is the most important element because it has the unique ability to form stable covalent bonds with other atoms, resulting in the formation of complex molecular structures. Due to the presence of carbon, biomolecules are generally called organic molecules.
The study of biomolecules is important because life processes such as respiration, digestion, circulation, excretion, growth, reproduction, and heredity depend entirely on the structure and function of these molecules. Biomolecules interact with each other in a highly organized manner to maintain life activities in living organisms.
The major classes of biomolecules include carbohydrates, proteins, lipids or fats, nucleic acids, vitamins, enzymes, and hormones. Among these, proteins, vitamins, nucleic acids, and fats are particularly important in understanding the chemistry of life.
Molecules of Life
The term “molecules of life” refers to those chemical compounds that are indispensable for the existence and functioning of living organisms. Every living cell contains numerous biomolecules that work together to maintain cellular organization and metabolic activities.
Biomolecules may be small molecules such as amino acids, fatty acids, vitamins, and nucleotides, or large macromolecules such as proteins, nucleic acids, and polysaccharides. Small biomolecules often combine to form larger complex molecules. For example, amino acids combine to form proteins, while nucleotides combine to form nucleic acids like DNA and RNA.
Biomolecules are synthesized within living cells through various biochemical reactions. These reactions are controlled by enzymes and regulated according to the needs of the organism. Biomolecules are continuously broken down and synthesized in living organisms, a process collectively known as metabolism.
Metabolism consists of two types of reactions: anabolism and catabolism. Anabolism refers to the synthesis of complex molecules from simpler substances, while catabolism refers to the breakdown of complex molecules to release energy.
The proper functioning of living organisms depends on the balance and interaction of biomolecules. Any deficiency or abnormality in biomolecules may lead to diseases and physiological disorders.
Biological Importance of Biomolecules
Biomolecules are essential for maintaining life because they perform numerous structural, functional, regulatory, and protective roles in living organisms.
Structural Importance
Many biomolecules form the structural framework of cells and tissues. Proteins, lipids, and nucleic acids are major structural components of living cells.
Proteins form important cellular structures such as cell membranes, muscles, connective tissues, hair, nails, skin, and enzymes. Lipids form the basic structure of biological membranes. Nucleic acids are present in the nucleus and cytoplasm and store genetic information.
Without biomolecules, cells would not maintain their shape, integrity, or organization.
Source of Energy
Certain biomolecules serve as major sources of energy. Carbohydrates and fats are especially important for energy production.
Glucose obtained from carbohydrates undergoes oxidation during cellular respiration to produce energy in the form of ATP (adenosine triphosphate). Fats serve as concentrated energy reserves because they contain more energy per gram than carbohydrates.
Proteins may also be used as an energy source during starvation or deficiency of carbohydrates and fats.
Energy released from biomolecules is necessary for growth, movement, muscle contraction, nerve conduction, biosynthesis, and maintenance of body temperature.
Regulation of Metabolism
Biomolecules regulate various metabolic and physiological activities in living organisms. Enzymes, hormones, and vitamins play important regulatory roles.
Enzymes are protein molecules that catalyze biochemical reactions inside the body. Without enzymes, metabolic reactions would occur too slowly to support life.
Hormones regulate growth, reproduction, digestion, blood sugar levels, and other physiological processes. Vitamins act as coenzymes or cofactors in many metabolic reactions.
Thus, biomolecules control and coordinate body functions.
Storage and Transmission of Genetic Information
Nucleic acids such as DNA and RNA are responsible for storage, replication, and transmission of genetic information from one generation to the next.
DNA contains genes that determine hereditary characteristics and control protein synthesis. RNA helps in the expression of genetic information and protein formation.
The continuity of life and inheritance of traits depend entirely on nucleic acids.
Protection and Defense
Certain biomolecules protect the body against harmful conditions and pathogens. Antibodies, which are proteins, help defend the body against infections.
Lipids provide insulation and protect internal organs from mechanical injury. Pigments and antioxidants protect cells from oxidative damage.
Blood clotting proteins prevent excessive blood loss during injury.
Growth and Repair
Biomolecules are essential for growth, tissue repair, and maintenance of body structures. Proteins are particularly important for growth because they are required for synthesis of new cells and tissues.
Children, pregnant women, and recovering patients require adequate biomolecules for proper growth and healing.
Transport Functions
Some biomolecules help transport substances within the body. Hemoglobin, a protein present in red blood cells, transports oxygen from lungs to tissues.
Lipoproteins transport lipids in blood circulation. Membrane proteins regulate movement of substances across cell membranes.
Introduction to Proteins
Proteins are complex nitrogen-containing biomolecules composed of amino acids linked together by peptide bonds. They are among the most important biomolecules because they perform numerous structural, catalytic, transport, regulatory, and protective functions.
The word protein is derived from the Greek word “proteios,” meaning primary or of first importance. Proteins are often called the building blocks of life because they form the major structural and functional components of cells and tissues.
Proteins are made up of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur and phosphorus. The basic structural units of proteins are amino acids. There are about twenty common amino acids found in proteins.
Amino acids join together through peptide bonds to form long chains called polypeptides. One or more polypeptide chains fold into specific three-dimensional structures to form proteins.
Proteins may be classified into simple proteins, conjugated proteins, and derived proteins based on composition and structure.
Functions of Proteins
Proteins perform a wide variety of functions in living organisms.
Structural Functions
Proteins form muscles, skin, hair, nails, connective tissues, and cell membranes.
Enzymatic Functions
Most enzymes are proteins that accelerate biochemical reactions.
Transport Functions
Proteins such as hemoglobin transport oxygen and nutrients.
Hormonal Functions
Some hormones such as insulin are proteins.
Defense Functions
Antibodies protect the body against infections.
Contractile Functions
Proteins such as actin and myosin help in muscle contraction.
Storage Functions
Certain proteins store nutrients and minerals.
Deficiency of proteins may lead to diseases such as kwashiorkor and marasmus characterized by stunted growth, muscle wasting, and weakness.
Introduction to Vitamins
Vitamins are organic compounds required in very small amounts for normal growth, metabolism, and maintenance of health. They are essential micronutrients because the body cannot synthesize sufficient quantities of most vitamins.
Vitamins do not provide energy directly, but they are necessary for proper functioning of enzymes and metabolic pathways. Many vitamins act as coenzymes that assist enzymes during biochemical reactions.
Vitamins are classified into two major groups:
Fat-Soluble Vitamins
These include vitamins A, D, E, and K. They dissolve in fats and are stored in the body.
Water-Soluble Vitamins
These include vitamin C and the B-complex vitamins. They dissolve in water and are not stored extensively in the body.
Each vitamin has specific biological functions and deficiency symptoms.
Functions and Importance of Vitamins
Vitamin A is important for vision, skin health, and immunity. Deficiency causes night blindness.
Vitamin D helps in calcium absorption and bone formation. Deficiency causes rickets in children and osteomalacia in adults.
Vitamin E acts as an antioxidant and protects cells from damage.
Vitamin K is essential for blood clotting.
Vitamin C is important for collagen formation, wound healing, and immunity. Deficiency causes scurvy.
Vitamin B complex is necessary for energy metabolism and nervous system function.
Vitamins are obtained mainly from fruits, vegetables, milk, eggs, fish, meat, cereals, and sunlight in the case of vitamin D.
Introduction to Nucleic Acids
Nucleic acids are complex biomolecules responsible for storage, transmission, and expression of genetic information. They are found in all living cells and viruses.
The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Nucleic acids are polymers made up of smaller units called nucleotides. Each nucleotide consists of three components:
Nitrogenous base
Pentose sugar
Phosphate group
DNA contains deoxyribose sugar and the bases adenine, guanine, cytosine, and thymine. RNA contains ribose sugar and uracil instead of thymine.
DNA is mainly located in the nucleus and serves as the hereditary material. RNA is involved in protein synthesis.
Functions of Nucleic Acids
DNA stores genetic information and controls hereditary characteristics. It directs the synthesis of proteins and regulates cellular activities.
RNA helps in the transfer and translation of genetic information during protein synthesis. The three major types of RNA are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
Nucleic acids are essential for cell division, growth, reproduction, mutation, and evolution.
Introduction to Fats and Lipids
Fats and lipids are hydrophobic biomolecules composed mainly of carbon, hydrogen, and oxygen. They are insoluble in water but soluble in organic solvents such as ether and chloroform.
Lipids include fats, oils, waxes, phospholipids, steroids, and cholesterol. Fats are usually solid at room temperature, whereas oils are liquid.
Fats are formed by the combination of glycerol and fatty acids through ester bonds.
Functions of Fats
Fats serve as concentrated energy reserves in living organisms. They provide more energy than carbohydrates and proteins.
Lipids form important components of cell membranes. Phospholipids and cholesterol maintain membrane structure and fluidity.
Fats protect internal organs from mechanical injury and provide insulation against heat loss.
Certain vitamins such as vitamins A, D, E, and K require fats for absorption.
Lipids also act as precursors for hormones and signaling molecules.
Saturated and Unsaturated Fats
Fatty acids may be saturated or unsaturated.
Saturated fats contain only single bonds between carbon atoms and are generally solid at room temperature. Excess intake may increase cholesterol levels.
Unsaturated fats contain one or more double bonds and are generally liquid at room temperature. They are considered healthier because they help maintain normal cholesterol levels.
Relationship Between Biomolecules
All biomolecules are interconnected and work together to maintain life processes. Proteins, lipids, nucleic acids, vitamins, and carbohydrates interact continuously during metabolism.
For example, DNA controls protein synthesis, enzymes regulate lipid metabolism, and vitamins assist enzymes during biochemical reactions. Proper nutrition is therefore essential to maintain balanced biomolecule levels in the body.
Importance of Biomolecules in Human Health
Balanced intake of biomolecules is essential for maintaining health and preventing diseases. Deficiency or excess of biomolecules may lead to serious health problems.
Protein deficiency causes growth retardation and muscle wasting. Vitamin deficiency leads to disorders such as scurvy, rickets, and anemia. Abnormal lipid metabolism may cause obesity and cardiovascular diseases. Genetic disorders may result from abnormalities in nucleic acids.
Thus, understanding biomolecules is important in medicine, nutrition, biotechnology, genetics, and physiology.
Conclusion
Biomolecules are the fundamental chemical substances responsible for the structure, function, and continuity of life. They include proteins, vitamins, nucleic acids, fats, carbohydrates, and other organic compounds present in living organisms. Biomolecules provide energy, regulate metabolism, store genetic information, support growth and repair, and maintain cellular organization. Proteins act as structural and functional molecules, vitamins regulate metabolic reactions, nucleic acids control heredity and protein synthesis, while fats serve as energy reserves and membrane components. The interaction of these biomolecules sustains all life processes. Therefore, biomolecules are rightly called the molecules of life and form the foundation of biological and biochemical sciences.
MODULE 2: Proteins and Amino Acids
Molecules of Life (MD-CHM-2.1)
B.Sc. Zoology – RTU Hojai University
Comprehensive Study Material
Introduction to Proteins and Amino Acids
Proteins are among the most important biomolecules found in living organisms and are often called the “building blocks of life.” They are essential for the structure, function, growth, repair, and regulation of the body. Every living cell contains proteins, and almost all biological activities depend directly or indirectly on proteins. Proteins are required for muscle formation, enzyme action, hormone production, immune defense, transport of substances, and maintenance of body tissues.
Proteins are large, complex organic molecules composed of smaller units called amino acids. Amino acids are linked together by peptide bonds to form long chains known as polypeptides. One or more polypeptide chains fold into specific three-dimensional structures to form functional proteins.
Proteins are made up mainly of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur and phosphorus. Nitrogen is an important component that distinguishes proteins from carbohydrates and fats.
The study of proteins and amino acids is important because they participate in almost every physiological and biochemical process occurring in living organisms.
Sources of Proteins
Proteins are obtained from both plant and animal sources. A balanced diet containing sufficient proteins is essential for growth, tissue repair, enzyme production, and maintenance of health.
Animal Sources of Proteins
Animal proteins are generally considered high-quality proteins because they contain all essential amino acids in proper proportions. These proteins have high biological value and are easily digested by the human body.
Major animal sources of proteins include:
Meat
Fish
Eggs
Milk
Cheese
Curd
Poultry products
Egg protein is considered one of the best quality proteins because it contains all essential amino acids in balanced amounts.
Milk proteins such as casein and lactalbumin are important for growth and development, especially in children.
Fish and meat proteins are rich in essential amino acids and are important body-building foods.
Plant Sources of Proteins
Plant proteins are obtained from cereals, pulses, legumes, nuts, seeds, and vegetables. Although many plant proteins are deficient in one or more essential amino acids, they are still important dietary sources of proteins.
Major plant sources include:
Pulses
Soybean
Lentils
Peas
Beans
Groundnuts
Rice
Wheat
Soybean is considered one of the richest plant protein sources.
Combining different plant foods such as cereals and pulses improves protein quality because deficiencies of one amino acid may be compensated by another food source.
Composition of Proteins
Proteins are complex nitrogenous organic compounds composed of amino acids. The major elements present in proteins are:
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Some proteins also contain:
Sulfur (S)
Phosphorus (P)
Iron
Copper
Zinc
The basic structural units of proteins are amino acids. Amino acids are linked together through peptide bonds formed between the amino group of one amino acid and the carboxyl group of another amino acid.
The sequence and arrangement of amino acids determine the structure and function of proteins.
Proteins differ from one another based on:
Number of amino acids
Type of amino acids
Sequence of amino acids
Three-dimensional arrangement
Even a slight change in amino acid sequence may alter protein function significantly.
Biological Value of Proteins
Biological value refers to the efficiency with which a dietary protein can be utilized by the body for growth, repair, and maintenance. It indicates the quality of protein based on the proportion of absorbed protein retained in the body.
Proteins containing all essential amino acids in proper proportions have high biological value.
Animal proteins generally have higher biological value than plant proteins because they contain balanced essential amino acids.
Egg protein has one of the highest biological values and is often used as a standard for comparison.
Proteins with low biological value may lack one or more essential amino acids and therefore cannot fully support growth and tissue maintenance.
Biological value depends on:
Amino acid composition
Digestibility
Absorption efficiency
Balance of essential amino acids
High biological value proteins are especially important during childhood, pregnancy, growth, and recovery from illness.
Amino Acids
Amino acids are the basic building blocks or monomers of proteins. They are organic compounds containing both an amino group (-NH₂) and a carboxyl group (-COOH).
Every amino acid contains:
Amino group
Carboxyl group
Hydrogen atom
Variable side chain called R-group
The general structure of amino acids may be represented as:
H_2N-CH(R)-COOH
The R-group differs among amino acids and determines their chemical properties and functions.
There are about twenty common amino acids involved in protein formation in living organisms.
Amino acids are amphoteric in nature, meaning they can act as both acids and bases.
Structure of Amino Acids
The central carbon atom in an amino acid is called the alpha carbon. It is attached to:
Amino group (-NH₂)
Carboxyl group (-COOH)
Hydrogen atom
Side chain (R-group)
The amino group gives basic properties, while the carboxyl group gives acidic properties.
The side chain may be:
Simple
Branched
Aromatic
Acidic
Basic
Sulfur-containing
The diversity of side chains leads to differences in protein structure and function.
Classification of Amino Acids
Amino acids may be classified in different ways.
Based on Nutritional Requirement
Essential Amino Acids
Essential amino acids are those amino acids that cannot be synthesized by the human body in sufficient quantities and must be obtained through food.
Important essential amino acids include:
Lysine
Methionine
Valine
Leucine
Isoleucine
Phenylalanine
Threonine
Tryptophan
Deficiency of essential amino acids affects growth, tissue repair, and protein synthesis.
Children require higher amounts of essential amino acids for proper development.
Non-Essential Amino Acids
Non-essential amino acids are those that can be synthesized by the body and therefore are not essential in the diet under normal conditions.
Examples include:
Glycine
Alanine
Serine
Aspartic acid
Glutamic acid
Although the body can synthesize them, they still play important physiological functions.
Based on Chemical Nature
Neutral Amino Acids
These contain equal numbers of amino and carboxyl groups.
Acidic Amino Acids
These contain additional carboxyl groups.
Basic Amino Acids
These contain additional amino groups.
Aromatic Amino Acids
These contain aromatic rings.
Sulfur-Containing Amino Acids
These contain sulfur atoms.
Peptides and Polypeptides
When two amino acids combine through a peptide bond, they form a dipeptide. The peptide bond is formed by removal of a water molecule during condensation reaction.
The peptide bond formation may be represented as:
Amino\ Acid_1 + Amino\ Acid_2 \rightarrow Dipeptide + H_2O
Three amino acids form a tripeptide, while many amino acids linked together form a polypeptide.
Proteins are composed of one or more polypeptide chains folded into specific shapes.
Peptide bonds are strong covalent bonds that stabilize protein structure.
Difference Between Amino Acids and Proteins
| Amino Acids | Proteins |
|---|---|
| Simple organic molecules | Complex macromolecules |
| Basic units of proteins | Made of amino acids |
| Small molecular size | Large molecular size |
| Contain amino and carboxyl groups | Contain long polypeptide chains |
| About 20 common types | Thousands of different proteins |
| Example: Glycine | Example: Hemoglobin |
Thus, amino acids are the building blocks, whereas proteins are the final complex products formed from amino acids.
Protein Structure
Proteins possess highly organized structures necessary for proper biological function. Protein structure is divided into four levels:
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
Primary Structure of Proteins
The primary structure refers to the linear sequence of amino acids in a polypeptide chain.
The amino acids are connected by peptide bonds in a specific order.
The sequence of amino acids is genetically determined by DNA.
Even a single change in amino acid sequence may alter protein function. For example, sickle cell anemia results from substitution of one amino acid in hemoglobin.
The primary structure determines higher levels of protein organization.
Secondary Structure of Proteins
The secondary structure refers to local folding of the polypeptide chain due to hydrogen bonding between amino acids.
The two main types are:
Alpha helix
Beta pleated sheet
The alpha helix is a spiral structure stabilized by hydrogen bonds.
The beta pleated sheet consists of folded polypeptide strands arranged side by side.
Secondary structure provides stability and flexibility to proteins.
Examples:
Keratin in hair shows alpha helix structure.
Silk fibroin contains beta pleated sheets.
Tertiary Structure of Proteins
The tertiary structure refers to the three-dimensional folding of a polypeptide chain.
This structure is formed due to interactions between side chains of amino acids, including:
Hydrogen bonds
Ionic bonds
Hydrophobic interactions
Disulfide bonds
The tertiary structure determines the functional shape of proteins.
Globular proteins such as enzymes and hemoglobin possess tertiary structure.
Loss of tertiary structure often results in loss of biological activity.
Quaternary Structure of Proteins
The quaternary structure refers to the arrangement of two or more polypeptide chains into a functional protein.
Each polypeptide chain is called a subunit.
The subunits are held together by weak interactions such as hydrogen bonds and ionic interactions.
Hemoglobin is an example of quaternary structure because it consists of four polypeptide chains.
Quaternary structure allows complex proteins to perform specialized functions.
Protein Reactions
Proteins undergo various chemical and physical reactions that affect their structure and function.
Important protein reactions include:
Denaturation
Coagulation
Denaturation of Proteins
Denaturation refers to the disruption or unfolding of the natural three-dimensional structure of proteins without breaking peptide bonds.
During denaturation, secondary, tertiary, and quaternary structures are destroyed, resulting in loss of biological activity.
The process may be caused by:
Heat
Acids
Alkalis
Radiation
Organic solvents
Heavy metals
For example, boiling of egg white causes denaturation of albumin protein.
Denatured proteins often lose solubility and functional properties.
Enzymes become inactive after denaturation because their active sites are destroyed.
Coagulation of Proteins
Coagulation refers to precipitation or solidification of denatured proteins.
When proteins are denatured, they may aggregate and form insoluble masses called coagulum.
Example:
Formation of curd from milk
Clotting of blood
Cooking of egg white
Coagulation is usually irreversible.
Factors Affecting Proteins
Several physical and chemical factors influence protein structure and activity.
Temperature
High temperature may cause denaturation and coagulation of proteins. Moderate temperature is necessary for normal enzyme activity.
pH
Extreme acidic or alkaline conditions alter ionic charges and hydrogen bonds, affecting protein structure.
Each protein has an optimum pH for proper function.
Salts and Chemicals
Heavy metals and strong chemicals may precipitate or denature proteins.
Radiation
Ultraviolet rays and radiation may damage proteins and alter their structure.
Mechanical Agitation
Excessive shaking or stirring may denature certain proteins.
Biological Importance of Proteins
Proteins are essential for:
Growth and tissue repair
Enzyme formation
Hormone production
Immune defense
Oxygen transport
Muscle contraction
Cell signaling
Deficiency of proteins leads to malnutrition diseases such as kwashiorkor and marasmus.
Importance of Amino Acids in Metabolism
Amino acids participate in:
Protein synthesis
Energy production
Neurotransmitter synthesis
Hormone formation
Growth and repair
Certain amino acids are precursors of biologically important compounds such as hemoglobin, hormones, and nucleotides.
Conclusion
Proteins and amino acids are fundamental biomolecules essential for life. Amino acids are the basic structural units of proteins and contain amino and carboxyl groups. Essential amino acids must be obtained through diet, while non-essential amino acids can be synthesized by the body. Proteins are complex macromolecules formed by peptide-linked amino acids and possess primary, secondary, tertiary, and quaternary structures. Protein structure determines biological function. Proteins perform numerous roles including structural support, enzymatic catalysis, transport, immunity, growth, and regulation of metabolism. Important protein reactions include denaturation and coagulation, both influenced by factors such as temperature, pH, and chemicals. Understanding proteins and amino acids is therefore essential for studying biochemistry, physiology, nutrition, genetics, and molecular biology.