Biomolecules Class 11 Biology Chapter 9 Notes

Biomolecules Class 11 Biology Chapter 9 Notes

Biomolecules

Biomolecules, also known as biological molecules or macromolecules, are the complex molecules that make up the structures and perform the functions of living organisms. These molecules are essential for various biological processes and play a fundamental role in maintaining life. There are four main classes of biomolecules:

1. Carbohydrates: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio. They serve as a primary source of energy in living organisms and play a crucial role in energy storage, structural support, and cell recognition. Common examples of carbohydrates include glucose, starch, cellulose, and glycogen.
2. Lipids: Lipids are a diverse group of hydrophobic molecules that include fats, oils, phospholipids, and steroids. They are essential for energy storage, insulation, forming cellular membranes, and serving as signaling molecules. Lipids also play a role in protecting vital organs.
3. Proteins: Proteins are complex macromolecules composed of amino acids. They are involved in numerous biological functions, including enzymatic catalysis, structural support, transportation of molecules, immune responses, and cell signaling. The structure and function of proteins are highly diverse, and they are considered the workhorses of the cell.
4. Nucleic Acids: Nucleic acids include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), which are essential for storing and transmitting genetic information. DNA carries the genetic instructions for the development, functioning, and reproduction of all known living organisms, while RNA plays a key role in protein synthesis.

In addition to these four main classes, biomolecules also include other compounds like vitamins and minerals, which are essential for specific biochemical functions in living organisms.

Chemical Analysis of Living Tissues

The chemical analysis of living tissues is essential for identifying the types of organic compounds present in organisms. This analysis helps us understand the molecular composition of living organisms. Here’s a summary of how this analysis is typically conducted:

1. Sample Preparation: A sample of living tissue, such as a leaf or a piece of liver, is collected. The tissue is then ground into a thick slurry. This sample will contain various organic and inorganic compounds.
2. Extraction: The ground tissue is treated with a specific solvent, such as trichloroacetic acid (Cl3CCOOH), to extract the compounds from the tissue. This creates a mixture containing a wide range of compounds.
3. Filtration: The mixture is filtered through cheesecloth or cotton to separate it into two fractions: the filtrate (acid-soluble pool) and the retentate (acid-insoluble fraction).
4. Analysis: Scientists then analyze the acid-soluble pool, which contains a wide variety of organic compounds. Techniques such as chromatography, spectroscopy, and mass spectrometry may be used to identify and characterize these compounds.
5. Elemental Analysis: In addition to organic compounds, the elemental composition of the living tissue is determined. This analysis provides information about the presence of elements like carbon, hydrogen, oxygen, chlorine, and more.
6. Ash Analysis: In some cases, the tissue is fully burnt, and the remaining “ash” is analyzed to identify inorganic elements and compounds present in the sample.

By following these steps, scientists can identify and classify the types of organic compounds found in living organisms. These compounds can include amino acids, lipids, nucleic acids, and more. The specific techniques and methods used for analysis may vary depending on the goals of the study and the compounds of interest.

Primary Metabolites and Secondary Metabolites

1. Primary Metabolites:
   • Definition: Primary metabolites are a class of organic compounds that are essential for the basic growth, development, and normal physiological functions of an organism. They are involved in fundamental processes required for life, such as energy production, cell structure, and essential metabolic pathways.
   • Examples: Primary metabolites include compounds like amino acids, nucleic acids, simple sugars, lipids, vitamins, and various other molecules that are crucial for the day-to-day operations of an organism.
   • Functions: Primary metabolites have well-defined functions and are essential for life processes. For example, amino acids are the building blocks of proteins, while nucleic acids (DNA and RNA) carry genetic information.
2. Secondary Metabolites:
   • Definition: Secondary metabolites are organic compounds found in living organisms, primarily in plants, fungi, and some microorganisms. These compounds are not directly involved in the basic life processes of an organism. Instead, they are often produced as byproducts or play roles in ecological interactions and defense mechanisms.
   • Examples: Secondary metabolites are incredibly diverse and include compounds like alkaloids, flavonoids, essential oils, antibiotics, pigments, and various other specialized molecules. They often contribute to the unique properties of different species, such as the characteristic scents or colors of flowers.
   • Functions: The functions of secondary metabolites can vary widely. Some serve as defensive chemicals, protecting plants from herbivores or pathogens. Others may attract pollinators or deter predators. Additionally, many secondary metabolites have commercial and medicinal value, such as natural medicines derived from plants.

While primary metabolites have well-established roles in an organism’s physiology, the functions of secondary metabolites can be more complex and context-dependent. Some secondary metabolites are still not fully understood, and their roles continue to be a subject of scientific investigation.

Biomacromolecules

Biomacromolecules, also known as macromolecules or macromolecular compounds, are large organic molecules typically found in the acid-insoluble fraction of living organisms. They are characterized by their high molecular weights, usually exceeding 10,000 daltons (Da). These biomacromolecules play essential roles in various biological processes and are responsible for the structural and functional complexity of living organisms. The four main classes of biomacromolecules are proteins, nucleic acids, polysaccharides, and lipids.

1. Proteins:
   • Structure: Proteins are made up of long chains of amino acids linked together by peptide bonds. These chains fold into specific three-dimensional structures.
   • Functions: Proteins have diverse functions, including enzymes that catalyze biochemical reactions, structural support, transport of molecules, and as antibodies in the immune system.
2. Nucleic Acids:
   • Structure: Nucleic acids, such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), consist of chains of nucleotides. These nucleotides contain a sugar, a phosphate group, and a nitrogenous base.
   • Functions: Nucleic acids store and transmit genetic information. DNA carries the genetic code for the synthesis of proteins, while RNA plays a role in protein synthesis.
3. Polysaccharides:
   • Structure: Polysaccharides are long chains of simple sugar (monosaccharide) units linked together by glycosidic bonds.
   • Functions: Polysaccharides are involved in energy storage (e.g., glycogen and starch), structural support (e.g., cellulose in plant cell walls), and cell recognition.
4. Lipids:
   • Structure: Lipids are diverse, with varying structures, but they generally consist of long hydrocarbon chains. They are nonpolar and hydrophobic.
   • Functions: Lipids serve as energy storage molecules (e.g., triglycerides), structural components of cell membranes (phospholipids and cholesterol), and in signaling and insulation.

The acid-soluble pool mainly represents the composition of the cytoplasmic content, which contains small molecules like sugars, amino acids, and organic acids. These small molecules are collectively referred to as micromolecules or simply biomolecules. Water is the most abundant chemical in living organisms, making up a significant portion of their composition.

It’s important to note that while lipids have relatively small molecular weights, they come under the acid-insoluble fraction due to their organization into structures like cell membranes, which are not water-soluble. This fraction includes vesicles derived from disrupted cell membranes.

Proteins

Proteins are essential macromolecules found in living organisms, and they play a wide range of critical roles in various biological processes. They are polymers composed of amino acids, and each protein is a unique sequence of amino acids linked together by peptide bonds.

Key features of proteins include:

1. Polypeptides: Proteins are often referred to as polypeptides because they are made up of long, linear chains of amino acids. The sequence and arrangement of amino acids in a protein are determined by the genetic code.
2. Diverse Amino Acid Composition: There are 20 different types of amino acids commonly found in proteins, and these amino acids differ in their side chains (R groups). This diversity in amino acid composition allows for the vast array of proteins with distinct structures and functions.
3. Essential Amino Acids: Amino acids are classified into two groups: essential and non-essential. Essential amino acids are those that the human body cannot synthesize on its own and must be obtained from the diet. Non-essential amino acids are produced within the body. A balanced diet is necessary to ensure a supply of essential amino acids.

Proteins have numerous functions in living organisms:

1. Enzymes: Many proteins act as enzymes, which are biological catalysts that facilitate chemical reactions. Enzymes are involved in processes such as digestion, energy production, and DNA replication.
2. Transport Proteins: Some proteins serve as carriers or transporters, aiding in the movement of ions, molecules, or other substances across cell membranes or throughout the bloodstream.
3. Antibodies: Proteins like antibodies are part of the immune system’s defense mechanism, helping the body recognize and fight off pathogens and foreign invaders.
4. Hormones: Certain proteins, such as insulin, function as hormones that regulate various physiological processes within the body.
5. Structural Proteins: Proteins like collagen provide structural support in tissues, contributing to the strength and elasticity of skin, tendons, and bones.
6. Storage Proteins: Proteins like ferritin store iron in the body for future use, and ovalbumin serves as a storage protein in eggs.
7. Muscle Contraction: Muscle proteins like actin and myosin are responsible for muscle contraction.
8. Gene Expression: RNA polymerase is a protein responsible for transcribing DNA into RNA during gene expression.

Ribulose bisphosphate carboxylase-oxygenase (RuBisCO) is one of the most abundant proteins on Earth and is vital for photosynthesis, as it is involved in carbon fixation, allowing plants to convert carbon dioxide into organic compounds. Collagen is the most abundant protein in the animal kingdom and provides structural support in tissues such as skin, cartilage, and tendons.

Polysaccharides

Polysaccharides are a class of macromolecules consisting of long chains of sugar (monosaccharide) units linked together. These sugar units serve as the building blocks of polysaccharides. Polysaccharides have various roles in living organisms and are primarily composed of three types: cellulose, starch, and glycogen. Here are some key points about polysaccharides:

1. Composition: Polysaccharides are composed of multiple sugar molecules (monosaccharides) linked together through glycosidic bonds. Each polysaccharide may consist of the same type of monosaccharide or a combination of different monosaccharides.
2. Cellulose: Cellulose is a common polysaccharide found in the cell walls of plants. It is a homopolymer, meaning it consists of repeating glucose units. Cellulose provides structural support to plant cells and is responsible for the rigidity and strength of plant cell walls.
3. Starch: Starch is another important polysaccharide, serving as a storage form of energy in plants. It is also composed of glucose units but is a branched polysaccharide. Starch can be broken down into glucose when needed for energy.
4. Glycogen: Glycogen is the animal equivalent of starch. It is found in animals, particularly in the liver and muscles. Like starch, glycogen is a branched polysaccharide composed of glucose units. It serves as a short-term energy storage molecule in animals.
5. Inulin: Inulin is a polysaccharide composed of fructose units and is found in certain plants, particularly in the roots of some species. Inulin is not digested in the human small intestine and is used as a dietary fiber.
6. Chitin: Chitin is a complex polysaccharide made up of N-acetylglucosamine units and is found in the exoskeletons of arthropods (insects, spiders, crustaceans) and the cell walls of fungi. Chitin provides structural support and protection.
7. Polysaccharide Structures: Polysaccharides can have various structural configurations. Starch forms helical structures, while cellulose has a linear structure without complex helices. The structural differences in polysaccharides determine their properties and functions.
8. Reducing and Non-Reducing Ends: In a polysaccharide chain (e.g., glycogen), the end where the first monosaccharide unit is attached is called the reducing end, and the opposite end is called the non-reducing end.

Nucleic Acids

Nucleic acids are macromolecules found in the acid-insoluble fraction of living tissues, and they are essential for storing, transmitting, and expressing genetic information. These biomacromolecules play a central role in heredity and the functioning of living organisms. Here are some key points about nucleic acids:

1. Nucleic Acid Components: Nucleic acids are composed of repeating units called nucleotides. Each nucleotide consists of three essential components: a heterocyclic compound (nitrogenous base), a monosaccharide (sugar), and a phosphate group.
2. Nitrogenous Bases: There are five nitrogenous bases found in nucleic acids: adenine (A), guanine (G), uracil (U), cytosine (C), and thymine (T). Adenine and guanine are purines, while uracil, cytosine, and thymine are pyrimidines. In DNA, thymine is present, while in RNA, uracil replaces thymine.
3. Sugar Component: The sugar component in nucleic acids can be either ribose or 2′-deoxyribose. If it is ribose, the nucleic acid is called ribonucleic acid (RNA). If it is 2′-deoxyribose, the nucleic acid is called deoxyribonucleic acid (DNA). These sugars are pentoses, which means they have five carbon atoms.
4. Polynucleotides: Nucleic acids are composed of long chains of nucleotides, creating a linear polynucleotide structure. The sugar-phosphate backbone of the polynucleotide chain forms the structural framework, with the nitrogenous bases extending from it. Complementary base pairing, such as A-T (adenine-thymine) and G-C (guanine-cytosine), allows DNA to form double-stranded helical structures.
5. Functions: DNA serves as the primary genetic material in most organisms and carries the genetic instructions for the development, functioning, growth, and reproduction of living organisms. RNA has various roles, including carrying out protein synthesis through processes like transcription and translation.
6. Genetic Code: The sequence of nitrogenous bases in DNA encodes the genetic information, and it is often referred to as the genetic code. This code is transcribed into RNA and ultimately translated into the sequence of amino acids in proteins.
7. Variants: While DNA and RNA are the two primary types of nucleic acids, variations exist. For example, there are small RNA molecules involved in various cellular processes, such as transfer RNA (tRNA) and ribosomal RNA (rRNA).
8. Genetic Diversity: Differences in the sequence of nucleotides in DNA are responsible for genetic diversity among individuals and species. These differences result in variations in physical traits, behaviors, and susceptibility to diseases.

Proteins

The structure of proteins is fundamental to their function in biological systems. Proteins are complex macromolecules composed of amino acid chains, and their structure can be described at four levels:

1. Primary Structure: The primary structure of a protein refers to the linear sequence of amino acids in the polypeptide chain. It specifies the order in which the amino acids are linked together. This sequence is critical because it determines the protein’s unique properties and functions. The two ends of the protein chain are known as the N-terminal (beginning) and C-terminal (end) amino acids.
2. Secondary Structure: In the secondary structure of a protein, the linear polypeptide chain begins to fold or coil due to hydrogen bonding between amino acids. Two common secondary structures are the α-helix and the β-sheet. In an α-helix, the polypeptide chain forms a helical structure, resembling a spiral staircase. In a β-sheet, the chain forms a sheet-like structure. These secondary structures contribute to the protein’s stability and shape.
3. Tertiary Structure: The tertiary structure of a protein describes the three-dimensional arrangement of the entire protein molecule. It results from further folding and twisting of the secondary structure elements. The tertiary structure is essential for the protein’s function because it determines how the protein interacts with other molecules and substrates. This complex three-dimensional structure is often unique to each protein.
4. Quaternary Structure: Some proteins are composed of multiple subunits, each of which has its own unique tertiary structure. The quaternary structure refers to the arrangement and interactions between these subunits within a multi-subunit protein complex. It can involve linear or three-dimensional arrangements, depending on how the subunits come together. For example, adult human hemoglobin consists of four subunits: two α-type subunits and two β-type subunits.

Each level of protein structure is essential for the protein’s proper function, and any alterations can result in a loss of function or even denaturation, which is the disruption of the protein’s structure. Proteins perform a wide range of biological roles, including enzyme catalysis, structural support, transport, signaling, and immune defense, and their structure directly influences these functions.

The intricate folding and interactions between amino acids and protein subunits give rise to the vast diversity of proteins found in living organisms, each with a specific structure tailored to its unique function. Understanding the structure of proteins is crucial for unraveling their roles in biological systems and for developing applications in fields such as medicine and biotechnology.

Enzymes

Enzymes are biological catalysts, and they play a crucial role in speeding up biochemical reactions in living organisms. Here are some key points about enzymes:

1. Enzymes Are Proteins: Most enzymes are proteins, and they are composed of amino acid chains. The primary structure of an enzyme is the sequence of amino acids in this chain. This primary structure is essential for the enzyme’s function.
2. Enzyme Structure: Like other proteins, enzymes have secondary and tertiary structures. The tertiary structure results in the formation of pockets or crevices within the enzyme molecule. One of these pockets is known as the active site. The active site is a specific region of the enzyme where the substrate, the molecule the enzyme acts upon, binds. The unique three-dimensional structure of the active site is crucial for enzyme-substrate interactions.
3. Enzyme-Substrate Interaction: Enzymes function by binding to their specific substrates. The active site of an enzyme is complementary in shape and chemistry to its substrate. This allows the substrate to fit snugly into the active site, forming an enzyme-substrate complex. Enzymes are highly specific, meaning each enzyme catalyzes a particular reaction by binding to a specific substrate.
4. Catalysis: Enzymes speed up chemical reactions by lowering the activation energy required for the reaction to occur. They do this by stabilizing the transition state of the reaction, which enables the reaction to proceed more readily. Importantly, enzymes do not alter the overall free energy change or equilibrium position of a reaction. Instead, they facilitate the attainment of the equilibrium state more rapidly.
5. Enzyme Names: Enzymes are often named based on their substrates and the type of reaction they catalyze. For example, the enzyme “amylase” catalyzes the hydrolysis of starch (amylose and amylopectin) into simpler sugars. Enzymes typically end with the suffix “-ase.”
6. Enzyme Regulation: Enzyme activity can be regulated by various mechanisms, including allosteric regulation, competitive and non-competitive inhibition, and post-translational modifications. These mechanisms allow cells to control when and to what extent particular reactions occur.
7. Optimal Conditions: Enzymes have specific temperature and pH optima at which they function most efficiently. Outside these optimal conditions, the enzyme’s activity may be reduced or even denatured. However, some extremophile enzymes are adapted to function in extreme conditions, such as high temperatures.

Enzymes are essential for the proper functioning of metabolic pathways, and they play a vital role in various biological processes, including digestion, respiration, and DNA replication. They are highly specific, efficient, and essential for life processes. Additionally, researchers have harnessed the power of enzymes for a wide range of applications in biotechnology, medicine, and industry.

Chemical Reactions

1. Physical vs. Chemical Changes: Chemical compounds can undergo two types of changes. Physical changes involve alterations in shape or state without breaking chemical bonds. For example, melting ice into water or water turning into vapor is a physical change.
2. Chemical Reactions: In a chemical reaction, chemical bonds are broken and new bonds are formed, resulting in the transformation of one or more substances into different products. These reactions are at the heart of all biochemical processes.

Rate of Reactions:

1. Rate: The rate of a chemical reaction refers to the speed at which the reaction proceeds, typically measured as the change in the amount of product formed per unit of time.
2. Influence of Temperature: Temperature plays a significant role in determining the rate of chemical reactions. In general, the rate of a chemical reaction approximately doubles for every 10°C increase in temperature. Conversely, a 10°C decrease in temperature reduces the rate by half.
3. Catalysis: Enzymes are remarkable catalysts that accelerate chemical reactions. Catalysts are substances that increase the rate of a reaction without being consumed in the process. Enzyme-catalyzed reactions occur at much higher rates than uncatalyzed reactions.

Enzymes:

1. Definition: Enzymes are biological catalysts, typically composed of proteins, that facilitate specific chemical reactions in living organisms. They are highly selective, meaning each enzyme catalyzes a particular reaction.
2. Enzyme Mechanism: Enzymes work by providing an appropriate environment (the active site) for the reaction to occur. They bind to specific substrates (reactant molecules) at their active sites, forming enzyme-substrate complexes.
3. Rate Enhancement: Enzymes dramatically enhance the rate of reactions. For instance, the enzyme carbonic anhydrase increases the rate of converting carbon dioxide and water into carbonic acid by a factor of about 10 million.
4. Diverse Enzymes: Living organisms have thousands of different enzymes, each responsible for catalyzing a unique chemical or metabolic reaction.
5. Metabolic Pathways: In complex biochemical processes, multiple enzymes may act sequentially to convert a starting compound into multiple end products. This sequence of enzyme-catalyzed reactions is referred to as a metabolic pathway. For example, glucose can be converted into pyruvic acid through a series of reactions catalyzed by different enzymes.

Enzymes are essential for life and are involved in a wide range of metabolic processes, including digestion, respiration, and the synthesis of various molecules within cells. Their remarkable specificity and efficiency make them critical components of living organisms.

High Rates of Chemical Conversions In Enzymes

Enzymes significantly accelerate chemical conversions by lowering the activation energy required for a reaction. Here’s a more detailed explanation of how enzymes achieve this:

1. Active Site: Enzymes are proteins with three-dimensional structures that include a specific region called the “active site.” The active site is a pocket or cleft within the enzyme where the substrate, the reactant molecule, binds.
2. Enzyme-Substrate Complex Formation: For a reaction to occur, the substrate (S) must bind to the active site of the enzyme (E), forming what’s known as the enzyme-substrate complex (ES).
3. Transient Nature of ES Complex: The formation of the ES complex is a transient and reversible process. The substrate diffuses toward the active site and temporarily binds to the enzyme.
4. Transition State Structure: During the formation of the ES complex, the substrate undergoes a change in its molecular structure, reaching a state known as the transition state. This state represents an intermediate structure that the substrate must pass through to convert into the product.
5. Energy Barrier: The transition state structure is energetically unfavorable, and it has higher potential energy compared to both the substrate and the product. The energy difference between the substrate and the transition state is known as the activation energy (Ea). This activation energy represents the energy input required to reach the transition state.
6. Catalytic Role of Enzymes: Enzymes catalyze reactions by stabilizing the transition state structure, making it easier for the substrate to reach this state. Enzymes achieve this by providing an appropriate microenvironment in the active site and facilitating the breaking and formation of chemical bonds.
7. Lowering Activation Energy: The key role of enzymes is to reduce the activation energy required for the reaction to occur. By doing so, enzymes make it energetically favorable for the substrate to convert into the product. This reduction in activation energy makes the reaction occur more rapidly.
8. Exothermic and Endothermic Reactions: Enzymes can facilitate both exothermic reactions (releasing energy) and endothermic reactions (requiring energy input). Whether a reaction is exothermic or endothermic, the activation energy barrier is lowered by the enzyme.

Nature of Enzyme Action

The nature of enzyme action can be described as a series of steps in the catalytic cycle. Here’s a breakdown of how enzymes work:

1. Substrate Binding: The process begins when a substrate (S) binds to the active site of the enzyme (E). The active site is a specific region on the enzyme that can accommodate the substrate molecule. The binding of the substrate to the enzyme forms the enzyme-substrate complex (ES).
2. Induced Fit: The binding of the substrate induces a conformational change in the enzyme. This conformational change results in the enzyme fitting more tightly around the substrate. The induced fit ensures a snug interaction between the substrate and the enzyme’s active site.
3. Chemical Bond Alteration: With the substrate securely bound to the active site, the enzyme’s active site, which provides an appropriate microenvironment, facilitates the breaking of chemical bonds within the substrate. This catalytic activity leads to the formation of the enzyme-product complex (EP).
4. Product Release: Following the chemical reaction, the enzyme releases the products of the reaction (P), which are now separate from the enzyme. The enzyme is then free to participate in another round of catalysis.
5. Enzyme Recycling: After releasing the products, the enzyme returns to its original conformation, allowing it to bind to another molecule of the substrate. The enzyme can go through the catalytic cycle repeatedly, making it highly efficient in catalyzing reactions.

The catalytic cycle of an enzyme action is essential for the efficient conversion of substrates into products. Enzymes enable these reactions to occur more rapidly by lowering the activation energy required for the conversion. The enzyme does not become consumed in the reaction but is available for further reactions, making it a reusable catalyst. This ability to accelerate reactions and maintain their integrity is a fundamental characteristic of enzymes in biological systems.

Factors Affecting Enzyme Activity

Factors affecting enzyme activity are crucial in regulating biochemical reactions. Here’s more detail on some of these factors:

Temperature and pH:

• Enzymes have specific temperature and pH ranges at which they are most active. This optimal temperature and pH are known as the enzyme’s optimum.
• Most enzymes work best at human body temperature (around 37°C) and a neutral pH, but this can vary. For example, digestive enzymes in the stomach work best in an acidic environment.
• Enzymes denature (lose their shape and function) at extreme temperatures and pH levels. High temperatures disrupt the weak chemical bonds that maintain the enzyme’s structure, while extreme pH levels can change the charges on amino acids, affecting the enzyme’s active site.

Concentration of Substrate:

• The rate of an enzymatic reaction generally increases as the concentration of the substrate increases. More substrate molecules mean more opportunities for the enzyme to catalyze the reaction.
• However, there’s a limit to this increase in reaction rate. Once all the enzyme molecules are actively engaged with substrate molecules (saturated), increasing substrate concentration further won’t increase the reaction rate.
• The maximum rate of the reaction, when the enzyme is saturated with substrate, is referred to as Vmax.

Chemical Inhibitors:

• Chemicals that bind to enzymes and inhibit their activity are known as inhibitors. Inhibitors can affect enzyme activity in various ways.
• Competitive inhibitors: These molecules closely resemble the substrate and bind to the active site of the enzyme. This competition reduces the binding of the actual substrate, thus decreasing enzyme activity. An example is malonate, which competes with succinate for the active site of the enzyme succinic dehydrogenase.
• Non-competitive inhibitors: These molecules bind to a location on the enzyme other than the active site (allosteric site), causing a conformational change in the enzyme that reduces its activity. Non-competitive inhibitors can’t be overcome by increasing substrate concentration.
• Uncompetitive inhibitors: These molecules bind to the enzyme-substrate complex and prevent the release of the product. This type of inhibition typically occurs later in the enzymatic reaction.
• Inhibition is an important mechanism for regulating enzyme activity, both in normal metabolic processes and in drug design for medical purposes.

Understanding these factors and their effects on enzyme activity is essential for comprehending the regulation of biochemical pathways and the design of drugs that can target specific enzymes. Enzymes play a central role in numerous biological processes, and their activity must be tightly controlled for an organism to function properly.

Classification and Nomenclature of Enzymes

Enzymes play a vital role in biochemical reactions by catalyzing specific reactions and facilitating the conversion of substrates into products. To organize this diverse group of catalysts, enzymes are classified into different classes and subclasses based on the types of reactions they catalyze. The system used to name and categorize enzymes is known as the Enzyme Commission Number (EC number). Here’s a brief overview of the enzyme classification system:

1. Oxidoreductases/Dehydrogenases (EC 1.x.x.x):
   • These enzymes catalyze oxidation-reduction reactions, transferring electrons between two substrates, S and S’.
   • Example: Alcohol dehydrogenase, which converts alcohol to an aldehyde.
2. Transferases (EC 2.x.x.x):
   • Transferases facilitate the transfer of functional groups (other than hydrogen) from one substrate to another.
   • Example: Transaminase enzymes transfer amino groups between amino acids in amino acid metabolism.
3. Hydrolases (EC 3.x.x.x):
   • Hydrolases are responsible for catalyzing hydrolysis reactions. They cleave various types of chemical bonds, such as ester, ether, peptide, glycosidic, C-C, C-halide, or P-N bonds.
   • Example: Lipase, which hydrolyzes ester bonds in triglycerides during fat digestion.
4. Lyases (EC 4.x.x.x):
   • Lyases catalyze the removal of specific groups from substrates by mechanisms other than hydrolysis, resulting in the formation of double bonds.
   • Example: Decarboxylases, which remove carboxyl groups from amino acids during the Krebs cycle.
5. Isomerases (EC 5.x.x.x):
   • Isomerases are involved in the interconversion of isomers, including optical, geometric, or positional isomers.
   • Example: Triose phosphate isomerase, which catalyzes the conversion between dihydroxyacetone phosphate and glyceraldehyde-3-phosphate in glycolysis.
6. Ligases (EC 6.x.x.x):
   • Ligases are enzymes that catalyze the formation of bonds between two substrates, joining them together.
   • Example: DNA ligase, which joins DNA fragments by creating phosphodiester bonds in DNA replication and repair.

Each enzyme is named with a four-digit EC number based on the class to which it belongs. The number sequence represents the enzyme’s classification hierarchy, ranging from class to subclass and further subclass, with the last digit specifying a particular enzyme within the subclass. This systematic nomenclature allows scientists to categorize and identify enzymes based on their specific catalytic activities and reactions.

For example, the enzyme lactate dehydrogenase, which catalyzes the conversion of lactate to pyruvate, is classified as an oxidoreductase and is assigned the EC number 1.1.1.27. This number denotes that it is in the first class, subclass 1, sub-subclass 1, and specific enzyme number 27 within that sub-subclass.

Co-factors

Enzymes are essential biological catalysts that facilitate and accelerate biochemical reactions. While they are primarily composed of protein chains (polypeptides), many enzymes require the assistance of non-protein components known as cofactors to be catalytically active. Cofactors can be classified into three main categories: prosthetic groups, co-enzymes, and metal ions.

1. Prosthetic Groups:
   • Prosthetic groups are organic compounds that are tightly and permanently bound to the apoenzyme (the protein part of the enzyme) and are an integral part of the enzyme’s active site.
   • They play a direct role in the enzyme’s catalytic activity.
   • Example: In enzymes like peroxidase and catalase, which are involved in the breakdown of hydrogen peroxide, the prosthetic group haem is a crucial part of the active site and participates in the reaction.
2. Co-enzymes:
   • Co-enzymes are organic molecules that temporarily associate with the apoenzyme during the course of catalysis.
   • They often participate in a variety of different enzymatic reactions, serving as co-factors for multiple enzymes.
   • Many co-enzymes are derived from essential dietary vitamins.
   • Examples of co-enzymes include nicotinamide adenine dinucleotide (NAD) and its phosphate derivative NADP, both of which contain the vitamin niacin (nicotinamide).
3. Metal Ions:
   • Some enzymes require metal ions as cofactors for their catalytic activity.
   • Metal ions can coordinate with specific side chains of amino acids at the enzyme’s active site and often interact with substrates as well.
   • These metal ions play a role in maintaining the enzyme’s three-dimensional structure and facilitating chemical reactions.
   • Example: Zinc is a cofactor for the proteolytic enzyme carboxypeptidase.

The presence of these cofactors is essential for the catalytic activity of enzymes. The catalytic activity is lost or significantly reduced when the cofactor is removed from the enzyme, demonstrating their crucial role in enzymatic reactions. Coenzymes are especially interesting because many of them are derived from essential vitamins, highlighting the vital role of nutrition in supporting enzymatic functions.

The interaction between the apoenzyme and its cofactor(s) allows enzymes to perform a wide range of chemical transformations efficiently, and this diversity of cofactors contributes to the versatility of enzymes in biological systems.