BIOLOGICAL MOLECULES

 BIOLOGICAL MOLECULES

BIOCHEMISTRY:
The branch of biology which explains the biochemical basis of life is called biochemistry.

Importance Of Biochemistry:

• It provides information about all the processes carried out in the living organism.
• It helps us to understand abnormal mechanisms which lead to disease and development of medicines and equipment for the treatment of diseases.
• It also provides information on cell differentiation.
• It also explains about growth of cells.
• It has enabled us to understand the mechanism of memory.

CHEMICAL COMPOSITION OF CELL:
All living organisms are composed of cells and living cells contain a living material called protoplasm which chemically contains 70 to 90% of water. Besides water, organic molecules and biochemicals are the main constituent of protoplasm.

BIOCHEMICAL’S:
The compounds produced by living organisms are called biochemicals. Only six elements—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—form 98% of the biochemical and body weight of organisms.

Types Of Biochemical’s:

• Proteins
• Carbohydrates
• Lipids
• Nucleic acids
• Conjugated molecules

WATER:
Water is the most abundant component of organisms. Its amount in living cells varies from 70% to 90%. Water provides the medium in which all biochemical reactions take place and has played a major role in the evolution of biological systems. Water is a polar molecule. The oxygen part of the molecule has a net negative charge, and the hydrogen part has a net positive charge. Thus the molecule as a whole shows polarity.

Biologically Important Properties Of Water:
Some biologically important properties of water are given below:

• Behave As Best Solvent:
  Water properties as a solvent depend on the fact that it is a polar molecule. Water effectively weakens the attraction between ions of opposite charge. Water is therefore a good solvent, ionic solids, and polar molecules readily dissolving in it. It also acts as a solvent to many non-polar substances. This is of great biological importance because all the chemical reactions that take place in cells do so in aqueous solutions.

• Slow To Absorb And Release Heat (High Specific Heat Capacity):
  Water has a very high heat capacity. This means that water is good at maintaining its temperature. This thermal stability makes it the most suitable medium for cells.

• High Heat Of Vaporization And Low Freezing Point:
  It is also an important thermal property of water. Water requires a higher amount of heat energy to change into vapors and also requires to lose a lot of heat to freeze. Thus in the presence of water, protoplasm is not at the risk of boiling or freezing except in drastic conditions.

• An Amphoteric Molecule:
  Water molecules are amphoteric because they act both as an acid and a base. Therefore, it is a perfect medium for the biochemical reactions occurring in cells. It acts as a buffer and helps to prevent changes in the pH of cells, which reduces the chance of any interference in the metabolism of the cell.

• Cohesive Force In Water Molecules:
  Due to cohesive forces, water molecules do not break apart, which helps it flow freely. The strong cohesion forces that exist between water molecules play an important part in the movement of water up the capillary-like vessels and tracheids in the stems of plants.

• Organic Molecules:
  The modern definition of organic molecules is modified as the molecules containing carbon as the basic element bonded covalently with a hydrogen atom.

Synthesis Of Large Molecules By Condensation:
Large molecules or macromolecules are huge and highly organized molecules that form the structure and carry out the activities of cells. Macromolecules are constructed from monomers by a process called condensation. This type of condensation is called dehydration synthesis because two monomers join together when water is removed and a bond is made.

Breaking Of Large Molecules By Hydrolysis:
A process during which polymers are broken down into their subunits (monomers) by the addition of H₂O is called hydrolysis. During this process, a water molecule breaks into H⁺ and OH⁻ ions. -OH group attaches to one monomer, and H attaches to the other.

Carbon: Organic chemistry is the chemistry of carbon of the living world. Carbon very widely in their properties and adaptations. Carbon is a tetravalent element. It forms four covalent bonds with other atoms.

Biological Molecules:

Proteins:

Introduction: Proteins play a vital role in the formation of structure in organisms. The dry weight of the cell contains about 50% of proteins. The name protein was suggested by Berzelius in 1838 and in 1883 G.J. Murdler recognized the importance of protein.

Definition: Proteins can be defined as the polymers of amino acids, where specific amino acids link together in a definite manner to perform a particular function of protein.

Structure Composition Of Protein: Proteins are complex organic compounds having C, H, O, and N as elements but sometimes they contain P and S also.

Synthesis Of Protein Molecule: Amino acid as a building block of protein. Proteins are macromolecules or polymers of amino acid monomers. These amino acids are linked together by a specialized bond or linkage called peptide linkage.

During protein synthesis through condensation, each amino acid becomes joined to other amino acids forming a long continuous unbranched polymer called polypeptide. The sequence of amino acids in the peptide chain is specific for each protein.

Structure Of Protein: These are four basic structural levels of proteins.

• Primary Structure: Polypeptide chain containing a linear sequence of amino acids e.g., insulin.
• Secondary Structure: Polypeptide chains twisted or spirally coiled e.g., keratin.
• Tertiary Structure: The arrangement of secondary structure into the three-dimensional (fold or super fold) structure having peptide, hydrogen, ionic, and disulphide bonds e.g., lysozyme.
• Quaternary Structure: It is the arrangement formed by the union of two or more polypeptide chains e.g., hemoglobin.

Functions Of Protein:

• Proteins are a rich source of energy.
• Proteins, along with lipids, are used in the formation of plasma membranes and other membranes of the cell.
• Muscles are made up of two contractile proteins named Actin and Myosin.
• Contraction and relaxation of these muscle proteins are responsible for locomotion.
• The shape of the protein molecule is directly related to its function. In general, proteins fall into two groups.

Globular And Fibrous:

• Keratin is a fibrous protein. It is used in the formation of hair, nails, and is also found in the skin.
• Hemoglobin is the protein present in red blood cells and is responsible for the transport and supply of oxygen to body cells.
• All enzymes present in the body cells of animals and plants are proteins. They control all types of biochemical reactions occurring within cells.
• Proteins are stored food substances in plants. Stored food in seeds is used for the germination and development of seeds into young plants.

Carbohydrates: Carbohydrates are organic compounds present in all living organisms. The group contains carbon, oxygen, and hydrogen. Carbohydrates are called hydrated carbons because the hydrogen and oxygen are mostly found in the same ratio as in water, i.e., 2:1. Examples include sugar, starch, glycogen, and cellulose. Carbohydrates are divided into three classes.

Types of Carbohydrates:

1. Monosaccharides:

   • Simple sugars that cannot be hydrolyzed into smaller sugars.
   • General formula: $\text{C}_n\text{H}_{2n}\text{O}_n$.
   • Usually sweet, crystalline solids that dissolve in water.
   • Classified based on the number of carbon atoms (e.g., triose, tetrose, pentose, hexose).
   • Common examples: Glucose (found in fruits, sweet corn, honey), Fructose (found in sugarcane), Galactose (found in milk as part of lactose).

2. Oligosaccharides:

   • Composed of 2 to 10 monosaccharides.
   • Disaccharides (two monosaccharides) are the most common type, e.g., sucrose (table sugar), lactose (milk sugar), and maltose.
   • Oligosaccharides with 3 to 10 monosaccharides include substances like Dextrin.

3. Polysaccharides:

   • Made up of hundreds or thousands of monosaccharides linked by glycosidic bonds.
   • Common examples: Starch, Glycogen, Cellulose.
   • General formula: $(\text{C}_6\text{H}_{10}\text{O}_5)_n$.

Specific Polysaccharides:

• Starch: A storage carbohydrate in plants; consists of chains of glucose molecules in forms like amylose and amylopectin. Found in cereals, legumes, potatoes.
• Cellulose: Found in plant cell walls, made of long straight chains of glucose. It is hydrophilic and provides structural support.
• Glycogen: Known as "animal starch," it is a storage carbohydrate in animals, highly branched and stored in the liver, muscles, and other tissues.

Functions of Carbohydrates:

• Energy Source: Carbohydrates are a primary energy source for metabolism in the body.

These summaries cover the basic structure, types, and functions of carbohydrates. Let me know if you need further assistance or clarification on any specific topic.

Carbohydrates (Additional Functions):

• Storage Food Molecules: In plants, excess glucose is stored as starch, and in animals as glycogen.
• Structural Role: Carbohydrates serve as building blocks, with cellulose forming plant cell walls and chitin providing support in animal exoskeletons (like arthropods).
• Complex Molecules: They form complex conjugated molecules, including glycolipids and glycoproteins.

Lipids:

• Definition: Lipids are organic compounds insoluble in water but soluble in organic solvents. They have less oxygen compared to carbohydrates and are primarily composed of fatty acids and glycerol.

Types of Lipids:

1. Acylglycerol (Fats and Oils):

   • Made of glycerol and fatty acids.
   • Provide energy and are divided into:
     • Saturated Fats: Found in animals, solid at room temperature (e.g., stearin).
     • Unsaturated Oils: Found in plants, liquid at room temperature (e.g., linoleic acid in cottonseed oil).

2. Waxes:

   • Simple lipids formed from fatty acids and long-chain alcohols.
   • Water-repellent and used for protection in plants and animals.

3. Phospholipids:

   • Key components of biological membranes, consisting of a hydrophobic and a hydrophilic end.
   • Vital for cell membrane permeability and transport functions.

4. Terpenoids:

   • Based on isoprenoid units, include classes like terpenes, steroids, and carotenoids.
     • Terpenes: Volatile, used in essential oils (e.g., menthol, camphor).
     • Steroids: Includes compounds like cholesterol.
     • Carotenoids: Pigments found in plants, aiding in photosynthesis (e.g., carotene).

Nucleic Acids:

• Discovery: Isolated by Friedrich Miescher from the nuclei of pus cells, named "nuclein," later renamed nucleic acid due to its acidic nature.
• Types:
• DNA (Deoxyribonucleic Acid): Confined to the nucleus.
• RNA (Ribonucleic Acid): Mostly found in the cytoplasm.

Nucleic Acids as Informational Macromolecules:

• DNA and RNA: Both are types of nucleic acids involved in storing and transferring genetic information. DNA encodes genetic instructions, while RNA assists in protein synthesis.

DNA as Hereditary Material:

• Early experiments, including Griffith’s transformation experiment and later confirmation by Hershey and Chase, established DNA as the genetic material.
• Genetic Code: DNA consists of specific sequences of nitrogenous bases, encoding vast amounts of information.

RNA as a Carrier of Information:

• Location: DNA remains in the nucleus, while RNA serves as an intermediary, carrying genetic instructions to the cytoplasm.
• Protein Synthesis: Genetic information flows from DNA to mRNA (messenger RNA) in two main steps:
  1. Transcription: DNA information is transcribed to mRNA, which then moves to the cytoplasm.
  2. Translation: tRNA (transfer RNA) and rRNA (ribosomal RNA) help translate the mRNA code into a specific sequence of amino acids, forming proteins.

The page also includes diagrams illustrating the transcription process in detail.

Conjugated Molecules:

Conjugated molecules are formed when biomolecules of two different types combine, functioning as a unit.

Types of Conjugated Molecules:

1. Glycolipids or Cerebrosides:

   • Formed when carbohydrates combine with lipids, producing glycolipids.
   • Important for brain function and are constituents of the nervous system. Examples include galactolipids and sulfolipids in chloroplasts.

2. Glycoproteins or Mucoproteins:

   • Produced when proteins conjugate with carbohydrates.
   • The protein forms the core structure, and the carbohydrate part extends as a branched chain.
   • Found in mucus, synovial fluid (as lubricants), connective tissue matrix, and cell membranes. Egg albumin and certain hormones like gonadotropins are also glycoproteins.

3. Nucleoproteins:

   • Nucleic acids conjugated with proteins.
   • Found in the nucleus, weakly acidic, and soluble in water.

4. Lipoproteins:

   • Formed by conjugating lipids with proteins.
   • Assist in lipid transport in the blood plasma.
   • Found in cell membranes, mitochondria, endoplasmic reticulum, and other cellular structures.

These conjugated molecules play various roles in biological systems, from structural functions to biochemical transport. Let me know if you need any more details on these or any other topics covered.

Nucleotide Structure:

• Components:
  • Pentose Sugar: Ribose in RNA, deoxyribose in DNA.
  • Phosphoric Acid: Attached to the fifth carbon of the sugar.
  • Nitrogenous Base: The organic base of the nucleotide.

These points offer a concise overview of carbohydrates, lipids, and nucleic acids in biological systems. Let me know if you'd like more details on any specific part.

Biological Molecules

 Biology XI Notes - Biological Molecules - Short Questions Answers

Chapter # 02 - Biology - XI

Q.1: What is biochemistry? What is the importance of biochemistry?

Ans:
Introduction of Biochemistry:
Biochemistry is a branch of biology that deals with the study of chemical processes in the bodies of living organisms.

Importance of Biochemistry:

• It helps to understand all chemical processes that occur in the bodies of living organisms, such as the formation of body structures, protein synthesis, and various metabolic processes.
• It explains abnormal reactions responsible for diseases.
• It provides information about cell differentiation. After fertilization, the zygote undergoes changes that lead to the formation of different organs in the body, such as the brain, muscles, lungs, kidneys, alimentary canal, and other organs.
• It explains cell growth.
• It provides knowledge about organs, tissues, cells, their molecules, and chemically bonded atoms.

Q.2: What are the biologically important properties of water?

Ans:
The biologically important properties of water are as follows:

• Best Solvent:
  Water is the best solvent for many substances. Most important processes occur in the presence of water.

• High Heat Capacity:
  Water absorbs and releases heat slowly. Its specific heat capacity is high, meaning it requires more heat to increase its temperature.

• High Heat of Vaporization:
  Water requires a high amount of heat energy to convert into vapor, so water molecules remain in a stable form.

• An Amphoteric Molecule:
  Water can act as both an acid and a base, making it amphoteric. In acidic conditions, it donates electrons to form H⁺ ions, and in basic conditions, it gains electrons to form OH⁻ ions.

• Due to this property, water acts as the best medium for chemical processes in living cells.

  Water acts as a buffer; it is neutral, neither acidic nor basic, with a pH of 7. This buffering helps prevent pH changes in a solution when an acid or alkali is added, helping to maintain pH stability in cellular metabolism.

  Cohesive Force in Water Molecules:
  There is an attraction among water molecules known as cohesive force, which keeps water molecules together due to hydrogen bonding. This cohesion assists in transporting substances both outside and inside cells.

Q.3: Describe the formation of organic molecules (condensation)?

Ans:
Formation of Large Molecules:
The molecules in living organisms are typically larger in size, called macromolecules (or polymers). These are formed by combining smaller molecules called micromolecules (or monomers).

Macromolecules are formed by a process known as condensation. When two micromolecules (monomers) join, a hydroxyl group (OH) from one monomer combines with a hydrogen (H) from another monomer, forming water. By releasing water, the two monomers bond to form a macromolecule. This condensation process (also known as dehydration) removes water, requiring a specific enzyme and energy.

Q.4: Describe the breaking of molecules (Hydrolysis)?

Ans:
Hydrolysis is the process in which macromolecules or polymers break down into smaller monomers or sub-units by adding water.

During hydrolysis, a water molecule splits into H⁺ and OH⁻ ions with the help of an enzyme. The H⁺ group attaches to one monomer, while the OH⁻ group attaches to another monomer, breaking the bond between the two. As a result, the two monomers separate, releasing energy.

Q.5: What is a chemical bond? Describe its types?

Ans:
A chemical bond is the attractive force that combines atoms together. Chemical bonds are of two main types.

• Ionic Bond:
  This bond is formed due to the loss or gain of electrons.

• Covalent Bond:
  This bond is formed by the mutual sharing of electrons between two atoms. In organic compounds, covalent bonds are formed between elements, and these bonds store energy.

Types of Covalent Bonds: Carbon can form three types of covalent bonds:

• Single Covalent Bond:
  This bond is formed by the mutual sharing of one electron pair between atoms.
  Example: $CH_3 - CH_3$ (Ethane)

• Double Covalent Bond:
  This bond is formed by the mutual sharing of two electron pairs between two atoms.
  Example:

  mathematica
  
      H   H
       \ /
        C = C
       / \
      H   H
  

  (Ethene)

• Triple Covalent Bond:
  This bond is formed by the mutual sharing of three electron pairs between atoms.
  Example: $H - C \equiv C - H$ (Ethyne)

Q.6: Write a note on Proteins?

Ans:
Proteins:
Proteins are complex organic compounds consisting of carbon, hydrogen, oxygen, nitrogen, sulfur, and sometimes phosphorus. They are formed by the combination of amino acids.

The amino acids are of twenty types, allowing various proteins to form through the linkage of amino acids. When amino acids are joined together, they create a polypeptide chain.

R is a side chain attached to a protein. This side chain provides additional characteristics to the compound. When two amino acids are joined by a chemical process, a dipeptide compound is formed.

When three amino acids combine, a tri-peptide compound is created, and linking many amino acids together results in a synthesized protein.

Structure of Proteins:
According to the structure of proteins, there are four types:

• Primary Structure:
  In this structure, amino acids are arranged in a linear manner in a polypeptide chain, known as the primary structure. This protein also contains disulfide (S-S) bonds.

• Secondary Structure:
  In a polypeptide chain, when amino acids are arranged in a spiral manner, it forms the secondary structure of protein, creating a helical (screw-like) structure.

• Tertiary Structure:
  When amino acids are folded or super-folded, displaying a three-dimensional structure, it is referred to as the tertiary structure of protein.

• Quaternary Structure:
  When two or more polypeptide chains are combined to form a large-sized molecule, it is known as the quaternary structure of protein (e.g., hemoglobin in blood). There are two types of quaternary proteins.

• When the peptide chains are similar, it is called homogeneous quaternary structure.
• When peptide chains are different, it is known as heterogeneous quaternary structure.  

Q.7: What are the Functions of Proteins?

Ans:
Functions of Proteins:

• Proteins form the cell structure and body of an organism.
• They form seeds and other parts in plants.
• They produce plasma membrane and other cell organs.
• Proteins create substances in animals that contribute to the formation of skin, muscles, nails, and hair.
• Hemoglobin in blood contains protein.
• Proteins assist in food digestion, muscle expansion and contraction, and blood clotting.
• They act as enzymes, which are organic catalysts that increase the rate of chemical reactions.
• Proteins function as hormones, growth factors, and gene activators.
• They also serve as antibodies, antigens, and fibrin.

Q.8: What are carbohydrates? What are their types?

Ans:
Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, making up about 1% of protoplasm. They are present in all living organisms.

Based on molecular size, carbohydrates are classified into three groups:

• Mono-saccharides
• Oligo-saccharides
• Poly-saccharides

Mono-saccharides:
These are the carbohydrates that cannot be further broken down into simpler sugars, e.g., Glucose and Fructose.

Types of Mono-saccharides (Based on Carbon Atoms):

• Trioses: Sugars with 3 carbon atoms.
• Tetroses: Sugars with 4 carbon atoms.
• Pentoses: Sugars with 5 carbon atoms.
• Hexoses:
  These sugars have 6 carbon atoms.

All mono-saccharides are found in white solid crystals, have a sweet taste, and are easily soluble in water.

Mono-saccharides are commonly found in various fruits and vegetables. Glucose and fructose are present in grapes. Fructose, the sweetest sugar, is also found in honey. Lactose sugar is present in milk, with galactose as part of it. Glucose, fructose, and galactose are hexose sugars.

Oligo-Saccharides:
These carbohydrates are composed of two to ten mono-saccharide compounds. Upon hydrolysis, oligo-saccharides yield two to ten mono-saccharide molecules.

These carbohydrates form by the union of two similar or different sugars through a condensation process, releasing a water molecule. Examples of di-saccharides are as follows:

• Glucose + Glucose → Maltose + H₂O
  $(C_6H_{12}O_6) + (C_6H_{12}O_6) \rightarrow (C_{12}H_{22}O_{11})$
• Glucose + Fructose → Sucrose + H₂O
• Glucose + Galactose → Lactose + H₂O

Sucrose, a common sugar, is widely used and obtained from sugar cane or beet. It is formed by combining glucose and fructose. Sugar cane and beet are cultivated for sucrose production.

Poly-Saccharides:
Poly-saccharides are carbohydrates formed by combining many mono-saccharides, e.g., Starch, Glycogen, Cellulose, etc.

Q.9: What is starch?

Ans:
Starch:
Starch consists of many glucose molecules linked together in a straight or branched manner.

Starch is found in leaves, roots, and seeds in granular form, such as in wheat, potatoes, rice, etc. It is insoluble in water but becomes soluble when boiled. Through hydrolysis, it breaks down into simple sugars and participates in energy production through oxidation.

Q.10: What is Glycogen?

Ans:
Glycogen:
It is the animal starch. When many glucose molecules link together in a chain-like manner, glycogen forms. It is present in the muscles and liver of animals, as well as in bacteria and fungi.

Glycogen is produced by the liver, which converts excess glucose into glycogen. This glycogen is stored in the liver and muscles. When there is a shortage of glucose in the body, glycogen is converted back into glucose to provide energy. This process helps maintain the glucose balance in the blood. Glycogen is insoluble in water.

Q.11: What is Cellulose?

Ans:
Cellulose:
Cellulose is composed of many glucose molecules, about 2000 to 3000. It is only produced in plants and is a key component of the cell wall.

In animals, cellulose cannot be digested by enzymes. However, specific bacteria in the caecum of the alimentary canal assist in digesting cellulose through the action of certain enzymes.

Q.12: What are the functions of Carbohydrates?

Ans:
Functions of Carbohydrates:

• Carbohydrates produce energy through oxidation, which is used for various functions.
• Carbohydrates can be converted into other substances. In plants, excess glucose is stored as starch, which can be converted back to glucose when needed. In animals, glucose is converted into glycogen.
• Complex carbohydrate molecules form the structure of living organisms and strengthen organs. In plants, cellulose is formed from carbohydrates.

Q.13: What are Lipids? Name the different types of Lipids?

Ans:
Lipids are organic compounds such as oil, butter, waxes, fats, natural rubber, and vitamins A, E, and K, as well as steroids like cholesterol. They are composed of carbon, hydrogen, and a minimal amount of oxygen.

Bloor proposed the term "lipid" in 1943. Lipids are defined as organic compounds that are insoluble in water but soluble in Bloor’s reagent mixture of diethyl ether and ethyl alcohol (2:1 ratio) or other fat solvents like benzene, acetone, chloroform, and ether. Lipids form fatty acids upon hydrolysis.

Lipids are found in both plants and animals. In plants, they are usually present in seeds, fruits, and nuts.

Classification of Lipids:
Lipids are divided into the following groups:

• Acylglycerol (Fats and Oils)
• Waxes

Q.14: Write a note on Acylglycerol (Fats and Oils)?

Ans:
Acylglycerol (Fats and Oils):
These lipids may be neutral fats or oils.

Neutral Fats and Oils:
These are esters of fatty acids and glycerol, also known as triglycerides. When three molecules of fatty acids combine with one molecule of glycerol, a lipid molecule, triglyceride, is formed.

Oils are liquid at room temperature because they contain unsaturated fatty acids, whereas fats are solid because they contain saturated fatty acids.

Oils are rich in unsaturated fatty acids, such as groundnut oil, mustard oil, cotton oil, and olive oil. Animal fats are a mixture of saturated and unsaturated fatty acids. Oils are typically found in plants. Cotton seeds contain linolein, which has linoleic acid.

Q.15: What are Waxes?

Ans:
Waxes are esters of fatty acids with monohydroxy alcohol of long chains or cholesterol instead of alcohol. They contain an odd number of carbon atoms (C₂₅ to C₃₅). They are water-insoluble and flexible. Waxes are found in the coatings of stems, stalks, leaves, and fruits, and can be used in cosmetics, creams, ointments, and polishes.

Waxes are also used as machine lubricants. In the early days, wax was obtained from whales, but it is now sourced from a desert plant called Simmondsia chinensis or jojoba. Jojoba is rich in wax esters as storage lipids in its seeds.

Q.16: What are Phospholipids?

Ans:
Phospholipids:
Phospholipids are esters of fatty acids with alcohol, containing phosphorus. They are found in all living cells and help regulate cell permeability and transport processes.

Phospholipid molecules have two ends:

• Hydrophilic end (head): Upper part, considered water-loving.
• Hydrophobic end (tail): Lower part, considered water-fearing.

• Phospholipids are actually compound lipids because one fatty acid in the lipid is replaced by a phosphate group. Other compound lipids include Glycolipids and Sphingolipids.

  Glycolipids:
  These lipids are linked to a sugar molecule. Upon hydrolysis, they release sugar, fatty acid, and a nitrogenous compound. They are found in chloroplasts.

  Sphingolipids:
  These are found in animals but not in plants.

Q.17: Write a note on Terpenoids?

Ans:
Terpenoids:
These are large lipid compounds composed of isoprenoid units (C₅H₈ units). The main classes of terpenoids are:

• Terpenes
• Steroids
• Carotenoids

Terpenes:
Terpenes are an important class of lipids obtained through the steam distillation of plants. Some terpenoids are essential oils responsible for the fragrance of various plants, such as roses, peppermint, camphor, cloves, sandalwood, eucalyptus, citrus, and Ocimum basilicum (Niazbo).

Importance of Terpenes:

• Some terpenes are used in perfumes, e.g., Myrcene from bay oil, Geraniol from rose oil, Limonene from lemon oil, and Menthol from peppermint oil.
• Some terpenes' derivatives are present in vitamins A₁ and A₂.
• They are a significant component of chlorophyll.
• They act as intermediate compounds in cholesterol formation.
• Terpenes are also used in the synthesis of rubber and latex.

Steroids:
These fats do not form soap with NaOH or KOH. Steroids consist of three six-membered rings (A, B, and C) and one five-membered ring (D), forming a structure known as perhydro-cyclopentano-phenanthrene.

These rings are connected and contain a total of 17 carbon atoms, called the steroid nucleus. Common examples of steroidal lipids include cholesterol, vitamin D, and cortisone.

Cholesterol is found in animal tissues, nerve tissues, and the spinal cord. It is also present in egg yolks, various oils, and fats. Cholesterol is synthesized in the liver and acts as a precursor in the biosynthesis of sex hormones, vitamins, and steroidal hormones, such as cortisone.

Carotenoids:
Carotenoids are also included in this group. They are pigments that produce red, orange, yellow, and brown colors in plants. Vitamin A is a derivative of carotene, found in carrots, tomatoes, and leaves.

The red pigment carotene and yellow pigment xanthophyll are present in many plants. Tetrapyrrole pigment is present in chlorophyll and cytochromes.

Q.18: What are the functions of Lipids?

Ans:
Functions of Lipids:

• They are the main source of energy, providing double the energy of carbohydrates and proteins.
• Lipids serve as stored energy in the body, available for use when needed.
• They contribute to the structural framework of living tissues, forming plasma membranes, vacuole membranes, mitochondria, nuclei, chloroplasts, etc.
• Lipids help dissolve vitamins A and D, preventing their decomposition.
• They are a component of the electron transport system in mitochondria.
• Lipids are found in the outer cuticle of insects, making them waterproof.
• They form a protective covering on the surface of stems, leaves, and fruits.
• Waxes are used in cosmetics, ointments, creams, and polishes.

Q.19: What are Nucleic acids?

Ans:
Nucleic Acids:
Nucleic acids are organic substances containing carbon, hydrogen, oxygen, nitrogen, and phosphorus. There are two types of nucleic acids.

Deoxyribo-Nucleic Acid (DNA):
DNA is present in the nucleus. It transfers hereditary characteristics to new cells. It contains a sugar molecule called deoxyribose.

Ribo-Nucleic Acid (RNA):
RNA is formed in the nucleus and migrates to the cytoplasm. It contains ribose sugar and participates in protein synthesis.

Structure of DNA and RNA:
DNA and RNA are composed of small units called nucleotides, which consist of three parts:

• A pentose sugar (containing 5 carbon atoms)
• A phosphate group
• Nitrogen bases

• Pentose sugar is of two types:

  • Ribose Sugar: Present in RNA.
  • De-Oxyribose Sugar: Found in DNA.

  The nitrogen bases are of the following types:

  • Adenine
  • Guanine
    (These are purine-type compounds)
  • Cytosine
  • Thymine
    (These are pyrimidine-type compounds)

  Uracil:
  It is the nitrogen base present in RNA, replacing thymine.

  Function:

• DNA is located in the nucleus. It serves as the genetic material, transferring hereditary characteristics to new cells.
• RNA is formed in the nucleus by DNA and then transferred into the cytoplasm, where it participates in protein synthesis.

Q.20: What is the difference between DNA and RNA?

Ans:
Difference Between DNA & RNA:

• DNA is composed of two filaments that form a double-helix structure, linked together like a spring. RNA consists of separate filaments and does not form a double helix.
• DNA contains de-oxyribose sugar, while RNA contains ribose sugar.
• In DNA, the nitrogen base thymine is present, while in RNA, thymine is replaced by uracil.
• DNA acts as genetic material, helping to transfer hereditary traits, while RNA participates in protein synthesis.

Q.21: Write a note on Nucleotides?

Ans:
Nucleotides:
These compounds are the subunits of nucleic acids. In cells, there are three types of nucleotides:

• Mononucleotides
• Dinucleotides
• Polynucleotides

• Mononucleotides:
  These nucleotides are found singly in the cell or as part of other molecules. They are not attached to DNA or RNA. Mononucleotides contain additional phosphate groups. For example, ATP (Adenosine triphosphate) contains three phosphates and is produced from ADP (Adenosine diphosphate), which contains two phosphates. ATP is an energy-rich compound, used in various bodily functions.

  Dinucleotide:
  When two nucleotides are attached by a covalent bond, a dinucleotide molecule forms, e.g., NAD (Nicotinamide adenine dinucleotide). The two nucleotides in NAD are connected by phosphate groups.

  NAD acts as a co-enzyme, a non-protein organic part of an enzyme. It helps remove hydrogen atoms from substrates and, by gaining hydrogen, converts into NADH.

  Polynucleotide:
  When many nucleotides are linked together, they form polynucleotides. DNA and RNA are examples of polynucleotides. DNA nucleotides transfer genetic information to new cells, while RNA participates in protein synthesis.

  Genetic information is encoded in a "genetic code." Nitrogen bases in nucleic acids form different codes that interact with amino acids to control the arrangement of amino acids and the amount of protein produced.

Q.22: Explain that DNA acts as a genetic material?

Ans:
DNA as Hereditary Material:
DNA, a component of genes, contains hereditary characteristics passed to new cells or generations, establishing it as hereditary material.

Griffith demonstrated DNA as genetic material through transformation in bacteria. Living bacteria acquire DNA from dead bacteria, transforming from harmless to virulent, proving DNA’s role as genetic material.

Another proof by Hershey and Chase showed that DNA from one bacterial cell could transfer to another via bacteriophage virus. When a bacteriophage infects a bacterial cell, only its DNA enters the cell, while the outer protein coat remains outside. The viral DNA takes control of the host cell's biochemical functions.

Q.23: How DNA behaves as genetic material?

Ans:
DNA is a polynucleotide composed of deoxyribose sugar, a phosphate group, and four types of nitrogen bases. The sugar and phosphate do not play any role in forming the genetic code. The four nitrogen bases are arranged in a specific sequence, encoding information. These bases can form multiple combinations of genetic codes from 20 amino acids. DNA strands consist of billions of nucleotides, allowing for the encoding of vast amounts of information in genetic codes.

Q.24: How RNA acts as a carrier of information?

Ans:
Ribonucleic acid (RNA) serves as an information carrier from DNA to ribosomes for protein synthesis.

RNA is crucial for protein synthesis and exists in three types:

• Messenger RNA (mRNA)
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)

These RNA types are formed in the nucleus by DNA and transferred to the cytoplasm to participate in protein synthesis within ribosomes.

The genetic information is transferred from DNA to mRNA and then to the cytoplasm for protein synthesis in two steps:

• Transcription
• Translation

Transcription:
Transcription is the first step in protein synthesis, occurring in the nucleus. During this process, DNA produces a single-stranded RNA molecule from one of its strands. This RNA molecule is called messenger RNA (mRNA) as it carries the genetic message from DNA.

The mRNA then transports the message from the nucleus to the ribosome in the cytoplasm, indicating the formation of a specific type of protein.

Translation:
During translation, tRNA and rRNA play key roles. rRNA attaches to the ribosome, while tRNA in the cytoplasm transfers specific amino acids to the ribosome. This process translates the mRNA’s information into an amino acid sequence, producing a particular type of protein.

Q.25: What are conjugated molecules? Describe briefly the different types of conjugated molecules?

Ans:
Conjugated Molecules:
When biomolecules from two different groups combine, conjugated molecules are formed. Different types of conjugated molecules include:

• Glycolipids
• Glycoproteins (Mucoids)
• Nucleoproteins
• Lipoproteins

Glycolipids:
These are formed when fatty acids and carbohydrates combine. They also contain nitrogen and are derivatives of carbohydrate glycerides. Examples include galactolipids and sulpholipids found in chloroplasts, and cerebrosides found in the brain.

Glycoproteins (Mucoids):
When carbohydrates and proteins link, glycoproteins are formed. They are commonly found in animal and plant cells as oligo- and polysaccharides. Examples include egg albumin and gonadotropic hormone. Some glycoproteins are present in cell membranes.

Nucleoproteins:
These are combinations of proteins with nucleic acids in the nucleus. They are less acidic and soluble in water.

Lipoproteins:
When lipids and proteins link, lipoproteins form, such as cholesterol and lecithin lipids linked to simple proteins. These compounds help transport lipids in blood plasma.

Lipoproteins are found in the membranes of the endoplasmic reticulum, nuclei, mitochondria, and in the nerve sheath, chloroplasts, and bacterial membranes.

---

---

---

---

---

---

• Phospholipids
• Terpenoids

---