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: (Ethane)Double Covalent Bond:
This bond is formed by the mutual sharing of two electron pairs between two atoms.
Example:(Ethene)
Triple Covalent Bond:
This bond is formed by the mutual sharing of three electron pairs between atoms.
Example: (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. - Glucose + Glucose → Maltose + H₂O
- Glucose + Fructose → Sucrose + H₂O
- Glucose + Galactose → Lactose + H₂O
- 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.
- Acylglycerol (Fats and Oils)
- Waxes
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:
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:
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:
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
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