BiomoleculesClass 11 Biology NCERT Solutions
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Q1Exercises
What are macromolecules? Give examples.
Solution
Biomacromolecules are large, complex chemical compounds found in living organisms. They are polymers with high molecular weights, typically in the range of ten thousand daltons (Da) and above. They are found in the acid-insoluble fraction when a living tissue is chemically analysed.
Based on the chapter, there are three main types of true macromolecules:
- Proteins: These are heteropolymers of amino acids linked by peptide bonds. For example, Collagen and RuBisCO.
- Polysaccharides: These are long chains (polymers) of monosaccharides (sugars) linked by glycosidic bonds. For example, Cellulose, Starch, and Glycogen.
- Nucleic Acids: These are polymers of nucleotides. For example, Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).
Lipids are also found in the acid-insoluble fraction, but they are not strictly macromolecules as their molecular weight does not exceed 800 Da. They are included in the macromolecular fraction because they are components of cell membranes, which form water-insoluble vesicles during tissue analysis.
Q2Exercises
What is meant by tertiary structure of proteins?
Solution
The tertiary structure of a protein refers to its overall three-dimensional (3-D) shape. It is formed when the long polypeptide chain, which may already have secondary structures like helices, is folded upon itself, much like a hollow woolen ball.
This folding is stabilized by various interactions between the side chains (R groups) of the amino acids. The tertiary structure results in the formation of a compact, globular shape with specific crevices or pockets, one of which is the 'active site' in enzymes. This 3-D structure is absolutely necessary for the biological activities of most proteins, including their function as enzymes, hormones, or receptors.
Q3Exercises
Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry which manufactures the compounds by isolation. Find out who are the buyers.
Solution
The chapter describes several small molecular weight biomolecules (micromolecules). Here are the structures of 10 such compounds based on the information and diagrams in the text:
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Glucose (a sugar): A hexose monosaccharide. Formula:
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Ribose (a sugar): A pentose monosaccharide, a component of RNA. Formula:
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Glycine (an amino acid): The simplest amino acid where the R group is H. Structure: A central carbon atom bonded to , , , and another .
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Alanine (an amino acid): An amino acid where the R group is a methyl group (). Structure: A central carbon atom bonded to , , , and .
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Serine (an amino acid): An amino acid where the R group is a hydroxymethyl group (). Structure: A central carbon atom bonded to , , , and .
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Glycerol (a simple lipid): Trihydroxy propane. Formula:
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Palmitic acid (a fatty acid): A saturated fatty acid with 16 carbon atoms. Formula:
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Adenine (a nitrogenous base): A purine base found in DNA and RNA. Formula:
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Uracil (a nitrogenous base): A pyrimidine base found in RNA. Formula:
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Adenylic acid (a nucleotide): Composed of adenine, ribose sugar, and a phosphate group.
(Note: The chapter provides diagrammatic representations for most of these in Figure 9.1. For detailed chemical structures, further reference may be needed.)
The second and third parts of the question regarding industrial manufacturing and buyers require external research beyond the scope of this textbook chapter. However, many of these compounds are indeed manufactured on a large scale. For example, amino acids and vitamins (many of which are co-enzymes) are produced for the pharmaceutical, food, and animal feed industries. Sugars like glucose are produced for the food and beverage industry. These industries are major buyers.
Q4Exercises
Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., Cosmetics etc.)
Solution
Based on the provided chapter, we can identify some proteins with therapeutic applications from their functions listed in Table 9.5:
- Insulin: Listed as a hormone. It is widely used as a therapeutic agent to manage diabetes mellitus by regulating blood sugar levels.
- Antibody: Listed as fighting infectious agents. Antibodies, specifically monoclonal antibodies and immunoglobulins, are used therapeutically to treat various diseases, including infections, cancer, and autoimmune disorders.
- Trypsin: Listed as an enzyme. As a therapeutic agent, it is used as a digestive aid and in wound cleaning preparations due to its proteolytic activity.
The chapter focuses on the biological roles of proteins and does not detail their other applications in industries like cosmetics. However, it mentions Collagen as an intercellular ground substance. In the cosmetics industry, collagen and its derivatives (like hydrolyzed collagen) are used in skincare products for their moisturizing and film-forming properties. This information is supplementary to the chapter content.
Q5Exercises
Explain the composition of triglyceride.
Solution
A triglyceride is a type of lipid, commonly known as a fat or oil. Its composition is based on two types of building blocks: glycerol and fatty acids.
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Glycerol: A simple three-carbon molecule with three hydroxyl (–OH) groups. Its chemical name is trihydroxy propane.
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Fatty Acids: These are long hydrocarbon chains with a carboxyl group (–COOH) at one end. The hydrocarbon chain can be saturated (no double bonds) or unsaturated (one or more double bonds).
A triglyceride molecule is formed when three fatty acid molecules are chemically bonded to a single glycerol molecule. This bonding occurs through a process called esterification, where the carboxyl group of each fatty acid reacts with one of the hydroxyl groups of glycerol, forming an ester bond and releasing a molecule of water for each bond formed. Therefore, a triglyceride consists of one glycerol backbone esterified with three fatty acids. The three fatty acids can be of the same type or different types.
Q6Exercises
Can you attempt building models of biomolecules using commercially available atomic models (Ball and Stick models).
Solution
Yes, building models of biomolecules using commercially available atomic model kits (ball and stick models) is a practical and effective way to understand their three-dimensional structure.
Procedure:
- Assign Colors: Use the standard color code for atoms: black for Carbon (C), white for Hydrogen (H), red for Oxygen (O), and blue for Nitrogen (N).
- Select a Molecule: Choose a simple biomolecule described in the chapter, such as the amino acid Alanine or the sugar Glucose.
- Assemble the Structure:
- For Alanine, you would take a black ball (the central α-carbon) and connect it to:
- A blue ball (Nitrogen of the amino group), which is then connected to two white balls (Hydrogens).
- Another black ball (Carbon of the carboxyl group), which is double-bonded to one red ball (Oxygen) and single-bonded to another red ball attached to a white ball (the -OH group).
- A white ball (Hydrogen).
- A black ball (methyl group carbon), which is then connected to three white balls (Hydrogens).
- For Alanine, you would take a black ball (the central α-carbon) and connect it to:
- Use Sticks for Bonds: Use short, rigid sticks for single bonds and flexible or paired sticks for double bonds to accurately represent the molecular geometry.
This activity helps in visualizing the spatial arrangement of atoms, bond angles, and the overall shape of the molecule, which is crucial for understanding its function.
Q7Exercises
Draw the structure of the amino acid, alanine.
Solution
Alanine is an α-amino acid. Its structure consists of a central carbon atom (the α-carbon) bonded to four different groups:
- An amino group ()
- A carboxyl group ()
- A hydrogen atom ()
- A variable R group, which for alanine is a methyl group ()
The structure is as follows:
COOH
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H₂N--C--H
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CH₃
This structure shows the four different substituents attached to the central alpha-carbon atom.
Q8Exercises
What are gums made of? Is Fevicol different?
Solution
According to Table 9.3 in the chapter, gums are classified as 'Polymeric substances' and are examples of secondary metabolites found in plants.
Composition of Gums: Gums are natural complex polysaccharides. Polysaccharides are long chains of monosaccharide units. Therefore, gums are primarily composed of various sugars and their derivatives, making them a type of carbohydrate.
Is Fevicol different? Yes, Fevicol is completely different from natural gums. The chapter does not mention Fevicol, but for clarification:
- Natural Gums are biological in origin, derived from plants, and are polysaccharides.
- Fevicol is a synthetic adhesive. It is a man-made polymer, typically based on polyvinyl acetate (PVA). Its chemical composition and origin are entirely different from natural gums.
Q9Exercises
Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.
Solution
This question describes a practical laboratory activity. The textbook chapter focuses on the chemical composition and structure of biomolecules but does not detail the procedures for these qualitative tests. However, some common standard tests are:
- Test for Proteins (Biuret Test): Add a few drops of Biuret reagent to the sample solution. A change in color from blue to violet or purple indicates the presence of peptide bonds, and thus protein.
- Test for Fats and Oils (Sudan III Test or Grease Spot Test):
- Sudan III Test: Add a few drops of Sudan III stain to the sample. The appearance of red-colored oil globules indicates the presence of fats or oils.
- Grease Spot Test: Place a drop of the sample on a piece of paper. A translucent spot that does not dry indicates the presence of fats or oils.
- Test for Amino Acids (Ninhydrin Test): Add a few drops of Ninhydrin reagent to the sample and heat it. The appearance of a deep blue or purple color indicates the presence of amino acids.
Testing Samples:
- Fruit Juice: Likely to test positive for amino acids and negative for proteins and fats.
- Saliva: Likely to test positive for proteins (due to enzymes like amylase) and amino acids.
- Sweat: Contains trace amounts of amino acids and urea, might show a weak positive test for amino acids. Mostly water and salts.
- Urine: In a healthy individual, it should test negative for proteins and fats. It contains urea and may contain trace amino acids.
Q10Exercises
Find out how much cellulose is made by all the plants in the biosphere and compare it with how much of paper is manufactured by man and hence what is the consumption of plant material by man annually. What a loss of vegetation!
Solution
This is a research-based question that requires gathering data from external sources, as the textbook chapter does not provide these specific quantitative figures. The chapter states that plant cell walls are made of cellulose and that paper is cellulosic, highlighting its abundance and importance.
To answer this question, one would need to:
- Find the annual production of cellulose: Research scientific estimates for the net primary production of biomass by plants in the biosphere and the proportion of that biomass which is cellulose. Cellulose is the most abundant organic polymer on Earth.
- Find the annual production of paper: Look up industrial and forestry statistics for the total tonnage of paper and paperboard manufactured globally each year.
- Compare the figures: Calculate the ratio or percentage of total cellulose production that is used for paper manufacturing.
- Analyze the impact: The final statement, "What a loss of vegetation!", prompts a discussion on sustainability, deforestation, and the importance of recycling paper to reduce the consumption of virgin plant material.
This exercise is designed to make the student appreciate the scale of natural processes versus human industrial activity and its environmental impact.
Q11Exercises
Describe the important properties of enzymes.
Solution
Enzymes are biological catalysts that accelerate the rate of chemical reactions in living organisms. Based on the chapter, their important properties are as follows:
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Proteinaceous Nature: Almost all enzymes are proteins. They have a complex three-dimensional tertiary structure which is crucial for their function. There are some nucleic acids (ribozymes) that also behave like enzymes.
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Active Site: Each enzyme has a specific region in its tertiary structure called an 'active site'. This is a crevice or pocket into which the substrate fits, and where the catalytic reaction takes place.
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Catalytic Property: Enzymes greatly increase the rate of reactions, sometimes by millions of times. They do this by lowering the 'activation energy' required for the substrate to be converted into the product, making the transition easier.
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High Specificity: Enzymes are highly specific in their action. A particular enzyme typically catalyzes only one type of chemical reaction for a specific substrate or a group of closely related substrates.
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Sensitivity to Temperature and pH: Enzyme activity is maximal at a specific temperature and pH, known as the 'optimum' temperature and pH. Activity declines sharply above or below these optimal values. High temperatures can cause denaturation (loss of structure and function), while low temperatures lead to temporary inactivation.
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Saturation Kinetics: The velocity of an enzymatic reaction increases with substrate concentration up to a certain point, after which it reaches a maximum velocity (). At this point, the enzyme is 'saturated' with the substrate, and adding more substrate does not increase the reaction rate.
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Regulation and Inhibition: Enzyme activity can be regulated. Some chemicals called 'inhibitors' can shut off enzyme activity. Competitive inhibitors, for example, resemble the substrate and compete for the active site.
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Requirement of Co-factors: Some enzymes require non-protein components called 'co-factors' to be catalytically active. The protein part is called the apoenzyme. Co-factors can be prosthetic groups, co-enzymes (often derived from vitamins), or metal ions.