GSEB Class 11 Biology Solutions Chapter 9 Biomolecules

Question 1. What are macromolecules? Give examples.
Answer: Chemical compounds having molecular weights more than one thousand daltons and found in the acid-insoluble part are known as macromolecules. For example, polysaccharides and nucleic acids are good instances.
In simple words: Macromolecules are large chemical compounds. They weigh over a thousand daltons and are found in the part that doesn't dissolve in acid. Polysaccharides and nucleic acids are examples.

Exam Tip: Remember to include both the definition of macromolecules (molecular weight and solubility fraction) and specific examples like polysaccharides and nucleic acids to get full marks.

Question 2. Illustrate a glycosidic, peptide and a phospho-diester bond.
Answer: In a polypeptide or protein, amino acids join together through a peptide bond. This bond forms when the carboxyl (-COOH) group of one amino acid reacts with the amino (\( \text{NH}_2 \)) group of the next amino acid, releasing water (a process called dehydration). In a polysaccharide, individual monosaccharides connect via a glycosidic bond. This bond also forms through dehydration, occurring between two carbon atoms of two adjacent monosaccharides.
In a nucleic acid, a phosphate group links the 3'-carbon of one sugar in one nucleotide to the 5'-carbon of the sugar in the following nucleotide. The bond between the phosphate and the hydroxyl group of sugar is an ester bond. Since there is one such ester bond on each side, it is called a phospho-diester bond.
(The original source provides a diagram illustrating a DNA strand with its 5' and 3' ends, and detailed structures of Thymine-Adenine, Guanine-Cytosine base pairs, and the Phospho-diester linkage between a phosphate group and sugar, indicating \( \text{O=P-OH} \) and \( \text{HO-P=O} \).)
In simple words: Peptide bonds join amino acids in proteins by removing water. Glycosidic bonds join simple sugars in complex sugars, also by removing water. Phospho-diester bonds link sugar and phosphate parts in DNA, forming a strong backbone.

Exam Tip: For each bond type, specify the molecules it links (e.g., amino acids for peptide), the groups involved (e.g., carboxyl and amino for peptide), and the type of reaction (dehydration). A clear, labeled diagram is often crucial for full understanding.

Question 3. What is meant by the tertiary structure of proteins?
Answer: The long protein chain folds in on itself, much like a hollow woolen ball. This specific folded shape is what we call the tertiary structure of the protein. This structure is essential for many biological activities performed by proteins.
(The original source includes a diagram showing a coiled protein chain, with labels N and C for the N-terminus and C-terminus, illustrating the complex 3D folding of a tertiary structure.)
In simple words: The tertiary structure is how a protein's long chain folds into a specific 3D shape, similar to a tangled ball of wool. This shape is very important for the protein to do its job.

Exam Tip: When defining tertiary structure, emphasize its 3D folding (like a "hollow woolen ball") and its functional importance for biological activity.

Question 4. Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry that manufactures the compounds by isolation. Find out who are the buyers?
Answer: The most exciting part of chemistry involves isolating thousands of compounds, both small and large, from living organisms, determining their structure, and even synthesizing them if possible. If one were to list biomolecules, it would include thousands of organic compounds such as amino acids, sugars, and more. Alkaloids, flavonoids, rubber, essential oils, antibiotics, colored pigments, scents, gums, and spices are often called 'secondary metabolites'. Many of these are beneficial for 'human welfare' (e.g., rubber, drugs, spices, scents, and pigments). Some secondary metabolites also hold ecological importance.
(The original source provides chemical structures for the following 10 small molecular weight biomolecules: Glucose (\( \text{C}_6\text{H}_{12}\text{O}_6 \)), Ribose (\( \text{C}_5\text{H}_{10}\text{O}_5 \)), Glycine, Alanine, Serine (all amino acids), Palmitic acid (Fatty acid), Glycerol, Triglyceride (showing R1, R2, R3 as fatty acids), Phospholipid (Lecithin), and Cholesterol.)
**Industries and Buyers:**
Many industries manufacture these compounds through isolation or synthesis. For instance:
1. **Pharmaceutical Industry:** Produces amino acids, antibiotics, and certain hormones. Buyers include hospitals, pharmacies, and research institutions.
2. **Food and Beverage Industry:** Uses sugars (like glucose, ribose), glycerol, and fatty acids. Buyers include food manufacturers, bakeries, and consumers.
3. **Cosmetic Industry:** Utilizes fatty acids, glycerol, and specific proteins. Buyers are cosmetic companies and individual consumers.
4. **Chemical Industry:** Manufactures various intermediates and compounds. Buyers are diverse industries needing raw materials.
5. **Agricultural Industry:** Uses some compounds for crop enhancement or animal feed. Buyers include farms and agricultural companies.
In simple words: Chemistry helps us get many different small compounds from living things, and we can also make them. These compounds include sugars, amino acids, and fats. Industries like medicine, food, cosmetics, and farming use these compounds. Hospitals buy drugs, food companies buy sugars, and makeup brands buy fats for their products.

Exam Tip: For questions asking for structures, a labeled drawing is usually expected. When discussing industries and buyers, provide concrete examples of both the industry and the end-users for clarity.

Question 5. Proteins have a primary structure. If you are given a method to know which amino-acid is at either of the two termini (ends) of a protein, can you connect this information to the purity or homogeneity of a protein?
Answer: Yes, if we are given a method to know the sequence of proteins, we can link this information to the purity of a protein. The accurate sequence of a specific amino acid is very crucial for the protein's proper functioning. Any alteration in the sequence can be associated with the purity or homogeneity of a protein.
In simple words: Yes, if we know the amino acid at the start or end of a protein, we can use this to check how pure the protein is. The exact order of amino acids is vital for a protein to work correctly. If the order is different, it means the protein might not be pure.

Exam Tip: Focus on how the *exact sequence* of amino acids (especially at the termini) is a key indicator of a protein's identity and, by extension, its purity or homogeneity.

Question 6. Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (eg. Cosmetics etc.)
Answer: Here is a list of proteins used as therapeutic agents and their other applications:
**Therapeutic Agents:**
1. **Human Albumin:** Utilized in cases of liver sclerosis and Nephrotic Syndrome.
2. **Antibodies:** Gamma globulins are employed to treat many conditions such as tetanus, snake bites, and Guillain-Barré Syndrome.
3. **Enzymes:** These proteins are also used in various conditions, like pancreatic malfunction; doctors often prescribe pancreatin.
4. **Polypeptide hormones:** Used to treat hormone deficiency diseases:
* Insulin: For diabetes.
* Growth Hormone: For dwarfism.
**Cosmetic Use:**
* **Keratolytic protein substances** are used to soften hard skin.
* **Egg protein** is used for skin tightening.
In simple words: Proteins are used as medicines and in beauty products. For instance, human albumin helps with liver issues, and antibodies fight diseases. Hormones like insulin treat diabetes. In cosmetics, proteins can soften skin and make it tighter.

Exam Tip: Provide clear, distinct examples for both therapeutic and cosmetic applications, making sure to name specific proteins or protein types and their related conditions/effects.

Question 7. Explain the composition of triglyceride?
Answer: Triglycerides consist of a single molecule of glycerol connected to three fatty acids.
1. **Glycerol:** It is a 3-carbon alcohol with three hydroxyl (-OH) groups.
2. **Fatty Acids:** These are long-chain hydrocarbons with a carboxylic group (-COOH) at one end.
3. **Ester Bonds:** Glycerol and fatty acids form ester bonds when they connect.
4. **Saturation:** If the carbons in the fatty acid chain have only single bonds, the triglyceride is saturated. If there are double bonds (\( \text{C=C} \)), it is unsaturated.
5. **Physical Nature:** The structure of the fatty acids largely determines the physical properties of the fat (e.g., solid or liquid at room temperature).
In simple words: Triglycerides are made of one glycerol part and three fatty acid parts. Glycerol is a small alcohol. Fatty acids are long chains with a special acid group. They join with ester bonds. If the chains have only single bonds, it's a saturated fat; if they have double bonds, it's unsaturated. The fatty acids decide how the fat behaves.

Exam Tip: When explaining triglyceride composition, be sure to mention both glycerol and fatty acids, the type of bond (ester), and how saturation affects their physical state.

Question 8. Can you describe what happens when milk is converted into curd or yogurt, from your understanding of proteins?
Answer: In milk, there is lactose (milk sugar). When milk changes into curd or yogurt, the lactase enzyme converts lactose into lactic acid.
\( \text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \xrightarrow{\text{Lactase}} \text{C}_6\text{H}_{12}\text{O}_6 + \text{C}_6\text{H}_{12}\text{O}_6 \)
\( \implies \) Lactose + Water \( \xrightarrow{\text{Lactase}} \) Glucose + Galactose
This lactic acid is responsible for the coagulation of casein, which is the protein in milk. The milk proteins clump together due to the increased acidity, forming the thicker texture of curd or yogurt.
In simple words: When milk turns into curd, bacteria change the milk sugar (lactose) into lactic acid. This acid makes the milk's protein (casein) clump together and solidify, creating the curd.

Exam Tip: Key points to mention are the conversion of lactose to lactic acid by lactase, and how this increased acidity leads to the coagulation of casein protein, resulting in curd formation.

Question 9. Can you attempt building models or biomolecules using commercially available atomic models (Ball and stick models)
Answer: Yes, we can definitely build models of biomolecules using commercially available atomic models, like ball-and-stick sets. These kits allow us to represent atoms with different colored balls and bonds with sticks, helping to visualize molecular structures in three dimensions.
In simple words: Yes, we can build models of biomolecules using ball and stick kits. These kits help us see what molecules look like in 3D.

Exam Tip: Acknowledge the feasibility and educational value of using physical models to understand complex biomolecular structures.

Question 10. Attempt titrating an amino acid against a weak base and discover the number of dissociating (ionizable) functional groups in the amino acid.
Answer: Amino acids are organic compounds that contain both an amino group (\( \text{NH}_2 \)) and an acidic group (carboxyl, -COOH) attached to the same carbon atom. When we attempt titrating an amino acid against a weak base, it dissociates and reveals two main functional groups that can ionize:
* The carboxyl group (-COOH), which is an acidic group.
* The amino group (\( \text{NH}_2 \)), which is a basic group.
Depending on the amino acid, the side chain (R-group) can also have ionizable groups, increasing the total number of dissociating groups.
In simple words: When you mix an amino acid with a weak base, you find out it has parts that can become charged. These are usually the acid part (carboxyl group) and the base part (amino group). Some amino acids have extra charged parts in their side chains.

Exam Tip: Highlight the presence of both acidic (carboxyl) and basic (amino) ionizable groups in a standard amino acid, and note that the R-group can add more.

Question 11. Draw the structure of the amino acid, alanine.
Answer: (The original source provides a chemical structure diagram for Alanine. It shows a central carbon atom bonded to:
* A carboxyl group (\( \text{COOH} \))
* An amino group (\( \text{NH}_2 \))
* A hydrogen atom (H)
* A methyl group (\( \text{CH}_3 \)) as its side chain.)
In simple words: Alanine is an amino acid. Its structure has a central carbon atom connected to a hydrogen, an amino group, a carboxyl group, and a small methyl group.

Exam Tip: For amino acid structures, always remember the central alpha carbon, the amino group, the carboxyl group, and the hydrogen atom, with the R-group defining the specific amino acid (for alanine, the R-group is \( \text{CH}_3 \)).

Question 12. What are gums made of? Is Fevicol different?
Answer: Gums are polymeric substances, meaning they are made of many repeating units, which come under the category of secondary metabolites of plants. They are natural products produced by plants. Fevicol, on the other hand, is a synthetic gum. This means it is man-made and produced through chemical processes, unlike natural plant gums.
In simple words: Gums are natural sticky stuff from plants. Fevicol is different because it's a man-made, artificial glue.

Exam Tip: Distinguish clearly between natural gums (plant-derived secondary metabolites) and synthetic adhesives like Fevicol (man-made polymers).

Question 13. Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat, and urine for them.
Answer: Here are qualitative tests for proteins and fats, and how they can be applied to biological samples:
**Test for Protein (Biuret Test):**
An alkaline suspension of a protein, when treated with an aqueous copper sulfate solution, yields a violet color. The intensity of this color indicates the amount of protein present, making this test both qualitative (detects presence) and quantitative (measures amount).
* **Application:** When testing fruit juice, saliva, sweat, or urine: A violet color indicates the presence of protein. Fruit juice typically has little to no protein, while saliva, sweat, and urine may contain varying amounts, especially under certain physiological conditions.
**Test for Fat:**
Dissolve the fat in alcohol and then add a few drops of distilled water. An emulsion of liquid in water will appear on the surface. Then, add a few drops of Sudan IV and oil red 'O' stain. The emulsion will turn red.
* **Application:** When testing fruit juice, saliva, sweat, or urine: Fats are generally not found in significant amounts in fruit juice, saliva, or sweat. However, some fat might be present in urine in certain pathological conditions, which would show a red emulsion with the stains.
**Test for Amino Acids:**
A common test for amino acids is the **Ninhydrin Test**. When ninhydrin reagent is added to a solution containing amino acids and heated, it produces a deep blue or purple color (except for proline and hydroxyproline, which give a yellow color).
* **Application:** Amino acids are found in all these biological fluids. Saliva and urine will show a positive result. Fruit juice will likely show a weak or negative result unless it contains protein breakdown products.
In simple words: To check for protein, add a special blue liquid (copper sulfate in alkaline solution); if it turns violet, protein is there. To check for fat, mix it with alcohol and water, then add a red dye; if it turns red, fat is present. For amino acids, use ninhydrin and heat; it will turn blue or purple if amino acids are there. You can use these tests on things like fruit juice, spit, sweat, and pee to see what's inside.

Exam Tip: For each test, state the reagent, the expected positive result (color change), and provide a brief explanation of how it works (e.g., color intensity for protein quantity). Also, consider the likely results for common biological samples mentioned.

Question 14. Find out how much cellulose is made by all the plants in the biosphere and compare it with how much paper is manufactured by man and hence what is the consumption of plant material by man: annually. What a loss of vegetation!
Answer: The largest portion of photosynthesis is converted into cellulose. However, this quantity varies significantly from one geographical area to another.
Here are some general estimations of primary production (which largely contributes to cellulose):
1. **Desert:** Less than 2 kg cal/m²/Day
2. **Grassland, deep lakes & mountain forest:** 2-12 kcal/m²/Day
3. **Moist forest, shallow lake, moist grassland, and moist agricultural land:** 2-40 kg cal/m²/Day
Similar data can be used to calculate the total cellulose secretion in the world per year. There is a significant increase in industrialization, which in turn boosts the use of paper. Because of this increased demand, a great extent of vegetation is being lost annually.
**Comparison with Paper Manufacturing and Plant Material Consumption:**
While exact figures fluctuate, global cellulose production by plants is enormous, far exceeding human consumption for paper. However, the *rate* of deforestation for pulp and paper, coupled with other demands for timber, fuel, and agriculture, leads to a substantial loss of vegetation. Annually, millions of tons of wood are harvested for paper alone, representing a significant portion of accessible forests, particularly in specific regions. This heavy consumption contributes to habitat loss, climate change, and reduced biodiversity.
In simple words: Plants make a huge amount of cellulose through photosynthesis, but this amount changes based on the area. People use a lot of plants for making paper, and this use is growing because of more industries. Even though plants make a lot of cellulose, our increasing demand for paper and other plant products means we are losing a lot of trees and plants every year, which is bad for the environment.

Exam Tip: Emphasize the vast natural production of cellulose, but then pivot to the impact of human consumption (especially for paper) as a driver of vegetation loss, linking it to industrialization and environmental concerns.

Question 15. Describe the important properties of enzymes.
Answer: Here are some important properties of enzymes:
1. An enzyme, like any protein, possesses a primary structure (amino acid sequence). It also has secondary and tertiary structures, which are crucial for its function.
2. Every enzyme features an 'active site', which is a specific crevice or pocket where the substrate molecules bind perfectly.
3. Enzymes are highly specific in their action. A particular enzyme typically acts only on a particular substrate or a very similar group of substrates. Different enzymes catalyze unique chemical or metabolic reactions.
\( \text{X} + \text{Y} \xrightarrow{\text{Enzyme}} \text{X-Y} \)
For example, an enzyme can catalyze the linking together of two compounds:
\( \text{X} + \text{Y} + \text{C} = \text{C} \implies \text{X-Y} + \text{C} = \text{C} \) (This example from the source seems incomplete or illustrative of a generic reaction rather than specific linking)
A better example would be: \( \text{A} + \text{B} \xrightarrow{\text{Enzyme}} \text{AB} \) (Enzymes can facilitate the formation of various bonds like carbon-oxygen (c-o) or carbon-sulfur (c-s) bonds, etc.)
In simple words: Enzymes are proteins with a specific 3D shape, including a special spot called the 'active site' where other molecules fit. They are very picky, meaning each enzyme usually works on only one type of molecule or reaction. Enzymes also help join different compounds together.

Exam Tip: Key properties of enzymes to remember are their protein nature, the presence of an active site, high specificity, and their role as catalysts in biochemical reactions.