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BBCCT-101: Molecules of Life

BBCCT-101: Molecules of Life

IGNOU Solved Assignment Solution for 2023

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Assignment Code: BBCCT-101/TMA/2023

Course Code: BBCCT-101

Assignment Name: Molecules of Life

Year: 2023

Verification Status: Verified by Professor

 

Answer all the questions given below. All Questions carry equal marks.

 

Q1) (A) Write a brief note on Friedrich Wohler’s contribution to the origin of Biochemistry.

Ans) Friedrich Wöhler was a German chemist who is credited with pioneering the field of biochemistry. He is best known for his ground-breaking experiment that challenged the prevailing belief of the time known as the "vitalist" theory, that living matter could only be produced from previously living matter.

 

Wöhler demonstrated that organic compounds, such as urea, could be synthesized from inorganic compounds. This paved the way for further research into the chemical basis of life and led to the understanding of the structure and function of biomolecules. Wöhler's contribution to biochemistry is considered as a major turning point in the field and he is often referred to as the "father of biochemistry".

 

Q1) (B) Discuss important inorganic elements and their biological functions.

Ans) Inorganic elements and their biological functions:


Q2) Define the following bonds/interactions with suitable examples: hydrogen bond, hydrophobic bond, Vander Waals, and Electrostatic interactions.

Ans)

Hydrogen Bond: Hydrogen bonds are weak bonds formed between the positively charged hydrogen atom of one molecule and the negatively charged atom (such as oxygen or nitrogen) of another molecule. These bonds are important in determining the three-dimensional structure of biological molecules such as proteins and nucleic acids. Example: Hydrogen bonds form between the nitrogen-hydrogen and oxygen-hydrogen groups in DNA, stabilizing its double-helix structure.

 

Hydrophobic Bond: Hydrophobic bonds are the result of the non-polar nature of certain molecules, which leads to their exclusion from water and their aggregation in a hydrophobic environment. These bonds play a critical role in the formation of the lipid bilayer of cell membranes. Example: The hydrophobic tails of phospholipids in the cell membrane aggregate together, forming a hydrophobic barrier that separates the interior of the cell from the external environment.

 

Vander Waals Interactions: Vander Waals interactions are weak, non-covalent bonds that result from the fluctuation of the electron cloud around atoms and molecules. These interactions help determine the three-dimensional structures of biological molecules, including protein-protein and protein-ligand interactions. Example: Vander Waals interactions between the aromatic residues in proteins and small molecule ligands help stabilize protein-ligand complexes.

 

Electrostatic Interactions: Electrostatic interactions are forces of attraction or repulsion between charged atoms or molecules. These interactions are important in determining the three-dimensional structure of biological molecules, including protein-protein and protein-ligand interactions. Example: Electrostatic interactions between positively charged residues in a protein and negatively charged ligand help stabilize protein-ligand complexes.

 

Q3) (A) Describe and draw the general structure of amino acid.

Ans) Amino acids are the building blocks of proteins. Each amino acid has a unique structure, but they all share a common backbone consisting of a central carbon atom (C), also known as the alpha carbon, which is bonded to an amino group (-NH2), a carboxyl group (-COOH), and a side chain (R group).

 

The general structure of an amino acid can be represented as follows:

 





 

where N represents the nitrogen atom of the amino group, C represents the carbon atom, and R represents the side chain. The R group can be a simple hydrogen atom or a more complex functional group and determines the unique properties of each amino acid.

 

Amino acids can participate in peptide bonds to form polypeptides, which can then fold into complex proteins. The sequence of amino acids in a polypeptide chain determines the final three-dimensional structure and function of a protein.

 


Q3) (B) With the help of neatly labelled diagrams explain the peptide bond.

Ans) A peptide bond is a covalent bond that links two amino acids together in a polypeptide chain. It is formed by a condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another amino acid, releasing a molecule of water (H2O).

 

Here is a diagram that represents the formation of a peptide bond:

 

 


In this diagram, the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another amino acid, forming a covalent bond between the nitrogen and carbon atoms. This reaction releases a molecule of water (H2O). The resulting bond between the nitrogen and carbon atoms is called a peptide bond.

 

The formation of peptide bonds between multiple amino acids results in the formation of a polypeptide chain. The sequence of amino acids in the polypeptide chain determines the final three-dimensional structure and function of a protein.

 

Q4) (A) What are stereoisomers?

Ans) Stereoisomers are isomeric compounds that have the same chemical formula and bond connectivity but differ in the spatial arrangement of their atoms. In other words, stereoisomers are molecules that have the same atoms, but they are arranged differently in space. There are two main types of stereoisomers:

 

  1. Enantiomers: Enantiomers are stereoisomers that are mirror images of each other but are not superimposable. They are also referred to as "optical isomers." Enantiomers have identical physical and chemical properties, except for their behaviour in polarized light and their interaction with chiral environments.

  2. Diastereomers: Diastereomers are stereoisomers that are not mirror images of each other and are also not superimposable. Diastereomers have different physical and chemical properties, and they differ in the arrangement of their stereogenic centers.

Stereoisomers play an important role in biological systems, as they can determine the properties and functions of biological molecules, including enzymes and other proteins, and can also affect the activity of drugs and other small molecules.

 


Q4) (B) Explain different types of glycosidic bonds with suitable examples?

Ans) Glycosidic bonds are covalent bonds that link monosaccharides, or simple sugars, together to form complex carbohydrates, such as oligosaccharides and polysaccharides.

 

There are three main types of glycosidic bonds, each with a different linkage between the monosaccharides:

 

  1. alpha (α) linkage: An alpha (α) linkage is a glycosidic bond that forms between the 1-carbon of one monosaccharide and the 4-carbon of another monosaccharide. An example of an α-linked disaccharide is maltose, which is formed from two glucose molecules.

  2. beta (β) linkage: A beta (β) linkage is a glycosidic bond that forms between the 1-carbon of one monosaccharide and the 4-carbon of another monosaccharide. An example of a β-linked disaccharide is lactose, which is formed from one glucose molecule and one galactose molecule.

  3. gamma (γ) linkage: A gamma (γ) linkage is a glycosidic bond that forms between the 1-carbon of one monosaccharide and the 4-carbon of another monosaccharide. An example of a γ-linked disaccharide is cellobiose, which is formed from two glucose molecules.

 

Each type of glycosidic bond determines the structure and properties of the resulting carbohydrate, and they play important roles in various biological processes, including energy storage, cell recognition, and immune response.

 


Q4) (C) Mutarotation

Ans) Mutarotation refers to the rotation of the plane of polarized light caused by a change in the configuration of a chiral molecule in solution. It is a dynamic process in which a molecule with multiple stereoisomers interconverts between different conformations. This process is often observed in carbohydrates, particularly in the cyclic form, where the anomeric carbon undergoes mutarotation. Mutarotation results in an equilibrium mixture of stereoisomers, with the specific distribution determined by the relative stability of each conformation. Mutarotation occurs due to the intermolecular hydrogen bonding in solution and results in an average molecule that has intermediate optical rotation between the different stereoisomers.


 

Q5) Write a detailed note on plant and animal storage polysaccharides with suitable diagrams and examples.

Ans) Polysaccharides are complex carbohydrates consisting of many monosaccharide units bonded together through glycosidic linkages. In both plants and animals, polysaccharides serve as storage molecules for energy and other biological functions. Here, the storage polysaccharides in plants and animals along with their structures, functions, and examples.

 

Plant Storage Polysaccharides

 

Starch: Starch is the most common storage polysaccharide in plants, which is made up of two types of polymers, amylose, and amylopectin. Amylose is a linear polymer consisting of several thousand α-D-glucose units linked together by α-1,4-glycosidic bonds. Amylopectin is a branched polymer with α-1,4-glycosidic bonds between glucose units and α-1,6-glycosidic bonds at branching points. Starch is found in the form of grains in the cytoplasm of plant cells, mainly in seeds, roots, and tubers. Examples of plants that store starch as a reserve food are potatoes, rice, wheat, and maize.

 

Glycogen: Glycogen is another type of storage polysaccharide found in some plant species, such as fungi, algae, and bacteria, but it is mainly found in animals. Glycogen is a highly branched polymer with α-1,4-glycosidic bonds between glucose units and α-1,6-glycosidic bonds at branching points, like amylopectin. Glycogen is primarily stored in the liver and muscles of animals, where it serves as a source of energy during periods of fasting or high-energy demands.

 

Animal Storage Polysaccharides

 

Glycogen: Glycogen is the primary storage polysaccharide in animals, particularly in the liver and muscles. As mentioned earlier, glycogen is a highly branched polymer consisting of glucose units linked together by α-1,4-glycosidic bonds and α-1,6-glycosidic bonds at branching points. In the liver, glycogen is broken down into glucose and released into the bloodstream to maintain blood sugar levels. In muscles, glycogen is broken down to provide energy during physical activity.

 

Chitin: Chitin is another type of storage polysaccharide found in the exoskeleton of insects, crustaceans, and other arthropods. Chitin is a linear polymer consisting of N-acetylglucosamine units linked together by β-1,4-glycosidic bonds. Chitin serves as a structural component of the exoskeleton and provides protection against predators and environmental stresses.

In summary, both plants and animals use storage polysaccharides to store energy and perform other biological functions. Starch and glycogen are the most common storage polysaccharides in plants and animals, respectively. Chitin is a storage polysaccharide found in the exoskeleton of arthropods. The structures and functions of these polysaccharides differ depending on their chemical composition and location of storage.

 

Q6) (A) What is disaccharide. Explain with two suitable examples.

Ans) Disaccharide is a type of carbohydrate that consists of two simple sugars (monosaccharides) chemically bonded together. Disaccharides are the smallest units of carbohydrates that can be digested by the human body and are broken down into their constituent monosaccharides during digestion. There are several common types of disaccharides, including:

  1. Sucrose: This is a disaccharide made up of one molecule of glucose and one molecule of fructose. It is commonly known as table sugar and is widely used as a sweetener in food and drink products.

  2. Lactose: This is a disaccharide made up of one molecule of glucose and one molecule of galactose. It is the primary sugar found in milk and is also known as milk sugar. People with lactose intolerance cannot properly digest lactose due to a lack of the enzyme lactase, which breaks down lactose into its component sugars.

 

These are just two examples of disaccharides. There are several other disaccharides that play important roles in human nutrition and metabolism.

 

Q6) (B) Give a detailed account on glycoconjugates.

Ans) Glycoconjugates are a class of biomolecules that are composed of carbohydrates (also known as saccharides or sugars) covalently bonded to other types of molecules, such as lipids, proteins, or nucleic acids. These conjugates play important roles in many biological processes, including cell recognition and signalling, immune defence, and structural support.

 

Glycoconjugates are composed of a carbohydrate moiety (or glycans), which can be linear or branched chains of monosaccharides, and a non-carbohydrate moiety, such as a protein, lipid, or nucleic acid. The carbohydrates in glycoconjugates can be further modified by addition of functional groups, such as sulphate or phosphate groups, which can alter their properties and influence their interactions with other biomolecules.

 

One well-known class of glycoconjugates is glycoproteins, which are proteins with covalently attached carbohydrate chains. Glycoproteins play important roles in many biological processes, including cell-cell recognition, immune response, and cell signalling. For example, the surface of cells is often covered with a layer of glycoproteins that serve as recognition markers, allowing cells to identify and communicate with each other.

 

Q7) (A) Describe classification of lipids?

Ans) Lipids are a diverse class of biomolecules that are broadly classified into several categories based on their chemical structure and biological functions. The following are the main classes of lipids:

  1. Fats (or Triglycerides): These are the most abundant lipids in the human body and are composed of a glycerol molecule covalently bonded to three fatty acid molecules. They are an important energy source and are stored in the body as adipose tissue.

  2. Phospholipids: These are lipids that are composed of a glycerol molecule covalently bonded to two fatty acid molecules and a phosphate group. Phospholipids are the main component of cell membranes and are important for maintaining their structure and fluidity.

  3. Steroids: These are a group of lipids that are characterized by a complex ring structure. Steroids include hormones, such as testosterone and estrogen, and cholesterol, which is a component of cell membranes and a precursor to other steroids.

  4. Waxes: These are lipids that are composed of long-chain fatty acids and alcohols. They are hydrophobic and are used by plants and animals as a barrier to protect against water loss and environmental damage.

  5. Prostaglandins: These are a group of lipids that are derived from fatty acids and play important roles in regulating a variety of physiological processes, including inflammation, blood pressure, and pain perception.

  6. Fat-Soluble Vitamins: These are vitamins that are soluble in fat and include vitamins A, D, E, and K. They play important roles in maintaining overall health and preventing various diseases.

 

These are the main classes of lipids, and they play important roles in a variety of biological processes, including energy storage, cell membrane structure and function, hormone regulation, and disease prevention. Understanding the classification and properties of lipids is important for understanding their biological functions and the effects of lipid imbalances in human health.

 

Q7) (B) Explain the importance of lipids as signalling molecules.

Ans) Lipids play important roles as signalling molecules in many biological processes. Unlike water-soluble signalling molecules, such as hormones and neurotransmitters, lipids are hydrophobic and can diffuse through cell membranes to reach their target proteins. This allows lipids to convey signals rapidly and efficiently to a wide range of target proteins within the cell.

 

One well-known class of lipid signalling molecules are the eicosanoids, which are derived from fatty acids and play important roles in regulating a variety of physiological processes, including inflammation, blood pressure, and pain perception. For example, prostaglandins, which are a type of eicosanoid, play important roles in regulating inflammation and pain by binding to specific receptors on cells and activating signalling pathways.

 

Another important class of lipid signalling molecules are the sphingolipids, which are composed of a sphingosine backbone covalently bonded to a fatty acid. Sphingolipids play important roles in regulating cell signalling and growth, as well as cell-cell communication and cell-matrix interactions.

 

In addition, phospholipids themselves can act as signalling molecules by undergoing changes in their composition and localization within the cell membrane. For example, changes in the levels of specific phospholipids, such as phosphatidylinositol 4,5-bisphosphate (PIP2), can lead to changes in the localization of signalling proteins and the activation of signalling pathways.

 

Q8 Enlist water-and fat-soluble vitamins. Write a detailed note on classification of vitamins with examples.

Ans) Vitamins are organic compounds that are essential for normal growth, development, and overall health. They are classified into two main categories based on their solubility: water-soluble vitamins and fat-soluble vitamins. Water-soluble vitamins are soluble in water and are not stored in the body to any significant degree. They must be obtained from the diet on a regular basis to meet the body's needs. Examples of water-soluble vitamins include:

  1. Vitamin B Complex: This group of vitamins includes vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folic acid), and vitamin B12 (cobalamin). These vitamins play important roles in energy metabolism, nervous system function, and red blood cell production.

  2. Vitamin C (Ascorbic Acid): This vitamin is an antioxidant that is important for maintaining healthy skin, gums, and connective tissue, and for boosting the immune system.

 

Fat-soluble vitamins are soluble in fat and can be stored in the body, so they do not need to be obtained from the diet daily. However, it is still important to consume adequate amounts of these vitamins, as excesses can lead to toxicity. Examples of fat-soluble vitamins include: 

  1. Vitamin A (Retinol): This vitamin is important for vision, immune function, and the maintenance of healthy skin and mucous membranes.

  2. Vitamin D (Calciferol): This vitamin is important for calcium metabolism and the maintenance of healthy bones and teeth.

  3. Vitamin E (Tocopherol): This vitamin is an antioxidant that is important for protecting cell membranes from damage.

  4. Vitamin K (Phylloquinone): This vitamin is important for blood clotting and bone health.

 

Q9) (A) Describe and draw nucleosides and nucleotides.

Ans) Nucleosides and nucleotides are the building blocks of nucleic acids, such as DNA and RNA. Nucleosides consist of a nitrogenous base (such as adenine, guanine, cytosine, or uracil) and a sugar molecule (ribose or deoxyribose). Nucleotides are nucleosides that have an additional phosphate group attached to the sugar molecule.

 

Nucleosides and nucleotides play important roles in many biological processes, such as DNA replication and repair, genetic information storage and transmission, and cellular energy production. The nitrogenous bases in nucleotides are the source of the genetic information stored in DNA, while the phosphate groups provide the energy needed for DNA replication and other cellular processes.

Nucleosides



Nucleotides


Q9) (B) Write the experimental evidence showing nucleic acids as genetic material.

Ans) There have been several experimental studies that have provided evidence that nucleic acids, specifically DNA, are the genetic material. Some of the key experiments are:

 

The Hershey-Chase Experiment: In 1952, Alfred Hershey and Martha Chase conducted an experiment to determine whether DNA or protein was the genetic material of the T2 bacteriophage. They used radioactive isotopes to label either the DNA or the protein component of the phage and then infected bacteria with the labelled phage. After the phage particles had entered the bacteria, Hershey and Chase used a blender to break open the phage particles and separate the bacterial cells from the phage components. They then used a centrifuge to separate the bacteria from the phage components and found that the radioactive label was in the bacterial cells, indicating that the genetic material was DNA, not protein.

 

Avery, MacLeod, and McCarty experiment: In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty conducted an experiment to determine if DNA was the genetic material of Streptococcus pneumoniae. They took purified DNA from a strain of S. pneumoniae and used it to transform a non-pathogenic strain into a pathogenic strain. This transformation demonstrated that DNA was indeed the genetic material, as it was able to carry the genetic information responsible for pathogenicity.

 

The Meselson-Stahl experiment: In 1958, Matthew Meselson and Franklin Stahl conducted an experiment to determine how DNA replication occurs. They grew bacteria in a medium containing heavy nitrogen (15N) and then switched the medium to one containing lighter nitrogen (14N). Over several generations, they found that the DNA in the bacteria became lighter, demonstrating that DNA replication was semi-conservative, meaning that each daughter DNA molecule contains one original (heavy) strand and one newly synthesized (light) strand.

 

Q10) (A) Describe and draw the structure of Watson-Crick Model of DNA.

Ans) The Watson-Crick model of DNA, also known as the double helix model, is a structure of DNA that was proposed by James Watson and Francis Crick in 1953. It describes DNA as a double-stranded helix composed of nucleotides, which are the building blocks of DNA. Each nucleotide is composed of a sugar molecule (deoxyribose), a nitrogenous base (adenine, guanine, cytosine, or thymine), and a phosphate group.

 

In the Watson-Crick model, the two strands of DNA run in opposite directions and are held together by hydrogen bonds between the nitrogenous bases. The nitrogenous bases are connected to the sugar-phosphate backbone of the DNA molecule by glycosidic bonds. The nitrogenous bases form specific pairs, with adenine always pairing with thymine and guanine always pairing with cytosine. This specific pairing of the nitrogenous bases is known as base pairing, and it is the mechanism that allows DNA to carry genetic information.


Watson-Crick Model of DNA

 

 

Q10) (B) Explain the chemical basis behind the increased U.V. absorption of denatured DNA.

Ans) The increased UV absorption of denatured DNA, compared to its native, double-stranded form, is due to differences in the electronic structure of the two forms of DNA.

 

In its native, double-stranded form, DNA has a more stable electronic structure, with electrons distributed evenly in a manner that minimizes the potential energy of the molecule. This stability results in a lower absorption of UV light and a correspondingly lower UV absorbance maximum, typically around 260 nm.

 

In contrast, when DNA is denatured or melted, the hydrogen bonds between the complementary base pairs are broken, causing the double-stranded structure to unwind into single strands. This disruption of the stable electron distribution results in an increased absorption of UV light, with a corresponding increase in the UV absorbance maximum, typically to around 260-270 nm.

 

This change in UV absorbance is used as a simple and quick method for determining the degree of denaturation of DNA in solution, with a higher absorbance indicating a higher degree of denaturation. This principle is commonly used in spectrophotometric analysis to quantify the amount of double-stranded DNA present in a sample and is a critical component of many molecular biology techniques, such as DNA sequencing and analysis of gene expression.

 


 

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