BIOLOGY 5 Marks Questions

Proteins are macromolecules formed by the polymerization of amino acids. Structurally, proteins are divided into four levels.

1. Primary structure – It is the linear sequence of amino acids in a polypeptide chain.
2. Secondary structure – The polypeptide chain is coiled to form a three-dimensional structure.
3. Tertiary structure – The helical polypeptide chain is further coiled and folded to form a complex structure.
4. Quaternary structure – More than one polypeptide chains assemble to form the quaternary structure.

Milk has many globular proteins. When milk is converted into curd or yoghurt, these complex proteins get denatured, thus converting globular proteins into fibrous proteins. Therefore, by the process of denaturation, the secondary and tertiary structures of proteins are destroyed.

Yes. The biomolecules can be represented by the ball and stick model. The bonds which hold the atoms are represented by sticks, whereas the atoms are represented by balls.
Example: In the model of D-glucose, the oxygen atoms are represented by pink balls, the hydrogen atoms by green balls, while the carbon atoms are represented by grey balls.

Yes, if we are given a method to know the sequence of proteins, we can connect this information to the purity of a protein. It is known that an accurate sequence of a certain amino acid is very important for the functioning of a protein. If there is any change in the sequence, it would alter its structure, thereby altering the function. If we are provided with a method to know the sequence of an unknown protein, then using this information, we can determine its structure and compare it with any of the known correct protein sequence. Any change in the sequence can be linked to the purity or homogeneity of a protein. For example, any one change in the sequence of hemoglobin can alter the normal hemoglobin structure to an abnormal structure that can cause sickle cell anemia.

	Molecule	Structure
1.	Adenosine
2.	Thymidine
3.	Sucrose
4.	Maltose
5	Lactose
6.	Ribose
7.	DNA
8.	RNA
9.	Glycerol
10.	Insulin

	Compound	Manufacturer	Buyer
1.	Starch products	Kosha Impex (P) Ltd.	Research laboratories, educational institutes, and other industries, which use biomolecules as a precursor for making other products.
2.	Liquid glucoseMarudhar apparels	Marudhar apparels
3.	Various enzymes such as amylase, protease, cellulase	Map (India) Ltd

Glycosidic bond is formed normally between carbon atoms, 1 and 4, of neighbouring monosaccharide units.
Peptide bond is a covalent bond that joins the two amino acids by – NH – CO linkage.

Phosphodiester bond is a strong covalent bond between phosphate and two sugar groups. Such bonds form the sugar phosphate backbone of nucleic acids.

The important properties of enzymes are as follows:

1. The enzymes are generally proteins which are high molecular weight complex globular proteins. They can associate with non-protein substance for their activity.
2. The enzymes do not start a chemical reaction but only accelerate it. They combine temporarily with the substrate molecules and are not consumed or changed permanently in the reaction which they catalyse.
3. The enzyme controlled reactions are reversible.
4. The enzymes are specific in action. An enzyme catalyses only a particular kind of reaction or acts on a particular substrate only.
5. The enzymes are thermo labile i.e., heat sensitive and can function best at an optimum temperature. Similarly, enzymes show maximum activity at optimum pH.
6. The enzymes are inactivated by poisons and radiation.

1. Test for protein

Biuret’s test – If Biuret’s reagent is added to protein, then the colour of the reagent changes from light blue to purple.

2. Test for fats and oils

Grease or solubility test

3. Test for amino acid

Ninhydrin test – If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue, or purple, depending on the amino acid.

	Item	Name of the test	Procedure	Result	Inference
1.	Fruit juice	Biuret’s test	Fruit juice + Biuret’s reagent	Colour changes from light blue to purple.	Protein is present.
		Greasetest	To a brown paper, add a few drops of fruit juice.	No translucent spot.	Fats and oils are absent or are in negligible amounts.
		Ninhydrin test	Fruit juice +Ninhydrin reagent + boil for 5 minutes.	Colourless solution changes to pink, blue, or purple colour.	Amino acids are present.
2.	Saliva	Biuret’s test	Saliva + Biuret’s reagent	Colour changes from light blue to purple.	Proteins are present.
		Greasetest	On a brown paper, add a drop of saliva.	No translucent spot	Fats/oils are absent.
		Ninhydrin test	Saliva + Ninhydrin reagent + boil for 5 minutes.	Colourless solution changes to pink, blue, or purple colour.	Amino acids are present.
3.	Sweat	Biuret’s test	Sweat + Biuret’s reagent	No colour change	Proteins are absent.
		Solubility test	Sweat + Water	Oily appearance	Fats/oil may be present.
		Ninhydrin test	Sweat + Ninhydrin reagent + boil for 5 minutes	No colour change, solution remains colourless.	Amino acids are absent.
4.	Urine	Biuret’s test	Few drops of urine + Biuret’s reagent	Colour changes from light blue to purple.	Proteins are present.
		Solubility test	Few drops of urine + Water	Little bit of oily appearance.	Fats may or may not be present.
		Ninhydrin test	Few drops of urine + Ninhydrin reagent + boil for 5 minutes.	Colourless solution changes to pink, blue, or purple colour depending on the type of amino acid.	Amino acids are present.

On esterification, triglyceride is produced. The ester is called monoglyceride, diglyceride and triglyceride depending on the number of fatly acids attached to a glycerol
molecule.

Turn over of biomolecules means that they are constantly being changed into some other biomolecules and also made from some other biomolecules.

1. Rakesh would pick T and U cards as thymine is present only in DNA and uracil is present only in RNA.
2. Uracil does not form H-bonding with other nucleic acid as uracil is found in RNA and RNA is single-stranded molecule.
3. A nucleic acid is a polymer of nucleotides which is composed of three components.

• Heterocyclic compound-nitrogen base (adenine, guanine, uracil, cytosine and thymine). The skeletal heterocyclic in DNA/ RNA is called as purine and pyrimidines. Adenine and guanine are purines while uracil (only in RNA), thymine (only in DNA) and cytosine are pyrimidines.
• Monosaccharide (ribose or deoxyribose).
• Phosphoric acid or phosphate.

In living systems, metabolism involves two following types of pathways.

1. The anabolic pathway is called biosynthetic pathway. It leads to a more complex structure from a simpler structure, e.g., the pathway involving the conversion of acetic acid into cholesterol. These pathways consume energy.
2. The catabolic pathway leads to simpler structure from a complex structure, e.g., thepathway involving conversion of glucose into lactic acid in our skeletal muscles. This pathway leads to the release of energy, e.g., energy is liberated when glucose is degrated to lactic acid in our skeletal muscles.

1. Double helix model of DNA (Walton-Crick model of DNA).
2. (A) 2 nm (B) 3.4 rim (C) 0.34 run.
3. The bonds between C and G are three.
4. This is B-form of DNA.
5. B-DNA is right-handed spiral structure.

1. Amino acids are the building blocks of proteins.
2. Besides building blocks of proteins, amino acids are involved in the synthesis of a number of compounds such as hormones, amine buffers, antibiotics, prokaryotic cell wall, etc.
3. Such pills might be harmful in long run and one should have balanced diet and exercise regularly to built muscles naturally.
4. Vikas's teacher was concerned about his students health, and knows scientific ethics and had knowledge about harmful effects of such products.

Structure of Protein: Primary Structure: The sequence of amino acids i.e., the positional information in a protein-which is the first amino acid, which is second, and so on - is called the primary structure of a protein. A protein is imagined as a line, the left end represented by the first amino acid and the right end represented by the last amino acid. The first amino acid is also called as N-terminal amino acid. The last amino acid is called the C-terminal amino acid. A protein thread does not exist throughout as an extended rigid rod. Secondary Structure: Regularly repeating local structures stabilized by hydrogen bonds. The most common examples are the alpha helix, beta sheet and turns. Because secondary structures are local, many regions of different secondary structure can be present in the same protein molecule. Tertiary structure: The overall shape of a single protein molecule; the spatial relationship of the secondary structures to one another. Tertiary structure is generally stabilized by nonlocal interactions, most commonly the formation of a hydrophobic core, but also through salt bridges, hydrogen bonds, disulfide bonds, and even post-translational modifications. The term “tertiary structure” is often used as synonymous with the term fold. The Tertiary structure is what controls the basic function of the protein. Quaternary Structure: Some proteins are an assembly of more than one polypeptide or subunits. The manner in which these individual folded polypeptides or subunits are arranged with respect to each other (e.g. linear string of spheres, spheres arranged one upon each other in the form of a cube or plate etc.) is the architecture of a protein otherwise called the quaternary structure of a protein.

Nature of bond linking monomers in a polymer. Glycosidic Bond: A glycosidic bond is a certain type of functional group that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. Peptide Bond: A peptide bond (amide bond) is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water (HO). This is a dehydration synthesis reaction (also known as a condensation reaction), and usually occurs between amino acids. The resulting CO-NH bond is called a peptide bond, and the resulting molecule is an amide. The four-atom functional group -C(=O)NH- is called an amide group or (in the context of proteins) a peptide group. Polypeptides and proteins are chains of amino acids held together by peptide bonds, as is the backbone of PNA. Polyamides, such as nylons and aramids, are synthetic molecules (polymers) that possess peptide bonds.
Phosphodiester Bond: A phosphodiester bond is a group of strong covalent bonds between a phosphate group and two other molecules over two ester bonds. Phosphodiester bonds are central to all life on Earth, as they make up the backbone of the strands of DNA. In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon of another, deoxyribose in DNA and ribose in RNA.

Factors Affecting Enzymatic Action Temperature and pH: Enzymes generally function in a narrow range of temperature and pH. Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH. Activity declines both below and above the optimum value. Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat. Concentration of Substrate: With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first. The reaction ultimately reaches a maximum velocity (Vmax) which is not exceeded by any further rise in concentration of the substrate. This is because the enzyme molecules are fewer than the substrate molecules and after saturation of these molecules, there are no free enzyme molecules to bind with the additional substrate molecules. Effect of Inhibitor: The activity of an enzyme is also sensitive to the presence of specific chemicals that bind to the enzyme. When the binding of the chemical shuts off enzyme activity, the process is called inhibition and the chemical is called an inhibitor. When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as. Competitive inhibitor: Due to its close structural similarity with the substrate, the inhibitor competes with the substrate for the substrate binding site of the enzyme. Consequently, the substrate cannot bind and as a result, the enzyme action declines, e.g., inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure. Such competitive inhibitors are often used in the control of bacterial pathogens. "Lock and Key” Model: Enzymes are very specific, and it was suggested by Emil Fischer in 1894 that this was because both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This is often referred to as “the lock and key” model. However, while this model explains enzyme specificity, it fails to explain the stabilization of the transition state that enzymes achieve. The “lock and key” model has proven inaccurate, and the induced fit model is the most currently accepted enzyme-substrate-coenzyme figure. Induced Fit Model: In 1958, Daniel Koshland suggested a modification to the lock and key model: since enzymes are rather flexible structures, the active site is continually reshaped by interactions with the substrate as the substrate interacts with the enzyme. As a result, the substrate does not simply bind to a rigid active site; the amino acid side chains which make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function. In some cases, such as glycosidases, the substrate molecule also changes shape slightly as it enters the active site. The active site continues to change until the substrate is completely bound, at which point the final shape and charge is determined.

Primary structure of a protein includes number of polypeptides, number and sequence of amino acids in each polypeptide.
The development of new stearic relationships of amino acids present in linear sequence inside the polypeptides leads to the formation of secondary structure of proteins.
Tertiary structure involves interactions that are caused by binding and folding of a-helix or P sheets leading to the formation of rods, spheres or fibres. Tertiary structure is stabilized by several types of bonds such as, H-bonds, ionic bonds, covalent bonds, van der Waal’s interactions hydrophobic bonds, etc.

Mechanisms of Enzymatic Actions:

1. Lowering the activation energy by creating an environment in which the transition state is stabilized (e.g. straining the shape of a substrate-by binding the transition-state conformation of the substrate/ product molecules, the enzyme distorts the bound substrate(s) into their transition state form, thereby reducing the amount of energy required to complete the transition).
2. Lowering the energy of the transition state, but without distorting the substrate, by creating an environment with the opposite charge distribution to that of the transition state.
3. Providing an alternative pathway: For example, temporarily reacting with the substrate to form an intermediate ES complex, which would be impossible in the absence of the enzyme.
4. Reducing the reaction entropy change by bringing substrates together in the correct orientation to react. Considering AHỊ alone overlooks this effect.
5. Increases in temperatures speed up reactions. Thus, temperature increases help the enzyme function and develop the end product even faster. However, if Sheated to heated too much, the enzyme's shape deteriorates and only when the temperature comes back to normal does the enzyme regain its shape. Some enzymes like thermolabile enzymes work best at low temperatures.

The catalytic cycle of an enzyme action can be described in the following steps:

1. First, the substrate binds to the active site of the enzyme, fitting into the active site.
2. The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate.
3. The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new enzyme- product complex is formed.
4. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again.

Nucleic acids are long chain macromolecules which are formed by end to end polymerization of large number of repeated units called nucleotides. Nucleic acids show a wide range of secondary structures. A secondary structure is the set of interactions between bases and sugar phosphate backbone and is responsible for the shap that nucleic acid. James Watson and Francis Crick proposed a secondary structure of DNA molecules based on the crystallographic studies.

1. DNA or deoxyribonucleic acid is a helically twisted double-chain polydeoxyribo- nucleotide macromolecule.
2. The two strands of DNA run anti-parallely to each other called as DNA duplex.
3. The spiral twisting of DNA has two types of alternate grooves, i.e., major and minor.
4. One turn of 360° of the spiral has about 10 nucleotides on each strand of DNA occupying a distance of about 3.4 nm.
5. The nucleotides within each strand are held together by the phosphodiester bonds between the 5' carbon of one nucleotide and the 3' carbon of the adjacent nucleotide. This strong covalent bond holds the sugar/phosphate backbone together.
6. The two strands of DNA are held together by weak hydrogen boiias between the nitrogenous bases. These hydrogen bonds are base specific. That is adenine forms 2hydrogen bonds with thymine CA=T and cytosine forms 3 hydrogen bonds with guanine (C=G).
7. As specific and different nitrogen bases occur on two DNA chains, they are said to be complementary, i.e., urine lies opposite to pyrimidine. This purine-pyrimidine pairing also contributes to the thickness of strand, i.e., 2nm, and makes the two chains complementary.​​​​​​

Nucleic acids exhibit a wide variety of secondary structures. For example, one of the secondary structures exhibited by DNA is the famous Watson - Crick Model. This model says that DNA exists as a double helix. The two strands of polynucleotide’s are antiparallel, i.e. run in the opposite direction. The backbone is formed by the sugar-phosphate-sugar chain. The nitrogen bases are projected more or less perpendicular to this backbone but face inside. A and G of one strand compulsorily base pairs with T and C respectively on the other strand. There are two hydrogen bonds between A and T and three hydrogen bonds between G and C. Each strand appears like a helical staircase. Each step of ascent is represented by a pair of bases. At each step of ascent, the strand turns 36°. One full turn of the helical strand would involve ten steps or ten base pairs. Attempt drawing a line diagram. The pitch would be 34 A. The rise per base pair would be 3.4 A. This form of DNA with the above mentioned salient features is called B-DNA.