Proteins Questions in English

(D) The primary structure of a protein refers to the linear sequence of amino acids in a polypeptide chain.
This sequence is determined by the genetic information encoded in the $DNA$.
It involves the specific number of amino acids,the types of amino acids present,and their specific order or sequence in the chain.
Therefore,all these factors contribute to defining the primary structure of a protein.

(C) The secondary structure of proteins refers to the local folding of the polypeptide chain into regular patterns. The two most common types of secondary structures are the $\alpha$-helix (helical) and the $\beta$-pleated sheet (pleated sheet). These structures are stabilized by hydrogen bonds between the amino and carboxyl groups of the polypeptide backbone. Therefore,a polypeptide chain can exhibit a helical coiled structure or a pleated sheet structure.

(C) The secondary structure of a protein refers to the local folded structures that form within a polypeptide due to interactions between atoms of the backbone.
Specifically,the folding of the polypeptide chain into structures like $\alpha$-helices and $\beta$-pleated sheets is primarily stabilized by hydrogen bonds formed between the carbonyl oxygen $(C=O)$ of one amino acid and the amino hydrogen $(N-H)$ of another amino acid in the chain.
Therefore,the correct answer is hydrogen bond.

(B) The secondary structure of proteins refers to the local folding of the polypeptide chain into regular patterns.
Hydrogen bonding between the carbonyl oxygen $(C=O)$ and the amide hydrogen $(N-H)$ of the polypeptide backbone stabilizes these structures.
This folding results in the formation of rigid,stable structures such as the $\alpha$-helix (a helical structure) or $\beta$-pleated sheets (a tubular or sheet-like arrangement).
Therefore,the correct description for these structures is a rigid tubular or helical structure.

(C) The structure of proteins is described at four levels:
$1$. Primary structure: The sequence of amino acids in a polypeptide chain.
$2$. Secondary structure: The folding of the polypeptide chain into specific shapes like $\alpha$-helices or $\beta$-pleated sheets,stabilized by hydrogen bonds.
$3$. Tertiary structure: The overall three-dimensional folding and coiling of a single polypeptide chain,which gives it a functional shape.
$4$. Quaternary structure: The arrangement of multiple polypeptide chains (subunits) into a single functional protein complex.
Therefore,the three-dimensional arrangement of a single polypeptide chain corresponds to the tertiary structure.

(C) The primary structure of a protein refers to the linear sequence of amino acids.
Secondary structure refers to the local folding of the polypeptide chain into structures like $\alpha$-helices and $\beta$-pleated sheets.
Tertiary structure represents the overall three-dimensional folding of a single polypeptide chain,which is essential for the biological activity of the protein.
Quaternary structure refers to the arrangement of multiple polypeptide subunits in a multi-subunit protein complex.
Therefore,the three-dimensional structure of an entire polypeptide chain is known as the tertiary structure.

(B) The quaternary structure of a protein refers to the arrangement of multiple polypeptide subunits into a single functional complex.
These subunits are held together by various non-covalent interactions and,in some cases,covalent bonds.
The stabilizing forces include:
$1$. Hydrogen bonds: Formed between polar side chains or backbone atoms.
$2$. Disulfide bonds: Covalent linkages between cysteine residues.
$3$. Hydrophobic interactions: Clustering of non-polar side chains away from the aqueous environment.
$4$. Ionic bonds (salt bridges): Electrostatic attractions between oppositely charged amino acid side chains.
Therefore,all these interactions contribute to the stability of the quaternary structure.

(A) Hemoglobin is a quaternary protein structure found in red blood cells. It consists of $4$ polypeptide chains: $2$ alpha $(\alpha)$ chains and $2$ beta $(\beta)$ chains. Each chain is associated with a heme group containing iron, which allows the molecule to bind oxygen.

(D) Hemoglobin is a quaternary protein consisting of four polypeptide chains: two alpha $(α)$ chains and two beta $(β)$ chains.
Each polypeptide chain is associated with one heme group,which contains an iron $(Fe^{2+})$ ion at its center.
Since there are four polypeptide chains in total,there are four heme groups present in one molecule of hemoglobin.
Therefore,the correct answer is $4$.

(B) Melanin is a complex polymer derived from the amino acid tyrosine and is responsible for the pigmentation of skin,hair,and eyes in animals.
$Actin$ and $Tubulin$ are cytoskeletal proteins involved in cell structure and movement.
$Flagellin$ is the protein subunit that makes up the bacterial flagellum.

(D) Conjugated proteins are proteins that are covalently bonded to a non-protein component called a prosthetic group.
$1$. Hemoglobin is a conjugated protein consisting of the protein globin and the prosthetic group heme (an iron-containing porphyrin ring).
$2$. Cytochrome is also a conjugated protein containing a heme group.
$3$. Chlorophyll is not a protein; it is a pigment molecule.
$4$. Myosin and Actin are simple proteins (contractile proteins) found in muscle fibers.
Therefore,among the given options,Hemoglobin and Cytochrome are examples of conjugated proteins,but since the question asks for a pair and includes chlorophyll (which is not a protein),we must identify the most accurate classification. However,based on standard biological classification,Hemoglobin is the classic example of a conjugated protein.

(C) Scleroproteins (also known as fibrous proteins) are structural proteins that are insoluble in water and most common organic solvents. Examples include keratin,collagen,and elastin. In contrast,globular proteins like hemoglobin,myoglobin,and actin are generally soluble in water or salt solutions.

(B) Amino acids are classified based on the nature of their $R$-group side chains.
$1$. Alanine $(A)$ has a non-polar,hydrophobic methyl group as its $R$-group.
$2$. Serine $(S)$ contains a hydroxyl group $(-OH)$ in its $R$-group,which makes it polar but uncharged at physiological $pH$.
$3$. Valine $(V)$ has a non-polar,branched hydrocarbon side chain.
$4$. Histidine $(H)$ has an imidazole ring in its $R$-group,which can be positively charged depending on the $pH$.
Therefore,Serine is the correct answer as it is polar and uncharged.

(A) Phenylalanine contains a benzyl side chain,which is hydrophobic and non-polar.
Tyrosine contains a phenolic hydroxyl group attached to the benzene ring,which makes it polar and uncharged at physiological $pH$.
Therefore,phenylalanine is an amino acid with a non-polar '$R$' group,and tyrosine is an amino acid with a polar and uncharged '$R$' group.

(A) An amphoteric molecule is one that can act as both an acid and a base.
Amino acids,such as $Glycine$,contain both an amino group ($-NH_2$,which is basic) and a carboxyl group ($-COOH$,which is acidic).
In an aqueous solution,$Glycine$ exists as a zwitterion,where the carboxyl group loses a proton $(COO^-)$ and the amino group gains a proton $(NH_3^+)$.
Because of this dual nature,$Glycine$ is amphoteric.
$Glucose$,$Fructose$,and $Starch$ are carbohydrates and do not possess both acidic and basic functional groups in this manner.

(C) polypeptide chain is a polymer of amino acids linked by peptide bonds.
Each amino acid has an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$.
In a polypeptide chain,the amino acid at one end has a free amino group,which is called the $N$-terminal end.
The amino acid at the opposite end has a free carboxyl group,which is called the $C$-terminal end.
Therefore,if one end contains an $NH_2$ group,the other end contains a $-COOH$ group.

(C) Proteins are classified into two types based on their molecular shape: fibrous proteins and globular proteins.
Fibrous proteins are formed when polypeptide chains run parallel and are held together by hydrogen and disulfide bonds.
This structure is characteristic of the secondary structure of proteins,where the polypeptide chains form stable,thread-like structures (e.g.,keratin,collagen).
Therefore,the fibrous form is observed in the secondary structure of proteins.

(B) Valine and Cysteine are both amino acids.
Amino acids are linked together by a peptide bond to form proteins.
$A$ peptide bond is formed between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the adjacent amino acid through a dehydration reaction (removal of a water molecule).
Therefore,the correct bond connecting these two amino acids is the peptide bond.

(C) Statement $P$ is false because the quaternary structure of proteins refers to the spatial arrangement of multiple polypeptide subunits (or monomers) in a multi-subunit complex,not the shape of a single chain.
Statement $Q$ is false because the quaternary structure specifically requires the presence of two or more polypeptide chains (subunits) held together by non-covalent interactions. $A$ single polypeptide chain can only exhibit primary,secondary,and tertiary structures.
Therefore,both statements are incorrect.

(D) $1$. Hemoglobin is a conjugated protein because it consists of a protein part (globin) and a non-protein prosthetic group (heme,which contains iron).
$2$. Due to the presence of the heme group,hemoglobin has a high affinity for oxygen,making it an essential protein for the transport of $O_2$ in the blood.
$3$. Therefore,both statements are true. Statement $P$ explains why hemoglobin is capable of binding to $O_2$ (the prosthetic group),which makes statement $P$ the correct explanation for statement $Q$.

$(C)$ The classification of amino acids based on their $R$ groups is as follows:
$(A)$ Polar and uncharged $R$ group: Cysteine contains a sulfhydryl group which is polar but uncharged at physiological pH. Thus, $(A-iv)$.
$(B)$ Non-polar $R$ group: Methionine contains a non-polar thioether side chain. Thus, $(B-i)$.
$(C)$ Polar and negatively charged $R$ group: Glutamic acid contains a carboxyl group in its side chain, which is negatively charged at physiological pH. Thus, $(C-ii)$.
$(D)$ Polar and positively charged $R$ group: Lysine contains an amino group in its side chain, which is positively charged at physiological pH. Thus, $(D-iii)$.
Therefore, the correct matching is $A-iv, B-i, C-ii, D-iii$.

(C) The correct matches are as follows:
$(A)$ Immune protein: Immunoglobulin (Antibodies are proteins that act as immune agents) - $(iv)$
$(B)$ Pigment protein: Melanin (Melanin is a pigment protein responsible for skin color) - $(iii)$
$(C)$ Involved in $O_2$ transport: Haemoglobin (Haemoglobin is a protein that transports oxygen in the blood) - $(i)$
$(D)$ Protein essential for photosynthesis: Chlorophyll (Note: While chlorophyll is a pigment, in the context of protein-pigment complexes in photosynthesis, it is often associated with proteins like those in photosystems) - $(ii)$
$(E)$ Protein for muscle contraction: Myosin (Myosin is a motor protein involved in muscle contraction) - $(v)$
Thus, the correct sequence is $(A-iv, B-iii, C-i, D-ii, E-v)$.

(A) Simple proteins are those that yield only amino acids upon hydrolysis.
Albumin is a classic example of a simple protein found in egg white and blood plasma.
Nucleoproteins,lipoproteins,and glycoproteins are classified as conjugated proteins because they contain a non-protein component (prosthetic group) attached to the protein part.

(B) Proteins are heteropolymers made of amino acids.
An amino acid consists of a central carbon atom bonded to an amino group $(-NH_2)$,a carboxyl group $(-COOH)$,a hydrogen atom,and a variable side chain known as the $R$ group.
While the amino group,carboxyl group,and hydrogen atom are common to all amino acids,the $R$ group varies among the $20$ different amino acids.
This variation in the $R$ group is responsible for the unique chemical properties of each amino acid,which in turn leads to the structural and functional diversity observed in protein molecules.

(D) The correct matches are as follows:
$(a)$ Actin is a contractile protein involved in muscle movement: $(a-iv)$.
$(b)$ Immunoglobulin (antibody) is a protein that provides immunity against pathogens: $(b-ii)$.
$(c)$ Melanin is a pigment responsible for the coloration of the skin and body: $(c-iii)$.
$(d)$ Hemoglobin is a respiratory pigment present in red blood cells responsible for the transport of respiratory gases like oxygen: $(d-i)$.
Therefore,the correct sequence is $(a-iv, b-ii, c-iii, d-i)$.

(C) Proteins are heteropolymers made of amino acids.
Amino acids are linked together by peptide bonds to form long polypeptide chains.
These chains fold into specific three-dimensional structures to function as proteins.
Therefore,amino acids are the fundamental building blocks of proteins.

(C) Proteins are heteropolymers of amino acids.
Amino acids are linked together by a covalent bond known as a $Peptide$ bond.
This bond is formed by the dehydration synthesis reaction between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the adjacent amino acid.
Therefore,the correct option is $C$.

(B) Enzymes are primarily composed of proteins. Proteins are polymers of amino acids. In a protein chain,individual amino acids are joined together by a covalent bond known as a peptide bond. This bond is formed between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the adjacent amino acid through a dehydration reaction (removal of a water molecule).

(B) The correct statement is that there are many types of proteins. Proteins are long chains of amino acids. Due to the vast number of combinations and sequences of amino acids,countless types of proteins exist in living organisms,performing diverse biological functions.
Other options are incorrect because:
$1$. There are thousands of types of enzymes,not just $2$.
$2$. While $DNA$ contains four types of nitrogenous bases,it is a complex macromolecule,and the statement is an oversimplification.
$3$. The number of chromosomes is specific to each species and is not a fixed value of $80$ for all organisms.

(B) Amino acids are classified based on the nature of their '$R$' group.
Non-polar amino acids have hydrophobic '$R$' groups that do not interact with water.
Among the given options:
$1$. Tyrosine contains a phenolic hydroxyl group,making it polar.
$2$. Tryptophan contains an indole ring; while it has a nitrogen atom,it is generally classified as non-polar due to the large hydrophobic aromatic structure.
$3$. Histidine contains an imidazole ring and is basic/polar.
$4$. Threonine contains a hydroxyl group,making it polar.
Therefore,Tryptophan is the correct answer as it is the most non-polar among the choices provided.

(C) Amino acids are classified based on the nature of their '$R$' group.
$1$. Leucine has a non-polar,hydrophobic '$R$' group.
$2$. Lysine has a positively charged (basic) '$R$' group.
$3$. Glutamine has a polar,uncharged '$R$' group containing an amide functional group.
$4$. Alanine has a non-polar,hydrophobic '$R$' group.
Therefore,the correct answer is Glutamine.

(C) Amino acids are classified based on the nature of their '$R$' group.
$1$. Arginine is a polar,positively charged amino acid.
$2$. Asparagine is a polar,uncharged amino acid.
$3$. Aspartic acid (aspartate) contains a carboxyl group in its side chain,making it polar and negatively charged at physiological $pH$.
$4$. Alanine has a non-polar,hydrophobic methyl group as its side chain.
Therefore,the correct option is $C$.

(A) Amino acids are classified based on the nature of their '$R$' group.
$1$. Arginine contains a guanidino group in its side chain,which is polar and carries a positive charge at physiological $pH$.
$2$. Asparagine has a polar but uncharged '$R$' group (amide group).
$3$. Aspartic acid has a polar and negatively charged '$R$' group (carboxyl group).
$4$. Alanine has a non-polar,hydrophobic '$R$' group (methyl group).
Therefore,Arginine is the correct answer.

(B) The secondary structure of proteins refers to the local folded structures that form within a polypeptide due to interactions between atoms of the backbone.
There are two main types of secondary structures: the $\alpha$-helix and the $\beta$-pleated sheet.
The $\beta$-pleated sheet consists of polypeptide chains that are held together by hydrogen bonds between the carbonyl oxygen of one chain and the amide hydrogen of an adjacent chain,resulting in a flat,pleated appearance.

(B) In a polypeptide chain,the secondary structure,such as the $\alpha$-helix,is stabilized by hydrogen bonds.
These hydrogen bonds form between the carbonyl oxygen $(C=O)$ of one amino acid residue and the amide hydrogen $(N-H)$ of another amino acid residue located further along the chain.
This regular pattern of hydrogen bonding causes the polypeptide chain to coil into a helical shape.

(B) Fibrous proteins are characterized by long,thin,fiber-like structures. These proteins are formed when polypeptide chains run parallel to each other and are held together by hydrogen and disulfide bonds. This structure is primarily a secondary structure,as it involves the regular folding of the polypeptide chain into a stable,elongated shape.

(C) Hemoglobin is a quaternary protein structure found in red blood cells. It consists of four polypeptide chains: two $\alpha$-globin chains and two $\beta$-globin chains. These chains are held together by non-covalent interactions to form a functional globular protein capable of binding oxygen.

(D) Amino acids are organic compounds containing an amino group $(-NH_2)$ and an acidic carboxyl group $(-COOH)$ attached to the same carbon atom,which is called the $\alpha$-carbon.
They are substituted methanes where the four substituent groups occupying the four valency positions are a hydrogen atom $(H)$,a carboxyl group $(-COOH)$,an amino group $(-NH_2)$,and a variable group designated as the $R$-group.
While the amino,carboxyl,and hydrogen groups are common to all amino acids,the $R$-group varies among different amino acids.
This variation in the chemical nature of the $R$-group (which can be a hydrogen atom,a methyl group,a hydroxy-methyl group,etc.) is responsible for the biological diversity and specific properties of different amino acids.

(C) peptide bond is formed between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the adjacent amino acid.
During this condensation reaction,a molecule of water $(H_2O)$ is eliminated.
Therefore,the formation of a peptide bond involves the removal of a water molecule.

(B) The given structural formula represents an amino acid.
An amino acid is an organic compound containing an amino group $(-NH_2)$,a carboxyl group $(-COOH)$,a hydrogen atom,and a variable side chain $(R)$ attached to a central alpha-carbon atom.
In the provided structure,the group labeled '$X$' is the amino group,which is represented as $-NH_2$.

(A) The correct matching is as follows:
$(1)$ Primary protein: The sequence of amino acids is determined by genetic information (Gene-controlled),so $(1-R)$.
$(2)$ Secondary protein: Polypeptide chains form structures like $\alpha$-helices or $\beta$-pleated sheets,so $(2-S)$.
$(3)$ Tertiary protein: This represents the complex three-dimensional folding of a single polypeptide chain,so $(3-Q)$.
$(4)$ Quaternary protein: This involves the assembly of multiple polypeptide subunits into globular or fibrous functional proteins,so $(4-P)$.
Therefore,the correct sequence is $(1-R), (2-S), (3-Q), (4-P)$.

(B) Assertion $A$ is true because proteins are indeed heteropolymers formed by the polymerization of amino acids linked by peptide bonds.
Reason $R$ is also true because there are $20$ standard amino acids that serve as the building blocks for proteins in living organisms.
However,the fact that there are $20$ types of amino acids does not explain why proteins are polymers; rather,it describes the diversity of the monomers that make up the polymer.
Therefore,$R$ is not the correct explanation for $A$.

(C) Amino acids are organic compounds containing an amino group $(-NH_2)$ and an acidic carboxyl group $(-COOH)$ attached to the same carbon atom,known as the $\alpha$-carbon.
They are substituted methanes where the four substituent groups occupying the four valency positions are a hydrogen atom,a carboxyl group,an amino group,and a variable group designated as the $R$ group.
Based on the nature of the $R$ group,there are many amino acids (e.g.,glycine,alanine,serine).
Therefore,the properties and types of amino acids vary specifically because of the nature of the $R$ group,not because the rest of the chemical structure differs.
Thus,statement $A$ is true,but statement $R$ is false because the basic backbone (amino,carboxyl,and hydrogen on the $\alpha$-carbon) remains the same for all amino acids.

(A) Amino acids contain both an acidic carboxyl group $(-COOH)$ and a basic amino group $(-NH_2)$ in the same molecule.
Due to the presence of both acidic and basic groups,they can react with both acids and bases,making them amphoteric.
In an aqueous solution,the carboxyl group can lose a proton to form a carboxylate ion $(-COO^-)$ and the amino group can accept a proton to form an ammonium ion $(-NH_3^+)$,resulting in a zwitterion.
Because they exist as charged ions (zwitterions) in solution,they behave as electrolytes and can migrate in an electric field.
Therefore,both statements are true,and the fact that they act as electrolytes is a direct consequence of their amphoteric nature (zwitterion formation).

(D) Assertion $(A)$ is false because hemoglobin is a protein molecule consisting of four polypeptide chains (two $\alpha$ and two $\beta$ subunits),each associated with a heme group. The interactions occur between the polypeptide chains,not just the heme groups.
Reason $(R)$ is true because hemoglobin exhibits a quaternary structure,which refers to the spatial arrangement of multiple polypeptide subunits in a protein.
Therefore,$A$ is false and $R$ is true.

(B) The provided figure shows the quaternary structure of a protein consisting of four polypeptide subunits. This specific arrangement of two alpha and two beta subunits is characteristic of the hemoglobin molecule. Hemoglobin is a globular protein that transports oxygen in the blood. Myoglobin,in contrast,is a monomeric protein with a single polypeptide chain. Leghemoglobin is also a monomeric protein found in root nodules. Actin is a structural protein involved in muscle contraction.

(A) The provided figure represents the structure of hemoglobin. Hemoglobin is a quaternary protein consisting of four polypeptide subunits (two $\alpha$ and two $\beta$ chains). Each subunit contains a prosthetic group called the heme group,which contains an iron $(Fe^{2+})$ ion at its center. In the diagram,$P$ points to one of the polypeptide subunits,while the heme group is associated with these subunits. However,in the context of standard $NCERT$ diagrams for hemoglobin,the subunits are often labeled to show the heme-containing polypeptide chains. Given the options,the heme group is the functional prosthetic group containing iron. Therefore,the most appropriate answer is that $P$ represents the heme group.

(C) The figure represents the quaternary structure of hemoglobin. Hemoglobin is a protein consisting of four polypeptide subunits: two $\alpha$ chains and two $\beta$ chains. In the standard $NCERT$ diagram of hemoglobin,the labels $M$ and $N$ point to the $\beta$ chains,while $P$ points to the $\alpha$ chains. Therefore,$M$ indicates a $\beta$ chain. Since the option provided is $\alpha$ chain,and based on standard textbook diagrams,the question likely intended to ask for the $\alpha$ chain or the labels were swapped. Given the options,if $M$ is intended to be one of the subunits,and $\alpha$ is the only valid polypeptide chain listed besides the generic 'peptide chain',$C$ is the most appropriate choice in many contexts where $M$ and $N$ are $\alpha$ chains.

(A) The provided figure represents the quaternary structure of the hemoglobin molecule. Hemoglobin is a tetrameric protein consisting of four polypeptide chains: two $\alpha$-chains and two $\beta$-chains. In the standard representation of this diagram,the parts labeled $N$ and $M$ represent the $\beta$-chains,while the parts labeled $P$ represent the $\alpha$-chains. Therefore,the part labeled $N$ represents the $\beta$-chain.

(D) The figure represents the structure of hemoglobin,which is a classic example of a protein with a quaternary structure. $A$ quaternary structure is formed when two or more polypeptide chains (subunits) assemble to form a functional protein complex. In the case of hemoglobin,it consists of four polypeptide subunits (two $\alpha$ and two $\beta$ chains). Therefore,the correct answer is quaternary structure.