Proteins Questions in English

(B) Conjugated proteins are composed of simple proteins combined with a non-protein component known as a prosthetic group or cofactor.
Upon hydrolysis,these proteins yield amino acids and the non-protein prosthetic group.
Examples include: mucin in saliva (prosthetic group: carbohydrate),casein in milk (prosthetic group: phosphoric acid),and haemoglobin in blood (prosthetic group: iron-containing pigment).

(B) Molisch's test is a chemical test used to detect the presence of carbohydrates in a sample.
It is not used for the detection of proteins.
Millon's test,Biuret test,and Ninhydrin test are all standard laboratory procedures used to identify proteins or amino acids.

(B) nanopeptide is composed of $9$ amino acids linked together. In a polypeptide chain,the number of peptide linkages is always $(n-1)$,where $n$ is the number of amino acids. Therefore,for a nanopeptide,the number of peptide linkages is $9 - 1 = 8$.

(B) The isoelectric point $(pI)$ is defined as the specific $pH$ value at which an amino acid or protein carries no net electrical charge.
At this $pH$,the molecule exists as a zwitterion,meaning the positive and negative charges are balanced.
Because the net charge is zero,the amino acid will not migrate toward either the anode or the cathode when placed in an electric field.

(D) Histidine is a basic amino acid that contains an imidazole ring in its side chain ($R$-group).
This ring structure is responsible for the unique buffering capacity of histidine at physiological $pH$ levels.

(B) The helical structure of protein (specifically the $\alpha$-helix) is stabilized by hydrogen bonds between the amide group of the same peptide chain.
These hydrogen bonds are formed between the $-NH-$ group of one amino acid residue and the carbonyl oxygen $(C=O)$ of the fourth amino acid residue in the sequence.

(C) Sulphanilic acid exists as a Zwitter ion.
It contains both an acidic group $(-SO_3H)$ and a basic group $(-NH_2)$ in the same molecule.
The proton from the sulphonic acid group is transferred to the amino group,resulting in the formation of a dipolar ion known as a Zwitter ion,represented as $H_3N^+-C_6H_4-SO_3^-$.

(D) Aromatic amino acids contain an aromatic ring in their side chain. Among the given options, Valine, Leucine, and Serine are aliphatic amino acids.
Tyrosine is an aromatic amino acid because it contains a phenol group (a benzene ring with a hydroxyl group) in its side chain.
Its chemical name is $\alpha$-amino-$\beta$($p$-hydroxyphenyl)propionic acid. Due to the presence of this aromatic nucleus, it exhibits aromatic properties.

(D) Tryptophan is a heterocyclic amino acid because its side chain contains an indole ring,which is a heterocyclic structure (a bicyclic structure consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring).

(B) An amino acid is optically active if it contains at least one chiral carbon atom (an asymmetric carbon atom bonded to four different groups).
Glycine has the structure $NH_2-CH_2-COOH$. Since the central carbon atom is bonded to two identical hydrogen atoms,it is achiral and therefore optically inactive.
All other naturally occurring amino acids have at least one chiral carbon atom (the $\alpha$-carbon) and are thus optically active.
Therefore,the statement 'All amino acids except glycine are optically active' is correct.

(D) Proteins are complex macromolecules that are generally insoluble in non-polar solvents like alkanes,alkenes,and alkynes. However,benzene is often used in laboratory procedures to dissolve or extract certain types of proteins or lipid-protein complexes due to its specific chemical properties. Therefore,among the given options,benzene is the most effective solvent for removing or dissolving protein-based stains or samples.

(A) The tripeptide present in most living cells is glutathione.
It is composed of $3$ amino acids,namely glycine,glutamic acid,and cysteine.
It functions as an antioxidant and acts as a coenzyme in various cellular processes.

(D) The ninhydrin test is a chemical test used to detect amino acids or proteins. When a protein or amino acid reacts with ninhydrin,it produces a characteristic blue or purple color,indicating a positive result.
Benedict's solution is used to detect reducing sugars. Monosaccharides and many disaccharides (like maltose and lactose) act as reducing sugars and give a positive result (red/orange precipitate).
Since proteins are not reducing sugars,they give a negative result with Benedict's solution.
Therefore,a protein is the compound that gives a positive ninhydrin test and a negative Benedict's solution test.

(C) Insulin is a peptide hormone composed of two polypeptide chains,referred to as chain $A$ and chain $B$.
Chain $A$ consists of $21$ amino acid residues,and chain $B$ consists of $30$ amino acid residues.
These two chains are linked together by two inter-chain disulphide bridges (between $A7-B7$ and $A20-B19$).
Additionally,there is one intra-chain disulphide bridge within chain $A$ (between $A6-A11$).
Therefore,the total number of disulphide linkages present in an insulin molecule is $3$.

(B) Statement $(i)$ is false because glycine is achiral (it has no chiral centre).
Statement $(ii)$ is true because amino acids like isoleucine have two chiral centres, while glycine has none.
Statement $(iii)$ is true because all amino acids incorporated into proteins during translation possess the $L$-configuration.
Statement $(iv)$ is false because proline is an amino acid found in proteins that contains a $2^{\circ}$ amino group (it is an imino acid).
Therefore, statements $(ii)$ and $(iii)$ are correct.

(C) Proteins are essential macromolecules found in all living organisms,including plants,animals,bacteria,and fungi.
Option $A$ is correct because proteins are present in all living cells.
Option $B$ is correct because proteins are polymers of amino acids,which always contain Carbon $(C)$,Hydrogen $(H)$,Oxygen $(O)$,and Nitrogen $(N)$.
Option $C$ is incorrect because proteins are synthesized by all living organisms,not just the plant kingdom. Animals and microorganisms also synthesize their own proteins.
Option $D$ is correct because proteins can be synthesized in a laboratory setting using techniques like solid-phase peptide synthesis or recombinant $DNA$ technology.

(D) Glycine is the simplest amino acid. The general structure of an amino acid is $NH_2-CH(R)-COOH$. In glycine,the $R$ group is replaced by a hydrogen atom $(-H)$,making its formula $NH_2-CH_2-COOH$.

(D) Amino acids are amphoteric molecules containing both an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$.
In an aqueous solution,the carboxyl group can lose a proton to become a negatively charged carboxylate ion $(-COO^-)$,and the amino group can accept a proton to become a positively charged ammonium ion $(-NH_3^+)$.
This dipolar ion,which carries both positive and negative charges simultaneously,is known as a Zwitterion.
Since all amino acids (acidic,basic,and neutral) possess these functional groups,they can all exist as Zwitterions at their respective isoelectric points.

(D) Non-essential amino acids are those that can be synthesized by the human body.
Since the body can produce them,they are not strictly required in the diet.
Therefore,both statements $(b)$ and $(c)$ are correct.

(B) The most abundant protein in the animal world is $Collagen$.
$Chitin$ is a polysaccharide found in the exoskeleton of arthropods.
$Peptidoglycan$ is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria.
$Hyaluronic$ $acid$ is a glycosaminoglycan,which is a type of polysaccharide.
Therefore,$Collagen$ is the correct answer as it is the primary structural protein in the extracellular matrix of various connective tissues in animals.

(C) In a protein,amino acids are linked together by a peptide bond.
This bond is formed by the reaction between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the next amino acid,resulting in the elimination of a water molecule.
Glycosidic bond: Formed between two monosaccharides in carbohydrates.
Phosphodiester bond: Formed in nucleic acids ($DNA$ or $RNA$) between the phosphate group and the sugar molecule.
Hydrogen bond: Responsible for the secondary and tertiary structure of proteins,but not for the primary linkage of amino acids.

(A) The secondary structure of proteins is stabilized by hydrogen bonds and exists in two forms: $\alpha$-helix and $\beta$-pleated sheet.
Fibroin,a protein found in silk,is a classic example of a protein that exhibits a $\beta$-pleated sheet structure.
Haemoglobin exhibits a quaternary structure.
Most enzymes exhibit a tertiary structure.
$\alpha$-Keratin is a fibrous protein that exhibits an $\alpha$-helical structure.
Therefore,the correct option is $A$.

(B) The quaternary structure of a protein refers to the arrangement of multiple folded protein subunits in a multi-subunit complex.
$1$. Myoglobin consists of a single polypeptide chain and exhibits a tertiary structure.
$2$. Haemoglobin is a classic example of a protein with a quaternary structure,as it is composed of four polypeptide subunits ($2$ alpha and $2$ beta chains).
$3$. Keratin is a fibrous protein that primarily exhibits a secondary structure (alpha-helical structure).
Therefore,the correct answer is Haemoglobin.

(A) The provided structure is of Aspartic acid.
An amino acid is classified based on the number of amino $(-NH_2)$ and carboxyl $(-COOH)$ groups present in its structure.
If the number of carboxyl groups is greater than the number of amino groups,the amino acid is acidic in nature.
In the given structure,there are two carboxyl groups (one in the main chain and one in the side chain) and only one amino group.
Therefore,due to the presence of an extra carboxylic group,it is acidic in nature.

(D) The primary structure of a protein refers to the linear sequence of amino acids.
Secondary structures,such as the $\alpha$-helix and $\beta$-pleated sheet,represent the local folding of the polypeptide chain.
The tertiary structure represents the overall three-dimensional folding of the entire polypeptide chain,which is essential for the biological activity of the protein.
Therefore,the tertiary structure is the one that provides the three-dimensional view of the protein.

(B) Amino acids are classified based on the nature of their $R$ group.
$1$. Basic amino acids contain an extra amino group in their side chain,making them positively charged at physiological $pH$. Examples include $Lysine$,$Arginine$,and $Histidine$.
$2$. Acidic amino acids contain an extra carboxyl group in their side chain,making them negatively charged. Examples include $Glutamic$ $acid$ and $Aspartic$ $acid$.
$3$. Glycine and Alanine are neutral amino acids.
Therefore,$Lysine$ and $Arginine$ are basic amino acids.

(C) The amino acid $Glycine$ is a crucial precursor in the biosynthesis of $Heme$.
It provides the nitrogen and carbon atoms required for the formation of the porphyrin ring structure of $Heme$.

(B) Amino acids are classified based on their side chains. Alcoholic amino acids are those that contain a hydroxyl $(-OH)$ group in their side chain.
Among the given options,$Threonine$ and $Serine$ are the two amino acids that possess a hydroxyl group in their side chain.
Therefore,they form an alcoholic amino acid pair.

(D) Essential amino acids are those amino acids that cannot be synthesized by the human body. Therefore,they must be obtained through the diet. Lysine is classified as an essential amino acid because the human body lacks the metabolic pathways to produce it.

(C) The tertiary structure of a protein is essential for its biological activity because it creates a specific three-dimensional shape.
In this structure,the polypeptide chain folds upon itself,bringing distant amino acid side groups into close proximity to form an active site.
The Reason statement is incorrect because the tertiary structure is maintained by various non-covalent interactions such as hydrogen bonds,ionic bonds,hydrophobic interactions,and van der Waals forces,in addition to covalent disulfide bridges,not just multiple covalent bonds.

(A) Collagen is a fibrous protein consisting of three polypeptide chains coiled around each other in a triple helix structure.
The stability of this triple helix is primarily maintained by interchain hydrogen bonds.
These hydrogen bonds form between the $>NH$ group of the glycine residue in one strand and the $-CO$ group of the amino acid residues in the other two strands.
Additionally,the presence of proline and hydroxyproline residues provides structural rigidity and a 'locking' effect,which further stabilizes the collagen helix.
Both the Assertion and the Reason are scientifically accurate,and the Reason provides a complementary structural detail that supports the stability described in the Assertion.

(C) The tertiary structure of a protein is essential for its biological activity because it creates the specific three-dimensional shape,including the active site in enzymes,required for its function.
Regarding the Reason,while right-handed helices are the most common in proteins due to steric constraints,it is incorrect to state that *only* right-handed helices are observed,as left-handed helices can exist in specific contexts or synthetic peptides.
Therefore,the Assertion is correct,but the Reason is incorrect.

(B) Methionine and cysteine are the only two proteinogenic amino acids that contain sulfur $(S)$ in their side chains. Sulfur is an essential element for the structure and function of proteins,as it allows for the formation of disulfide bonds,which stabilize the tertiary structure of proteins.

(B) Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet. For human beings,there are nine essential amino acids: histidine,isoleucine,leucine,lysine,methionine,phenylalanine,threonine,tryptophan,and valine. Among the given options,Phenylalanine is an essential amino acid.

(A) Proteins are composed of $20$ types of amino acids. Plants can synthesize all of these,whereas animals cannot synthesize all of them. About $10$ amino acids are synthesized by animals through processes like transamination. Amino acids that cannot be synthesized by the body and must be obtained through diet are called essential amino acids. Amino acids that the body can synthesize are termed non-essential amino acids. Isoleucine is an essential amino acid,and its deficiency is known to cause the deregulation of blood sugar levels.

(B) The haemoglobin molecule is a quaternary protein structure consisting of four polypeptide chains.
It is composed of two $\alpha$-chains,each containing $141$ amino acids,and two $\beta$-chains,each containing $146$ amino acids.

(A) In haemoglobin,the buffering action is primarily performed by the imidazole group of the $Histidine$ residues. This residue can accept or donate protons,which helps in maintaining the $pH$ of the blood.

(B) Ornithine is a non-proteinogenic amino acid,meaning it is not incorporated into proteins during translation.
It acts as an intermediate in the urea cycle,where it is formed by the hydrolysis of arginine and subsequently reacts with carbamoyl phosphate to produce citrulline.

(A) The exoskeleton of birds (feathers,scales on legs) and mammals (hair,nails,claws) is primarily composed of $Keratin$.
$Keratin$ is a fibrous structural protein.
Therefore,the correct answer is $Protein$.

(A) Proteins are polymers of amino acids. In these amino acids,the amino group $(-NH_2)$ and the carboxylic acid group $(-COOH)$ are attached to the same carbon atom,which is known as the $\alpha$-carbon. Therefore,the amino acids found in proteins are exclusively $\alpha$-amino acids.

(C) Amino acids are organic compounds containing an amino group $(-NH_2)$ and a carboxylic acid group $(-COOH)$ attached to the same carbon atom,known as the $\alpha$-carbon.
They are considered substituted methanes because the four valency positions of the central carbon are occupied by a hydrogen atom,a carboxyl group,an amino group,and a variable $R$-group.
Since they contain carbon-hydrogen bonds,they are classified as organic compounds,not inorganic.
Glycine is the simplest amino acid where the $R$-group is a hydrogen atom.

(A) Proteins are heteropolymers made up of amino acids. Although there are many amino acids,only $20$ types of amino acids are commonly involved in the formation of proteins in living organisms. These are known as proteinogenic amino acids.

(B) The general structure of an amino acid is $R-CH(NH_2)-COOH$. The identity of the amino acid depends on the $R$ group attached to the central carbon atom.
$1$. In the first structure,the $R$ group is $H$. This is Glycine,the simplest amino acid.
$2$. In the second structure,the $R$ group is $CH_3$. This is Alanine.
$3$. In the third structure,the $R$ group is $CH_2OH$. This is Serine.
Therefore,the sequence is Glycine,Alanine,Serine.

(B) An amino acid is an organic compound containing an amino group $(-NH_2)$,a carboxyl group $(-COOH)$,a hydrogen atom $(-H)$,and a variable side chain ($-R$ group) attached to a central alpha-carbon atom.
While the amino group,carboxyl group,and hydrogen atom are common to all amino acids,the chemical nature of the $R$ group varies among different amino acids.
This $R$ group determines the specific properties of each amino acid,such as its size,charge,and hydrophobicity,leading to the diversity observed in amino acids.

(A) The classification of amino acids based on their chemical nature is as follows:
$1$. Acidic amino acids contain an extra carboxyl group $(-COOH)$. Example: Glutamic acid (Glutamate).
$2$. Basic amino acids contain an extra amino group $(-NH_2)$. Example: Lysine.
$3$. Neutral amino acids have an equal number of amino and carboxyl groups. Example: Valine.
Matching the columns:
$P$ (Acidic) matches with $III$ (Glutamate).
$Q$ (Basic) matches with $I$ (Lysine).
$R$ (Neutral) matches with $II$ (Valine).
Therefore, the correct sequence is $(P-III), (Q-I), (R-II)$.

(C) Amino acids are classified based on the nature of their side chains ($R$-groups).
$1$. Aromatic amino acids contain a benzene ring or a heterocyclic ring in their side chain. Examples include Phenylalanine,Tyrosine,and Tryptophan.
$2$. Cysteine is a sulfur-containing amino acid with a thiol $(-SH)$ group in its side chain. It is not aromatic.
Therefore,the correct option is $C$.

(A) Collagen is the most abundant protein in the animal world,as it is a major structural component of connective tissues.
RuBisCO (Ribulose$-1,5-$bisphosphate carboxylase-oxygenase) is the most abundant protein in the whole biosphere because it is essential for the process of photosynthesis in plants,which are the primary producers of the biosphere.

(D) Amino acids are the building blocks of proteins.
When two amino acids combine,the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of another amino acid.
This reaction results in the elimination of a water molecule $(H_2O)$ and the formation of a covalent bond known as a peptide bond $(-CO-NH-)$.
Therefore,the correct option is $D$.

(D) The correct matches are as follows:
$P$. Collagen: It acts as the intercellular ground substance $(V)$.
$Q$. Trypsin: It is an enzyme $(IV)$.
$R$. Insulin: It is a hormone $(I)$.
$S$. Antibody: It fights against infectious agents $(III)$.
$T$. Receptor: It acts as a sensory receptor $(II)$.
$U$. $GLUT-4$: It enables glucose transport into cells $(VI)$.
Therefore,the correct sequence is $(P-V), (Q-IV), (R-I), (S-III), (T-II), (U-VI)$.

(A) Amino acids are classified into two types based on their requirement in the diet:
$1$. Essential amino acids: These cannot be synthesized by the human body and must be obtained through the diet.
$2$. Non-essential amino acids: These are synthesized by the human body and therefore are not strictly required in the diet.
Since the question asks about amino acids synthesized in our body,they are termed as non-essential amino acids.