Proteins Questions in English

(D) $Collagen$ is the most abundant protein in the animal kingdom. It is a structural protein that forms the primary component of connective tissues. Structurally,it is classified as a fibrous protein because its polypeptide chains are arranged in long,parallel strands that form fibers,providing tensile strength to tissues. Unlike globular proteins,which are soluble in water,fibrous proteins like $Collagen$ are generally insoluble.

(D) Proteins are classified into two main types based on their molecular shape: fibrous (fibrillar) and globular proteins.
Fibrillar proteins,such as $Collagen$,$Elastin$,and $Myosin$,have a long,thread-like structure and are generally insoluble in water.
$Albumin$ is a globular protein,which is spherical in shape and typically soluble in water.
Therefore,$Albumin$ is not a fibrillar protein.

(A) Elastin is considered the most resistant of all body proteins to chemical changes.
Thousands of years old 'mummies' still have their arteries intact due to the presence of well-preserved elastin fibers.

(A) The nucleus contains chromatin,which is composed of $DNA$ and proteins. The primary proteins associated with $DNA$ in the nucleus are histones. Histones are basic proteins that are classified as simple proteins because they consist only of amino acids and do not contain any non-protein prosthetic groups. Therefore,simple proteins are the primary type found in the nucleus.

(D) conjugated protein is a protein that functions in interaction with one or more non-amino acid groups (prosthetic groups).
$(d)$ Flavoprotein is a conjugated protein because it contains a non-proteinaceous prosthetic group,specifically $FMN$ (Flavin mononucleotide) or $FAD$ (Flavin adenine dinucleotide).
Globulin,Albumin,and Histone are examples of simple proteins,which consist only of amino acids.

(D) Glycoproteins are a type of conjugated protein where protein molecules are covalently bonded to carbohydrate groups. Therefore,they consist of protein and carbohydrates.

(B) Proteins are considered the most diverse molecules in the cell because they are polymers of amino acids. There are $20$ different types of amino acids that can be arranged in various sequences and lengths to form a vast array of proteins with unique structures and functions. These include enzymes,structural components,hormones,antibodies,and transport molecules,which perform almost all cellular activities.

(D) The correct answer is $D$. No cell can survive without proteins because they are the fundamental building blocks of the cell and are essential for structural support,enzymatic activity,transport,and signaling processes. While enzymes are also proteins,the term 'protein' is the broader and more fundamental category required for cellular existence.

(B) Proteins are complex organic macromolecules composed of amino acids.
Each amino acid consists of an amino group $(-NH_2)$,a carboxyl group $(-COOH)$,a hydrogen atom,and a variable side chain ($R$-group) attached to a central alpha-carbon.
The fundamental elements present in all amino acids and thus in all proteins are Carbon $(C)$,Hydrogen $(H)$,Oxygen $(O)$,and Nitrogen $(N)$.
Some proteins may also contain Sulphur $(S)$ due to the presence of amino acids like cysteine and methionine,but the primary elemental composition defining proteins is $C, H, O, N$.

(D) Conjugated proteins are proteins that are covalently bonded to non-protein components called prosthetic groups.
$A$. Chromoproteins contain a pigment as a prosthetic group (e.g.,hemoglobin).
$B$. Phosphoproteins contain phosphate groups as prosthetic groups (e.g.,casein in milk).
$C$. Glycoproteins contain carbohydrates as prosthetic groups (e.g.,mucin).
Since all these examples represent proteins associated with non-protein moieties,they are all classified as conjugated proteins.

(A) The $\alpha$-helical structure of proteins was proposed by Linus Pauling and Robert Corey in $1951$. They used $X$-ray crystallography data to determine the secondary structure of proteins,identifying the hydrogen bonding patterns that stabilize the $\alpha$-helix.

(C) Aleurone grains are specialized protein storage bodies found in the endosperm of many seeds,such as wheat,maize,and barley.
They are essentially proteinaceous in nature and serve as a reserve food material for the developing embryo during germination.

(C) Proteins are complex macromolecules known as polypeptides. They are linear chains formed by the polymerization of amino acids. These amino acids are linked together by peptide bonds to form long chains,which then fold into specific three-dimensional structures to become functional proteins.

(A) The basic structure of proteins,specifically the alpha-helix and beta-pleated sheet models,was proposed by Linus Pauling in $1951$. $G$.$N$. Ramachandran is also famous for the Ramachandran plot,which describes the allowed conformations of the polypeptide backbone. Given the options provided,Linus Pauling is the correct answer as he pioneered the study of protein secondary structure.

(A) An amino acid is optically active if it contains a chiral carbon atom (an asymmetric carbon atom bonded to four different groups).
In $Glycine$ $(NH_2-CH_2-COOH)$,the central carbon atom is bonded to two hydrogen atoms.
Since two groups attached to the central carbon are identical,it is achiral and therefore not optically active.
All other amino acids listed ($Valine$,$Leucine$,$Isoleucine$) contain a chiral center and are optically active.

(C) Glycine is considered the simplest amino acid because its side chain ($R$-group) is a single hydrogen atom $(H)$.
It has the chemical formula $NH_2-CH_2-COOH$.
Due to the presence of a hydrogen atom instead of a larger functional group,it is the only achiral amino acid among the $20$ standard amino acids.

(D) The correct answer is $D$. Sulphur is a key constituent of specific amino acids,namely cysteine and methionine. It is also found in vitamins such as biotin and thiamine,as well as in coenzyme $A$.

(A) Nitrogen is a fundamental element in the structure of amino acids,which are the building blocks of proteins.
Every amino acid contains an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$.
Since proteins are polymers of amino acids,nitrogen is an essential component of all proteins.
Lipids and carbohydrates primarily consist of carbon,hydrogen,and oxygen,and do not contain nitrogen as a structural constituent.

(A) Mucin is a type of glycoprotein found in saliva.
It acts as a lubricant that helps in the formation of the food bolus and facilitates swallowing.
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to amino acid side-chains.

(A) Proteins are complex polymers made up of long chains of amino acids linked by peptide bonds. During the process of hydrolysis,these peptide bonds are broken down by enzymes such as proteases and peptidases. The final result of complete protein hydrolysis is a mixture of individual amino acids,which can then be absorbed by the body.

(C) The correct answer is $C$. Proteins are the main constituents of food that are essential for life. They are primarily used in the body as building substances because they are the fundamental components of protoplasm,which is the living part of the cell. Without proteins,the structural integrity and repair mechanisms of the body would fail,making survival impossible.

(A) Proteins are complex macromolecules composed of long chains of amino acids linked by peptide bonds.
Amino acids are the fundamental building blocks or the smallest structural units of proteins.
During the process of digestion or hydrolysis,proteins are broken down into their constituent amino acids.

(B) $Casein$ is the primary protein found in milk. It serves as a vital source of nutrition for young mammals. $Rennin$ is an enzyme that helps in the digestion of $Casein$, while $Galactose$ is a sugar and $Glycine$ is an amino acid.

(B) The anhydro bonds (covalent bonds formed by the removal of a water molecule) in proteins are known as peptide bonds.
These bonds are formed between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the adjacent amino acid through a dehydration synthesis reaction.

(C) $Essential$ amino acids are those that cannot be synthesized by the human body and must be obtained through the diet.
Since the body cannot produce them, they are considered essential for survival and must be supplied via food sources.

(B) When catabolism of proteins exceeds synthesis of proteins,the proteins in the body are broken down more to meet energy requirements rather than being used to build up protoplasm. Consequently,the body becomes weak,run-down,and susceptible to diseases.

(A) Proteins are the fundamental building blocks of the body.
They are essential for the growth,repair,and maintenance of tissues.
New cells are primarily composed of proteins,which are required for cell division and structural integrity.
Therefore,proteins are the most essential nutrient for the growth and formation of new cells.

(A) Proteins are complex macromolecules of high molecular weight that contain carbon $(C)$,hydrogen $(H)$,oxygen $(O)$,and nitrogen $(N)$.
The presence of nitrogen is a key feature that distinguishes proteins from carbohydrates and fats,which typically contain only $C, H,$ and $O$.
Additionally,some proteins may contain trace amounts of other elements like sulphur,phosphorus,iron,copper,or iodine.
Therefore,proteins are the correct answer.

(C) Amino acids are classified as essential or non-essential based on whether the human body can synthesize them.
Essential amino acids cannot be synthesized by the body and must be obtained through the diet.
Non-essential amino acids can be synthesized by the human body.
Among the given options,$Lysine$,$Methionine$,and $Isoleucine$ are essential amino acids.
$Alanine$ is a non-essential amino acid because the human body can synthesize it from pyruvate.

(D) Proteins are classified based on their chemical composition into simple,conjugated,and derived proteins.
Simple proteins are those that yield only amino acids upon hydrolysis.
Examples of simple proteins include albumins,globulins,and histones.
Nucleoproteins,glycoproteins,and lipoproteins are examples of conjugated proteins,as they contain a protein part combined with a non-protein prosthetic group (nucleic acid,carbohydrate,and lipid,respectively).
Therefore,$D$ is the correct answer.

(C) Nicotinamide (a form of Niacin or Vitamin $B_3$) is a water-soluble vitamin.
In the human body,it can be synthesized from the essential amino acid $Tryptophan$.
Approximately $60 \ mg$ of $Tryptophan$ is required to synthesize $1 \ mg$ of Niacin.
This metabolic pathway occurs primarily in the liver.

(B) The simplest amino acid is $Glycine$ $(NH_2-CH_2-COOH)$.
It is the only amino acid that does not have a chiral carbon atom because its side chain ($R$-group) is a single hydrogen atom $(H)$.
Other amino acids have more complex side chains attached to the $\alpha$-carbon.

(B) Haemoglobin is a chromoprotein consisting of two parts.
One part $(96\%)$ is a specific simple protein known as globin $(histone)$.
The other part $(4\%)$ is a non-specific prosthetic group,which is an iron-containing pigment called haem.

(D) Haemoglobin is a conjugated protein consisting of a protein part called globin and a non-protein part called haem.
Each haem group contains an iron atom in the ferrous $(Fe^{2+})$ state.
This iron atom is held at the center of the porphyrin ring by four coordinate bonds with the nitrogen atoms of the pyrrole rings.
Additionally,the iron atom is attached to the globin protein chain via a coordinate bond with a specific histidine residue (proximal histidine).

(C) The amino acid $Tyrosine$ serves as a precursor for the synthesis of several important biological molecules.
$1$. $Thyroxine$ $(T_4)$ and $Triiodothyronine$ $(T_3)$ are thyroid hormones synthesized from $Tyrosine$ residues in the protein $Thyroglobulin$.
$2$. $Adrenaline$ (epinephrine) and $Noradrenaline$ (norepinephrine) are catecholamines synthesized from $Tyrosine$ via the pathway involving $L-DOPA$ and $Dopamine$.
$3$. $Melanin$,the pigment responsible for skin,hair,and eye color,is also synthesized from $Tyrosine$ through a series of enzymatic reactions involving $Tyrosinase$.

(B) Insulin is a peptide hormone consisting of $51$ amino acids in total.
It is composed of two polypeptide chains,chain $A$ and chain $B$,which are linked together by disulfide bridges.
Chain $A$ consists of $21$ amino acid residues,and chain $B$ consists of $30$ amino acid residues.
Therefore,option $(b)$ is the correct statement.

(C) The correct answer is $C$.
Methionine is a sulphur-containing amino acid because it possesses a sulphur atom in its side chain ($R$-group).
Other sulphur-containing amino acids include Cysteine.

(B) Protein denaturation is a process in which proteins lose their quaternary,tertiary,and secondary structures due to the application of external stress or compounds such as strong acids,bases,concentrated inorganic salts,or heat.
During this process,the $3D$ structure (tertiary and secondary) of the protein is disrupted,causing the protein to unfold and lose its biological activity.
The primary structure,which is defined by the sequence of amino acids ($AA$ sequence) held together by peptide bonds,remains intact because denaturation does not break these covalent bonds.

(C) The simplest amino acid is $Glycine$.
In $Glycine$,the $R$-group (side chain) is a single hydrogen atom $(-H)$.
The general structure of an amino acid is $H_2N-CH(R)-COOH$.
For $Glycine$,$R = H$,resulting in the formula $H_2N-CH_2-COOH$.
It is the only achiral amino acid because it does not have a chiral carbon atom.

(D) The correct statement is that the sequence of amino acids determines the primary structure of proteins.
$DNA$ is a polymer of deoxyribonucleotides,not ribonucleotides.
Not all carbohydrates break down into glucose; for example,some break down into fructose or galactose.
$RNA$ and $DNA$ share the same purine bases (Adenine and Guanine); they differ in their pyrimidine bases (Uracil in $RNA$ vs. Thymine in $DNA$).
The primary structure of a protein is defined by the specific sequence of amino acids linked by peptide bonds.

(B) Silk and wool are natural fibers that are proteinaceous in nature.
Silk is primarily composed of the protein fibroin.
Wool is primarily composed of the protein keratin.
Polyethylene and Terylene are synthetic polymers.
Cellulose is a polysaccharide (carbohydrate).

(B) Non-essential amino acids are those that the human body can synthesize on its own. The synthesis of these amino acids is a biosynthetic process,which is a part of protein anabolism. Anabolism refers to the metabolic pathways that construct molecules from smaller units,requiring energy. Therefore,the synthesis of non-essential amino acids occurs during the process of protein anabolism.

(C) Milk contains a primary protein known as $Casein$.
$Lactose$ is a disaccharide sugar found in milk,not a protein.
$Myosin$ is a motor protein found in muscle fibers.
$Pepsin$ is a digestive enzyme found in the stomach.
Therefore,the correct answer is $Casein$.

(B) The formation of disulfide bonds in proteins occurs through the oxidation of the thiol $(-SH)$ groups found in the side chains of the amino acid cysteine.
Two cysteine residues are brought together,and the oxidation of their thiol groups results in the formation of a covalent disulfide bond $(-S-S-)$.
This bond plays a crucial role in stabilizing the tertiary and quaternary structures of proteins.

(C) Proteins are highly specific to each species. While fats,carbohydrates,and vitamins are relatively similar across different organisms,the sequence and structure of proteins (encoded by $DNA$) are unique to each individual and species,making them the most variable component among different animals.

(B) Amino acids are classified based on the nature of their $R$-group.
$1$. Acidic amino acids contain an extra carboxyl group $(-COOH)$ in their side chain,making them acidic. Examples include Glutamic acid and Aspartic acid.
$2$. Basic amino acids contain an extra amino group $(-NH_2)$ in their side chain. Examples include Lysine and Arginine.
$3$. Neutral amino acids like Valine have non-polar or polar uncharged side chains.
Therefore,Glutamic acid is an acidic amino acid.

(B) Amino acids are classified based on their synthesis in the human body.
$1$. Essential amino acids: These cannot be synthesized by the body and must be obtained through the diet.
$2$. Non-essential amino acids: These can be synthesized by the body.
Therefore,amino acids that are not synthesized in the body are known as essential amino acids.

(C) Proteins are polymers of amino acids. Each amino acid contains an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$. Since the amino group contains nitrogen,nitrogen is an essential component of all proteins. Carbohydrates,fats,and oils primarily consist of carbon,hydrogen,and oxygen,and do not contain nitrogen as a structural component.

(B) dipeptide is a molecule consisting of two amino acids joined by a single peptide bond.
When the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of another amino acid,a molecule of water $(H_2O)$ is eliminated,resulting in the formation of a peptide bond $(-CO-NH-)$.
Since there are two amino acids involved,it is termed a dipeptide.

(C) Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet.
Among the given options,$Tryptophan$ is an essential amino acid.
Alanine,Glycine,and Tyrosine are non-essential amino acids as they can be synthesized by the human body.