Proteins Questions in English

(A) Amino acids are organic compounds containing an amino group $(-NH_2)$ and a carboxylic acid group $(-COOH)$ attached to the same carbon atom,which is known as the $\alpha$-carbon.
In proteins,all amino acids are $\alpha$-amino acids because the amino group is attached to the $\alpha$-carbon atom.
Valine is a standard proteinogenic amino acid,and therefore,it is an $\alpha$-amino acid.

(A) $\alpha$-keratin is a fibrous protein. Fibrous proteins are characterized by long,thread-like structures that are held together by hydrogen bonds and disulfide bridges. Due to their highly ordered,repetitive structure and the presence of hydrophobic amino acid residues,they are generally insoluble in water. In contrast,hemoglobin and ribonuclease are globular proteins,which are typically soluble in water. Adenine is a nitrogenous base that has limited solubility but is more soluble than fibrous proteins like keratin.

(B) Globular proteins maintain their specific three-dimensional structure through hydrogen bonds,ionic bonds,and hydrophobic interactions.
When a protein is subjected to extreme physical conditions like high temperature or extreme $pH$,these weak bonds are disrupted.
This causes the protein to lose its specific biological activity and its native three-dimensional conformation,a process known as denaturation.
Therefore,the correct answer is Denaturation.

(C) Proteins are essential for the growth and repair of body tissues. They are the building blocks of the body,forming muscles,skin,enzymes,and hormones. Carbohydrates and fats primarily provide energy,while vitamins are required for metabolic regulation.

(A) Proteins are polymers of amino acids.
When two amino acids join together,a peptide bond is formed between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the other.
During this process,a molecule of water $(H_2O)$ is removed.
Since a water molecule is removed to form the bond,this process is known as dehydration synthesis or condensation reaction.

(D) 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 the building blocks of proteins and participate in protein synthesis.
There are $20$ standard amino acids that are commonly found in proteins in living organisms.
Therefore,all the given statements are correct.

(C) Feathers are primarily composed of a structural protein called keratin. Silk is also a protein fiber,primarily composed of fibroin. Both are examples of fibrous proteins that provide structural integrity to biological organisms. Therefore,the correct answer is $C$ (Proteins).

(C) Hemoglobin is a conjugated protein found in red blood cells $(RBCs)$.
Its primary function is to bind with oxygen in the lungs and transport it to various tissues throughout the body.
Therefore,it acts as an oxygen carrier in the blood.
Option $C$ is the correct statement.

(A) Amino acids are classified as essential and non-essential based on whether the human body can synthesize them.
Essential amino acids cannot be synthesized by the human body and must be obtained through the diet.
Non-essential amino acids can be synthesized by the human body.
Glycine is a non-essential amino acid because the human body can produce it.
Phenylalanine,Arginine,and Methionine are essential amino acids that must be supplied through food.

(A) Proteins are the most important structural components of the body. They are polymers of amino acids and form the fundamental building blocks of cells,tissues,and organs. Collagen is the most abundant protein in the animal world,providing structural support to various tissues.

(C) Phosphoproteins are a group of proteins that are chemically bonded to a substance containing phosphoric acid.
Casein,the primary protein found in milk,is a well-known example of a phosphoprotein.
It contains phosphate groups attached to the serine residues of the protein chain,which are essential for its biological function and structure.
Mucin is a glycoprotein,fibrinogen is a blood-clotting protein,and myosin is a contractile protein found in muscle fibers.

(B) Amino acids are organic compounds containing an amino group and an acidic carboxyl group as substituents on the same carbon,called the $\alpha$-carbon.
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 a hydrogen atom $(-H)$.
Therefore,the structure of glycine is $NH_2-CH_2-COOH$.

(B) Proteins are the most abundant organic molecules of the living system. They are essential for all living organisms as they form the structural components of cells,act as enzymes,hormones,and antibodies,and are involved in almost all biological processes. Therefore,proteins are considered the essential building blocks of life.

(A) Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet.
Alanine is a non-essential amino acid because the human body can synthesize it from pyruvate.
Valine,Histidine,and Methionine are all essential amino acids that must be supplied in the diet.

(A) peptide chain is formed by the linkage of amino acids through peptide bonds.
An amino acid has the general structure $NH_2 - CH(R) - COOH$.
When amino acids polymerize,the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of the next amino acid,releasing a water molecule $(H_2O)$ to form a peptide bond $(-CO-NH-)$.
Therefore,the repeating unit in a peptide chain is represented as $... - NH - CH(R) - CO - NH - CH(R) - CO - ...$.
Option $A$ and $C$ represent this structure correctly.

(A) Collagen is the most abundant protein in the animal kingdom,and in the human body,it accounts for approximately $25-30\%$ of the total protein content. It provides structural support to various tissues,including skin,bones,tendons,and ligaments.

(D) Proteins are polymers of amino acids. The basic structure of 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 $R$-group. Therefore,all proteins contain Carbon $(C)$,Hydrogen $(H)$,Oxygen $(O)$,and Nitrogen $(N)$. Sulfur $(S)$ is present in specific amino acids like cysteine and methionine. Phosphorus $(P)$ is generally absent in the primary structure of proteins,although it may be found in conjugated proteins (like phosphoproteins),but it is not a fundamental element of the protein structure itself.

(C) Proteins are heteropolymers of amino acids.
There are $20$ different types of amino acids that can be linked in various sequences to form a polypeptide chain.
The diversity in proteins arises primarily because of the specific sequence of amino acids in the polypeptide chain.
While the $R$-group determines the properties of individual amino acids,the overall structure and function of a protein are determined by the unique sequence of these amino acids.

(D) Aromatic amino acids are those that contain an aromatic ring in their side chain.
$1$. Phenylalanine contains a benzene ring.
$2$. Tyrosine contains a phenol group (a benzene ring with a hydroxyl group).
$3$. Tryptophan contains an indole ring.
Since all three options listed contain aromatic rings in their side chains,they are all classified as aromatic amino acids.
Therefore,the correct answer is $D$.

(D) $1$. Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon, i.e., the $\alpha$-carbon. Hence, they are often called $\alpha$-amino acids. They can be structurally considered as substituted methanes where the four substituent groups occupy the four valency positions of the $\alpha$-carbon: hydrogen, carboxyl group, amino group, and a variable $R$ group.
$2$. The chemical and physical properties of amino acids are essentially determined by the $R$ group. Since the other three groups are constant in all $\alpha$-amino acids, they differ from each other only by the nature of the $R$ group.
$3$. Based on the nature of the $R$ group, there are many amino acids. For example, if the $R$ group is hydrogen, it is glycine; if it is a methyl group, it is alanine; and if it is a hydroxymethyl group $(-CH_2OH)$, it is serine.
$4$. Therefore, all the given statements are correct.

(B) The specificity and functional diversity of proteins are primarily determined by the specific sequence of amino acids in their polypeptide chain.
While the number and types of amino acids are important,the unique order (sequence) in which they are arranged dictates the protein's folding pattern,three-dimensional structure,and ultimately its biological function.
Therefore,the correct answer is the sequence of amino acids.

(D) Amino acids are classified based on the number of amino and carboxyl groups present in their structure.
Acidic amino acids contain one amino group and two carboxyl groups.
Both Glutamic acid and Aspartic acid possess two carboxyl groups,making them acidic in nature.
Therefore,the correct option is $(d)$.

(B) The secondary structure of proteins,such as the $\alpha$-helix,is primarily 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 polypeptide chain.
While peptide bonds hold the primary sequence of amino acids together,the specific helical folding is maintained by the regular pattern of hydrogen bonding.

(D) In India,the majority of the population follows a vegetarian diet. Pulses (legumes) are the most common and affordable source of plant-based protein for vegetarians. They are rich in amino acids and are a staple in the Indian diet,providing essential nutrition.

(C) Casein is the primary protein found in milk,accounting for about $80\%$ of the total protein content in bovine milk.
It is a phosphoprotein that exists in milk as colloidal particles called casein micelles.
These micelles help in the transport of calcium and phosphate in the milk.
Therefore,the correct option is $C$.

(A) Hemoglobin is the oxygen-carrying pigment found in red blood cells,while myoglobin is the oxygen-binding protein found in muscle tissues.
Both of these proteins contain a heme group as their prosthetic group.
The central metal ion present in the heme group of both hemoglobin and myoglobin is iron $(Fe^{2+})$.
Therefore,iron is the common element found in both.

(C) Horns,nails,and hair are primarily composed of a tough,fibrous structural protein known as $Keratin$.
$Keratin$ is a type of scleroprotein that provides mechanical strength and protection to these structures.
It is rich in sulfur-containing amino acids like cysteine,which form disulfide bridges,contributing to its hardness and durability.

(B) Antibodies,also known as immunoglobulins $(Ig)$,are large,$Y$-shaped proteins produced by plasma cells.
They are essential components of the immune system that identify and neutralize foreign objects such as bacteria and viruses.
Chemically,antibodies are composed of polypeptide chains,making them proteins.

(A) Collagen is the most abundant protein in the animal kingdom,and in the human body,it accounts for approximately $25-30\%$ of the total protein content. It provides structural support to tissues such as skin,tendons,ligaments,and bones. Therefore,the correct option is $A$.

(A) Adult hemoglobin $(HbA)$ is a quaternary protein structure consisting of four polypeptide subunits.
It is composed of two $\alpha$-globin chains and two $\beta$-globin chains.
Therefore,the composition is $2$ $\alpha$ and $2$ $\beta$ chains.

(A) Hemoglobin is a complex protein found in red blood cells that is responsible for transporting oxygen throughout the body.
It consists of a protein part called globin and a non-protein part called heme.
The heme group contains an iron ion in the ferrous state,represented as $Fe^{2+}$,which is essential for binding with oxygen molecules.

(C) molecule of hemoglobin, which is a type of globin protein, is a quaternary structure composed of $4$ polypeptide chains.
These chains consist of $2$ alpha ($\alpha$) chains and $2$ beta ($\beta$) chains.
Therefore, the total number of polypeptide chains in a single molecule of globin protein is $4$.

(D) $Clupeine$ is a type of protamine protein found in the sperm of certain fish,specifically in the genus $Clupea$ (herring).
It is a basic protein rich in arginine that replaces histones in the sperm chromatin to facilitate tight $DNA$ packaging.
Since $Clupeine$ is specifically a fish protamine,it is not found in human sperm,pigeon sperm,or human ovum.
Therefore,none of the provided options are correct.

(D) Proteins are long chains of amino acids linked together by peptide bonds.
When these peptide bonds are hydrolyzed or broken,the protein chain is broken down into its constituent monomers.
The fundamental building blocks of proteins are amino acids.
Therefore,breaking the peptide bonds results in the release of individual amino acids.

(D) Proteins are considered the building blocks of the body. They are essential for the growth,repair,and maintenance of body tissues. Proteins are composed of amino acids,which are required for the synthesis of new cells and the structural components of the body,such as muscles,skin,and enzymes.

(B) Amino acids that are incorporated into proteins during translation are called proteinogenic amino acids. There are $20$ standard amino acids that make up proteins.
Ornithine is an amino acid that plays a significant role in the urea cycle,but it is not coded by the genetic code and is not incorporated into proteins during protein synthesis.
Arginine,Aspartic acid,and Tyrosine are all standard proteinogenic amino acids.

(C) Proteins are known as the building blocks of the body. They are essential for the growth of tissues and the repair of damaged cells and tissues. Therefore,both growth and repair are primary functions of proteins in the human body.

(A) The general structure of an amino acid is $R-CH(NH_2)-COOH$.
In this structure,$R$ represents the side chain.
For the simplest amino acid,the $R$ group is a hydrogen atom $(H)$.
When $R = H$,the amino acid is Glycine $(NH_2-CH_2-COOH)$.
Since Glycine has the smallest possible side chain,it is considered the simplest amino acid.

(D) Hemocyanin is a copper-containing respiratory protein found in the hemolymph of many mollusks,including snails.
Each functional subunit of the hemocyanin molecule in snails (such as Helix pomatia) typically consists of a polypeptide chain containing approximately $4500$ amino acids.
Therefore,the correct option is $D$.

(C) Among the given options,groundnut (Arachis hypogaea) is a legume and is a rich source of plant-based proteins and healthy fats. While rice,wheat,and pearl millet are primarily sources of carbohydrates,groundnut provides a significantly higher protein content per unit weight.

(C) Insulin is a peptide hormone produced by the beta cells of the pancreas.
It consists of two polypeptide chains: the $A$ chain and the $B$ chain.
The $A$ chain contains $21$ amino acids,and the $B$ chain contains $30$ amino acids.
These two chains are linked together by disulfide bridges.
Therefore,the total number of amino acids in a mature insulin molecule is $21 + 30 = 51$ amino acids.

(A) Frederick Sanger was the scientist who determined the complete amino acid sequence of the insulin molecule in $1953$.
For this pioneering work in protein sequencing,he was awarded the Nobel Prize in Chemistry in $1958$.
Insulin consists of two polypeptide chains,chain $A$ and chain $B$,linked by disulfide bridges.

(B) In biochemistry,the prefixes $D-$ and $L-$ are used to denote the stereochemical configuration of molecules,specifically referring to the spatial arrangement of atoms around a chiral center.
These designations are based on the configuration of glyceraldehyde,which is the simplest sugar.
$L-$ indicates that the molecule has a configuration related to $L$-glyceraldehyde,where the functional group (such as the amino group in amino acids) is on the left side in a Fischer projection.
It is important to note that $L-$ does not necessarily mean the molecule is levo-rotatory (which refers to the rotation of plane-polarized light); rather,it describes the relative configuration.

(B) In biochemistry,the prefixes $D-$ and $L-$ are used to denote the configuration of chiral molecules,specifically based on their structural relationship to the glyceraldehyde molecule.
$L-$ stands for the configuration where the functional group (such as the amino group in amino acids) is on the left side in a Fischer projection.
While $L-$ isomers are often levorotatory (rotating plane-polarized light to the left),the $L-$ designation specifically refers to the relative configuration (stereochemistry) rather than the optical rotation property itself.
Therefore,in the context of $L-malic$ acid and $L-lysine$,$L$ represents the specific stereochemical configuration.

(B) The $L-$ and $D-$ designations for amino acids refer to the configuration of the molecule relative to glyceraldehyde,not its optical rotation.
$L-$amino acids are those where the amino group is on the left side in a Fischer projection.
While $L-$amino acids are often levorotatory,this is not a universal rule,as some $L-$amino acids can be dextrorotatory.
However,in the context of standard biochemistry multiple-choice questions,$L-$amino acids are frequently associated with the levorotatory property,though the term refers to the spatial configuration (stereochemistry) rather than the direction of light rotation.

(C) Lysine and tryptophan are essential amino acids. They are considered essential because the human body cannot synthesize them and they must be obtained through the diet. In the context of plant breeding,these are often referred to as limiting amino acids in cereal crops.

(A) Amino acids are classified based on their side chains. $Cysteine$ and $methionine$ are unique because they contain the element $Sulfur$ in their side chains. $Cysteine$ contains a thiol $(-SH)$ group,while $methionine$ contains a thioether group. Therefore,the correct option is $A$.

(C) Amino acids are the building blocks of proteins. Among the $20$ standard amino acids,only two contain sulfur in their side chains: $Cysteine$ and $Methionine$.
$Cysteine$ contains a thiol group $(-SH)$,while $Methionine$ contains a thioether group $(-S-CH_3)$.
Therefore,the correct group is $Cysteine$ and $Methionine$.

(B) Amino acids are organic compounds containing an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$.
Sulfur-containing amino acids are those that possess a sulfur atom in their side chain ($R$-group).
$Cysteine$ contains a thiol group $(-SH)$,and $Methionine$ contains a thioether group $(-S-CH_3)$.
Therefore,$Cysteine$ and $Methionine$ are the sulfur-containing amino acids.

(C) The correct answer is $C$.
$1$. Carbohydrates like starch,glycogen,and sucrose are polymers or dimers of monosaccharides.
$2$. Starch and glycogen are polysaccharides made of glucose units.
$3$. Sucrose is a disaccharide made of glucose and fructose.
$4$. Insulin is a peptide hormone composed of amino acids,not monosaccharides.