Proteins Questions in English

(B) Conjugated proteins are proteins that are covalently bonded to non-protein groups (prosthetic groups).
$1$. Glycoproteins are conjugated proteins where the prosthetic group is a carbohydrate.
$2$. Lecithoproteins contain lipids (lecithin).
$3$. Lipoproteins contain lipids.
$4$. Metalloproteins contain metal ions.
Therefore,the correct option is $B$.

(D) Hemoglobin $(Hb)$ is a quaternary protein consisting of four polypeptide subunits: two $\alpha$-chains and two $\beta$-chains.
Each polypeptide chain contains one heme group.
Each heme group contains one iron $(Fe^{2+})$ atom at its center.
Therefore,since there are four heme groups in one hemoglobin molecule,there are a total of four iron atoms present in one quaternary structure of $Hb$.

(A) Amino acids are classified based on the nature of their $R$ group.
$1$. Alanine has a methyl group $(-CH_3)$ as its $R$ group,which is non-polar and hydrophobic.
$2$. Arginine has a positively charged,basic $R$ group.
$3$. Glycine has a hydrogen atom $(-H)$ as its $R$ group,which is technically non-polar,but Alanine is the classic example of a non-polar amino acid with a hydrocarbon side chain.
$4$. Tyrosine has a phenolic hydroxyl group,making it polar.
Therefore,Alanine is the most appropriate answer for a standard non-polar $R$ group.

(A) Amino acids are organic compounds that contain both an amino group $(-NH_2)$ and a carboxylic acid group $(-COOH)$ in their structure.
Because of the presence of the basic amino group and the acidic carboxyl group,amino acids can act as both acids and bases.
In a solution,they can exist as zwitterions,where the amino group is protonated $(-NH_3^+)$ and the carboxyl group is deprotonated $(-COO^-)$,allowing them to function as amphoteric molecules.

(B) The given structure represents a dipeptide formed by the condensation of two amino acids.
In a peptide bond,the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of another amino acid.
The peptide bond is represented as $-CO-NH-$.
In the provided structure,the segment between the two alpha-carbon atoms is $-C(=O)-X-$.
Comparing this with the peptide bond structure $-CO-NH-$,it is clear that $X$ represents the nitrogen atom $(N)$.

(D) polypeptide chain is a polymer of amino acids linked by peptide bonds.
In a polypeptide chain,the amino acid at one end has a free amino group $(-NH_2)$,which is known as the $N$-terminal amino acid.
The amino acid at the other end has a free carboxyl group $(-COOH)$,which is known as the $C$-terminal amino acid.
Therefore,the group present at the $N$-terminal is the amino group.

(B) The most widely accepted classification of amino acids,based on the chemical nature of their $R$-groups (side chains),was proposed by Albert $L$. Lehninger in his seminal textbook,'Biochemistry'. This classification categorizes amino acids into non-polar,polar uncharged,positively charged,and negatively charged groups.

(C) Hemoglobin is a quaternary protein consisting of $4$ polypeptide subunits: $2$ alpha chains and $2$ beta chains.
Each polypeptide chain is associated with a non-protein prosthetic group called a heme group.
Therefore,a single hemoglobin molecule contains $4$ heme groups,each capable of binding one molecule of oxygen $(O_2)$.

(A) Collagen is the most abundant protein in the whole animal world. It provides structural support to various tissues like skin,tendons,and bones. In contrast,Rubisco is the most abundant protein in the whole biosphere (plant world).

(B) Proteins,specifically antibodies (immunoglobulins),are specialized molecules that fight against infectious pathogens. They recognize and bind to specific antigens on the surface of pathogens to neutralize them or mark them for destruction by the immune system.

(C) Amino acids are organic compounds containing an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$ attached to the same carbon atom,known as the $\alpha$-carbon.
The carboxyl group $(-COOH)$ acts as an acid because it can donate a proton $(H^+)$,while the amino group $(-NH_2)$ acts as a base because it can accept a proton $(H^+)$.
Because amino acids possess both acidic and basic functional groups,they can react with both acids and bases,making them amphoteric in nature.
This property allows them to exist as zwitterions at a specific $pH$ (isoelectric point).

(D) Proteins are polymers of amino acids. In proteins,amino acid molecules are linked to each other by peptide bonds.
When the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of another amino acid,a molecule of water is eliminated,and a peptide bond $(-CONH-)$ is formed.
Therefore,the correct option is $D$.

(D) The tertiary structure of a protein represents its overall three-dimensional shape.
It is formed by the folding and coiling of the polypeptide chain,which is stabilized by various interactions such as hydrogen bonds,ionic bonds,hydrophobic interactions,and disulfide bridges.
While the primary structure is the linear sequence of amino acids and the secondary structure involves local folding (like $\alpha$-helices and $\beta$-pleated sheets),the tertiary structure provides the functional $3D$ conformation of the protein molecule.

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

(B) 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.
These structures are 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.
Common examples of secondary structures include the $\alpha$-helix and $\beta$-pleated sheets.
Therefore,the correct option is $B$.

(D) The quaternary structure of proteins refers to the arrangement of multiple polypeptide chains (subunits) into a single functional complex.
These subunits are held together by non-covalent interactions,which include hydrogen bonds,ionic bonds,and hydrophobic interactions.
Disulfide bonds (covalent) can also stabilize the structure between subunits.
However,a general 'covalent bond' (such as a peptide bond) is responsible for the primary structure (the linear sequence of amino acids) within a single polypeptide chain,not for the association of subunits in the quaternary structure.
Therefore,the general term 'covalent bond' is the correct answer as it refers to the primary structure linkage.

(B) Protein synthesis in living organisms primarily involves $20$ standard amino acids.
These amino acids are encoded by the genetic code and are linked together by peptide bonds to form polypeptide chains (proteins).
While other amino acids exist in nature,these $20$ are the fundamental building blocks used during the process of translation in cells.

(B) Amino acids are the building blocks of proteins. Albert $L$. Lehninger,in his seminal work on biochemistry,provided a systematic classification of amino acids based on the properties of their $R$-groups (side chains),such as polarity,charge,and chemical structure. This classification is widely accepted and used in biological sciences.

(B) Amino acids are classified based on the nature of their $R$-group side chains.
$1$. Alanine $(Ala)$ has a non-polar methyl group $(-CH_3)$ as its side chain.
$2$. Serine $(Ser)$ contains a hydroxyl group $(-OH)$ in its side chain,which makes it polar but uncharged at physiological $pH$.
$3$. Valine $(Val)$ has a non-polar isopropyl group as its side chain.
$4$. Proline $(Pro)$ is a non-polar imino acid.
Therefore,Serine is the correct answer as it is a polar,uncharged amino acid.

(C) In proteins,amino acids are linked together by a covalent bond known as a peptide bond.
This bond is formed by a dehydration synthesis reaction between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of the adjacent amino acid.
During this process,a molecule of water $(H_2O)$ is released.

(C) Proteins are complex macromolecules formed by the polymerization of smaller units called amino acids.
These amino acids are linked together by peptide bonds to form polypeptide chains,which fold into specific three-dimensional structures to function as proteins.
Glucose is a simple sugar (carbohydrate),glycogen is a polysaccharide (storage carbohydrate),and nucleic acids are polymers of nucleotides.

(D) Proteins are heteropolymers consisting of strings of amino acids.
These amino acids are linked together by peptide bonds to form long polypeptide chains.
Since amino acids are the repeating structural units that make up the protein molecule,proteins are considered polymers of amino acids.

(D) Proteins perform a wide variety of functions in living organisms,including transport (e.g.,membrane proteins),defense (e.g.,antibodies),and catalysis (e.g.,enzymes). However,hereditary traits are primarily determined by nucleic acids ($DNA$ and $RNA$),not proteins. Therefore,the statement that proteins are responsible for hereditary traits in all organisms is incorrect.

(B) RuBisCO stands for Ribulose bisphosphate carboxylase-oxygenase.
It is an enzyme involved in the first major step of carbon fixation in the Calvin cycle of photosynthesis.
Because photosynthesis is the primary process for energy production in plants,algae,and cyanobacteria,RuBisCO is synthesized in massive quantities globally.
Therefore,it is considered the most abundant protein in the entire biosphere.

(D) Proteins are complex macromolecules that exhibit varying solubility depending on their structure and the solvent environment.
$1$. Many proteins are soluble in water,especially globular proteins,due to the presence of hydrophilic amino acid residues on their surface.
$2$. Proteins are often highly soluble in dilute acidic or basic solutions because the change in $pH$ alters the ionization state of the amino acid side chains,increasing electrostatic repulsion between protein molecules.
$3$. Some proteins also show solubility in dilute alcohol solutions.
Therefore,proteins can be soluble in all the mentioned solvents depending on the specific type of protein and conditions.

(B) Keratin is a fibrous structural protein that forms the primary component of hair,feathers,scales,nails,and horns in vertebrates. It is characterized by its high content of the amino acid cysteine,which allows for the formation of disulfide bridges,providing strength and durability to these structures. Collagen is the most abundant protein in the animal kingdom,found in connective tissues. Melanin is a pigment,not a protein. RuBisCO is an enzyme involved in photosynthesis.

(D) Denaturation is a process in which proteins lose their quaternary,tertiary,and secondary structure by application of some external stress or compound.
High temperature disrupts the hydrogen bonds and hydrophobic interactions that stabilize the protein structure.
Strong acids and bases alter the $pH$ of the environment,which affects the ionic bonds and hydrogen bonding within the protein molecule.
Alcohol acts as a dehydrating agent and disrupts the hydrophobic interactions,leading to the unfolding of the protein.
Therefore,all these conditions can cause protein denaturation.

(A) An amino acid is an organic compound that contains both an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$ attached to the same carbon atom,known as the $\alpha$-carbon.
In this structure,the amino group $(-NH_2)$ acts as a base because the nitrogen atom has a lone pair of electrons that can accept a proton $(H^+)$.
Conversely,the carboxyl group $(-COOH)$ acts as an acid because it can donate a proton $(H^+)$.
Therefore,the basic group in an amino acid is the amino group $(-NH_2)$.

(C) An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent,such as water.
$Glucose$ and $Maltose$ are carbohydrates that dissolve in water but do not dissociate into ions,hence they are non-electrolytes.
$Amino$ $acids$ contain both an amino group $(-NH_2)$ and a carboxyl group $(-COOH)$. In a solution,they exist as $zwitterions$ (dipolar ions) depending on the $pH$,allowing them to conduct electricity.
$Nucleic$ $acids$ are large polymers (polynucleotides) that are generally considered macromolecules; while they have charged phosphate groups,$Amino$ $acids$ are the classic examples of small molecules that act as electrolytes due to their amphoteric nature.

(D) 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 ($-R$ group) attached to a central alpha-carbon atom.
While the amino and carboxyl groups are common to all amino acids,the chemical nature,properties,and classification of amino acids are determined by the specific structure of the side chain,known as the $R$-group.
Therefore,the $R$-group is responsible for the diversity in the properties and types of amino acids.

(B) The classification of amino acids is primarily based on the nature of their $R$-group (side chain) and the presence of specific functional groups attached to the $\alpha$-carbon.
This method categorizes amino acids into groups such as acidic,basic,neutral,polar,and non-polar based on the chemical properties of these functional groups.
While various systems exist,the functional group-based classification is the most standard and widely accepted approach in biochemistry,as it directly relates to the chemical behavior and structural role of the amino acids in proteins.

(A) Amino acids are classified based on the nature of their '$R$' group.
$1$. Leucine has an isobutyl group as its '$R$' group,which is hydrophobic and non-polar.
$2$. Asparagine contains an amide group,which is polar.
$3$. Glycine has a hydrogen atom as its '$R$' group. While it is technically non-polar,Leucine is the classic example of a non-polar,hydrophobic amino acid with a significant hydrocarbon side chain.
$4$. Aspartic acid contains a carboxylic acid group,which is polar and acidic.
Therefore,Leucine is the most appropriate answer for an amino acid with a non-polar '$R$' group.

(B) Amino acids are classified based on the nature of their $R$ group side chains.
$1$. Isoleucine has a non-polar,hydrophobic $R$ group.
$2$. Glutamine has an amide group in its side chain,which is polar but uncharged at physiological $pH$.
$3$. Aspartic acid has a carboxyl group in its side chain,making it polar and negatively charged (acidic).
$4$. Arginine has a guanidino group in its side chain,making it polar and positively charged (basic).
Therefore,Glutamine is the correct answer as it is polar and uncharged.

(A) Amino acids are classified based on the nature of their $R$ group.
$1$. Glutamic acid has a carboxylic acid group in its side chain,which makes it polar and negatively charged at physiological $pH$.
$2$. Arginine and Lysine are basic amino acids with positively charged $R$ groups.
$3$. Glycine has a hydrogen atom as its $R$ group,making it non-polar and neutral.
Therefore,Glutamic acid is the correct answer.

(D) Amino acids are classified based on the nature of their '$R$' group.
$1$. Aspartic acid and Glutamic acid have acidic '$R$' groups (negatively charged).
$2$. Threonine has a polar but uncharged '$R$' group (contains a hydroxyl group).
$3$. Lysine has a basic '$R$' group,which is polar and positively charged at physiological $pH$ due to the presence of an amino group in the side chain.
Therefore,Lysine is the correct answer.

(D) Histidine is a basic amino acid.
It contains an imidazole ring in its '$R$' group.
At physiological $pH$ (around $7.4$),the imidazole side chain of histidine can be protonated,making it polar and positively charged.
Therefore,the '$R$' group of histidine is polar and positively charged.

(C) 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.
Methionine contains a thioether group,and Tryptophan contains an indole ring; both are non-polar and hydrophobic.
Asparagine and Serine are polar uncharged.
Aspartic acid and Glutamic acid are acidic (polar charged).
Arginine and Lysine are basic (polar charged).
Therefore,the correct pair is Methionine and Tryptophan.

(B) Amino acids are classified based on the chemical nature of their '$R$' groups.
Polar uncharged amino acids contain functional groups like hydroxyl $(-OH)$ or amide $(-CONH_2)$ groups that can form hydrogen bonds but do not carry a net charge at physiological $pH$.
Threonine contains a hydroxyl group,and Tyrosine contains a phenolic hydroxyl group,making both polar and uncharged.
Histidine is basic (positively charged),Proline is non-polar,Aspartic acid is acidic (negatively charged),and Alanine and Leucine are non-polar.

(B) When two amino acid units are joined together by a peptide bond,the resulting molecule is called a dipeptide.
- $A$ peptide bond is formed between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of another amino acid,with the elimination of a water molecule $(H_2O)$.
- Disaccharides are formed by the linkage of two monosaccharides.
- Dinucleotides are formed by the linkage of two nucleotides.
- Polypeptides are chains of many amino acids linked together.

(C) peptide bond (or dipeptide bond) is formed by the condensation reaction between the carboxyl group $(-COOH)$ of one amino acid and the amino group $(-NH_2)$ of another amino acid.
During this process,a molecule of water $(H_2O)$ is eliminated.
Therefore,the bond is formed between the $-COOH$ group and the $-NH_2$ group.

(B) The $-CO-NH-$ linkage is known as a peptide bond.
It is formed when the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of another amino acid,resulting in the elimination of a water molecule $(H_2O)$.
This bond is characteristic of proteins,which are polymers of amino acids.

(D) Amino acids are the building blocks of proteins.
When two amino acids are linked by a peptide bond,they form a dipeptide.
When multiple (many) amino acid molecules are linked together through peptide bonds,they form a long chain known as a polypeptide.
Polypeptides are the fundamental components of proteins.

(B) Proteins are heteropolymers containing strings of amino acids.
They are formed by the polymerization of amino acids linked by peptide bonds.
One or more polypeptide chains fold and assemble to form a functional protein molecule.

(C) polypeptide chain is a linear polymer of amino acids linked by peptide bonds.
In a polypeptide chain,one end has a free amino group $(-NH_2)$,which is known as the $N$-terminal or amino-terminal end.
The other end of the chain has a free carboxyl group $(-COOH)$,which is known as the $C$-terminal or carboxyl-terminal end.
Therefore,the end containing the free amino group is called the $N$-terminal.

(A) 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,one end has a free amino group,which is known as the $N$-terminal.
The other end has a free carboxyl group,which is known as the $C$-terminal.
Therefore,the end containing a free carboxyl group is called the $C$-terminal.

(A) 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 stored in the $DNA$ (genes).
Changes in the gene sequence (mutations) lead to changes in the amino acid sequence,which subsequently affects the higher-order folding and function of the protein.

(C) The secondary structure of a protein refers to the local folding of the polypeptide chain into regular patterns such as $\alpha$-helices and $\beta$-pleated sheets.
These structures are stabilized primarily by $Hydrogen$ bonds formed between the carbonyl oxygen $(C=O)$ and the amino hydrogen $(N-H)$ of the peptide backbone.
Therefore,the correct option is $C$.

(B) In the secondary structure of proteins,the polypeptide chain is folded into specific shapes due to hydrogen bonding between the amino acid residues.
Specifically,the $\alpha$-helix is a common secondary structure where the polypeptide chain is coiled into a rigid,tubular,or spiral shape,stabilized by intramolecular hydrogen bonds between the carbonyl oxygen of one amino acid and the amino hydrogen of another residue located four positions away.
Therefore,the correct term for this structure is the helix.

(C) The $3D$ structure of a protein is primarily represented by its tertiary structure.
$1$. Primary structure refers to the linear sequence of amino acids.
$2$. Secondary structure refers to the local folding of the polypeptide chain into structures like $\alpha$-helices and $\beta$-pleated sheets.
$3$. Tertiary structure represents the overall three-dimensional folding of the entire polypeptide chain,which is essential for the biological activity of the protein.
$4$. Quaternary structure refers to the arrangement of multiple polypeptide subunits in a multi-subunit protein.

(C) The quaternary structure of a protein refers to the spatial arrangement and interaction of multiple polypeptide chains (subunits) that form a functional protein complex.
These subunits are held together by non-covalent interactions such as hydrogen bonds,ionic bonds,and hydrophobic interactions.
Most proteins with quaternary structure,such as hemoglobin,exhibit a $3D$ globular shape,which is essential for their biological activity.