Amino Acids and Proteins Questions in English

(C) The correct answer is $C$. $A$ zwitter ion is a dipolar ion that contains both positive and negative charges at different points within the same molecule.
For example,in amino acids,the amino group $(NH_2)$ accepts a proton to become $NH_3^+$ and the carboxyl group $(COOH)$ loses a proton to become $COO^-$,resulting in the structure: $NH_3^+ - CH_2 - COO^-$.
This is also known as an internal salt.

(B) Interferons are a group of signaling proteins made and released by host cells in response to the presence of several viruses. They belong to the class of glycoproteins and act as antiviral agents by inhibiting viral replication.

(D) molecular disease is a disease caused by an abnormality in the structure or function of a single molecule,typically a protein or a gene.
$Sickle-cell \text{ anaemia}$ is a classic example of a molecular disease caused by a mutation in the gene that codes for the $\beta$-globin chain of hemoglobin,leading to the production of abnormal hemoglobin $(HbS)$.

(A) Ninhydrin is a chemical reagent used to detect amino acids and proteins. In chromatography,it is sprayed onto the chromatogram to visualize the spots of amino acids,which appear as purple or violet colored spots.

(C) The compound $NH_2CH_2COOH$ is glycine,which is an amino acid.
In its structure,it contains an amino group $(-NH_2)$,which is basic,and a carboxylic acid group $(-COOH)$,which is acidic.
Therefore,it can act as both an acid and a base,forming a zwitterion in aqueous solution.

(D) zwitterion is formed by compounds that contain both an acidic group $(-COOH)$ and a basic group $(-NH_2)$ in the same molecule.
$H_2NCH_2COOH$ (Glycine) is an amino acid that exists as a zwitterion in aqueous solution:
$H_2NCH_2COOH \rightleftharpoons H_3N^+CH_2COO^-$

(B) Condensation polymers are formed by the repeated condensation reaction between two different bi-functional or tri-functional monomeric units,usually involving the elimination of small molecules like $H_2O$,$HCl$,or $NH_3$.
Protein is a natural polymer formed by the condensation of amino acids through peptide bonds,where a molecule of water is eliminated during each linkage formation.
Rubber,$PVC$,and Polythene are addition polymers formed by the repeated addition of monomer units without the loss of any small molecules.

(B) Fibrous proteins consist of long,thread-like polypeptide chains that are held together by strong $Hydrogen$ bonds and disulfide linkages. These interactions provide the structural stability and insolubility characteristic of fibrous proteins like keratin and collagen.

(D) Lysine has the structure $H_2N-(CH_2)_4-CH(NH_2)-COOH$.
It contains an amino group attached to the $\alpha$-carbon,making it an $\alpha$-amino acid.
Additionally,it contains two amino groups $(-NH_2)$ and one carboxyl group $(-COOH)$,which makes it a basic amino acid due to the excess of basic groups over acidic groups.
Therefore,both statements are correct.

(B) Proteins are natural polymers formed by the condensation of $\alpha$-amino acids.
These amino acids are linked together by peptide bonds ($-CONH-$ linkage).
Since the peptide bond is an amide linkage,proteins are classified as polyamides.

(A) Proteins are complex nitrogenous organic compounds which are polymers of $\alpha$-amino acids.
These amino acids are linked together by peptide bonds ($-CONH-$ linkage) formed by the condensation reaction between the amino group of one amino acid and the carboxyl group of another.
Therefore,proteins are condensation polymers of $\alpha$-amino acids.

(D) Proteins perform a wide variety of functions in biological systems.
$1$. They act as structural components of animal cells (e.g.,collagen,keratin).
$2$. They function as biological catalysts known as enzymes and as defensive agents known as antibodies.
$3$. They act as metabolic regulators (e.g.,hormones like insulin).
Therefore,all the given options are correct.

(D) Conjugated proteins are proteins that contain a non-protein component (prosthetic group) in addition to their polypeptide chains.
$1$. Glycoproteins contain carbohydrates as the prosthetic group.
$2$. Phosphoproteins contain phosphate groups.
$3$. Chromoproteins contain a colored prosthetic group.
Since all these examples contain non-protein components,they are all classified as conjugated proteins.

(D) Proteins are primarily structural components and functional catalysts (enzymes) in the body. They are essential for the formation of nails,skin,and muscles. While they can be broken down for energy in extreme conditions,they are not the primary source of energy for metabolism,as carbohydrates and fats serve that purpose.

(D) zwitterion is a dipolar ion that contains both positive and negative charges,resulting in a net charge of zero.
Amino acids like glycine and glutamic acid exist as zwitterions because they contain both an acidic $(-COOH)$ and a basic $(-NH_2)$ group.
Sulphanilic acid $(NH_2-C_6H_4-SO_3H)$ also exists as a zwitterion because the acidic $-SO_3H$ group transfers a proton to the basic $-NH_2$ group.
However,$p-$Aminobenzoic acid $(NH_2-C_6H_4-COOH)$ does not exist as a zwitterion in its stable form because the acidity of the carboxylic acid group is not strong enough to protonate the weakly basic aniline group effectively in the solid state compared to the sulfonic acid group in sulphanilic acid.

(D) Denaturation is a process that causes the protein to lose its specific three-dimensional shape.
During denaturation,the secondary and tertiary structures of the protein are disrupted due to the breaking of hydrogen bonds and other non-covalent interactions.
However,the primary structure (the sequence of amino acids) remains intact.
As a result,the protein loses its biological activity.

(D) Denaturation is a process that causes the alteration of the secondary and tertiary structures of proteins,leading to the loss of their biological activity.
This process can be triggered by physical changes such as $Heat$ or chemical agents such as $Mineral \ acids$ and $Bases$.
Therefore,all the given options contribute to the denaturation of proteins.

(A) Pepsin is a digestive enzyme that acts as a protease. It catalyzes the hydrolysis of peptide bonds in proteins,breaking them down into smaller peptides and amino acids. Therefore,the correct answer is that proteins are converted into amino acids.

(A) Proteins are formed by the condensation of $\alpha$-amino acids through the formation of peptide bonds ($-CONH-$ linkage).
Since the peptide bond is an amide linkage,proteins are classified as polyamides.

(C) Hemoglobin is a conjugated protein present in red blood cells.
Its primary function is to transport oxygen from the lungs to the tissues and return carbon dioxide from the tissues to the lungs.
Therefore,it acts as an oxygen carrier in the blood.

(D) The secondary structure of proteins refers to the local spatial arrangement of the polypeptide backbone.
It is primarily stabilized by hydrogen bonds between the carbonyl oxygen $(C=O)$ and the amide hydrogen $(N-H)$ of the peptide backbone.
The two most common types of secondary structures are the $\alpha$-helix and $\beta$-pleated sheet,which represent regular folding patterns of the polypeptide chain.

(B) The $\alpha-$amino acid that forms cross-links in peptide chains is $Cysteine$.
$Cysteine$ contains a thiol group $(-SH)$ in its side chain.
Two $Cysteine$ residues can undergo oxidation to form a disulfide bond $(-S-S-)$,which acts as a cross-link between different parts of a protein chain or between different polypeptide chains,stabilizing the tertiary structure of proteins.

(A) The primary structure of a protein refers to the specific sequence in which $\alpha-$amino acids are linked to each other by peptide bonds in a polypeptide chain.
This sequence determines the overall shape and function of the protein.

(B) The isoelectric point $(pI)$ of most neutral amino acids typically lies in the $pH$ range of $5.5$ to $6.3$.
Since the relationship between $pH$ and $pOH$ is given by $pH + pOH = 14$ at $25^{\circ}C$,we can calculate the $pOH$ range.
For $pH = 5.5$,$pOH = 14 - 5.5 = 8.5$.
For $pH = 6.3$,$pOH = 14 - 6.3 = 7.7$.
Therefore,the $pOH$ range for the isoelectric point is $7.7$ to $8.5$.

(D) The primary structure of a protein refers to the linear sequence of amino acids in a polypeptide chain.
The secondary structure of a protein refers to the regular folding patterns of continuous portions of the polypeptide chain,such as the $\alpha$-helix and $\beta$-pleated sheet structures,which are stabilized by hydrogen bonding.
The tertiary structure refers to the overall $3-D$ folding of the entire polypeptide chain.
Therefore,the correct description for the secondary structure is the regular folding patterns of continuous portions of the polypeptide chain.

(B) The cell membrane is primarily composed of proteins and lipids. It typically contains $46-76\% \text{ protein}$,$20-53\% \text{ lipid}$,and $1-8\% \text{ carbohydrate}$. Among these,proteins are the major structural components.

(C) Proteins are complex polymers of $ \alpha $-amino acids linked by peptide bonds.
During enzymatic hydrolysis,enzymes like proteases break these peptide bonds to yield $ \alpha $-amino acids as the final products.

(B) zwitterion is a molecule that contains both a positive and a negative charge,making it electrically neutral overall.
Amino acids,which contain both an acidic carboxyl group $(-COOH)$ and a basic amino group $(-NH_2)$,are capable of internal proton transfer.
In $NH_2-CH_2-COOH$ (glycine),the proton from the $-COOH$ group is transferred to the $-NH_2$ group,resulting in the formation of the zwitterion: $^+NH_3-CH_2-COO^-$.
Therefore,$NH_2-CH_2-COOH$ is the correct answer.

(A) An amino acid is chiral if it has a chiral carbon atom (an $\alpha$-carbon bonded to four different groups).
All naturally occurring $\alpha$-amino acids are chiral except for Glycine.
Glycine has the structure $NH_2-CH_2-COOH$,where the $\alpha$-carbon is bonded to two hydrogen atoms,making it achiral.
Valine,Alanine,and Proline all possess a chiral center at the $\alpha$-carbon.

(D) tripeptide is formed by the combination of $3$ amino acids. Since there are $20$ different amino acids available and each position in the tripeptide can be occupied by any of these $20$ amino acids,the total number of possible tripeptides is calculated as $20 \times 20 \times 20 = 20^3 = 8000$.

(B) An amino acid is achiral if it does not possess a chiral carbon atom (a carbon atom bonded to four different groups).
Glycine $(NH_2-CH_2-COOH)$ is the only naturally occurring achiral amino acid because its $\alpha-$carbon is bonded to two hydrogen atoms.
$2-$Methylglycine,also known as $\alpha-$aminoisobutyric acid $(NH_2-C(CH_3)_2-COOH)$,is also achiral because the $\alpha-$carbon is bonded to two identical methyl groups.
Therefore,$2-$Methylglycine is an achiral amino acid.

(C) The hormone $Insulin$ is responsible for maintaining blood sugar levels in the body. It is a peptide hormone produced by the beta cells of the pancreatic islets.

(B) $ATP$ (Adenosine triphosphate) is known as the energy currency of the cell. It stores and transfers energy required for various metabolic processes in living organisms.

(C) The human body cannot synthesize all the amino acids required for protein synthesis. Amino acids that the body cannot synthesize are called essential amino acids,which must be obtained through diet. Therefore,the statement that the human body can synthesize all required proteins is incorrect.

(D) The amino acid $Histidine$ contains an imidazole ring in its side chain. The structure of $Histidine$ consists of an $\alpha$-amino acid group attached to a $CH_2$ group,which is further linked to an imidazole ring.

(C) Hemoglobin is a quaternary protein consisting of $4$ polypeptide subunits: $2$ alpha chains and $2$ beta chains.

(D) The secondary structure of proteins refers to the regular folding patterns of the polypeptide backbone.
These structures are primarily stabilized by hydrogen bonding between the carbonyl oxygen $(C=O)$ and the amide hydrogen $(N-H)$ of the peptide backbone.
Common examples include the $\alpha-$helix and $\beta-$pleated sheet structures.

(A) peptide bond is a chemical bond formed between two molecules when the carboxyl group $(-COOH)$ of one molecule reacts with the amino group $(-NH_2)$ of the other molecule,releasing a molecule of water $(H_2O)$. The resulting linkage is the amide group,represented as $-CONH-$.

(A) The secondary structure of proteins refers to the local spatial arrangement of the polypeptide chain backbone.
It is primarily stabilized by hydrogen bonding between the carbonyl oxygen and the amide hydrogen of the peptide backbone.
Common examples include the $\alpha$-helix and $\beta$-pleated sheet structures.

(C) The secondary structure of proteins,such as the $\alpha$-helix,is stabilized by hydrogen bonding 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.

(B) Proteins are complex,nitrogenous organic compounds of high molecular mass.
By definition,proteins are macromolecules with a molecular weight generally greater than $10,000 \ u$.
They are polymers of $\alpha$-amino acids linked by peptide bonds.

(C) Denaturation is a process where the secondary and tertiary structures of a protein are destroyed due to physical or chemical changes (like heat or $pH$ change).
During this process,the primary structure (the sequence of amino acids) remains intact.
Globular proteins often unfold and may aggregate into fibrous-like structures,but the reverse process (fibrous to globular) is not a characteristic of denaturation.
Therefore,the statement that 'fibrous proteins are converted into globular proteins' is incorrect.

(A) Polypeptides are polymers formed by the condensation of amino acids linked together by peptide bonds. Therefore,the monomer unit of a polypeptide is an amino acid.

(B) The Biuret test is a chemical test used for detecting the presence of peptide bonds ($CONH$ linkages) in a substance.
Proteins and polypeptides contain multiple peptide bonds and thus give a positive Biuret test (violet color).
Urea also gives a positive Biuret test because it contains two amide groups.
Carbohydrates do not contain peptide bonds,therefore they do not give the Biuret test.

(D) An amino acid is optically active if it contains a chiral carbon atom.
In the general structure of an amino acid,$R-CH(NH_2)-COOH$,the central carbon is chiral if the side chain $R$ is not a hydrogen atom.
Glycine is the simplest amino acid where $R = H$.
Thus,the structure of glycine is $H_2N-CH_2-COOH$,which has two identical hydrogen atoms attached to the central carbon,making it achiral.
Therefore,all amino acids except glycine are optically active.

(C) The secondary structure of proteins refers to the shape in which a long polypeptide chain can exist.
This structure is primarily stabilized by $Hydrogen$ bonds between the carbonyl oxygen $(C=O)$ and the amide hydrogen $(N-H)$ of the polypeptide backbone.
These interactions lead to the formation of common structures such as the $\alpha$-helix and $\beta$-pleated sheets.

(D) The $\alpha$-helix is a common secondary structure of proteins.
It is formed by the coiling of the polypeptide chain into a right-handed screw (helix) due to hydrogen bonding between the $C=O$ group of one amino acid and the $N-H$ group of the fourth amino acid residue in the chain.

(C) Most naturally occurring amino acids are $L$-amino acids,not $D$-amino acids. $L$-amino acids have the $-NH_2$ group on the left side in the Fischer projection when the $-COOH$ group is at the top. Therefore,the statement that they generally have $D$-configuration is incorrect.

(D) Amino acids are organic compounds that contain both an amino group $(-NH_2)$ and a carboxylic acid group $(-COOH)$ attached to the same carbon atom,known as the $\alpha$-carbon.
Thus,the general structure is $R-CH(NH_2)-COOH$.