Amino Acids and Proteins Questions in English

(D) Amino acids contain both a carboxylic acid group $(-COOH)$ and an amino group $(-NH_2)$.
Every amino acid consists of a central alpha-carbon atom bonded to a hydrogen atom,an $R$ group (side chain),a carboxyl group,and an amino group.
Since both functional groups are present,the correct answer is $(d)$.

(D) Proteins are polymers of amino acids linked by peptide bonds.
On hydrolysis,proteins break down into their constituent amino acids.
The reaction is represented as:
$Dipeptide + H_2O \rightarrow Amino \ Acid_1 + Amino \ Acid_2$

(B) Enzymes are biological catalysts that are primarily composed of proteins.
Proteins are polymers of amino acids,which are linked by peptide bonds,making them polypeptides.
Therefore,enzymes belong to the class of polypeptides.

(D) The metal present in the blood is iron $(Fe)$,which is a central component of the hemoglobin molecule responsible for oxygen transport.

(B) zwitter ion is a molecule that contains both a positive and a negative charge,making it electrically neutral overall. This typically occurs in amino acids where the basic amino group $(-NH_2)$ accepts a proton from the acidic carboxyl group $(-COOH)$.
Among the given options,$(CH_3)_2CH.CH(NH_2)COOH$ is an $\alpha$-amino acid (Valine). It contains both an amino group and a carboxylic acid group,allowing for the internal proton transfer to form a zwitter ion:
$(CH_3)_2CH.CH(NH_2)COOH \rightleftharpoons (CH_3)_2CH.CH(NH_3^+)COO^-$.

(A) Polypeptide chains are long polymers consisting of amino acids linked together by peptide bonds.
Proteins are linear polymers formed by linking the $\alpha$-carboxyl group of one amino acid to the $\alpha$-amino group of another amino acid via a peptide bond (also known as an amide bond).
Therefore,the monomer of a polypeptide is an amino acid.

(B) Haemoglobin is a globular protein. It is a conjugated protein that transports oxygen in the blood.

(C) Albumin is a type of protein that is water-soluble and is found in various biological sources.
In an egg,specifically in the egg white,albumin is the primary protein present,accounting for approximately $54\%$ of the total protein content.
Therefore,among the given options,egg is the most abundant source of albumin.

(D) Proteins are classified into two types based on their molecular shape: fibrous proteins and globular proteins.
Fibrous proteins like $Keratin$ and $Collagen$ have a thread-like structure and are insoluble in water.
Globular proteins result from the folding of polypeptide chains into a spherical shape and are generally soluble in water.
$Haemoglobin$ and $Insulin$ are examples of globular proteins.
However,in the context of standard chemistry curriculum,$Haemoglobin$ is the most cited example of a globular protein.

(A) Leucine is an essential amino acid because it cannot be synthesized by the human body and must be obtained through the diet.
It is a branched-chain amino acid and is not classified as aromatic or basic.

(B) The $Molisch's$ test is a general test for the detection of carbohydrates,not proteins.
$Millon's$ test is used for the detection of phenolic groups (specifically tyrosine in proteins).
$Biuret$ test is used to detect the presence of peptide bonds in proteins.
$Ninhydrin$ test is used to detect amino acids and proteins (specifically the $\alpha$-amino group).

(C) Zwitter ion is a dipolar ion containing both a positive and negative charge in the following form: $R-CH(NH_3^+)-COO^-$.
In this structure,the $-NH_3^+$ group acts as the acidic part (proton donor) and the $-COO^-$ group acts as the basic part (proton acceptor).

(B) Adenosine triphosphate $(ATP)$ is the primary energy-carrying molecule found in the cells of all living organisms.
$ATP$ captures chemical energy obtained from the breakdown of food molecules and releases it to fuel various cellular processes.

(D) conjugated protein is a protein that functions in interaction with other (non-polypeptide) chemical groups attached by covalent bonding or weak interactions.
Phosphoprotein,glycoprotein,and chromoprotein are all examples of conjugated proteins.
Therefore,the correct option is $D$.

(B) The amino acids which cannot be synthesized by the human body are called essential amino acids,as they must be obtained through the diet.
There are $10$ such essential amino acids.

(D) The Biuret test is a chemical test used for detecting the presence of peptide bonds.
In the presence of peptides,a copper $II$ ion $(Cu^{2+})$ forms a violet-colored complex in an alkaline solution.
The reaction is represented as:
$(-CH(R)-CO-NH-)_{n} + Cu^{2+} \rightarrow \text{Violet Complex}$

(D) Proteins are primarily body-building substances that form structural components like muscles,skin,and nails. They are not the primary source of energy for metabolism,as carbohydrates and fats serve that purpose.

(C) The secondary structure of proteins,such as the $\alpha$-helix,is primarily stabilized by hydrogen bonding between the $C=O$ group of one amino acid residue and the $N-H$ group of another amino acid residue located further along the polypeptide chain.

(B) All amino acids contain an amine group and a carboxyl group attached to the same alpha carbon atom.
For an amino acid to be optically active,the alpha carbon must be chiral,meaning it must be bonded to four different groups.
In $Glycine$ $(H_2N-CH_2-COOH)$,the alpha carbon is bonded to two hydrogen atoms,making it achiral.
Therefore,$Glycine$ is the only optically inactive amino acid among the $20$ common amino acids.
Thus,the correct option is $B$.

(B) In many proteins,the linear polypeptide chains are cross-linked to provide structural stability.
The most common type of cross-link is the disulfide bond $(-S-S-)$.
This bond is formed by the oxidation of the thiol $(-SH)$ groups present in a pair of cysteine residues.
Therefore,cysteine is the amino acid responsible for cross-linking peptide chains.

(C) Amino acids are the building blocks of proteins. When proteins are digested or broken down,amino acids are left. The human body uses amino acids to make proteins to help the body in repairing body tissues,growth,and performing many other body functions.

(A) The protein that destroys the antigen when it enters a body cell is $Antibodies$.
$Antibodies$ are protective proteins produced by the immune system in response to the presence of a foreign substance,known as an antigen.

(B) Antibodies are specialized proteins produced by the immune system to identify and neutralize foreign substances like bacteria and viruses. They are classified as $Globular \text{ } proteins$ and are also known as $Immunoglobulins$ $(Ig)$. Therefore,both options $B$ and $C$ are technically correct,but in the context of biochemical classification,they are primarily identified as $Globular \text{ } proteins$.

(D) Proteins are polymers of amino acids.
$A$. Narvone is not a standard biochemical term.
$B$. Lecithin is a phospholipid.
$C$. Cellulose is a polysaccharide (carbohydrate).
$D$. Insulin is a peptide hormone composed of amino acid chains,which classifies it as a protein.
Therefore,the correct answer is $D$.

(A) . $\alpha$-Keratin is a fibrous protein. Fibrous proteins are generally insoluble in water due to their long,thread-like structure and extensive hydrogen bonding.

(B) The peptide bond is formed between two amino acids by the elimination of a water molecule.
$A$ dipeptide contains $1$ peptide linkage.
$A$ tripeptide contains $2$ peptide linkages.
In general,a peptide containing $n$ amino acid residues contains $(n-1)$ peptide linkages.
Therefore,a nanopeptide (which contains $9$ amino acid residues) contains $(9-1) = 8$ peptide linkages.

(D) The $\alpha$-helix is a common secondary structure found in proteins,where the polypeptide chain is coiled into a right-handed spiral.
$DNA$ typically exists as a double helix,while $RNA$ can form various complex structures but is not characterized by the $\alpha$-helix structure found in proteins.

(C) Proteins are linear polymers formed by linking the $-\alpha$-carboxyl group of one amino acid to the $-\alpha$-amino group of another amino acid with a peptide bond.
Thus,the peptide linkage is the primary structural feature of proteins.

(C) An amino acid is achiral if it does not possess a chiral center (a carbon atom bonded to four different groups).
Glycine is the only naturally occurring achiral amino acid because its side chain is a hydrogen atom,making the $\alpha$-carbon bonded to two identical hydrogen atoms.
Among the given options,$2-$hydroxymethyl serine (also known as isoserine derivative or similar structure) has two identical $-CH_2OH$ groups attached to the $\alpha$-carbon,making it achiral.
Therefore,the correct option is $C$.

(C) Amino acids are classified based on the nature of their side chains.
$Tyrosine$ contains a phenol group attached to the side chain,which is an aromatic ring.
$Alanine$,$Glycine$,and $Lysine$ are aliphatic amino acids and do not contain an aromatic ring.

(D) The isoelectric point is the $pH$ at which the amino acid does not migrate in an electric field.
This occurs because the amino acid exists predominantly as a zwitterion,which carries no net charge.
Therefore,it remains stationary under the influence of an electric field.

(B) The $3D$ structure of a protein is primarily determined by its amino acid sequence,but the $peptide \text{ } bond$ is the fundamental linkage that connects amino acid residues in a polypeptide chain.
It is formed through a condensation reaction between the acidic carboxyl group $(-COOH)$ of one amino acid and the basic amino group $(-NH_2)$ of another.
While the overall tertiary structure dictates specific biological activity,the $peptide \text{ } bond$ is the essential structural unit that maintains the integrity of the protein backbone.

(A) Isoleucine is an essential amino acid with the chemical formula $C_6H_{13}NO_2$.
Its systematic name is $2-amino-3-methylpentanoic acid$.
The structural formula is $CH_3-CH_2-CH(CH_3)-CH(NH_2)-COOH$.
Option $A$ and $C$ represent the same correct structure.

(A) The process of synthesizing a polypeptide chain from amino acids based on the genetic information encoded in $m-RNA$ is known as $Translation$.
This process requires the participation of $m-RNA$,$t-RNA$,and $r-RNA$.

(C) . Proteins are essential nutrients used in our body as a fuel for muscles and nerves,and they are primarily responsible for building and repairing body tissues.

(A) The peptide chain is formed by the condensation of amino acids through peptide bonds ($-CONH-$ linkage).
In this process,the carboxyl group $(-COOH)$ of one amino acid reacts with the amino group $(-NH_2)$ of another amino acid with the elimination of a water molecule $(H_2O)$.
The repeating unit in a polypeptide chain is represented as $-NH-CH(R)-CO-NH-CH(R)-CO-$.
Thus,option $A$ correctly represents the structure of a peptide chain.

(A) . Haemoglobin is a conjugated protein that acts as an oxygen carrier in the blood. Each haemoglobin molecule contains four $Fe^{2+}$ ions,which can bind with $4$ molecules of $O_2$ to form oxyhaemoglobin. The reaction is represented as: $Hb_4 + 4O_2 \to Hb_4O_8$.

(A) Stanley Miller performed an experiment to simulate the conditions of the early Earth,which resulted in the synthesis of amino acids.

(C) The bond that determines the secondary structure of proteins is the $Hydrogen \ bond$.
Depending on the hydrogen bonding patterns,the two main types of secondary structures are the $\alpha$-helix and the $\beta$-pleated sheet.

(C) The correct answer is $(C)$.
Insulin is a peptide hormone (protein) secreted by the beta cells of the pancreas that regulates the blood glucose level in the human body.

(A) The tripeptide hormone present in most living cells is $Glutathione$.
Three amino acids present in $Glutathione$ are glutamic acid,cysteine,and glycine.
$Glutathione$ is required for the action of several enzymes and of insulin.

(C) Haemoglobin is a globular protein that consists of $4$ polypeptide chains (subunits).
These consist of two $\alpha$-chains and two $\beta$-chains.

(C) The genetic code is a triplet code.
Each codon consists of a sequence of $3$ nucleotides in messenger $RNA$ $(m-RNA)$.
These $3$ nucleotides specify a particular amino acid during the process of protein synthesis.

(B) Insulin is a hormone which decreases sugar level in the blood.

(D) Proteins are complex macromolecules that are generally insoluble in non-polar organic solvents like benzene. Therefore,they can be easily separated or removed from benzene by filtration or sedimentation.

(D) . The $\alpha-$helix structure is formed when the chain of $\alpha-$amino acids coils as a right-handed screw due to the formation of hydrogen bonds between amide groups of the same peptide chain.
Specifically,the $NH$ group in one unit is linked to the carbonyl oxygen of the fourth unit by hydrogen bonding.
This hydrogen bonding is responsible for holding the helix in a stable position.

(B) The correct answer is $B$. Cell membranes are primarily composed of proteins and lipids. The protein content in cell membranes typically varies from $46-76\%$,while the lipid content (including phospholipids) ranges from $20-53\%$,and carbohydrates constitute $1-8\%$. Although phospholipids are a major structural component,proteins are generally the most abundant component by mass in most cell membranes.

(D) Let the three different amino acids be $A$,$B$,and $C$.
For a tripeptide formed by three different amino acids,the number of possible arrangements is given by the permutation of $3$ distinct items taken $3$ at a time.
The number of arrangements is $3! = 3 \times 2 \times 1 = 6$.
The possible tripeptides are: $ABC$,$ACB$,$BAC$,$BCA$,$CAB$,and $CBA$.
Thus,$6$ different tripeptide molecules are formed.

(C) is the correct answer.
Aspartic acid is an acidic amino acid because it contains an extra carboxylic acid group in its side chain.
Lysine,Arginine,and Histidine are basic amino acids.
The structure of Aspartic acid is $HOOC-CH_2-CH(NH_2)-COOH$.

(D) Lucas test is used for the distinction of alcohols,whereas the other tests are used for the identification of proteins or amino acids.