MCQ Bank

Proteins are formed by joining amino acids together through peptide bonds, which is a process of polymerization. Translation is the process by which ribosomes use mRNA to assemble the amino acid sequence, but the direct formation of the protein chain is polymerization.

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Lysine is represented by one-letter code i.e.,

A) I
B) Y
C) L
D) K

AI Explanation

Lysine is an amino acid represented by the one-letter code K in the standard amino acid coding system. The other options represent different amino acids: I is isoleucine, Y is tyrosine, and L is leucine.

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At isoelectric pH, an amino acid exists as

A) None of these
B) Cation
C) Zwitterion
D) Anion

AI Explanation

At the isoelectric pH, an amino acid has no net electrical charge. It exists mainly as a zwitterion, containing both a positively charged amino group and a negatively charged carboxyl group. The positive and negative charges balance each other.

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Which of the following is not the function of proteins?

A) Fight against the invading pathogens
B) Helps in transporting oxygen in the blood
C) Helps in digesting food
D) Carries genetic information

AI Explanation

Proteins perform many functions including immune defense, oxygen transport, and digestion through enzymes. Carrying genetic information is the function of nucleic acids such as DNA and RNA, not proteins.

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The peptide sequence tags are ……………............

A) The partial sequence of a peptide that can be revealed by consecutive peaks
B) The sequence of a peptide that is produced after MS2
C) The variation in the fragmentation site of a peptide
D) The mass difference between consecutive peaks in a peptide sequence

AI Explanation

Peptide sequence tags are short stretches of amino acid sequence information derived from tandem mass spectrometry (MS/MS) data. They are obtained from consecutive fragment ion peaks and represent a partial peptide sequence used for protein identification.

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Which of the following statements is un-true about 1’ (Primary) structure of proteins?

A) The 1-D (Primary) structure of proteins can be determined by Edman Degradation
B) The sequence of amino acids joined by a peptide bond
C) The Primary OR 1’ structure of a protein determines its initial properties.
D) The 1-D (Primary) structure of proteins can be determined by Nuclear Magnetic Resonance (NMR)

AI Explanation

NMR is mainly used to determine the three-dimensional structure and conformations of proteins, not their primary amino acid sequence. Primary structure is typically determined by methods such as Edman degradation or mass spectrometry. The other statements correctly describe the primary structure of proteins.

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Which of the following statements are true about 3-D (Tertiary) structure of proteins?

A) Primary structure of proteins determines the tertiary structure
B) 3’ Structures of proteins are formed as a result of hydrophobic interactions between polar R-groups
C) Combinations of Alpha helices, Beta sheets, coils and loops help form 3’ structures
D) 3’ structures are formed by different peptide chains that make up the proteins

AI Explanation

The amino acid sequence (primary structure) determines how a protein folds into its specific tertiary 3-D structure. Tertiary structure is stabilized by interactions among R-groups, including hydrophobic interactions, ionic bonds, and hydrogen bonds.

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Which of the following is responsible for determining a protein’s 3D shape?

A) Peptide bond
B) Interaction with molecular chaperons
C) Interaction with other polypeptides
D) Amino acid sequence

AI Explanation

A protein’s amino acid sequence determines how the polypeptide chain folds into its specific three-dimensional shape. The sequence dictates the interactions between amino acid side chains that drive folding. Chaperones and other polypeptides may assist or influence folding but do not determine the final shape.

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The significance of the number of PSTs that a protein reports ……..............

A) The more PSTs a protein reports, the more likely it is to be a peptide
B) The more PSTs a protein reports, the more likely it is to be a protein fragment
C) All of the these
D) The more PSTs a protein reports, the more likely it is to be the precursor protein

AI Explanation

A higher number of PSTs (peptide sequence tags) indicates that more regions of the protein have been detected and matched. This increases confidence that the identified protein is the original precursor protein rather than a small peptide or fragment.

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Beeta-pleated sheets are the examples of ...........................

A) 2’ OR 2-D OR Secondary Structure of proteins
B) 4’ OR 4-D OR Quaternary Structure of proteins
C) 1’ OR 1-D OR Primary Structure of proteins
D) 3’ OR 3-D OR Tertiary Structure of proteins

AI Explanation

Beta-pleated sheets are a type of secondary protein structure formed by hydrogen bonding between peptide backbone atoms. They are one of the two major secondary structures, along with alpha helices.

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Q10

The factors that affect the mass difference between consecutive peaks in a peptide sequence ……….......................

A) The mass of the amino acids
B) All of the above
C) The fragmentation site of the peptide
D) The type of fragmentation technique

AI Explanation

The mass difference between consecutive peaks in a peptide sequence depends on the amino acid masses involved, where fragmentation occurs, and the fragmentation technique used. These factors together influence the observed mass-to-charge differences in peptide mass spectrometry.

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Q11

The purpose of MS2 in protein identification is ………..................

A) To identify the protein in the sample
B) To determine the sequence of the protein
C) To identify the fragmentation technique used
D) To measure the mass of the intact molecule in sample

AI Explanation

MS2 involves analyzing fragment ions produced from a selected peptide precursor in tandem mass spectrometry. These fragment patterns allow researchers to determine the amino acid sequence of the peptide and help identify the protein. MS1 is primarily used to measure intact peptide masses before fragmentation.

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Q12

Which of the following statements is un-true about 2’ (Secondary) structure of proteins?

A) 2’ Structures of proteins are formed as a result of Hydrogen bond formation between N and C termini in a protein backbone
B) 2’ structures of proteins include Alpha helices and Beta sheets
C) 2’ Structures of proteins are formed as a result of peptides bond formation between N and C termini in a protein backbone
D) Hydrogen bonds are the reason of 2’ structures of proteins

AI Explanation

This statement is un-true because peptide bonds form the primary structure of proteins, not the secondary structure. Secondary structures such as alpha helices and beta sheets are stabilized by hydrogen bonds between backbone atoms. The peptide backbone already exists before secondary structure formation occurs.

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Q13

Which of the following statements is un-true about proteins?

A) Proteins properties are linked to the properties of amino acids.
B) Proteins structures are organized into 1’, 2’, 3’, 4’ modular conformations
C) Proteins are made by transcription of amino acids
D) Proteins spontaneously fold to take 3D forms

AI Explanation

This statement is un-true because proteins are made by translation of mRNA into amino acid sequences, not by transcription of amino acids. Transcription is the process of making RNA from DNA, while translation produces proteins. The other statements correctly describe protein properties and organization.

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Q14

How many bonded atoms are required to constitute a dihedral angle, such as phi or psi?

A) 2
B) 4
C) 3
D) 1

AI Explanation

A dihedral angle is defined by four sequentially bonded atoms, creating an angle between two planes. Protein backbone torsion angles such as phi and psi are examples of dihedral angles involving four atoms.

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Q15

Select the appropriate option of fragmentation techniques that can be used in MS2?

A) CID
B) ECD
C) ETD
D) All of the above

AI Explanation

CID, ECD, and ETD are all fragmentation techniques used in MS2 (tandem mass spectrometry). These methods produce fragment ions that provide information for peptide and protein identification.

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Q16

Proteins are made-up of amino acids; these amino acids are linked together by which of the following bonds?

A) Peptide bond
B) Ionic bond
C) Hydrogen bond
D) Disulfide bond

AI Explanation

Determining the protein sequence is the final and most definitive step when other identification approaches are insufficient. Sequence information provides direct evidence for confirming the identity of the protein.

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Q17

The final resort in protein search and identification …………...............

A) Comparing the mass of the intact molecule in the sample with the mass of known proteins
B) Determining the sequence of the protein
C) Identifying the fragmentation technique used
D) Matching experimental fragments with in silico fragments

AI Explanation

Determining the protein sequence is the final and most definitive step when other identification approaches are insufficient. Sequence information provides direct evidence for confirming the identity of the protein.

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Q18

The significance of the score that is calculated when comparing the mass of the intact molecule from MS2 with the theoretical mass of database proteins ……………...............

A) The score is a measure of the confidence that the protein that was originally analyzed has been identified
B) The score is a measure of the accuracy of the mass spectrometer
C) The score is a measure of the fragmentation efficiency of MS2
D) The score is a measure of the molecular weight of the protein

AI Explanation

Peptide sequence tags are generated from MS/MS data by comparing mass differences between consecutive peaks with known amino acid masses. The resulting sequence tags can then be matched against protein databases or compared with known protein masses to identify the protein.

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Q19

The peptide sequence tags used to identify proteins ………….............

A) By comparing the mass difference between consecutive peaks to the mass of known amino acids
B) By using a database of known peptide sequence tags to identify the protein
C) All of the above
D) By comparing the mass of the peptide sequence tag to the mass of known proteins

AI Explanation

Hydrogen bonds between the backbone carbonyl oxygen and amide hydrogen atoms stabilize protein secondary structures such as alpha helices and beta sheets. Peptide bonds form the primary structure, while hydrogen bonding is responsible for maintaining the secondary structure.