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All questions of Amino Acids and Proteins for MCAT Exam
The pI for a polyelectrolyte that contains three carboxyl groups and three amino groups whose pKa values are 4.0, 4.6, 6.3, 7.7, 8.9, and 10.2 is _______________
Correct answer is '7'. Can you explain this answer?
The pI for a polyelectrolyte that contains three carboxyl groups and three amino groups whose pKa values are 4.0, 4.6, 6.3, 7.7, 8.9, and 10.2 is _______________
|
Jay Nambiar answered |
Example the pI is a pH midway between the 3rd and 4th pKa values: pI = (6.3 + 7.7)/2 = 7.0. To confirm this conclusion, imagine how the net charge on the molecule will change as the solution is adjusted from strongly acidic to strongly basic pH. As the carboxylate groups and subsequently the ammonium groups begin to ionize, the net charge will change successively as follows: +3, +2, +1, 0, “1, “2, “3.
The net charge on the following peptide at pH 1 is _________________.
Correct answer is '2'. Can you explain this answer?
The net charge on the following peptide at pH 1 is _________________.
|
Vandana Chopra answered |
At pH 1 the charge distribution on the peptide will be as follows:
NH3+-Ala-Asp-Asn-Ile-Pro-Gln-Thr-Agr-COOH
Note that every peptide is written from amino to carboxy terminal, and at a very low pH such as 1 every side chain and main chain ionizable groups will be protonated. Hence net change will be decided by amino groups, as the sequence contain one basic amino acid (arginine) and only alanine contain free amino group, so the charge is due to positively charged amino group.
NH3+-Ala-Asp-Asn-Ile-Pro-Gln-Thr-Agr-COOH
Note that every peptide is written from amino to carboxy terminal, and at a very low pH such as 1 every side chain and main chain ionizable groups will be protonated. Hence net change will be decided by amino groups, as the sequence contain one basic amino acid (arginine) and only alanine contain free amino group, so the charge is due to positively charged amino group.
Which of the following amino acids will have Diastereomers.- a)Isoleucine
- b)Threonine
- c)both (a) and (b)
- d)None
Correct answer is option 'C'. Can you explain this answer?
Which of the following amino acids will have Diastereomers.
a)
Isoleucine
b)
Threonine
c)
both (a) and (b)
d)
None
|
|
Aashna Shah answered |
Stereoisomers that are mirror images of each other are called enantiomers.
Stereoisomers that are not mirror images of each other are called diastereomers.
Diastereomers are present only in those molecules which have more than one chiral carbon atoms, and isoleucine as well as threonine both have two chiral centers. Since both threonine and isoleucine have two chiral centres each, maximum number of stereoisomers in each case will be 2n = 22 = 4 (n is the number of chiral centres).
Stereoisomers that are not mirror images of each other are called diastereomers.
Diastereomers are present only in those molecules which have more than one chiral carbon atoms, and isoleucine as well as threonine both have two chiral centers. Since both threonine and isoleucine have two chiral centres each, maximum number of stereoisomers in each case will be 2n = 22 = 4 (n is the number of chiral centres).
Which of the following type of secondary conformation is in the same quadrant of the ramachandran plot- a)Right handed Alpha helix
- b)310 helix
- c)Beta sheets
- d)Left handed alpha helix
Correct answer is option 'A,B'. Can you explain this answer?
Which of the following type of secondary conformation is in the same quadrant of the ramachandran plot
a)
Right handed Alpha helix
b)
310 helix
c)
Beta sheets
d)
Left handed alpha helix
|
|
Anushka Basak answered |
Only right handed alpha helix and 310 helix lie in the same quadrant
Ramachandran Plot
Ramachandran Plot
The isoelectric point of lysine which has pKb 9.06, pKa 2.16 and pKR as 10.54 is ____________[Answer upto two decimal places]
- a)
- b)
- c)
- d)
- e)
Correct answer is '9.8'. Can you explain this answer?
The isoelectric point of lysine which has pKb 9.06, pKa 2.16 and pKR as 10.54 is ____________[Answer upto two decimal places]
a)
b)
c)
d)
e)
|
|
Niharika Choudhary answered |
Isoelectric point: In proteins the isoelectric point (pI) is defined as the pH at which a protein has no net charge.
In case of a basic amino acid, pI lies in between the pKb and pKR and is equal to the average of pKb and pKR(10.54+9.06)/2 = 9.77 = ~ 9.8.
In case of an acidic amino acid, pI lies in between the pKa and pKR and is equal to the average of pKa and pKR.
In case of a neutral amino acid, pI lies in between the pKb and pKa and is equal to the average of pKa and pKb.
In case of a basic amino acid, pI lies in between the pKb and pKR and is equal to the average of pKb and pKR(10.54+9.06)/2 = 9.77 = ~ 9.8.
In case of an acidic amino acid, pI lies in between the pKa and pKR and is equal to the average of pKa and pKR.
In case of a neutral amino acid, pI lies in between the pKb and pKa and is equal to the average of pKa and pKb.
An amino acid that yields acetoacetyl CoA during the catabolism of its carbon skeleton will be considered as ________.- a)Glycogenic
- b)Ketogenic
- c)Both glycogenic and ketogenic
- d)Essential
Correct answer is option 'B'. Can you explain this answer?
An amino acid that yields acetoacetyl CoA during the catabolism of its carbon skeleton will be considered as ________.
a)
Glycogenic
b)
Ketogenic
c)
Both glycogenic and ketogenic
d)
Essential
|
Orion Classes answered |
In case of Glycogenic amino acids pyruvate metabolites are formed and in case of ketogenic amino acids acetoacyl CoA is formed during the catabolism.
If pK1 = 2.34 and pK2 = 9.60, then the isoelectric point pI is?- a)5.87
- b)5.97
- c)3.67
- d)11.94
Correct answer is option 'B'. Can you explain this answer?
If pK1 = 2.34 and pK2 = 9.60, then the isoelectric point pI is?
a)
5.87
b)
5.97
c)
3.67
d)
11.94
|
|
Orion Classes answered |
pI = 1⁄2 (pK1 + pK2) = 1⁄2 (2.34 + 9.60) = 5.97.
Which of the following represents the two-dimensional structure of proteins?- a)Quaternary
- b)Tertiary
- c)Secondary
- d)Primary
Correct answer is option 'D'. Can you explain this answer?
Which of the following represents the two-dimensional structure of proteins?
a)
Quaternary
b)
Tertiary
c)
Secondary
d)
Primary
|
|
Orion Classes answered |
The primary structure of Protein represents the two-dimensional structure of proteins. The primary structure of proteins just contains amino acids linked together to form a long chain of a polypeptide. Quaternary, tertiary, and secondary structure refers to the three-dimensional structure of proteins.
Total number of known amino acids in biological systems is- a)20
- b)21
- c)22
- d)More than 900
Correct answer is option 'D'. Can you explain this answer?
Total number of known amino acids in biological systems is
a)
20
b)
21
c)
22
d)
More than 900
|
|
Juhi Sen answered |
There are various groups of amino acids:
• 20 standard amino acids
• 22 proteinogenic amino acids
• Over 80 amino acids created abiotically in high concentrations
• About 900 are produced by natural pathways
• Over 118 engineered amino acids have been placed into protein
• 20 standard amino acids
• 22 proteinogenic amino acids
• Over 80 amino acids created abiotically in high concentrations
• About 900 are produced by natural pathways
• Over 118 engineered amino acids have been placed into protein
A new amino acid was found on the surface of moon with no ionizable side chain and pKa value 1.8 and pKb value 9.5. The isoelectric point of this new amino acid is _____________ [Answer upto two decimal places]
Correct answer is between '5.64,5.66'. Can you explain this answer?
A new amino acid was found on the surface of moon with no ionizable side chain and pKa value 1.8 and pKb value 9.5. The isoelectric point of this new amino acid is _____________ [Answer upto two decimal places]
|
|
Niti Mukherjee answered |
Isoelectric point in case of no ionizable side chain is the average of pKa and pKb, (1.8+9.5)/2 = 5.65
If an amino acid with neutral side chain has pKa value of 3.4 and pKb value of 9.6 at which of the following pH the amino acid will migrate towards anode- a)6
- b)7.4
- c)2.3
- d)3.4
Correct answer is option 'B'. Can you explain this answer?
If an amino acid with neutral side chain has pKa value of 3.4 and pKb value of 9.6 at which of the following pH the amino acid will migrate towards anode
a)
6
b)
7.4
c)
2.3
d)
3.4
|
|
Anisha Pillai answered |
The isoelectric point here is the average of pKa and pKb which is (3.4+9.6)/2 = 6.5.
Every amino acid is negatively charged at pH above its pI and move towards Anode (+). So at pH 7.4 the overall charge on amino acid will be negative and it will move towards Anode. Only pH 7.4 is above the isoelectric part of amino acid (isoelectric point = 6.5)
Every amino acid is negatively charged at pH above its pI and move towards Anode (+). So at pH 7.4 the overall charge on amino acid will be negative and it will move towards Anode. Only pH 7.4 is above the isoelectric part of amino acid (isoelectric point = 6.5)
Amino acids that are most likely to be phosphorylated in a protein during a signalling event are- a)Serine and threonine
- b)Leucine and Isoleucine
- c)Tryptophan and Tyrosine
- d)Threonine and Arginine
Correct answer is option 'A'. Can you explain this answer?
Amino acids that are most likely to be phosphorylated in a protein during a signalling event are
a)
Serine and threonine
b)
Leucine and Isoleucine
c)
Tryptophan and Tyrosine
d)
Threonine and Arginine
|
|
Anisha Banerjee answered |
Phosphorylation is most likely to occur at hydroxyl group of side chain of amino acids i.e. serine and threonine. Hydroxyl group is not present in leucine, isoleucine, arginine and tryptophan.
Which of the following names do not represent the name of a peptide- a)WATSON
- b)EINSTEIN
- c)KENDREW
- d)LIPMAN
Correct answer is option 'A'. Can you explain this answer?
Which of the following names do not represent the name of a peptide
a)
WATSON
b)
EINSTEIN
c)
KENDREW
d)
LIPMAN
|
|
Maitri Sen answered |
There are 20 amino acids and 26 letters in English alphabet, hence 6 letters viz B, J, O, U, X , Z do not represent any amino acids, which means the name containing these amino acids will not be representing a peptide O is present in option (a), hence option (a), does not represent a peptide.
Which of the following amino acid shows highest absorbance at 280 nm- a)Phenylalanine
- b)Tyrosine
- c)Alanine
- d)Tryptophan
Correct answer is option 'D'. Can you explain this answer?
Which of the following amino acid shows highest absorbance at 280 nm
a)
Phenylalanine
b)
Tyrosine
c)
Alanine
d)
Tryptophan
|
|
Shivam Khanna answered |
Three aromatic amino acids (Tyr, Trp, and Phe) absorb most of the UV light in a protein. Tyrosine and tryptophan both absorb more than phenylalanine. Tryptophan shows four times more absorbance than tyrosine.
A person having a syndrome, where he has excessive flexibility in his body and can fold his arms and legs like a rubber, which is clinically known as Ehler Danlos Syndrome. Which of the following is true about this disease- a)It is due to malformation of cross links in collagen
- b)People with this syndrome were also called as Indian Rubber Man
- c)It is not found in world now
- d)It is lethal disease
Correct answer is option 'A,B'. Can you explain this answer?
A person having a syndrome, where he has excessive flexibility in his body and can fold his arms and legs like a rubber, which is clinically known as Ehler Danlos Syndrome. Which of the following is true about this disease
a)
It is due to malformation of cross links in collagen
b)
People with this syndrome were also called as Indian Rubber Man
c)
It is not found in world now
d)
It is lethal disease
|
|
Ameya Reddy answered |
The Ehlers-Danlos syndromes (EDS) are a group of related disorders caused by different genetic defects in collagen.Patients also have excessively flexible, loose joints. Ehler danlos syndrome is not lethal and individuals are still present so it is not eradicated from the world.
Identify the amino acids containing nonpolar, aliphatic R groups.- a)Phenylalanine, tyrosine, and tryptophan
- b)Glycine, alanine, leucine
- c)Lysine, arginine, histidine
- d)Serine, threonine, cysteine
Correct answer is option 'B'. Can you explain this answer?
Identify the amino acids containing nonpolar, aliphatic R groups.
a)
Phenylalanine, tyrosine, and tryptophan
b)
Glycine, alanine, leucine
c)
Lysine, arginine, histidine
d)
Serine, threonine, cysteine
|
Ava Brown answered |
Understanding Nonpolar, Aliphatic Amino Acids
Amino acids are the building blocks of proteins, and their properties are determined by their R groups (side chains). Nonpolar, aliphatic amino acids have hydrophobic side chains that do not interact favorably with water.
Identifying Nonpolar, Aliphatic Amino Acids
The correct answer to the question is option 'B', which includes the following amino acids:
Why Options A, C, and D Are Incorrect
Conclusion
In summary, the amino acids listed in option 'B' are characterized by their nonpolar, aliphatic side chains, distinguishing them from the other options that include polar or aromatic amino acids. Understanding these classifications is essential for grasping protein structure and function in biochemistry.
Amino acids are the building blocks of proteins, and their properties are determined by their R groups (side chains). Nonpolar, aliphatic amino acids have hydrophobic side chains that do not interact favorably with water.
Identifying Nonpolar, Aliphatic Amino Acids
The correct answer to the question is option 'B', which includes the following amino acids:
- Glycine - The simplest amino acid with a hydrogen as its side chain, making it nonpolar.
- Alanine - Contains a methyl group as its R group, also classified as nonpolar.
- Leucine - Has a branched-chain structure, contributing to its nonpolar nature.
Why Options A, C, and D Are Incorrect
- Option A (Phenylalanine, Tyrosine, Tryptophan) - Contains aromatic rings, making them more polar than purely aliphatic amino acids.
- Option C (Lysine, Arginine, Histidine) - These are polar and positively charged amino acids due to their side chains containing nitrogen.
- Option D (Serine, Threonine, Cysteine) - These amino acids contain hydroxyl or thiol groups, which are polar and can form hydrogen bonds.
Conclusion
In summary, the amino acids listed in option 'B' are characterized by their nonpolar, aliphatic side chains, distinguishing them from the other options that include polar or aromatic amino acids. Understanding these classifications is essential for grasping protein structure and function in biochemistry.
Which among the following is both glucogenic and ketogenic?- a)Isoleucine
- b)Leucine
- c)Lysine
- d)Histidine
Correct answer is option 'A'. Can you explain this answer?
Which among the following is both glucogenic and ketogenic?
a)
Isoleucine
b)
Leucine
c)
Lysine
d)
Histidine
|
|
Orion Classes answered |
Isoleucine produces both glucose and ketone bodies as an energy source.
A polypeptide chain contains two terminals – one carboxyl-terminal (C terminal) and the other amino-terminal (N terminal). Which of the following is true?- a)N terminal is synthesized last during translation
- b)C terminal is synthesized first during translation
- c)N terminal is represented on the right side and C terminal on the left side
- d)N terminal is represented on the left side and C terminal on the right side
Correct answer is option 'D'. Can you explain this answer?
A polypeptide chain contains two terminals – one carboxyl-terminal (C terminal) and the other amino-terminal (N terminal). Which of the following is true?
a)
N terminal is synthesized last during translation
b)
C terminal is synthesized first during translation
c)
N terminal is represented on the right side and C terminal on the left side
d)
N terminal is represented on the left side and C terminal on the right side
|
|
Orion Classes answered |
During translation, the first amino acid attached has an amino free end and the last amino acid has a carboxyl free end. Hence, the N terminal is represented on the left side and C terminal on the right side.
The two amino acids having R groups with a negative net charge at pH 7.0 are __________.- a)Aspartate and glutamate
- b)Arginine and histidine
- c)Cysteine and methionine
- d)Proline and valine
Correct answer is option 'A'. Can you explain this answer?
The two amino acids having R groups with a negative net charge at pH 7.0 are __________.
a)
Aspartate and glutamate
b)
Arginine and histidine
c)
Cysteine and methionine
d)
Proline and valine
|
|
Orion Classes answered |
H3 N+ – CH( CH2 COO–) – COO–
Glutamate: H3 N+ – CH( C2 H4 COO–) – COO–.
Glutamate: H3 N+ – CH( C2 H4 COO–) – COO–.
Which of the following is a true statement?- a)Tryptophan and tyrosine are significantly more polar than phenylalanine
- b)Leucine is commonly used as an ingredient in the buffers of SDS page
- c)Aspartate is an essential amino acid
- d)Lysine is a non-essential amino acid
Correct answer is option 'A'. Can you explain this answer?
Which of the following is a true statement?
a)
Tryptophan and tyrosine are significantly more polar than phenylalanine
b)
Leucine is commonly used as an ingredient in the buffers of SDS page
c)
Aspartate is an essential amino acid
d)
Lysine is a non-essential amino acid
|
Elizabeth Lee answered |
Explanation:
Tryptophan and tyrosine are significantly more polar than phenylalanine:
- Tryptophan and tyrosine contain polar functional groups such as hydroxyl and amino groups, making them more polar compared to phenylalanine which lacks such groups.
- The presence of polar groups in tryptophan and tyrosine allows for interactions with water molecules, leading to their higher polarity.
This statement is true because tryptophan and tyrosine have more polar side chains compared to phenylalanine, which is a nonpolar amino acid. The polarity of an amino acid side chain is determined by the presence of polar functional groups such as hydroxyl (-OH) and amino (-NH2) groups. Tryptophan and tyrosine both contain these polar functional groups in their side chains, making them significantly more polar than phenylalanine, which lacks such groups. This increased polarity allows tryptophan and tyrosine to interact more readily with water molecules and other polar substances, influencing their behavior in biological systems.
Tryptophan and tyrosine are significantly more polar than phenylalanine:
- Tryptophan and tyrosine contain polar functional groups such as hydroxyl and amino groups, making them more polar compared to phenylalanine which lacks such groups.
- The presence of polar groups in tryptophan and tyrosine allows for interactions with water molecules, leading to their higher polarity.
This statement is true because tryptophan and tyrosine have more polar side chains compared to phenylalanine, which is a nonpolar amino acid. The polarity of an amino acid side chain is determined by the presence of polar functional groups such as hydroxyl (-OH) and amino (-NH2) groups. Tryptophan and tyrosine both contain these polar functional groups in their side chains, making them significantly more polar than phenylalanine, which lacks such groups. This increased polarity allows tryptophan and tyrosine to interact more readily with water molecules and other polar substances, influencing their behavior in biological systems.
The naturally occurring proteins consist of- a)D-amino acids
- b)L-amino acids
- c)Both a and b
- d)None of these
Correct answer is option 'B'. Can you explain this answer?
The naturally occurring proteins consist of
a)
D-amino acids
b)
L-amino acids
c)
Both a and b
d)
None of these
|
|
Anshika Chavan answered |
All naturally occurring proteins from all living organisms consist of L amino acids.
Which of the following amino acid is/are not encoded by standard codons- a)Serine
- b)Selenocysteine
- c)Pyrolysine
- d)both b and c
Correct answer is option 'D'. Can you explain this answer?
Which of the following amino acid is/are not encoded by standard codons
a)
Serine
b)
Selenocysteine
c)
Pyrolysine
d)
both b and c
|
|
Akshat Saini answered |
Amino acids Selenocysteine and Pyrolysine are not encoded by standard codons but by stop codons.Selenocysteine is coded by UGA and Pyrolysine is coded by UAG.
UAG and UGA both are stop codon. Serine is encoded by 6 different codons.
UAG and UGA both are stop codon. Serine is encoded by 6 different codons.
On the Ramachandran plot two kind of angles are presented on the x and y axis named phi and psi respectively. These angles represent the:-- a)Torsion between Calpha – C and N – C respectively
- b)Torsion between N – C and Calpha – C respectively
- c)Torsion between N – Calpha and Calpha – C respectively
- d)Torsion between C – C and N – C respectively
Correct answer is option 'C'. Can you explain this answer?
On the Ramachandran plot two kind of angles are presented on the x and y axis named phi and psi respectively. These angles represent the:-
a)
Torsion between Calpha – C and N – C respectively
b)
Torsion between N – C and Calpha – C respectively
c)
Torsion between N – Calpha and Calpha – C respectively
d)
Torsion between C – C and N – C respectively
|
|
Aditi Basak answered |
Following figure represent the location of psi and phi angle:
Which of the following proteins primarily have alpha helix in their structure- a)Myoglobin
- b)Silk fibroin
- c)Ribonuclease
- d)Porin
Correct answer is option 'A'. Can you explain this answer?
Which of the following proteins primarily have alpha helix in their structure
a)
Myoglobin
b)
Silk fibroin
c)
Ribonuclease
d)
Porin
|
|
Shreya Chauhan answered |
Myoglobin contains only α helix. Around 75% of Myoglobin is α helix. Myoglobin consists of eight alpha helixes connected through turns. Silk fibroin and Porin contain only β sheets. Ribonuclease contains a combination of alpha helix and beta sheets.
The correct statement about the biosynthesis of amino acids are- a)Amino acids are synthesised from glycolytic and citric acid cycle intermediates
- b)Glutamate can be formed by amination of alpha ketogluterate
- c)Pyruvate on amination can form alanine
- d)There are 9 families of amino acids based on the metabolic precursors.
Correct answer is option 'A,B,C'. Can you explain this answer?
The correct statement about the biosynthesis of amino acids are
a)
Amino acids are synthesised from glycolytic and citric acid cycle intermediates
b)
Glutamate can be formed by amination of alpha ketogluterate
c)
Pyruvate on amination can form alanine
d)
There are 9 families of amino acids based on the metabolic precursors.
|
|
Saranya Mehta answered |
Only statement d is incorrect, there are 6 families of amino acids in which they can be grouped on the basis of their metabolic precursors.
1. α -Ketoglutarate
Glutamate → Glutamine/Proline (also form Ornithine)/Arginine
2. 3-Phosphoglycerate
Serine → Glycine/Cysteine (also form Methionine SAM-sulfur donar in mammals)
3. Oxaloacetate
Aspaitate/Asparagine/Methionine/Threonine/Lysine
4. Pyruvate
Alanine/Valine/Leucine/Isoleucine
5. Phosphoenolypyruvate and erythrose 4-phosphate Tryptophan/Phenylalanine Tyrosine (from Phenylalanine by hydroxylation)
6. Ribose 5-phosphate
Histidine
1. α -Ketoglutarate
Glutamate → Glutamine/Proline (also form Ornithine)/Arginine
2. 3-Phosphoglycerate
Serine → Glycine/Cysteine (also form Methionine SAM-sulfur donar in mammals)
3. Oxaloacetate
Aspaitate/Asparagine/Methionine/Threonine/Lysine
4. Pyruvate
Alanine/Valine/Leucine/Isoleucine
5. Phosphoenolypyruvate and erythrose 4-phosphate Tryptophan/Phenylalanine Tyrosine (from Phenylalanine by hydroxylation)
6. Ribose 5-phosphate
Histidine
Which of the following is not true about the secondary conformation of proteins- a)Secondary conformations arise from folding of backbone
- b)Random coils are most abundant secondary conformations
- c)Pi helix and 2.27 are alternate names of alpha helix
- d)Ramachandran plot explains the formation of peptide bond.
Correct answer is option 'A,C,D'. Can you explain this answer?
Which of the following is not true about the secondary conformation of proteins
a)
Secondary conformations arise from folding of backbone
b)
Random coils are most abundant secondary conformations
c)
Pi helix and 2.27 are alternate names of alpha helix
d)
Ramachandran plot explains the formation of peptide bond.
|
|
Sahana Sharma answered |
(a) is coll ect as formation of a secondary structure is the first step in the folding process that a protein takes to assume its native structure, (b) is incorrect as the most common secondary structures are alpha helices and beta sheets, (c) is incorrect as pi helix (or π -helix) is believed to be an evolutionary adaptation derived by the insertion of a single amino acid into a α -helix and 2.27 and d is incorrect as a Ramachandran plot is a way to visualize backbone dihedral angles ψ against φ of amino acid residues in protein structure. A Ramachandran plot can be used in two somewhat different ways. One is to show in theory which values, or conformations, of the ψ and φ angles are possible for an amino-acid residue in a protein.
For a protein with 100 amino acids, how many possible sequences are there?- a)(100)20
- b)(2)100
- c)(100)2
- d)(20)100
Correct answer is option 'D'. Can you explain this answer?
For a protein with 100 amino acids, how many possible sequences are there?
a)
(100)20
b)
(2)100
c)
(100)2
d)
(20)100
|
|
Orion Classes answered |
The general rule is, for a protein having ‘n’ residues, there are (20)n possible combinations. There are 20 different types of amino acids occurring naturally in proteins. Therefore, (20)100 is the correct answer.
The peptide C=O bond of the nth residue of the backbone of alpha-helix points along and forms a hydrogen bond with the peptide N—H group of which among the following residue?- a)(n+1)th
- b)(n+2)th
- c)(n+3)th
- d)(n+4)th
Correct answer is option 'D'. Can you explain this answer?
The peptide C=O bond of the nth residue of the backbone of alpha-helix points along and forms a hydrogen bond with the peptide N—H group of which among the following residue?
a)
(n+1)th
b)
(n+2)th
c)
(n+3)th
d)
(n+4)th
|
|
Aiden Davis answered |
Explanation:
Hydrogen bonding in alpha-helix structure:
- In an alpha-helix structure, the peptide C=O bond of the nth residue forms a hydrogen bond with the peptide N-H group of the (n+4)th residue.
- This hydrogen bonding pattern helps stabilize the alpha-helix structure.
Specific interaction:
- In this case, the peptide C=O bond of the nth residue points along and forms a hydrogen bond with the peptide N-H group of the (n+4)th residue.
- This specific interaction is a characteristic feature of the alpha-helix structure.
Correct answer:
- The correct option is (n+4)th residue, as the hydrogen bonding occurs between the C=O bond of the nth residue and the N-H group of the (n+4)th residue.
Who discovered the alpha-helix structure in a protein molecule?- a)Lynn Margulis
- b)Francis Collins
- c)Louis Pasteur
- d)Linus Pauling
Correct answer is option 'D'. Can you explain this answer?
Who discovered the alpha-helix structure in a protein molecule?
a)
Lynn Margulis
b)
Francis Collins
c)
Louis Pasteur
d)
Linus Pauling
|
|
Orion Classes answered |
Linus Pauling discovered the alpha-helix structure in a protein molecule. Lynn Margulis gave the theory of endosymbiosis. Francis Collins discovered the gene for Cystic Fibrosis. Louis Pasteur is also known as the father of immunology.
Which disease results from the dietary deficiency of vitamin C?- a)Jaundice
- b)Malaria
- c)Cancer
- d)Scurvy
Correct answer is option 'D'. Can you explain this answer?
Which disease results from the dietary deficiency of vitamin C?
a)
Jaundice
b)
Malaria
c)
Cancer
d)
Scurvy
|
|
Orion Classes answered |
The deficiency of vitamin C in diet results in Scurvy. Collagen is a triple helix and contains some hydroxylated residues. The enzyme (prolyl hydroxylase) that catalyzes this reaction requires vitamin C to maintain its activity.
Which of the following is an essential amino acid?- a)Cysteine
- b)Asparagine
- c)Glutamine
- d)Phenylalanine
Correct answer is option 'D'. Can you explain this answer?
Which of the following is an essential amino acid?
a)
Cysteine
b)
Asparagine
c)
Glutamine
d)
Phenylalanine
|
|
Orion Classes answered |
Phenylalanine is one of the 9 essential amino acids.
Which type of interactions are involved in the quaternary structure?- a)Only hydrogen bonds
- b)Hydrogen bonds and hydrophobic interactions
- c)Hydrogen bonds, hydrophobic interactions, and disulfide bonds
- d)Hydrogen bonds, hydrophobic interactions, disulfide bonds, and ionic interactions
Correct answer is option 'D'. Can you explain this answer?
Which type of interactions are involved in the quaternary structure?
a)
Only hydrogen bonds
b)
Hydrogen bonds and hydrophobic interactions
c)
Hydrogen bonds, hydrophobic interactions, and disulfide bonds
d)
Hydrogen bonds, hydrophobic interactions, disulfide bonds, and ionic interactions
|
|
Orion Classes answered |
Quaternary structure of a protein is made of a combination of any of the following interactions: i) Hydrogen bonds, ii) hydrophobic interactions, iii) disulfide bonds, iv) ionic interactions. Thus, the option containing all of the above options is correct.
In metal chelate affinity chromatography, divalent cations such as Zn+2 or Ni+2 is attached on the electrophoretic matrix and it binds to ___________- a)Trp tag
- b)Ala tag
- c)Gly tag
- d)His tag
Correct answer is option 'D'. Can you explain this answer?
In metal chelate affinity chromatography, divalent cations such as Zn+2 or Ni+2 is attached on the electrophoretic matrix and it binds to ___________
a)
Trp tag
b)
Ala tag
c)
Gly tag
d)
His tag
|
|
Orion Classes answered |
When 6 histidine residues are inserted consecutively through recombinant DNA technology, it is called as His tag. It has a high affinity for nickel. This strategy is used for the purification of recombinant proteins.
Which of the following interactions is shown in the figure below?
- a)Disulfide bond
- b)Hydrophobic interactions
- c)Hydrogen bonds
- d)Ionic interactions
Correct answer is option 'D'. Can you explain this answer?
Which of the following interactions is shown in the figure below?
a)
Disulfide bond
b)
Hydrophobic interactions
c)
Hydrogen bonds
d)
Ionic interactions
|
|
Orion Classes answered |
The interaction shown in the above figure is ionic interactions. Ionic interaction is the interaction between two charged groups. If the two charged groups are oppositely charged then they will attract, while two similar charges repel each other.
Which of the following interactions is crucial for the primary structure of proteins?- a)Hydrogen bond
- b)Di-sulfide bond
- c)Vander Waals interactions
- d)Peptide bond
Correct answer is option 'D'. Can you explain this answer?
Which of the following interactions is crucial for the primary structure of proteins?
a)
Hydrogen bond
b)
Di-sulfide bond
c)
Vander Waals interactions
d)
Peptide bond
|
|
Orion Classes answered |
Protein’s primary structure is made of amino acids linked together by a peptide bond. Thus, the peptide bond is crucial for the primary structure of proteins. Hydrogen bond, disulfide bond, Vander Waals interactions are all required in a higher level of organization.
______ is used as a reducing agent in SDS PAGE.- a)Sodium dodecyl sulfate (SDS)
- b)Ammonium persulphate (APS)
- c)Bisacrylamide
- d)2-mercaptoethanol
Correct answer is option 'D'. Can you explain this answer?
______ is used as a reducing agent in SDS PAGE.
a)
Sodium dodecyl sulfate (SDS)
b)
Ammonium persulphate (APS)
c)
Bisacrylamide
d)
2-mercaptoethanol
|
|
Orion Classes answered |
2-mercaptoethanol (beta-mercaptoethanol) is used as a reducing agent in SDS PAGE. It breaks the disulfide bonds and denatures the protein molecule. SDS is not a reducing agent, it disrupts non-covalent interactions between peptides. Ammonium persulphate (APS) and Bisacrylamide do not show any reducing properties.
Which structure of a protein is the arrangement of protein subunits in a multi-subunit complex?- a)Primary
- b)Secondary
- c)Tertiary
- d)Quaternary
Correct answer is option 'D'. Can you explain this answer?
Which structure of a protein is the arrangement of protein subunits in a multi-subunit complex?
a)
Primary
b)
Secondary
c)
Tertiary
d)
Quaternary
|
|
Orion Classes answered |
Quaternary structure of a protein is the arrangement of protein subunits in a multi-subunit complex. Many proteins are composed of more than one polypeptide chain. These polypeptide chains fold to form a subunit of a complex protein. All subunits combine to form a complete functional protein.
The term “electron density maps” is related to which of the following technique?- a)Optical microscopy
- b)NMR spectroscopy
- c)cryo-electron microscopy
- d)X-ray crystallography
Correct answer is option 'D'. Can you explain this answer?
The term “electron density maps” is related to which of the following technique?
a)
Optical microscopy
b)
NMR spectroscopy
c)
cryo-electron microscopy
d)
X-ray crystallography
|
|
Orion Classes answered |
X-ray crystallography is a technique where in electron density maps are obtained. Thus, the term “electron density maps” is related to X-ray crystallography. Other techniques mentioned do not involve electron density maps.
Which of the following elements is not visible in the maps of X-ray crystallography?- a)Nitrogen
- b)Carbon
- c)Oxygen
- d)Hydrogen
Correct answer is option 'D'. Can you explain this answer?
Which of the following elements is not visible in the maps of X-ray crystallography?
a)
Nitrogen
b)
Carbon
c)
Oxygen
d)
Hydrogen
|
|
Orion Classes answered |
Hydrogen atom is not visible in the electron density maps of X-ray crystallography. The reason behind this is the low electron density of the hydrogen atom. Hydrogen contains a minimum of one electron.
Which among the following residues is most likely to be present on the surface of a protein?- a)Val
- b)Leu
- c)Ile
- d)Arg
Correct answer is option 'D'. Can you explain this answer?
Which among the following residues is most likely to be present on the surface of a protein?
a)
Val
b)
Leu
c)
Ile
d)
Arg
|
|
Orion Classes answered |
Arg is most likely to be present on the surface of a protein because it is a polar residue. Generally, polar residues reside on the surface of a protein. Val, leu, and Ile are non-polar residues, hence, they are not likely to be present on the surface of a protein.
What are multi-subunit proteins called when some or all of its subunits are identical?- a)Monomers
- b)Polymers
- c)Protomers
- d)Oligomers
Correct answer is option 'D'. Can you explain this answer?
What are multi-subunit proteins called when some or all of its subunits are identical?
a)
Monomers
b)
Polymers
c)
Protomers
d)
Oligomers
|
|
Orion Classes answered |
Many proteins have a complex structure i.e. they have a multi-subunit structure. When some or all the sub-units of a complex protein are identical it is called oligomers.
Which among the following is a non-essential amino acid?- a)Serine
- b)Threonine
- c)Lysine
- d)Histidine
Correct answer is option 'A'. Can you explain this answer?
Which among the following is a non-essential amino acid?
a)
Serine
b)
Threonine
c)
Lysine
d)
Histidine
|
|
Orion Classes answered |
Serine is one of the 11 non-essential amino acids.
Which of the following is an imino acid?- a)Alanine
- b)Glycine
- c)Proline
- d)Serine
Correct answer is option 'C'. Can you explain this answer?
Which of the following is an imino acid?
a)
Alanine
b)
Glycine
c)
Proline
d)
Serine
|
|
Orion Classes answered |
Proline is secondary amino acid also called as an imino acid as it contains –C = NH – OH group.
Which of the following interactions is shown in the figure below?
- a)Disulfide bond
- b)Ionic interactions
- c)Hydrophobic interactions
- d)Hydrogen bonds
Correct answer is option 'D'. Can you explain this answer?
Which of the following interactions is shown in the figure below?
a)
Disulfide bond
b)
Ionic interactions
c)
Hydrophobic interactions
d)
Hydrogen bonds
|
|
Orion Classes answered |
The interaction shown in the above figure is the hydrogen bond. A hydrogen bond is the interaction between a hydrogen atom attached to an electronegative atom with another electronegative atom like oxygen in its vicinity. It is non-covalent in nature.
Which of the following is used for the reduction of disulfide bonds?- a)Urea
- b)Guanidine hydrochloride
- c)Iodoacetate
- d)Beta-mercaptoethanol/ dithiothreitol
Correct answer is option 'D'. Can you explain this answer?
Which of the following is used for the reduction of disulfide bonds?
a)
Urea
b)
Guanidine hydrochloride
c)
Iodoacetate
d)
Beta-mercaptoethanol/ dithiothreitol
|
|
Orion Classes answered |
Beta-mercaptoethanol/dithiothreitol is used forthe reduction of disulfide bonds. Urea and guanidine hydrochloride are denaturating agents, while Iodoacetate is used for acetylation of sulfhydryl groups.
Which of the following interactions is shown in the figure below?- a)Hydrogen bond
- b)Vander Waals interactions
- c)Ionic bond
- d)Disulfide bond
Correct answer is option 'D'. Can you explain this answer?
Which of the following interactions is shown in the figure below?
a)
Hydrogen bond
b)
Vander Waals interactions
c)
Ionic bond
d)
Disulfide bond
|
|
Orion Classes answered |
The interaction shown in the above figure is a disulphide bond. Two Cysteine residues are involved in the formation of a disulfide bond. It is covalent in nature.
Which of the following options contain only those amino acids that are likely to be present in the interior of a protein?- a)Arg, Val, Met
- b)Asp, Met, Phe
- c)Lys, Phe, Val
- d)Val, Met, Phe
Correct answer is option 'D'. Can you explain this answer?
Which of the following options contain only those amino acids that are likely to be present in the interior of a protein?
a)
Arg, Val, Met
b)
Asp, Met, Phe
c)
Lys, Phe, Val
d)
Val, Met, Phe
|
|
Orion Classes answered |
The option containing Val, Met, and Phe is the correct option. Val, Met, and Phe are all non-polar residues, hence, likely to be present in the interior of the protein. Arg, Asp, and Lys are polar residues.
A clinician, during the ultrasound of a pregnant lady found that the lady had multiple fracture of in her fetus. She did not report any trauma. Later a genetic abnormality was identified to cause this due to the non-formation of collagen in the fetus as the mutation replaced glycine to serine in collagen. The name of this syndrome is- a)Collagenopsis
- b)Collegeniosis
- c)Osteogenesis imperfecta
- d)Osteomalacia
Correct answer is option 'C'. Can you explain this answer?
A clinician, during the ultrasound of a pregnant lady found that the lady had multiple fracture of in her fetus. She did not report any trauma. Later a genetic abnormality was identified to cause this due to the non-formation of collagen in the fetus as the mutation replaced glycine to serine in collagen. The name of this syndrome is
a)
Collagenopsis
b)
Collegeniosis
c)
Osteogenesis imperfecta
d)
Osteomalacia
|
|
Aryan Gupta answered |
Osteogenesis imperfecta is also known as brittle bone disease. Most of the mutations that cause osteogenesis imperfecta type I occur in the COL1A1 gene. This gene encodes major component of type 1 collagen. Therefore in this disease, there is a problem with connective tissue due to lack of type 1 collagen. Glycine is the most abundant amino acid in collagen and this genetic change replaces glycine to serine, thereby reducing the amount of type I collagen produced in the body, which causes bones to be brittle and to fracture easily.
Which of the following statements is/are true about proteins and amino acids.- a)The typical length of the membrane spanning region of an integral membrane protein is 20-25 amino acids
- b)Methionine and glutamine are optically inactive
- c)Lysine and leucine are the only two amino acids which are exclusively ketogenic in nature
- d)Tyrosine, valine and histidine are both glucogenic and ketogenic in nature
Correct answer is option 'A,C'. Can you explain this answer?
Which of the following statements is/are true about proteins and amino acids.
a)
The typical length of the membrane spanning region of an integral membrane protein is 20-25 amino acids
b)
Methionine and glutamine are optically inactive
c)
Lysine and leucine are the only two amino acids which are exclusively ketogenic in nature
d)
Tyrosine, valine and histidine are both glucogenic and ketogenic in nature
|
|
Isha Bose answered |
Statement (a) is correct as usually the membrane spanning region of an integral membrane protein is 20-25 amino acid long.
Statement (b) is incorrect, because glycine is the only amino acid which is optically inactive as it has no chiral centre. All other amino acids have atleast one chiral centre, so all other amino acids except glycine are optically active.
Statement (c) is correct as lysine and leucine are the only two amino acids which are exclusively ketogenic in nature.
Statement (d) in incorrect as there are only five amino acids which are both glucogenic and ketogenic in nature. They are tyrosine, isoleucine, phenylalanine, tryptophan and threonine.
Statement (b) is incorrect, because glycine is the only amino acid which is optically inactive as it has no chiral centre. All other amino acids have atleast one chiral centre, so all other amino acids except glycine are optically active.
Statement (c) is correct as lysine and leucine are the only two amino acids which are exclusively ketogenic in nature.
Statement (d) in incorrect as there are only five amino acids which are both glucogenic and ketogenic in nature. They are tyrosine, isoleucine, phenylalanine, tryptophan and threonine.
Which of the following interactions is shown in the figure below?
- a)Disulfide bond
- b)Ionic interactions
- c)Hydrogen bonds
- d)Hydrophobic interactions
Correct answer is option 'D'. Can you explain this answer?
Which of the following interactions is shown in the figure below?
a)
Disulfide bond
b)
Ionic interactions
c)
Hydrogen bonds
d)
Hydrophobic interactions
|
|
Orion Classes answered |
The interaction shown in the above figure is hydrophobic interactions. Hydrophobic interactions involve interaction between two non-polar hydrophobic residues. It is non-covalent in nature.
Chapter doubts & questions for Amino Acids and Proteins - Biochemistry for MCAT 2025 is part of MCAT exam preparation. The chapters have been prepared according to the MCAT exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for MCAT 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.
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