Structure and Properties of Amino Acids

Q1: Which of the following is a nonprotein amino acid?

A Dopamine

B Hydroxylysine

C Cystine

D None of these

ANS:A - Dopamine

Dopamine is a type of co-enzyme which is non-protein amino acid.

Q2: What is the product of the catabolic breakdown of Alanine?

A Fumarate

B Oxaloacetate

C Pyruvate

D Malate

ANS:C - Pyruvate

After the NH3 group has been cleaved into the urea cycle, the remaining carbon skeleton is channeled into the gluconeogenic pathway to finally produce pyruvate.

Q3: Protein fluorescence arises primarily from which residue?

A Arginine

B Tryptophan

C Tyrosine

D Phenylalanine

ANS:B - Tryptophan

Tryptophan fluorescence wavelength is widely used as a tool to monitor changes in proteins and to make inferences regarding local structure and dynamics. We have predicted the fluorescence wavelengths of 19 tryptophans in 16 proteins, starting with crystal structures and using a hybrid quantum mechanical-classical molecular dynamics method with the assumption that only electrostatic interactions of the tryptophan ring electron density with the surrounding protein and solvent affect the transition energy. With only one adjustable parameter, the scaling of the quantum mechanical atomic charges as seen by the protein/solvent environment, the mean absolute deviation between predicted and observed fluorescence maximum wavelength is 6 nm.

The modeling of electrostatic interactions, including hydration, in proteins is vital to understanding function and structure, and this study helps to assess the effectiveness of current electrostatic models.

Q4: The α-amino acids have a carboxyl group with a pK around __________ , and an amino group with a pK near __________ .

A 1.1, and 12.1

B 6.5, and 8.0

C 3.3, and 10.5

D 2.2, and 9.4

ANS:D - 2.2, and 9.4

This answer is inaccurate. Typically the C terminus has a pka around 3 and the N terminus has a pka around 8. Although these are not exact numbers these are the relative values used.

Q5: When the amino acid alanine (R-group is CH3) is added to a solution with a pH of 7.3, alanine becomes

A a cation

B nonpolar

C a zwitterions

D an isotope

ANS:C - a zwitterions

No answer description is available. 

Q6: Which amino acid when exposed to ninhydrin produces a brown color?

A Asparagine

B Proline

C Alanine

D Valine

ANS:A - Asparagine

No answer description is available. 

Q7: Stereo chemical configuration of all a-amino acids derived from proteins is

A L

B D

C L and D

D None of these

ANS:A - L

No answer description is available. 

Q8: Which pair of amino acids absorbs the most UV light at 280 nm?

A Threonine & Histidine

B Trp & Tyrosine

C Cystein & Asparagine

D Phenylalnine & Proline

ANS:A - Threonine & Histidine

I think trp & tyrosine both are aromatic nonpolar molecules. That's why they absorb most UV light.

Q9: Which of the following is an essential amino acid?

A Tryptophan

B Methionine

C Lysine

D All of these

ANS:D - All of these

No answer description is available.

Q10: The sequence of letters 'WYQN' will represent

A Tryptophan, tyrosine, glutamic acid, asparagine

B Tryptophan, tyrosine, glutamine, asparagine

C Tryptophan, glutamine, tryptophan, asparagine

D Glutamine, tyrosine, tryptophan, aspartic acid

ANS:B - Tryptophan, tyrosine, glutamine, asparagine

Maximum amino acid 3 letter and single letter code given based on their First letters. For avoiding the repetition they provided following letters. TRY- W, Tyr- Y, Glu-Q, Asn-N.

Q11: Coomassie Blue stains the proteins by reacting with

A arginine residues

B free c-termini

C peptide bonds

D aromatic ring

ANS:A - arginine residues

No answer description is available. 

Q12: Which of the following is not the hydrophobic and aromatic amino acid?

A Phenylalanine

B Tyrosine

C Tryptophan

D None of these

ANS:D - None of these

If you read the statement correctly?

It says which is not hydrophobic and aromatic. All three amino acids are aromatic. So, the answer must be D.

Q13: Which of the following is not an essential amino acid?

A Aspartic acid

B Glutamic acid

C Glycine

D All of these

ANS:D - All of these

No answer description is available. 

Q14: What is the heaviest of the twenty amino acids?

A Phenylalanine

B Tryptophan

C Tyrosine

D Histidine

ANS:B - Tryptophan

Molecular masses:

Tryptophan 204.

Phenylalanine 165.

Tyrosin 181.

Histidine 155.

Q15: Which of the following amino acid contain an imidazolium moiety?

A Alanine

B Valine

C Cysteine

D Histidine

ANS:C - Cysteine

No answer description is available. 

Q16: Molecules that bear charged groups of opposite polarity are known as

A zwitterions

B ambions

C ion conversion

D amphions

ANS:A - zwitterions

In neutral solution both alpha amino and alpha caboxyl group are ionized resulting to charged form of amino acid called zwitterion.

Q17: An essential amino acid is one that

A is essentially easy to synthesize

B is essential to flagella motion

C the body cannot synthesize

D the body can synthesize under essential conditions

ANS:C - the body cannot synthesize

The non essentially amino acid that body can synthesize and the essential one is body can not synthesize.

Q18: The sulphur containing side chain of cysteine is

A ampiphillic, highly reactive and capable of reacting with another cysteine

B hydrophillc, highly reactive and capable of reacting with another cysteine

C hydrophobic, highly reactive and capable of reacting with another cysteine

D none of the above

ANS:C - hydrophobic, highly reactive and capable of reacting with another cysteine

The correct answer will be B that because the following charged:

Arginine - Arg - R.
Lysine - Lys - K.
Aspartic acid - Asp - D.
Glutamic acid - Glu - E.

Polar (may participate in hydrogen bonds)hydophilic:

Glutamine - Gln - Q.
Asparagine - Asn - N.
Histidine - His - H.
Serine - Ser - S.
Threonine - Thr - T.
Tyrosine - Tyr - Y.
Cysteine - Cys - C.
Methionine - Met - M.
Tryptophan - Trp - W.

Hydrophobic (normally buried inside the protein core):

Alanine - Ala - A.
Isoleucine - Ile - I.
Leucine - Leu - L.
Phenylalanine - Phe - F.
Valine - Val - V.
Proline - Pro - P.
Glycine - Gly - G.

Q19: Which of the following is a nonstandard amino acid?

A Cysteine

B Isoleucine

C Hydroxyproline

D Histidine

ANS:D - Histidine

A nonstandard amino acid is an amino acid that occurs naturally in cells but do not participate in peptide synthesis.

Some nonstandard amino acids are constituents of peptides, but they are generated by modification of standard amino acids in the peptide molecule by post-transnational modification.

Example of some non-standard amino acids: L-DOPA, GABA, 2-aminobutyric acid, dehydralanine, selenocysteine, pyrrolysine, N-formylmethionine, Hydroxyproline etc.

Q20: Which of the following amino acid is known as half-cystine residue?

A Cysteine

B Isoleucine

C Valine

D Histidine

ANS:A - Cysteine

Because cystine is formed when two cysteine residues are joined together thereby forming the disulfide bond.

Q21: How many different amino acids are there?

A 3

B 20

C 100

D An infinite number

ANS:B - 20

There much more amino acids than 20.

20 is the number of amino acids that can be incorporated into protein structure.

Q22: Serine and threonine are polar amino acids due to

A reactive hydroxyl group in the side chain

B reactive alcoholic group in the side chain

C reactive keto group in the side chain

D reactive aldehyde group in the side chain

ANS:A - reactive hydroxyl group in the side chain

What is the difference between hydroxyl and alcoholic group, both are OH?

Q23: Which of the following is not a sensible grouping of amino acids based on their polarity properties?

A Ala, Leu, and Val

B Arg, His, and Lys

C Phe, Trp, and Tyr

D Asp, Ile, and Pro

ANS:D - Asp, Ile, and Pro

Alanine, Leucine.and Valine are all non polar and aliphatic.
Arginine, histidine and lysine are positively charged.
Phenylalanine, tryptophan and tyrosine are aromatic.
The last options do not relate.

Q24: Proteins and macromolecular structures take on their higher order structures

A by self-assembly

B with the help of molecular chaperons

C with the help of precursor sequences that are removed from the final structures

D all of the above

ANS:D - all of the above

No answer description is available. 

Q25: In a polypeptide average mass of an amino acid residue is

A 110 daltons

B 118 daltons

C 80 daltons

D 150 daltons

ANS:A - 110 daltons

No answer description is available.

Q26: Amino acids required in the human diet and not synthesized by the body are called

A specialized

B trace

C essential

D accessory

ANS:C - essential

Non-essential amino acids were synthesized by the body. Essential amino acids not synthesized by the body.

Q27: What is the product of the catabolic breakdown of Arginine?

A Alpha-ketoglutarate

B Fumarate

C Oxaloacetate

D Succinate

ANS:A - Alpha-ketoglutarate

No answer description is available. 

Q28: Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?

A Asparagine & Glutamine

B Leucine & Glycine

C Histidine & Lysine

D Aspartate & Glutamate

ANS:D - Aspartate & Glutamate

pKr of Glutamate is 4.25.

pKr of Aspartate is 3.65.

If pH, for example the pH of 8, is greater than the pKr, then the amino acid loses a proton and bears its negative charge.

If the pH is less than the pKr value, then the amino acids keeps its proton, bearing a neutral charge.

PH of 8 is greater than the pKr values of Glu and Asp, so they both lose a proton and bear that negative charge on their respective are group.

Q29: What is the end product of leucine metabolism?

A Acetyl-CoA

B Pyruvic acid

C Oxaloacetic acid

D Acetyl carnitine

ANS:A - Acetyl-CoA

The leucine whenis metabolised, the amino group is cleaved leading to the formation of Urea, the remaining chain is leading to Acetyl-coa in mitochondria.

Q30: D-Alanine and L-Alanine are technically known as

A anomers

B enantiomers

C epimers

D polymer

ANS:B - enantiomers

Diastereomers are compounds that have similar configuration at some carbon and dissimilar configuration at some carbons.

Whereas epimers are compounds that differ in configuration at only one chiral carbon.

The point of difference arises in the fact that epimers have only one chiral carbon which is different in configuration whereas diastereomers can have any number of different configuration around its chiral carbons (except all being different).

If two compounds would differ at all stereocentres, they would be enantiomers or if a pair of stereoisomers are non-superimposable mirror images of each other, then they are enantiomers.

Q31: The isoelectric point of an amino acid is defined as the pH

A where the molecule carries no electric charge

B where the carboxyl group is uncharged

C where the amino group is uncharged

D of maximum electrolytic mobility

ANS:B - where the carboxyl group is uncharged

It halfway of dissociation process therefore it carried equal charges and net charger is Zero example net=+1+(-1).

Q32: Which amino acids would most likely reside in the membrane-anchoring domain of a membrane embedded protein?

A Isoleucine, valine and phenylalanine

B Phenylalanine, valine, and aspartate

C Leucine, threonine, and lysine

D Lysine, arginine and histidine

ANS:A - Isoleucine, valine and phenylalanine

Membrane-embedded proteins must be hydrophobic. So we need to choose which option of amino acids have hydrophobic are chains.

And charged are groups would disrupt membrane stability. We need to choose unchanged amino acids.

Q33: Which of the following amino acids can form hydrogen bonds with their side (R) groups?

A Asparagine

B Aspartic acid

C Glutamine

D All of these

ANS:B - Aspartic acid

Serin, threonine, Tyrosine, each contain polar hydroxyl groups that can participate in hydrogen bond formation the side chain of asparagine and glutamates each contain a Carbonyl group and an amide group, both of which can also participate in a hydrogen bond.



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