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Total Categories: 4
A peptide bond is characterized as an ionic bond that links amino acids.
Answer: False
A peptide bond is specifically an amide type of covalent chemical bond, not an ionic bond.
Peptide bond formation involves a linkage between the C2 atom of the first amino acid's carboxyl group and the N1 atom of the second amino acid's amino group.
Answer: False
Peptide bond formation occurs between the C1 atom of the carboxyl group of one amino acid and the N2 atom of the amino group of the subsequent amino acid.
Peptide bond formation is a condensation reaction where a water molecule is released.
Answer: True
The formation of a peptide bond is a condensation reaction, also known as dehydration synthesis, during which a molecule of water is eliminated.
In the formation of a peptide bond, the amino group loses a hydrogen atom (H), and the carboxyl group loses a hydroxyl group (OH).
Answer: True
During peptide bond formation, the carboxyl group loses a hydroxyl group (OH), and the amino group loses a hydrogen atom (H), with these components combining to form a water molecule.
The biological synthesis of peptide bonds necessitates energy, commonly derived from GTP.
Answer: False
While biological synthesis of peptide bonds requires energy, the primary energy currency utilized is adenosine triphosphate (ATP), not guanosine triphosphate (GTP).
What type of covalent bond defines the linkage between two consecutive alpha-amino acids in a peptide chain?
Answer: A peptide bond (amide type)
The covalent linkage connecting sequential alpha-amino acids in a peptide or protein chain is specifically an amide type of bond, known as a peptide bond.
In peptide bond formation, which atoms are involved in the linkage?
Answer: C1 of the first amino acid and N2 of the second
The peptide bond forms between the carbon atom numbered one (C1) of the carboxyl group of one amino acid and the nitrogen atom numbered two (N2) of the amino group of the next amino acid.
What molecule is released when two amino acids join via a peptide bond?
Answer: Water (H2O)
The formation of a peptide bond through condensation reaction results in the release of a single molecule of water (H2O).
What is the primary energy source for the biological synthesis of peptide bonds?
Answer: Adenosine triphosphate (ATP)
The energy required for the biological formation of peptide bonds is primarily supplied by the hydrolysis of adenosine triphosphate (ATP).
Which term is used as an alternative name for a standard peptide bond, distinguishing it from an isopeptide bond?
Answer: Eupeptide bond
The term 'eupeptide bond' is employed to specifically denote a standard peptide bond, differentiating it from an isopeptide bond.
The eupeptide bond is a term used to distinguish it from an isopeptide bond.
Answer: True
The term 'eupeptide bond' serves to differentiate standard peptide linkages from isopeptide bonds, which involve different amino acid side chains.
Peptide bonds exhibit significant UV absorption within the 300-400 nm spectral range.
Answer: False
Peptide bonds absorb UV radiation most strongly in the range of 190 to 230 nm, not 300-400 nm.
The partial double-bond character of the peptide bond arises from electron delocalization occurring on the oxygen atom.
Answer: False
The partial double-bond character of the peptide bond results from the delocalization of the lone pair of electrons on the nitrogen atom, not the oxygen atom.
The peptide group's partial double-bond character renders it non-planar.
Answer: False
Due to its partial double-bond character, the peptide group is planar, meaning all six atoms (Cα, C', N, Cα', and the two atoms of the peptide bond itself) lie in the same plane.
In most peptide bonds within folded proteins, the trans isomer is overwhelmingly preferred, with a population ratio of approximately 1000:1 compared to the cis isomer.
Answer: True
The trans isomer configuration is significantly more prevalent than the cis isomer in peptide bonds found in proteins, typically by a ratio of about 1000:1.
Peptide bonds involving proline (X-Pro) exhibit a markedly greater propensity for the cis isomer in comparison to other peptide bonds.
Answer: False
While peptide bonds involving proline (X-Pro) do show a higher proportion of the cis isomer (approximately 30:1 trans:cis ratio) compared to other peptide bonds, the trans isomer remains dominant.
The dihedral angle omega (ω) quantifies rotation around the bond connecting the carbonyl carbon and the alpha-carbon.
Answer: False
The dihedral angle omega (ω) specifically describes the rotation around the C'-N bond, which constitutes the peptide bond itself, not the bond between the carbonyl carbon and the alpha-carbon.
The cis isomer configuration of a peptide bond is associated with an omega (ω) angle of 180 degrees.
Answer: False
The cis isomer of a peptide bond corresponds to an omega (ω) angle of 0 degrees, whereas the trans isomer corresponds to an angle of 180 degrees.
The cis-trans isomerization of amide groups in peptide bonds proceeds rapidly at room temperature, exhibiting a half-life measured in milliseconds.
Answer: False
Cis-trans isomerization of peptide bonds is a relatively slow process at room temperature, with an approximate half-life of around 20 seconds, not milliseconds.
Peptidyl prolyl isomerases (PPIases) are naturally occurring enzymes that specifically catalyze the cis-trans isomerization of peptide bonds involving proline (X-Pro peptide bonds).
Answer: True
Peptidyl prolyl isomerases (PPIases) are enzymes dedicated to accelerating the cis-trans isomerization specifically for peptide bonds where proline is the C-terminal residue (X-Pro bonds).
The process of protein folding typically proceeds at a slower rate than the cis-trans isomerization of peptide bonds.
Answer: False
Protein folding is generally a much faster process, occurring on the millisecond timescale, compared to the cis-trans isomerization of peptide bonds, which takes seconds.
A nonnative isomer of a peptide bond can significantly disrupt or slow down the protein folding process, potentially preventing it from occurring until the native isomer is achieved.
Answer: True
The presence of a nonnative isomer configuration in certain peptide bonds can indeed impede or halt protein folding until the correct isomer is established, although the impact varies depending on the specific peptide bond.
Peptide bonds demonstrate high reactivity under physiological conditions owing to their single bond character.
Answer: False
Peptide bonds are relatively unreactive under physiological conditions due to resonance stabilization, which imparts partial double-bond character, making them less reactive than typical single bonds.
The peptide group's partial double-bond character renders it non-planar.
Answer: Rigid and planar
The partial double-bond character of the peptide bond restricts rotation and enforces planarity upon the amide group, comprising six atoms.
In most proteins, which isomer configuration (cis or trans) is predominantly found for peptide bonds?
Answer: Trans
The trans isomer configuration is overwhelmingly favored in peptide bonds within proteins, occurring at a much higher frequency than the cis isomer.
Which specific type of peptide bond shows a less extreme preference for the trans isomer (ratio ~30:1)?
Answer: Peptide bonds involving proline (X-Pro)
Peptide bonds where proline is the C-terminal residue (X-Pro bonds) exhibit a reduced preference for the trans isomer, with a trans:cis ratio closer to 30:1 compared to the typical 1000:1.
What does the dihedral angle omega (ω) represent in the context of a peptide bond?
Answer: Rotation around the C'-N bond (the peptide bond itself)
The dihedral angle omega (ω) specifically measures the rotation around the C'-N bond, which is the peptide bond linkage.
What is the approximate activation energy required for the cis-trans isomerization of peptide bonds?
Answer: 80 kJ/mol
The activation energy barrier for the cis-trans isomerization of peptide bonds is approximately 80 kJ/mol, reflecting the energy needed to overcome the partial double bond character.
What is the function of Peptidyl Prolyl Isomerases (PPIases)?
Answer: To catalyze the cis-trans isomerization of X-Pro peptide bonds.
Peptidyl prolyl isomerases (PPIases) are enzymes specifically responsible for catalyzing the cis-trans isomerization of peptide bonds involving proline residues.
How does the typical rate of protein folding compare to the rate of peptide bond cis-trans isomerization?
Answer: Protein folding is generally much faster.
Protein folding typically occurs on the millisecond timescale, which is significantly faster than the cis-trans isomerization of peptide bonds, which can take seconds.
Why are peptide bonds considered relatively unreactive under physiological conditions?
Answer: They are stabilized by resonance.
The resonance stabilization of the peptide bond, imparting partial double-bond character, significantly reduces its reactivity under physiological conditions.
Hydrolysis is the process used to break peptide bonds.
Answer: True
Peptide bonds are cleaved through hydrolysis, a reaction involving the addition of a water molecule across the bond.
The spontaneous hydrolysis of a peptide bond under neutral conditions is a very rapid process.
Answer: False
Under neutral conditions at room temperature, the spontaneous hydrolysis of a peptide bond is extremely slow, with a half-life estimated to be hundreds of years.
Peptidases are enzymes that facilitate the formation of peptide bonds.
Answer: False
Peptidases, also known as proteases, are enzymes that catalyze the hydrolysis (breaking) of peptide bonds, not their formation.
Proteases and peptidases are distinct types of enzymes with different functions regarding peptide bonds.
Answer: False
Proteases and peptidases are generally considered synonymous or closely related terms for enzymes that catalyze the hydrolysis of peptide bonds.
Conformational strain within a protein can contribute to peptide bond hydrolysis.
Answer: True
Conformational strain within a protein structure can destabilize peptide bonds, facilitating their non-enzymatic hydrolysis.
Many chemical reactions involving peptide bonds commence with a nucleophilic attack directed at the nitrogen atom.
Answer: False
The initial step in many chemical reactions involving peptide bonds, such as hydrolysis, is typically a nucleophilic attack on the carbonyl carbon atom.
A tetrahedral intermediate is formed during reactions like proteolysis involving peptide bonds.
Answer: True
The mechanism of peptide bond hydrolysis, including proteolysis, involves the transient formation of a tetrahedral intermediate.
What process is required to break a peptide bond?
Answer: Hydrolysis
Peptide bonds are broken down through the process of hydrolysis, which involves the addition of water.
What is the approximate Gibbs free energy released during the hydrolysis of a peptide bond?
Answer: 2-4 kcal/mol
The hydrolysis of peptide bonds releases approximately 2 to 4 kcal/mol (equivalent to 8 to 16 kJ/mol) of Gibbs free energy.
Which enzymes are responsible for catalyzing the hydrolysis of peptide bonds?
Answer: Peptidases (or Proteases)
Enzymes known as peptidases or proteases are responsible for catalyzing the hydrolysis of peptide bonds.
Besides enzymatic catalysis, what internal factor can contribute to peptide bond hydrolysis?
Answer: Conformational strain
Conformational strain within a protein's structure can act as an internal factor that promotes peptide bond hydrolysis, even in the absence of enzymes.
What is the typical initial step in a chemical reaction involving a peptide bond?
Answer: A nucleophilic attack on the carbonyl carbon.
Chemical reactions involving peptide bonds, such as hydrolysis, typically initiate with a nucleophilic attack on the electrophilic carbonyl carbon atom.
What intermediate structure is formed during reactions like proteolysis involving peptide bonds?
Answer: A tetrahedral intermediate
During the hydrolysis of peptide bonds, such as in proteolysis, a transient tetrahedral intermediate is formed as part of the reaction mechanism.
Nonribosomal peptides undergo synthesis through the action of ribosomes.
Answer: False
Nonribosomal peptides are synthesized by specialized enzymatic machinery, not by ribosomes, which are responsible for ribosomal peptide synthesis.
The synthesis of glutathione exclusively involves the formation of standard peptide bonds.
Answer: False
Glutathione synthesis involves an isopeptide bond in its first step, catalyzed by glutamate-cysteine ligase, before a standard peptide bond is formed in the second step.
Cyclols are molecular structures generated when a functional group targets a non-peptide bond.
Answer: False
Cyclols are formed when a functional group attacks a peptide bond, leading to cyclization, not when it attacks a non-peptide bond.
A disulfide bond is a type of crosslink that can be formed between two cysteine residues.
Answer: True
Disulfide bonds (-S-S-) are covalent crosslinks formed between the thiol groups of two cysteine residues, contributing to protein structure.
Desmosine constitutes a crosslink that involves solely a single lysine residue.
Answer: False
Desmosine is a complex crosslink formed from four lysine residues (specifically, three allysine residues and one lysine residue), not just one.
How are nonribosomal peptides synthesized?
Answer: Using specialized enzymes.
Nonribosomal peptides are synthesized by large, multi-domain enzymatic complexes known as nonribosomal peptide synthetases (NRPS).
The synthesis of glutathione involves which type of bond in its first step?
Answer: An isopeptide bond
The initial step in glutathione synthesis involves the formation of an isopeptide bond between glutamate and cysteine, catalyzed by glutamate-cysteine ligase.
What are cyclols, and how are they classified based on the attacking nucleophile?
Answer: Molecules resulting from functional groups attacking a peptide bond.
Cyclols are cyclic structures formed when a nucleophilic functional group attacks a peptide bond, leading to intramolecular cyclization.
What type of crosslink is formed between two cysteine residues?
Answer: Disulfide bond
A disulfide bond, formed by the oxidation of two thiol groups, is the characteristic crosslink that occurs between cysteine residues.