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The peptide unit (Cα – C’O – NH – Cα) is planer due to
(1) restriction around Cα – C’ bond
(2) restriction around C’ – N bond
(3) restriction around N – Cα bond
(4) hydrogen bonding between carbonyl oxygen and imino hydrogen of the peptide backbone
Why is the Peptide Unit Planar?
Proteins are fundamental biological macromolecules, and their structure determines their function. A key feature of protein structure is the planarity of the peptide unit (Cα – C’ – O – NH – Cα). But what makes this structural feature so rigid? The correct answer is:
(2) Restriction around the C’-N bond
Understanding the Planarity of the Peptide Bond
1. Resonance in Peptide Bonds
The peptide bond (C’-N) exhibits partial double-bond character due to resonance, which occurs between the lone pair on nitrogen and the carbonyl group:
O=C-NH ⇌ O⁻-C=N⁺
This delocalization of electrons restricts rotation around the C’-N bond, making the peptide bond rigid and planar.
2. Why Not Other Bonds?
- Cα – C’ bond: This is a regular single bond that allows free rotation.
- N – Cα bond: This is also a single bond and does not contribute to planarity.
- Hydrogen bonding (Option 4): While hydrogen bonding stabilizes secondary structures like α-helices and β-sheets, it does not enforce the planarity of an individual peptide unit.
Structural Consequences of Peptide Planarity
3. Cis vs. Trans Configuration
Most peptide bonds exist in the trans configuration, where the Cα groups of adjacent amino acids are positioned opposite each other to reduce steric hindrance.
- Trans form (~99%): More stable due to less steric clash.
- Cis form (~1%): Found in proline-containing sequences due to its cyclic structure.
4. Influence on Protein Secondary Structure
Because the peptide bond is planar, proteins adopt regular secondary structures such as:
- α-helix: Right-handed spiral stabilized by hydrogen bonds.
- β-sheet: Extended strands held together by hydrogen bonds.
- Turns and Loops: Connecting structures that allow flexibility.
5. Peptide Bond in Protein Folding and Function
The restricted rotation around the peptide bond has profound implications for:
- Protein folding: Determines the final 3D structure.
- Enzyme specificity: Active sites are shaped by rigid peptide linkages.
- Protein-protein interactions: Defined structures enable specific binding.
Conclusion
The peptide unit is planar due to the restricted rotation around the C’-N bond caused by resonance. This property influences protein structure, stability, and function, making it a fundamental concept in biochemistry and molecular biology.
47 Comments
Suman bhakar
March 27, 2025Done sir 👍
pallavi gautam
March 28, 2025done
Akshay mahawar
April 2, 2025Done 👍
Ujjwal
April 4, 2025Done
Lokesh Kumawat
April 5, 2025Done
Kabeer
April 6, 2025☑️
Priyam choudhary
April 24, 2025Done
Neha Yadav
September 25, 2025The peptide unit is planar due to the restricted rotation around the C’-N bond caused by resonance.
Aakansha sharma Sharma
September 25, 2025The peptide unit is planar due to the restricted rotation around the C’-N bond caused by resonance.
Soniya Shekhawat
September 25, 2025restriction around C’ – N bond option 2 is correct.
Kirti Agarwal
September 26, 2025C-N bond
Santosh Saini
September 26, 2025Hydrophobic interaction
Santosh Saini
September 26, 2025By mistake ho gya
Santosh Saini
September 26, 2025The peptide unit is planer due to the restricted rotation around the C-N bond caused by resonance
Neelam Sharma
September 26, 2025restriction around C’ – N bond kyunki carbonyl oxigen or amide ke nitrogen k bich partial double bond bnta h jisse resonance aa jata h esley ye rotate nhi ho skta
Preeti
September 29, 2025Option 2 is correct
Dharmpal Swami
September 26, 2025The peptide unit is planer due to the restricted rotation around the C-N bond caused by resonance
Partial double bond presence
sakshi vijay
September 26, 2025the peptide unit is planner due to restricted rotation in C alpha and N due to resonance
sakshi vijay
September 26, 2025proline is rigid cyclic structure so it occupy less area in plot
Kavita Choudhary
September 26, 2025Peptide bond is a planer due to the resticted rotation around the C- N bond caused by resonance and partial double bond is present
Mohd juber Ali
September 26, 2025NCC➡️NCC
C-N is peptide bond is planer C-N is phai restricted c-R group so no rotation
Mohd juber Ali
September 26, 2025C-N omega not phai
Minal Sethi
September 26, 2025The peptide bond is planar due to the restricted rotation around the C’-N bond caused by resonance
Devika
September 26, 2025Due to the restricted rotation around C’-N bond caused by resonance
Muskan Yadav
September 26, 2025The peptide bond is planar due to Restriction around the C’-N bond.
Kajal
September 26, 2025Option 2 restriction around C’-N
Pallavi Ghangas
September 26, 20252
Priya khandal
September 26, 2025C N bond
HIMANI FAUJDAR
September 27, 2025Ans The peptide bond become planer due to restriction around C’-N caused by resonance.
Khushi Singh
September 27, 2025C-N bond restricted due to resonance
Aafreen Khan
September 27, 2025Restriction around the C’-N bond is correct answer
Bhawna Choudhary
September 27, 2025Restricted rotation around the C’-N bond caused by resonance
Arushi Saini
September 28, 2025Peptide bond is planer due to the resticted rotation around the C- N bond caused by resonance and partial double bond is present
Mansukh Kapoor
September 28, 2025The correct answer is option 2nd
The peptide bond is in planer form due to the restriction of the C-N bond
Sakshi Kanwar
September 28, 2025C-N exhibit partial double bond character due to presence of lone pair on nitrogen which show resonance .
roopal sharma
September 28, 2025the restriction around c-N bond cause resonance.
Avni
September 28, 2025The peptide unit is planar due to the restricted rotation around the C’-N bond caused by resonance.
Anurag Giri
September 28, 2025The peptide unit is planar due to the restricted rotation around the C’-N bond caused by resonance
Khushi Mehra
September 28, 2025The peptide bond is planar because the C-N bond have partially double bond character due to resonance between lone pair of nitrogen and carbonyl group.
Neeraj Sharma
September 28, 2025The peptide bond is planner due to C’ and N bond
Heena Mahlawat
September 28, 2025Planarity due to partial double bond of C’ and N
Divya rani
September 29, 2025C-N bond make The peptide bond rigid and planar.
anjani sharma
September 29, 2025Answer 2
The peptide bond is planar due to the restricted rotation around the C’-N bond caused by resonance.
Priyanshi sharma
September 29, 2025Options 2ed is right answer
Priyanshi Sharma
September 29, 2025Options 2ed is correct answer
Priti khandal
September 30, 20252nd right Yes — I endorse Let’s Talk Academy as a very strong choice for your CSIR NET Life Science preparation, especially given that your preparation style (conceptual clarity + experimental-based studying + daily practice + CBT simulation) aligns with their method.
Pooja
October 5, 2025The peptide unit is planar due to the restricted rotation around the C’-N bond caused by resonance.