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Peptide Bonds: Features and Formation

Yazan Hamzeh, Meg Desko
  • Author
    Yazan Hamzeh

    I am an inspiring budding scientist, who currently works at a fertility unit. I graduated with BSc (honors) in Genetic Engineering from Jordan University of Science and Technology, and then pursued an MSc in Clinical Embryology at the University of Oxford where I graduated with merit. During the course of academic endeavors, I found a passion in writing, whether it being scientific writing or blog writing. Therefore, I am so glad to be a part of Study.com! I am looking forward to hopefully inspire the many budding students out there.

  • Instructor
    Meg Desko

    Meg has taught college-level science. She holds a Ph.D. in biochemistry.

What is a peptide bond? Learn the types, structure, and formation of the peptide bonds between amino acids. Understand proteins as a polymer of amino acids. Updated: 07/26/2021

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Frequently Asked Questions

How do you identify a peptide bond?

A peptide bond is occurs between the carboxyl group of one amino acid and an amine group with the other amino acid.

How do two amino acids bind?

Two amino acids bind via a peptide bond. The formation of a peptide bond occurs between a carboxyl group of one amino acid and an amine group of the other.

Proteins, which are vital to the functionality of all living organisms, are made up of multiple amino acid monomers linked together via peptide bonds. Peptide bonds are chemical covalent bonds linking one amino acid to the other, and they form between a carbon atom of one amino acid and a nitrogen atom of the other amino acid. The end of a protein with a free nitrogen atom is referred to as the N-terminus, while the other end of a protein with a free carbon atom is referred to as the C-terminus.

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Peptide Bonds and Protein Structure

Examples of amino acid structures
Amino Acids

Think back to a time when you liked to play, and when you liked to take ordinary objects, like paperclips, and turn them into other beautiful things, like necklaces. You did this by taking one paper clip, hooking it up with another one, and then adding another one on the end, and another one, and another one, until you had a long strand of paperclips. Similarly, amino acids, which are the building blocks of proteins, can come together to form different types of peptides and proteins.

Today, we're going to talk about forming those bonds between amino acids, and we'll also talk about the different types of molecules that can be made by making these bonds.

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A protein molecule is generally composed of a multitude of amino acids, or peptides, linked together via peptide bonds. The human body makes use of 20 naturally occurring amino acids. Proteins differ in the number and type of amino acids they possess.

Types of Peptides

Protein nomenclature can be dependent on the number of peptides they encompass. For example:

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As explained earlier, a protein is made of a sequence of amino acids linked together via peptide bonds in a process titled polymerization. The order and sequence of amino acids are specific to each protein, which gives rise to the protein's primary structure.

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As mentioned earlier, the formation of a peptide bond between two amino acids brings about the formation of a molecule of water. As a carboxyl group loses its hydroxyl (OH) and an amine group loses its hydrogen (H) atom, they combine to form one molecule of water for each peptide bond. This process is reversible; peptide bonds can be broken by the addition of a water molecule. The water molecule restores the hydroxyl (OH) to the carboxyl group and a hydrogen atom to the amine group, thus giving rise to two separate individual amino acids per peptide bond and releasing energy. This process is referred to as a hydrolysis reaction.


Hydrolysis of a Peptide Bond


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Deoxyribonucleic acid (DNA) serves as the code that dictates protein expression in both eukaryotic and prokaryotic cells. DNA is made of a sugar (deoxyribose), a phosphate group, and a nitrogenous base. The sugar and phosphate molecules together form what is called the sugar-phosphate backbone of DNA, which anchors to the nitrogenous base and gives it the ability to form hydrogen bonds with nitrogenous bases of the complementary DNA strand. Recent scientific breakthroughs allowed the development of peptide nucleic acids (PNAs). PNAs are man-made DNA look-alike substances, in which the sugar-phosphate backbone is replaced with a peptide polymer. Because of their flexible and uncharged nature, they bind to complementary DNA strands in a very efficient manner. Therefore, PNAs are used in research and diagnostic settings, in which they are employed in hybridization assays.

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  • A peptide bond is a chemical covalent bond that joins amino acids together to form proteins.
  • A peptide bond occurs between a carbon atom of one amino acid with a nitrogen atom of the other amino acid by removing a hydroxyl group and a hydrogen atom to form a molecule of water.
  • A peptide bond can be broken by the addition of water, which restores the hydroxyl and hydrogen atoms to each amino acid, releasing energy in the process. This reaction is called a hydrolysis reaction.
  • Peptides are grouped and named according to the number of amino acids the structure possesses.
  • The order and sequence of amino acids in a protein are crucial for protein shape and function.
  • Synthetic structures named peptide nucleic acids made by replacing the sugar-phosphate backbone of DNA with a peptide are used in research and diagnostics.

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How Peptides are Formed

In our cells, amino acids come together to form peptide bonds at places called ribosomes, which are sort of like a protein-building factory. We won't worry about that right now. What we're really concerned with is how these bonds form between two amino acids. Let's take the two amino acids, glycine and alanine.

The structures of glycine and alanine
Glycine and Alanine

One thing you'll notice is when we show amino acids that we're going to join together, we always show them from the amine side to the carboxylic acid side.

The side with the free amino group is known as the n-terminus of the amino acid. The side with the free carboxylic acid group is known as the c-terminus of the amino acid, or peptide. If glycine on the left and alanine on the right come together, they can form a dipeptide. The way that this happens is that the nitrogen on the amino group of the alanine forms a bond with the carbonyl carbon of the carboxylic acid on the glycine.

The byproduct of this reaction is water, which means that this is a dehydration reaction, or loss of water reaction.

The resulting molecule that's formed is a dipeptide, or peptide consisting of two amino acids. It would also be possible for this dipeptide to come into contact with another amino acid, such as serine. If it came into contact with serine, it is possible that it could form a tripeptide when the nitrogen of the serine amino acid bonded to the carbonyl carbon of the carboxylic acid on the alanine in the dipeptide.

Water would be a byproduct of this dehydration reaction, and we would be left with a tripeptide, consisting of glycine, alanine, and serine. So while it's pretty cool to see a tripeptide in all of its chemical glory, and see all of the bonds that make up these molecules, sometimes, it can be useful to have a shorthand, or have a different way to represent a peptide.

A dipeptide formed from glycine and alanine
Example of a Dipeptide

Writing Peptides

In the case of glycine-alanine dipeptide, we could represent them as two circles that are joined together (almost like they're part of a necklace), with the short names of the amino acids inside - in this case, gly and ala. If we were to add the serine that was part of our tripeptide to this, it would be gly-ala-ser (s-e-r). So you can think of this as a good way to represent a peptide, where the free amino group is on the left-hand side, and the carboxylic acid group is on the right-hand side.

Video Transcript

Peptide Bonds and Protein Structure

Examples of amino acid structures
Amino Acids

Think back to a time when you liked to play, and when you liked to take ordinary objects, like paperclips, and turn them into other beautiful things, like necklaces. You did this by taking one paper clip, hooking it up with another one, and then adding another one on the end, and another one, and another one, until you had a long strand of paperclips. Similarly, amino acids, which are the building blocks of proteins, can come together to form different types of peptides and proteins.

Today, we're going to talk about forming those bonds between amino acids, and we'll also talk about the different types of molecules that can be made by making these bonds.

How Peptides are Formed

In our cells, amino acids come together to form peptide bonds at places called ribosomes, which are sort of like a protein-building factory. We won't worry about that right now. What we're really concerned with is how these bonds form between two amino acids. Let's take the two amino acids, glycine and alanine.

The structures of glycine and alanine
Glycine and Alanine

One thing you'll notice is when we show amino acids that we're going to join together, we always show them from the amine side to the carboxylic acid side.

The side with the free amino group is known as the n-terminus of the amino acid. The side with the free carboxylic acid group is known as the c-terminus of the amino acid, or peptide. If glycine on the left and alanine on the right come together, they can form a dipeptide. The way that this happens is that the nitrogen on the amino group of the alanine forms a bond with the carbonyl carbon of the carboxylic acid on the glycine.

The byproduct of this reaction is water, which means that this is a dehydration reaction, or loss of water reaction.

The resulting molecule that's formed is a dipeptide, or peptide consisting of two amino acids. It would also be possible for this dipeptide to come into contact with another amino acid, such as serine. If it came into contact with serine, it is possible that it could form a tripeptide when the nitrogen of the serine amino acid bonded to the carbonyl carbon of the carboxylic acid on the alanine in the dipeptide.

Water would be a byproduct of this dehydration reaction, and we would be left with a tripeptide, consisting of glycine, alanine, and serine. So while it's pretty cool to see a tripeptide in all of its chemical glory, and see all of the bonds that make up these molecules, sometimes, it can be useful to have a shorthand, or have a different way to represent a peptide.

A dipeptide formed from glycine and alanine
Example of a Dipeptide

Writing Peptides

In the case of glycine-alanine dipeptide, we could represent them as two circles that are joined together (almost like they're part of a necklace), with the short names of the amino acids inside - in this case, gly and ala. If we were to add the serine that was part of our tripeptide to this, it would be gly-ala-ser (s-e-r). So you can think of this as a good way to represent a peptide, where the free amino group is on the left-hand side, and the carboxylic acid group is on the right-hand side.

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