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What Are Peptide Bonds?

Victoria Blackburn
Victoria Blackburn

Peptide bonds are a type of covalent bond that is only found within protein molecules. These bonds join amino acids together to create peptide chains, which are then joined together to form proteins. Covalent bonds form when one atom within a molecule shares one, two or three electrons with an atom from another molecule. These types of bonds are strong and can be difficult to break.

All proteins are made from chains of amino acids that bond together in a very specific way. Most amino acids have a single carboxyl group (-COOH) on one side and an amino group (-NH2) on the other. Adjacent amino acids can form a peptide bond when one acid's carboxyl group joins with the other's amino group.

When peptide bonds form, a water molecule is lost.
When peptide bonds form, a water molecule is lost.

When peptide bonds are formed between amino acids, a water molecule is lost. This type of reaction is called a condensation reaction. The water molecule (H2O) is created by the loss of a hydroxyl (-OH) from the carboxyl group and a hydrogen atom (H) from the amino group. The fact that all amino acids bond together in this way is one of the factors that determines the shape of the protein being made.

Single peptide bonds occur between each amino acid pairing. Proteins are also called polypeptides as they are often made up of tens and even hundreds of amino acids that have been joined together into peptide chains. This means that proteins contain many peptide bonds.

To break a peptide bond, a hydrolysis reaction — the opposite of a condensation reaction — must occur. Hydrolysis reactions take place when splitting proteins into peptide chains, or peptides into single amino acids. In hydrolysis, a water molecule is added to the peptide bond, causing the water to split. The hydroxyl group (-OH) attaches to the carboxyl group of one amino acid, and the hydrogen atom (H) attaches to the amino group of the other.

Peptide bonds are extremely stable, which means they are difficult to break. This is of particular importance for proteins, as they play vital roles in most lifeforms. For example, proteins called enzymes control almost all chemical reactions within living things. Also, the shape of a protein is of vital importance to how well that protein functions. The order of the amino acids that make up the protein, as well as the strength of the peptide bonds, are factors in determining and maintaining the shape of each particular type of protein.

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Discussion Comments


Peptidase is the enzyme that breaks down peptides(protien). So, no. Water alone will not break down your steak.


@cardsfan27 - Like you probably already know, proteins come in a huge variety of shapes. That is how enzymes work. They have a special shape that only fits with the exact shape of one or two other proteins. I would have to assume that the reason for the shape of proteins and enzymes is from the different peptide bonds that result from different amino groups.


@JimmyT - I don't know, though. Think about cooking a brisket or roast or another fairly tough piece of meat in a slow cooker. You are adding water and energy in the form of heat. Eventually, the meat starts to get tender, which would mean the proteins are breaking down by way of the peptide bonds being hydrolysed. It is definitely not an instant reaction, but I think it still happens.

I know there are a set number of amino acids that can make a huge number of proteins and enzymes. I was wondering if certain amino acid combinations end up with different types of peptide bonds, since their amino groups are all slightly different.


@jmc88 - I would say you are right. There would have to be some type of energy input to make the water split apart and the peptide bond to break. Since energy has to be conserved, I would guess that there is some sort of energy released during the condensation process that has to be put back into the system for the reverse reaction.

I am not for certain, but if I had to guess, I would say in a functioning body, the energy would be in the form of special enzymes that break apart the peptide bond and reattach water molecules. For a piece of meat, the necessary enzymes would probably be gone or at least not functioning to where they could perform the reactions.


Is it safe to say that hydrolysing a peptide bond is much more difficult than creating the peptide bond in the first place?

What all is involved in the process? It seems like it would take something besides just having water to make the final reaction happen. If you think about a piece of meat, it is mostly protein. Dipping a steak in water doesn't make the meat break apart into smaller proteins, does it?

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    • When peptide bonds form, a water molecule is lost.
      By: Ioana Davies (Drutu)
      When peptide bonds form, a water molecule is lost.