Antigen-Antibody

What happens when an antigen binds to an antibody?

Multiple weak interactions form between the antigen and amino acids in the antibody’s binding site.

What type of interactions hold an antigen and antibody together?

Multiple attractive and repulsive interactions between the antigen and antibody.

Why are the individual bonds between an antigen and antibody relatively weak?

Each individual interaction is weak, but many interactions together can create a strong binding.

What are the four types of interactions involved in antigen-antibody binding?

Hydrogen bonding, electrostatic forces, Van der Waals forces, and hydrophobic bonds.

What is hydrogen bonding?

A hydrogen atom is shared between two electronegative atoms.

What are electrostatic forces?

Oppositely charged groups attract each other.

What are Van der Waals forces?

Weak attractions between positive or negative charged regions of molecules.

What are hydrophobic bonds?

The association of hydrophobic groups, which tend to come together.

What is affinity?

The strength of a single antigen-antibody interaction.

What determines antibody affinity?

The total of the attractive and repulsive forces between the antigen and antibody.

What happens with a low-affinity antibody?

It binds the antigen weakly and tends to separate from it more easily.

What is avidity?

The overall strength of binding when a multivalent antibody binds to a multivalent antigen.

How is avidity different from affinity?

Affinity is the strength of one antigen-antibody interaction, while avidity is the combined strength of multiple interactions.

Why can avidity be more important than affinity in the body?

Naturally occurring antigens are often multivalent, meaning they have multiple binding sites.

Which antibody has greater avidity, IgM or IgG?

IgM has greater avidity than IgG.

Why does IgM have greater avidity than IgG?

IgM can make more antigen-antibody interactions at the same time, so its total binding strength is greater.

What are hypervariable regions?

Regions of an antibody that have different amino acid sequences and help determine what antigen the antibody can bind.

What usually happens to the hypervariable regions of two antibodies with different antigenic specificities?

They usually have different amino acid sequences.

Can two antibodies have different amino acid sequences but the same antigenic specificity?

Yes. Sometimes antibodies with different amino acid sequences can recognize the same antigen.

If two antibodies have the same specificity, will they necessarily have the same binding affinity?

No. Their binding affinities can be different.

Why can two antibodies that recognize the same epitope have different binding affinities?

They may have differences in the number and types of binding forces between the antibody and epitope.

What is an epitope?

The specific part of an antigen that an antibody binds to.