Avidity facts for kids
In biochemistry, avidity is about how strong a connection is when many small connections work together. Think of it like many tiny magnets holding two things together. Even if one magnet is weak, having lots of them makes the overall hold very strong.
This is different from affinity, which describes the strength of just one single connection. Avidity isn't just adding up the strengths of individual connections. It's about how these connections help each other, making the overall bond much stronger than you might expect.
How Antibodies Grab Hold
Avidity is often used to explain how antibodies work. Antibodies are like tiny defenders in your body. They have multiple "arms" that can grab onto harmful things, like antigens (parts of viruses or bacteria).
Imagine an antibody with several arms. Each arm might only hold onto an antigen weakly. But because the antibody has many arms, if one arm lets go, the others are still holding on. This keeps the antibody from floating away. The loose arm can then quickly grab hold again. This teamwork makes the overall connection very strong.
Each antibody has at least two places that can bind to an antigen. Some antibodies have many more. For example, IgM antibodies have 10 binding sites. This means they have very high avidity, even if each single binding site isn't super strong. Other antibodies, like IgG, IgE, and IgD, usually have two stronger binding sites.
What is Affinity?
Binding affinity measures the strength of a single connection. It looks at how quickly two things connect (on-rate) and how quickly they separate (off-rate).
Think of it like a puzzle piece fitting into another. Affinity tells you how well one specific piece fits into its spot. The stronger the affinity, the tighter the fit.
This strength is measured by something called the affinity constant (Ka). It's the opposite of the dissociation constant (Kd).
Scientists use different ways to measure affinity. They store these measurements in public databases like the Ki Database and BindingDB.
For example, affinity describes how strongly a part of an antigen, called an epitope, connects to a specific spot on an antibody, called a paratope. This connection involves different types of weak forces, like hydrogen bonds and hydrophobic forces.
Why Avidity Matters
Avidity tests are very useful in medicine. They help doctors figure out if someone has a new infection or an old one.
For example, avidity tests are used for viruses like rubella virus, cytomegalovirus (CMV), HIV, and hepatitis viruses. They look at the avidity of specific IgG antibodies.
If the antibodies have low avidity, it often means the infection is new. If they have high avidity, it suggests the infection happened a while ago. This helps doctors make better decisions about treatment.
There are two main types of avidity tests: the traditional chaotropic assay and the newer AVIcomp assay.
See also
In Spanish: Avidez para niños
- Amino acid residue
- Epitope
- Fab region
- Hapten
A number of technologies exist to characterise the avidity of molecular interactions including switchSENSE and surface plasmon resonance.
