Antibody Diagram Labeled

One Y-shaped antibody holding an antigen: 12 parts to name.

Antibody Diagram Labeled

Name Date

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1 2 3 4 5 6 7 8 9 10 11 12
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Write the name of each numbered part.Answer key

  1. Heavy chain
  2. Light chain
  3. Variable region
  4. Constant region
  5. Antigen-binding site (paratope)
  6. Fab region
  7. Fc region
  8. Hinge region
  9. Disulfide bonds
  10. Carbohydrate
  11. Antigen
  12. Epitope

Drawn for this site by script, 2026-09-26. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: the alveoli, close up

All 12 parts on the diagram

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Start here: 7 main parts 7

  1. Heavy chain The longer of the two kinds of polypeptide chain. Each antibody has two identical heavy chains; they differ between antibody classes.
  2. Light chain The shorter chain. Each antibody has two identical light chains. Each forms part of an antigen-binding site.
  3. Variable region The domains at the tip of each arm, one from each chain. Their amino acids vary most from antibody to antibody, which lets antibodies bind so many different antigens.
  4. Constant region The domains that vary little between antibodies of the same class. On the arms it lies below the variable region, and it makes up the whole stem.
  5. Antigen-binding site (paratope) Two identical sites that bind one particular epitope. They are at the ends of the arms, formed by heavy and light chain together.
  6. Fc region Crystallisable fragment: the stem, formed by the two heavy chains together. Many immune cells carry Fc receptors that grip it.
  7. Hinge region A flexible stretch of the heavy chains between arms and stem. It lets the arms bind epitopes at different distances apart.

Chains, regions and links: 8 3

  1. Fab region Antigen-binding fragment: one whole arm. It has a variable and a constant domain from each chain. An antibody has two.
  2. Disulfide bonds Link the two heavy chains at the hinge. They also link each light chain to its heavy chain.
  3. Carbohydrate Sugars (glycans) attached to the protein chains. Shown here between the two heavy chains of the stem. Antibodies are glycoproteins.

Binding an antigen: 4 2

  1. Antigen The foreign substance the antibody recognises, such as part of a pathogen.
  2. Epitope The specific part of an antigen that the antigen-binding site binds.

How this list was compiled: Read 2026-09-26. OpenStax Anatomy and Physiology 2e, section 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies, https://openstax.org/books/anatomy-and-physiology-2e/pages/21-4-the-adaptive-immune-response-b-lymphocytes-and-antibodies : antibodies as glycoproteins of heavy and light polypeptide chains with attached carbohydrates; two identical heavy and two identical light chains; classes differing mainly in their heavy chains; light chains forming part of the antigen-binding site; the Fc region formed by the two heavy chains, usually linked by disulfide bonds; Fc receptors on effector cells; two identical antigen-binding sites. Wikipedia, Antibody, https://en.wikipedia.org/wiki/Antibody : the paratope (antigen-binding site) binding an epitope; variable and constant domains of about 110 amino acids, VL and CL on the light chain, VH and three to four CH on the heavy chain; the two Fab fragments and the Fc trunk; the flexible hinge region letting antibodies bind epitopes at various distances; hypervariable regions in the variable domains; glycans on conserved residues. Licence: own work

The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work

How it works

Correctly label the anatomy of an antibody on one Y-shaped molecule: its four chains, the regions that span them, and the antigen held at one tip. Start with the 7 main parts.

Read the full guide

Chains and regions

Two identical heavy chains and two identical light chains make the Y. The regions cross them: each arm is a Fab region, the stem is the Fc region, and the variable region sits at each tip.

How it grips an antigen

Each arm ends in an antigen-binding site, built from one heavy and one light chain. It fits one epitope, a small part of the antigen. The hinge lets the two arms reach epitopes at different distances apart.

  • Heavy chains run the full length, stem and arms; light chains stay in the arms.

Questions and answers

How many chains does an antibody have?

Four: two identical heavy chains and two identical light chains, held together by disulfide bonds. Some antibodies join several of these units together.

What is the difference between the Fab and Fc regions?

Fab regions are the two arms, which bind antigen. The Fc region is the stem, made of the two heavy chains, which immune cells grip with their Fc receptors.

Why is it called the variable region?

Its amino acids vary most from one antibody to the next. That variety lets the immune system recognise millions of different antigens.

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