The correct answer is C. Twenty different amino acids exist in nature. Some proteins have a few dozen amino acids, while others have many thousands.

The correct answer is A. An organism’s DNA contains instructions for building all the proteins its body needs.

The correct answer is D. Hormones carry messages throughout the body. Antibodies help protect the body from foreign invaders, like bacteria and viruses. Transporters help vital substances enter and exit cells, and chaperones help other proteins fold into their proper shapes.

The correct answer is B. Enzymes speed up chemical reactions in the body by reducing the amount of energy needed for the reactions to proceed. Without enzymes, many of these reactions, such as those involved in breaking down food and replicating DNA, wouldn’t occur quickly enough to sustain life.

The correct answer is A. Amylase breaks down starch. Lactase is an enzyme that breaks down lactose, a sugar in milk. (The ending “-ase” often indicates that a molecule is an enzyme.) Hemoglobin and myosin are nonenzyme proteins that transport oxygen in the blood and help muscles move, respectively.

The correct answer is D. Folding is an important step in protein production because proteins’ shapes (structures) enable them to carry out their functions. Misshapen proteins can stop working and build up in tissues, causing disease.

The correct answer is B. Medicines typically work by either blocking or improving the activity of specific proteins in the body. Knowing the structures of these proteins can help scientists develop drugs that target the proteins. The NIGMS-supported Protein Data blank makes thousands of protein structures available online, and researchers developing medicines have used these structures to guide their work.

The correct answer is B. Scientists use CRISPR for gene, but all of the other tools can help reveal the structures of proteins.