Protein — Science definition

A macromolecule made of amino acids that does most of the cell's work; its monomer is an amino acid.

Where it is taught

In use

Digestion breaks food molecules into smaller components that can be absorbed; it does not simply transfer an intact food protein into a human muscle.

Carbon & the Macromolecules of Life

Questions using protein

Problem 1

The monomer (building block) of a protein is a(n)
  1. monosaccharide
  2. fatty acid
  3. amino acid
  4. nucleotide
Answer and explanation

amino acid

Proteins are polymers of amino acids; there are 20 kinds that cells string together in different orders.

Problem 2

Explain the phrase 'a protein's shape determines its function,' and connect it to why proteins can act as enzymes.
Answer and explanation

A protein's chain of amino acids folds into a specific 3-D shape, and that shape decides which molecules it can fit and interact with. Enzymes depend on this because their folded shape forms an active site that fits one specific substrate — change the shape and the enzyme can no longer do its job.

Problem 3

Protein function depends on sequence, folding and contextProtein function depends on sequence, folding and contextSequenceFolded structureInteractions depend on conditionsSequence → interactions / folding → possible function
Original symbolic amino-acid sequence and folded-chain model. It illustrates an explanatory relationship, not a solved structure of a named protein.
Interpret the supplied visual. Does an unfolded protein necessarily have a newly rewritten amino-acid sequence?
Answer and explanation

No. Its interactions and folding may change while much of the covalent chain sequence remains; hydrolysis and denaturation are different processes.

A protein consists of one or more folded polypeptides, chains of amino acids joined by peptide bonds. Each amino acid has a side group whose interactions influence folding. A different sequence can change a binding site, stability or location, but some sequence changes have little detectable effect. Denaturation disrupts an important folded arrangement; it is not the same as cutting every peptide bond. Enzymes, structural components, receptors and transporters are protein roles. A correct explanation connects a particular structural change to a tested function rather than saying all proteins behave alike.

No. Its interactions and folding may change while much of the covalent chain sequence remains; hydrolysis and denaturation are different processes.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 4

Carbohydrate and protein each release about 17 kJ per gram, while fat releases about 38 kJ per gram. How many kilojoules does 5.0 g of fat release?
Answer and explanation

190 kJ

5.0 g × 38 kJ/g = 190 kJ, roughly twice what the same mass of carbohydrate would release.

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