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1.4.1Unit 1 — Cell Biology

Protein Structure and Function

5 min read 4 parts Lesson 16 of 28

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Section 1 of 4Protein Structure

1.4.1 Protein Structure and Function
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Proteins are built from smaller units called amino acids joined together in a long chain.
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The order of amino acids in the chain is unique to each protein and is decided by the code in a gene.
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The chain then folds, forming bonds between different amino acids that hold it in a particular three-dimensional shape.
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The final shape allows the protein to do a specific job, and a different shape would give it a different function.
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Changing even one amino acid in the sequence can alter the folding and may stop the protein working properly.

Section 2 of 4Functions of Proteins

Proteins are the most varied group of biological molecules, with each type having its own shape.

Structural
  • Proteins such as those in tendons, ligaments and skin give strength and support to the body.
Enzymes
  • Enzymes such as amylase and pepsin are biological catalysts that speed up chemical reactions.
Hormones
  • Hormones such as insulin travel in the blood and carry chemical messages to target cells.
Antibodies
  • Antibodies recognise pathogens and help the immune system to destroy them.
Receptors
  • Receptor proteins in cell membranes bind signal molecules such as hormones so that the cell can respond.

Section 3 of 4Shape Equals Function

Shape Equals Function
Specific shape
  • A hormone receptor has a shape that fits only one hormone, so cells respond only to the correct signal.
Enzyme shape
  • An enzyme has a pocket that fits just one substrate, which is why enzymes are specific.
Damage
  • Heat or extreme pH can change a protein's shape, which stops it carrying out its function.

Section 4 of 4Exam Checklist & Tips

1.4.1 – Key Points for the Exam

  • Protein A molecule made of amino acids folded into a specific shape.
  • Amino acid A small molecule that is the building block of proteins.
  • Enzyme A protein that acts as a biological catalyst.
  • Antibody A protein that recognises and helps to destroy a specific pathogen.
  • Hormone A chemical messenger, sometimes a protein, carried in the blood.

Common Mistakes

  • Saying that all proteins are enzymes; enzymes are only one group of proteins.
  • Forgetting that the folded shape, not just the amino acid order, decides function.
  • Writing that the protein sequence is decided by the cell membrane; it is decided by the gene.
  • Thinking that proteins are made of fatty acids; they are made of amino acids.
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