A Level Biology Practice Exam 2025 – All-in-One Study Guide to Excel in Your A Levels!

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What best describes proteins?

Chains of nucleotides

Complex macromolecules made of polypeptides

Proteins are best described as complex macromolecules made of polypeptides, which are themselves long chains of amino acids linked by peptide bonds. These polypeptide chains fold into specific three-dimensional shapes that determine the protein's function. Proteins play critical roles in biological systems, acting as enzymes, structural components, signaling molecules, and more. Their complex structure and diversity allow them to perform a wide variety of functions essential for life.

The other descriptions do not accurately represent proteins. Nucleotides are the building blocks of nucleic acids like DNA and RNA, while single units of amino acids or simple sugars and lipids do not capture the intricate structure and function of proteins. Each protein is a unique sequence of amino acids that contributes to its specific role within cells and organisms.

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Single units of amino acids

Simple sugars and lipids

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