Proteins
Laura Armstrong
Teacher
Contents
Introduction to Proteins
Proteins are essential biological macromolecules composed of amino acids. They perform a vast array of functions within organisms, including structural support, catalysing biochemical reactions (enzymes), immune response (antibodies), and transport across membranes (transport proteins). The structure and function of a protein are determined by the sequence and folding of its amino acids.
Recall Questions
This topic requires prior knowledge of proteins from GCSE. You can test your knowledge on these below.
What are the monomers of proteins?
Amino acids.
What type of bond holds amino acids together in a protein?
Peptide bonds.
What determines the shape and function of a protein?
The sequence of amino acids and how the protein folds into its tertiary structure.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains proteins or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Structure of Proteins
- Proteins are made from amino acids with the elements carbon, hydrogen, oxygen, nitrogen and sulphur (note - only two amino acids contain sulphur).
- Proteins are polymers made from many amino acids.
- Primary Structure – The sequence of amino acids in a polypeptide chain held together by peptide bonds. These peptide bonds are made in condensation reactions.
- Secondary Structure – Hydrogen bonding forms α-helices and β-pleated sheets.
- Tertiary Structure – Further folding into a specific 3D shape due to interactions including hydrogen bonds, ionic bonds, and disulfide bonds.
- Quaternary Structure – Multiple polypeptide chains joined together, e.g., haemoglobin has 4 polypeptide chains.
Properties of Proteins
- Diverse Functions – Structural, enzymatic, transport, and signalling roles.
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Solubility – Some proteins (e.g., enzymes) are soluble, while others (e.g., structural proteins like collagen) are insoluble.
- Denaturation – High temperature or extreme pH can alter protein structure, affecting function.
Function of Proteins
- Enzymes – Biological catalysts (e.g., amylase, DNA polymerase).
- Structural Proteins – Provide support (e.g., collagen in connective tissues, keratin in hair and nails).
- Transport Proteins – Move substances across membranes (e.g., channel and carrier proteins). Haemoglobin transports oxygen in the blood,
- Hormones – Chemical messengers (e.g., insulin, glucagon).
- Antibodies – Part of the immune response, recognizing and neutralizing pathogens.
Key Terms
- Protein: A macromolecule composed of amino acids that performs various biological functions.
- Amino Acid: The monomer unit of proteins.
- Peptide Bond: A covalent bond that links amino acids together in a protein.
- Enzyme: A biological catalyst that speeds up chemical reactions.
- Denaturation: Loss of a protein's 3D shape due to temperature or pH changes.
- Quaternary Structure: A protein structure consisting of multiple polypeptide chains.
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Exam Tip
When describing proteins, always relate structure to function. Examiners look for explanations on how the tertiary structure determines enzyme active sites or how quaternary structures enable proteins to perform complex functions (e.g., haemoglobin carrying oxygen).
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Describe how the structure of a protein is related to its function. (4 marks)
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Primary structure determines the sequence of amino acids and thus the protein's properties. (1)
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Secondary structure forms α-helices or β-pleated sheets through hydrogen bonding. (1)
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Tertiary structure determines the 3D shape of the protein, held together by hydrogen, ionic and disulphide bonds. (1)
- Quaternary structure allows proteins to function as multi-polypeptide complexes, such as hemoglobin. (1)
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!