Topic: Non Enzymatic Protein Function

Proteins can play a wide array of roles in a cell or organism, such as non-enzymatic functions like binding.

Proteins can bind to a wide array of biomolecules with specificity. Non-enzymatic proteins are proteins that carry out functions that require the capacity to bind, but do not necessarily catalyze a reaction like enzymes. There are several different binding proteins that exist in the membrane of a cell and function as receptors or ion channels.

Receptors bind to signaling molecules to bring about changes in the biochemistry of a cell or causing the expression of chemicals. For example, insulin binds to receptors on cells and causes them to take in glucose molecules. The affinity of a ligand and a receptor is measured by a dissociation constant, Kd – this represents the concentration of ligand that is required for 50% binding. Lower Kds indicate stronger affinity. This is particularly important with transport proteins and receptors where high-affinity proteins tend to exist for low concentration receptors due to the scarcity of the ligand, the protein will have a high affinity for the ligand and thus a lower Kd.

Ion channels span the entire bilayer of the membrane allowing the passage of ions from one side of the membrane to the other. They have an aqueous pore, which becomes accessible to ions after a conformational change in the protein structure that causes the ion channel to open.

Practice Questions

 

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Key Points

• Non-enzymatic proteins are proteins that carry out functions that require the capacity to bind, but do not necessarily catalyze a reaction like enzymes.

• Receptors bind to signaling molecules to bring about changes in the biochemistry of a cell or causing the expression of chemicals. Affinity of ligands and receptors is measured by a dissociation constant, Kd. High affinity of a protein often indicates a low concentration of the respective ligand.

• Ion channels span the entire bilayer of the membrane allowing the passage of ions from one side of the membrane to the other.


Key Terms

Ligand: a molecule (such as a small peptide or drug molecule) that binds a receptor

Myosin: motor proteins in muscle contraction

Non-enzymatic protein: proteins that carry out functions that require the capacity to bind, but do not necessarily catalyze a reaction

Enzymes: a substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction

Receptors: special structures made of glycoproteins that can be found in cell membrane and bind to specialized molecules

Kd: dissociation constant, the concentration of ligand needed for 50% binding

Ion Channels: protein molecules that span across the cell membrane allowing the passage of ions from one side of the membrane to the other



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