Protein function

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Enzymes catalyze the biochemical reactions that occur in cells by lowering the activation energy necessary to transform a reactant into a product.

Kinases add phosphate groups to proteins (phosphorylates proteins)

Phosphatases are required to remove these phosphate groups (dephosphorylates proteins)

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How Do Proteins Provide Structural Support for Cells?

Microtubules play a major role in organizing the cytoplasm and in the distribution of organelles. They also form the mitotic spindle during cell division.

Actin filaments are involved in various forms of cell movement, including cell locomotion, contraction of muscle cells, and cell division.

Intermediate filaments are strong fibers that serve as architectural supports inside cells.

In the enzyme-catalyzed reaction, the enzyme binds to the reactant and facilitates its transformation into a product. Consequently, the enzyme-catalyzed reaction pathway has a smaller energy barrier (activation energy) to overcome before the reaction can proceed.

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What Do Proteins Do in the Plasma Membrane?

Plasma membrane proteins help the cell interact with its environment

Transporters carry a molecule (such as glucose) from one side of the plasma membrane to the other = ferrying nutrients across the plasma membrane

Receptors can bind an extracellular molecule (triangle), and this activates an intracellular process = receiving chemical signals from outside the cell, translating chemical signals into intracellular action

Enzymes in the membrane can do the same thing they do in the cytoplasm of a cell = transform a molecule into another form.

Anchor proteins can physically link intracellular structures with extracellular structures = anchoring the cell in a particular location

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patches of hydrophilic amino acids on the surfaces that extend into the water-based cytoplasm

patches of hydrophobic amino acids where the proteins contact lipids in the membrane bilayer

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big or small

mostly hydrophilic or mostly hydrophobic

exist alone or as part of a multi-unit structure

change shape frequently or remain virtually immobile