Foundations of Biology Exam 1 Practice Test 2026 - Free Biology Practice Questions and Study Guide

Integrins are transmembrane receptors that span the cell membrane and connect the extracellular environment to the cell’s interior. Outside the cell, they bind extracellular matrix proteins such as collagen, helping cells adhere to their surroundings. Inside the cell, their cytoplasmic tails link to the actin cytoskeleton through adaptor proteins, forming a bridge that supports cell shape and movement and also transmits signals that influence cellular behavior. They are not enzymes, not lipids making up the membrane, and not purely cytosolic scaffolding proteins—their defining role is linking collagen-containing matrix to the cytoskeleton across the membrane.