Cell Structure and Function: Foundations of Anatomy & Physiology

Cells: The Basic Unit of Life

Introduction to Cells

Cells are the fundamental structural and functional units of all living organisms. Understanding the properties and organization of cells is essential for grasping the principles of anatomy and physiology.

• Definition: A cell is the smallest unit of life, capable of performing all vital physiological functions.

• Organismal Activity: The activities of an organism depend on the individual and collective actions of its cells.

• Biochemical Activities: The biochemical functions of cells are determined by their subcellular structures (organelles).

• Continuity of Life: Life is perpetuated through cellular reproduction and inheritance.

Cell Structure

Three Main Parts of a Cell

All eukaryotic cells share three primary structural components:

• Plasma Membrane: The outer boundary that separates the cell from its environment.

• Cytoplasm: The material between the plasma membrane and the nucleus, containing cytosol and organelles.

• Nucleus: The control center housing genetic material (DNA).

Cytoplasm

• Cytosol: The fluid portion of the cytoplasm, primarily water with dissolved proteins, salts, sugars, and other solutes.

• Cytoplasmic Organelles: Specialized structures within the cytoplasm that perform distinct metabolic functions.

Plasma Membrane Structure and Function

Overview

The plasma membrane is a selectively permeable barrier that separates intracellular fluids from extracellular fluids and plays a dynamic role in cellular activity.

• Thickness: Approximately 7–10 nm.

• Composition: Phospholipid bilayer with associated proteins.

Membrane Proteins

• Integral Proteins: Embedded within the membrane; transmembrane proteins span the entire width and are involved in transport and signaling.

• Peripheral Proteins: Loosely attached to integral proteins; often function in signaling or maintaining cell shape.

• Glycocalyx: A biological marker composed of glycoproteins and glycolipids, important for cell recognition and interaction.

Membrane Lipids

• Phospholipids: Form the basic structure of the bilayer, with hydrophilic heads facing outward and hydrophobic tails inward.

• Glycolipids: Lipids with attached sugars, contributing to cell signaling and recognition.

• Cholesterol: Interspersed within the bilayer, stabilizing membrane fluidity and integrity.

Diagram: Plasma Membrane Components

The plasma membrane consists of a double layer of phospholipids with embedded proteins, cholesterol, and carbohydrates. Integral proteins span the membrane, while peripheral proteins are attached to its surface. The glycocalyx forms a carbohydrate-rich area on the cell's exterior.

Summary Table: Major Components of the Plasma Membrane

Component	Structure	Function
Phospholipid Bilayer	Double layer of phospholipids	Barrier; separates intracellular and extracellular environments
Integral Proteins	Embedded; may span membrane	Transport, signaling, cell adhesion
Peripheral Proteins	Attached to membrane surface	Support, signaling, enzymatic activity
Glycolipids/Glycoproteins	Lipids/proteins with carbohydrate chains	Cell recognition, signaling
Cholesterol	Interspersed within bilayer	Stabilizes membrane, regulates fluidity

Key Terms and Concepts

• Selective Permeability: The plasma membrane allows certain substances to pass while restricting others.

• Fluid Mosaic Model: Describes the dynamic arrangement of lipids and proteins in the membrane.

• Cell Signaling: Membrane proteins and glycolipids play crucial roles in communication between cells.

Example: Red Blood Cells

Red blood cells (erythrocytes) have a plasma membrane rich in glycolipids and proteins that determine blood type and facilitate oxygen transport.

Additional info: The study notes above expand on the provided slides and images, adding definitions, examples, and a summary table for clarity and completeness.