Cell Structures and Their Functions: Study Notes

Cell Structures and Their Functions

Course Objectives

This chapter focuses on understanding the structure and function of cells, including the plasma membrane, organelles, transport mechanisms, genetic material, and cell division. Mastery of these topics is essential for foundational knowledge in General Biology.

• Describe the structure and function of a cell

• Explain the plasma membrane's composition and function

• Identify and describe the functions of major cell organelles

• Understand transport mechanisms across the cell membrane

• Relate DNA and RNA structure to protein synthesis

• Describe the stages of mitosis and its role in cancer

Functions of the Cell

Overview of Cellular Functions

Cells are the basic units of life, performing essential functions necessary for the survival and reproduction of organisms.

• Basic unit of life: All living organisms are composed of cells.

• Synthesis of molecules: Cells produce proteins, lipids, nucleic acids, and carbohydrates.

• Communication: Cells communicate with each other via chemical and electrical signals.

• Cell metabolism and energy release: Cells carry out metabolic reactions to generate energy (e.g., ATP production).

• Reproduction and inheritance: Cells contain DNA, which is passed on during cell division.

Cell Structure

Organelles and Cytoplasm

Cells contain specialized structures called organelles, each with specific functions, suspended in a jelly-like substance called cytoplasm.

• Organelles: Specialized structures such as the nucleus, mitochondria, and ribosomes that perform distinct cellular functions.

• Cytoplasm: The semi-fluid matrix that holds organelles in place and allows for the movement of materials within the cell.

Cell Membrane

Structure and Function

The cell membrane, also known as the plasma membrane, is the outermost boundary of the cell, providing protection and regulating the movement of substances in and out of the cell.

• Selective barrier: Controls what enters and exits the cell.

• Encloses cytoplasm: Maintains the internal environment of the cell.

• Intracellular: Refers to materials inside the cell.

• Extracellular: Refers to materials outside the cell.

Structure of the Cell Membrane

The cell membrane is described by the Fluid Mosaic Model, consisting of a phospholipid bilayer with embedded molecules.

• Phospholipid bilayer: Double layer of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward.

• Cholesterol: Adds strength and stability to the membrane.

• Carbohydrates: Provide energy and serve as markers for cell recognition.

• Proteins: May span the membrane or be attached to its surface; function as channels, carriers, receptors, enzymes, and structural supports.

Phospholipid Structure

• Polar regions ("heads"): Hydrophilic (water-loving), exposed to water.

• Nonpolar regions ("tails"): Hydrophobic (water-fearing), oriented away from water.

Summary Table: Major Components of the Cell Membrane

Component	Structure	Function
Phospholipids	Bilayer with hydrophilic heads and hydrophobic tails	Forms the basic structure; barrier to most water-soluble substances
Cholesterol	Interspersed within the bilayer	Stabilizes membrane fluidity and integrity
Proteins	Integral (span membrane) or peripheral (surface)	Transport, signaling, enzymatic activity, structural support
Carbohydrates	Attached to proteins or lipids on extracellular surface	Cell recognition, adhesion, and signaling

Additional info:

• The Fluid Mosaic Model describes the dynamic and flexible nature of the cell membrane, where proteins and lipids can move laterally within the layer.