The Cell: Structure, Function, and Membrane Transport

The Cell

Basic Processes of Cells

Cells are the fundamental units of life, carrying out essential processes to maintain homeostasis and support the organism.

• Cell Metabolism: The sum of all chemical reactions in a cell, including anabolic (building up), catabolic (breaking down), and oxidation-reduction reactions.

• Substance Transport: Movement of compounds into, out of, or within the cell.

• Communication: Cells interact with their environment and other cells via chemical and electrical signals.

• Cell Reproduction: Many cells divide to produce new cells, essential for growth and repair.

Overview of Cell Structure

Major Components of Animal Cells

Animal cells share several key structural components, each with specialized functions.

• Plasma Membrane: The outer boundary of the cell, controlling entry and exit of substances.

• Cytoplasm: The region between the plasma membrane and nucleus, containing:

  • Cytosol: Also called intracellular fluid (ICF), a watery gel with proteins, dissolved solutes, and RNA.

  • Organelles: Specialized structures performing specific cellular functions (e.g., mitochondria, endoplasmic reticulum).

  • Cytoskeleton: A network of protein filaments providing structural support, shape, and transport within the cell.

• Nucleus: Contains most of the cell's DNA and is surrounded by a nuclear envelope; site of RNA synthesis and genetic control.

Functions of the Plasma Membrane

The plasma membrane is a dynamic structure with multiple roles:

• Physically isolates the cell from its surroundings.

• Provides structural support and communication with other cells.

• Regulates transport of substances into and out of the cell.

• Identifies the cell to other cells.

It also defines fluid compartments:

• Intracellular Space: Contains cytosol (ICF).

• Extracellular Space: Contains extracellular fluid (ECF).

Components of the Cytoplasm

• Cytosol (ICF): Site of many metabolic reactions; may contain inclusions (storage bodies).

• Organelles: Compartmentalize and perform specific cellular functions.

• Cytoskeleton: Maintains cell shape, anchors organelles, and facilitates intracellular transport.

Nucleus

• Surrounded by a double membrane (nuclear envelope).

• Contains DNA and is the site of RNA synthesis.

• Controls cellular functions by coding for and synthesizing proteins.