Cell Structure and Function

What is a Cell?

A cell is the basic structural, functional, and biological unit of all living organisms. Cells are often called the "building blocks of life" because all living things are composed of one or more cells. Cells carry out essential processes such as metabolism, energy conversion, and reproduction.

Prokaryotic vs. Eukaryotic Cells

Cells are classified into two main types: prokaryotic and eukaryotic. Prokaryotic cells (e.g., bacteria) lack a nucleus and membrane-bound organelles, while eukaryotic cells (e.g., animal and plant cells) have a nucleus and various organelles.

Common Cell Structures in Prokaryotes and Eukaryotes

• Plasma Membrane: A phospholipid bilayer that surrounds the cell, controlling the movement of substances in and out.

• Cytoplasm: The jelly-like substance inside the cell where cellular processes occur.

• Ribosomes: Small complexes that synthesize proteins by translating messenger RNA.

• DNA (Genetic Material): Contains the instructions for cell function and replication. In prokaryotes, DNA is found in the nucleoid region; in eukaryotes, it is enclosed in the nucleus.

Prokaryotic Cell Structure and Function

Prokaryotic cells have several specialized structures. Below is a table summarizing the main components and their functions:

Animal vs. Plant Cells

Features Unique to Animal Cells

• Lysosomes: Organelles containing digestive enzymes to break down waste.

• Centrioles: Structures involved in cell division.

Features Unique to Plant Cells

• Cell Wall: Rigid outer layer providing structural support.

• Chloroplasts: Organelles where photosynthesis occurs.

• Large Central Vacuole: Stores water, nutrients, and waste products.

Nucleus and Its Components

The nucleus is the control center of eukaryotic cells, housing genetic material and coordinating activities like growth and reproduction.

• Nucleus: Contains DNA and directs cell activities.

• Nuclear Envelope: Double membrane that surrounds the nucleus.

• Nuclear Pore: Openings in the envelope allowing transport of molecules.

• Nucleolus: Site of ribosome synthesis.

• Chromatin: DNA and protein complex; condenses to form chromosomes during cell division.

Ribosomes

• Function: Ribosomes synthesize proteins by translating mRNA.

• Free Ribosomes: Float in cytoplasm; produce proteins for use within the cell.

• Bound Ribosomes: Attached to the endoplasmic reticulum; produce proteins for export or for use in membranes.

Endomembrane System

The endomembrane system is a group of organelles that work together to modify, package, and transport lipids and proteins.

• Endoplasmic Reticulum (ER): Network of membranes; rough ER has ribosomes and synthesizes proteins, smooth ER synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Transport Vesicles: Small sacs that move molecules between organelles.

• Lysosomes: Contain digestive enzymes to break down macromolecules.

Route of a Secreted Protein

• Protein is synthesized in the rough ER.

• Transported in vesicles to the Golgi apparatus for modification.

• Packed into secretory vesicles and released from the cell via exocytosis.

Mitochondria and Chloroplasts

• Mitochondria: Site of cellular respiration; converts glucose and oxygen into ATP (energy).

• Chloroplasts: Site of photosynthesis; converts light energy into chemical energy (glucose).

• Evolutionary Origin: Both organelles are thought to have originated from free-living bacteria via endosymbiosis.

Cytoskeleton

The cytoskeleton is a network of protein fibers that provides structural support, organizes cell contents, and enables movement.

• Microtubules: Involved in cell shape, transport, and division (e.g., spindle fibers).

• Microfilaments: Involved in cell movement and muscle contraction.

• Intermediate Filaments: Provide mechanical strength to cells.

Cell Wall, Extracellular Matrix, and Cell Junctions

Eukaryotic Cell Structure and Function

Eukaryotic cells contain many specialized organelles. Below is a summary table of key components:

Additional info: Some details, such as the specific labeling of cell diagrams, were inferred based on standard textbook conventions and the provided word banks.