The Cell: Types, Functions, and Organelles

Introduction to Cells

• Cells are the smallest living organisms and the basic unit of life.
• Human body consists of trillions of cells.
• Cells have three main parts:
  • Membrane
  • Nucleus
  • Cytoplasm
• They function independently, creating energy and self-replicating.
• Cells communicate to form tissues, organs, and organisms.

Discovery of Cells

• Discovered by Robert Hooke in the 1600s.
• Named after their resemblance to monks' small rooms.

Types of Cells

• Diverse in size, structure, and function.
• Examples:
  • Sperm cell: Tadpole-like
  • Female egg cell: Spherical
  • Nerve cells: Thin tubes

Common Cell Structures (Organelles)

Nucleus

• Acts as cell headquarters, typically one per cell.
• Contains most of the DNA; mitochondria house some.
• Sends messages for growth, division, or death.
• Separated by the nuclear envelope; nuclear pores allow material exchange.

Plasma Membrane

• Envelops the cell, made mostly of phospholipids.
• Functions of receptors:
  • Gatekeepers: Allow/block molecules
  • Markers: Identify cells to immune system
  • Communicators: Facilitate cell communication
  • Fasteners: Bind cells to neighbors

Cytoplasm

• Interior of the cell, surrounds the nucleus.
• Contains organelles and cytosol.
• Site of important cellular reactions.

Cytoskeleton

• Provides structural support and flexibility.
• Involved in cell division and motility.
• Assists in cell signaling and material movement.

Endoplasmic Reticulum (ER)

• Processes and transports molecules.
• Synthesizes, folds, modifies, and transports proteins.
• Consists of rough and smooth ER.

Golgi Apparatus

• Receives processed molecules from ER.
• Functions like the cell's post office for packaging and labeling.

Mitochondria

• Known as the powerhouses of the cell.
• Convert food energy into adenosine triphosphate (ATP).
• Roles in calcium storage and cell death.

Ribosomes

• Translate RNA into proteins.
• Float freely or attach to the ER.

Cell Division

• Necessary for growth and repair.
• Two types: Mitosis and Meiosis.

Mitosis

• Common cell division method.
• Results in two identical diploid daughter cells.

Meiosis

• Produces sperm and egg cells.
• Involves the production of haploid cells with 23 chromosomes.

Selected Human Cell Types

Stem Cells

• Undifferentiated cells that can become specific cell types.
• Found in embryos and some adult tissues.

Bone Cells

• Consist of osteoclasts (dissolve bone), osteoblasts (form bone), and osteocytes (communicate with other bone cells).

Blood Cells

• Include red blood cells (oxygen transport), white blood cells (immune response), platelets (clotting).

Muscle Cells (Myocytes)

• Long tubular cells involved in movement and support.

Sperm Cells

• Motile, smallest human cells, haploid.

Female Egg Cells

• Largest human cells, haploid, combine with sperm during fertilization.

Fat Cells (Adipocytes)

• Store triglycerides for energy, produce hormones.

Nerve Cells (Neurons)

• Form communication system with axons and dendrites.
• Central body contains nucleus and organelles.

Conclusion

• Cells function both autonomously and as part of the larger network forming tissues and organs.