Cell Types and Organelles

Cell Types

Prokaryotic Cells

• Primitive, simple cells.

• Key Characteristics:

  • Lack a nucleus and membrane-bound organelles.

  • Absence of internal membranes.

  • All Prokaryotic cells belong to the Kingdom Monera (e.g., bacteria).

• Reactions occur throughout the cytoplasm, leading to less efficiency.

Components of Prokaryotic Cells:

• Capsule

• Cell wall

• Plasma membrane

• Cytoplasm

• Ribosomes

• Plasmid

• Pili

• Bacterial Flagellum

• Nucleoid (containing circular DNA)

Eukaryotic Cells

• Complex cells with a defined nucleus and membrane-bound organelles.

• Key Characteristics:

  • Contain internal membranes.

  • Organelles specialize in specific functions.

  • Present in Kingdoms: Plants, Animals, Protists, and Fungi.

Components of Eukaryotic Cells:

• Cell structures include:

  • Nucleus

  • Plasma membrane

  • Endoplasmic reticula (smooth and rough)

  • Golgi apparatus

  • Lysosomes

  • Mitochondrion

  • Cytoplasm (Cytosol and organelles)

  • Other structures (e.g., intermediate filaments, vacuoles, ribosomes)

Nucleus

• The largest organelle, encased in a double-layered membrane known as the nuclear envelope.

• Features:

  • Contains pores for the passage of larger molecules.

  • Functions as the control center for cellular functions.

  • Houses nucleoplasm and chromatin.

• Chromatin

  • Hereditary material that condenses to form chromosomes in cell division.

  • Composed of DNA and histone proteins.

Nucleolus

• Dark region within the nucleoplasm, where ribosomal RNA (rRNA) is produced.

• Site for ribosome assembly and important in nucleus-cytoplasm interactions.

Chromosomes

• Rod-shaped bodies visible during cell division, containing genetic information (genes).

• Formed from condensed chromatin.

• In humans, there are 23 pairs (total 46 chromosomes).

Cytoplasm

• A colloidal substance supporting organelles.

• Properties:

  • State can change, adapting to heat and metabolic activity.

Cell Membrane or Plasma Membrane

• Composed of proteins and phospholipids, acting as a selective barrier.

• Functions include:

  • Regulating material movement in/out of the cell.

  • Providing structural support.

  • Different membrane types (single-layered around lysosomes, double-layered around nucleus and mitochondria).

Fluid Mosaic Model

• Describes the structure of the plasma membrane:

  • Hydrophilic phosphate heads and hydrophobic fatty acid tails.

  • Includes integral proteins, carbohydrates, and phospholipid bilayer.

Smooth Endoplasmic Reticulum (SER)

• Structure: Interconnected flattened tubes and sacs, extending from the nuclear envelope.

• Functions:

  • Transports molecules throughout the cell.

  • Site of phospholipid and steroid synthesis.

  • Abundant in cells that produce steroid hormones.

  • Can form vesicles for transporting proteins/lipids.

Rough Endoplasmic Reticulum (RER)

• Similar to SER but with ribosomes attached.

• Functions:

  • Primarily responsible for producing proteins for export.

Endomembrane System

• A collective of structures (Nuclear Envelope, E.R., Cell Membrane, Golgi Apparatus) coordinating cellular processes.