Chapter_4_Cell_Structures

Cellular Structures

Cells

• Cells are divided into two groups:

  1. Prokaryotic

  2. Eukaryotic

• All cells share four components:

  1. Plasma membrane

  2. Cytoplasm

  3. DNA

  4. Ribosomes

Domains of Life

• Domain: Eukarya

  • PLANTAE (Multicellular, eukaryotic)

  • ANIMALIA (Multicellular, eukaryotic)

  • FUNGI (Multicellular, eukaryotic)

  • PROTISTA (Eukaryotic, unicellular and multicellular)

• Domain: Bacteria

  • EUBACTERIA (Unicellular, prokaryotic)

• Domain: Archaea

  • ARCHAEBACTERIA (Unicellular, prokaryotic)

Prokaryotic Cells

Prokaryotic Cell Characteristics

• Prokaryotic cells have distinct structural components:

  • Capsule

  • Cell wall

  • Plasma membrane

  • Cytoplasm

  • Nucleoid region (DNA)

  • Ribosomes

• Exterior structures:

  • Pilus

  • Flagella

Differences Between Prokaryotic and Eukaryotic Cells

1. Prokaryotic cells lack a true nucleus and membrane-bound organelles.

   • Instead, they have a nucleoid region.

2. Prokaryotic cells are generally much smaller in size (0.1-5 µm) compared to eukaryotic cells (10-100 µm).

3. Prokaryotic cells reproduce asexually primarily through binary fission.

Size Comparison

• Prokaryotic cells: Typically range from 1 - 10 µm.

• Eukaryotic cells: Typically range from 10 - 100 µm.

• Example: Human red blood cell is about 8 µm in diameter; approximately 250 can fit on the head of a pin.

Reproduction and Division of Prokaryotic Cells

• Asexual reproduction mainly occurs via binary fission.

• Prokaryotic cells are limited in size due to surface area-to-volume ratio constraints.

Eukaryotic Cells

Learning Objectives

• Identify and describe structures of eukaryotic plant and animal cells.

• Summarize functions of major cell organelles.

• Understand member functions of the endomembrane system.

• Describe the cytoskeleton and extracellular matrix.

• Label diagrams of plant and animal cells.

Key Terms

• Phospholipid bilayer

• Cytoplasm

• Nuclear envelope

• Cytoskeleton

• Microfilaments, Intermediate filaments, Microtubules

• Endomembrane system

• Nucleus, Ribosomes

• Golgi apparatus, Lysosomes

• Chloroplast, Vacuoles, Peroxisomes

Eukaryotic Cell Structure

• Nucleus:

  • Houses DNA in the form of chromatin.

  • Directs protein synthesis and ribosomal RNA synthesis in nucleolus.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; modifies and packages proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids, detoxifies, stores calcium.

• Ribosomes:

  • Comprised of large and small subunits.

  • Sites of protein synthesis; can be free in cytoplasm or attached to ER.

• Golgi Apparatus:

  • Modifies, sorts, and packages proteins and lipids for transport.

• Lysosomes:

  • Enzyme-filled organelles that digest macromolecules and recycle organelles.

• Vesicles and Vacuoles:

  • Membrane-bound sacs for storage and transport; vacuoles are larger than vesicles.

• Cytoskeleton:

  • Network of protein fibers: microfilaments, intermediate filaments, and microtubules.

  • Functions in cell shape, movement, and transport within the cell.

• Mitochondria:

  • Energy-producing organelles; site of ATP production; contain own DNA and ribosomes.

• Chloroplasts:

  • Involved in photosynthesis; contain their own DNA and ribosomes.

Unique Features of Plant Cells

• Cell Wall:

  • Rigid outer layer providing protection, structural support, and shape.

• Chloroplasts:

  • Site of photosynthesis; convert CO2 and water into glucose and O2.

• Vacuole:

  • Large central vacuole maintains turgor pressure and regulates water concentration.

Origin of Eukaryotes

• Theory of Endosymbiosis:

  • Proposes that mitochondria and chloroplasts originated from free-living prokaryotes.

  • Suggests that eukaryotic cells evolved from an amoeba-like ancestor that developed infoldings for a nucleus and engulfs prokaryotes.

Evidence Supporting Endosymbiosis

• Chloroplasts and mitochondria share traits with prokaryotes:

  • Similar in size, replicate by binary fission, double-membrane structures, circular DNA, and prokaryotic ribosomes.