Hoefnagels_Essentials4e_ch03_lecturePPT_Accessible

Cells as the Units of Life

• A cell is the smallest unit of life capable of independent function.

• All living organisms are composed of one or more cells.

• Biochemical processes occur inside cells to sustain life.

Microscopy: Tools for Observation

Light Microscopes

• Used to observe whole cells.

• Limitations on magnification compared to electron microscopes.

Electron Microscopes

• Transmission Electron Microscope (TEM): Views internal cell structures by transmitting electrons through cells.

• Scanning Electron Microscope (SEM): Examines cell surfaces by bouncing electrons off them.

• Confocal light microscopes increase resolution by focusing light on a small area, often using fluorescent dyes for clarity.

Size and Diversity of Cells

• Cells vary significantly in size:

  • Bacteria and archaea: Approximately 10x smaller than most plant and animal cells.

  • Frog eggs: About 10x larger than typical plant and animal cells.

• All cells possess common structural features: genetic material, ribosomes, cytoplasm, and a cell membrane.

• Smaller cells have a higher surface area-to-volume ratio, facilitating more efficient material exchange.

Classification of Life: Three Domains

Prokaryotes

• Includes bacteria and archaea.

• Small and simple structure, lacking a nucleus.

Eukaryotes

• Larger and more complex, possessing a nucleus and membrane-bound organelles.

• Includes protists, fungi, plants, and animals.

Anatomy of Different Cell Types

Bacterial Cells

• Prokaryotic, lack membrane-bound organelles.

• Ribosomes and DNA are free in the cytoplasm.

Animal Cells

• Eukaryotic, contain numerous membrane-bound organelles.

Plant Cells

• Similar to animal cells but also possess a large central vacuole, cell wall, and chloroplasts.

Cell Membranes

Structure and Function

• Composed of phospholipids:

  • Amphipathic molecules: Hydrophilic head (polar) and hydrophobic tails (nonpolar).

• Phospholipids form a bilayer when in water, creating a selectively permeable barrier.

• Membrane proteins serve various functions, including transport and communication.

Cell Wall in Plant Cells

• Composed of cellulose fibers, providing structure, regulating cell volume, and preventing cell lysis.

Eukaryotic Organelles and Functions

Nucleus

• Contains DNA and synthesizes ribosomes within the nucleolus.

• Responsible for protein production by exporting mRNA to ribosomes.

Ribosomes

• Sites of protein synthesis; can be free in the cytoplasm or associated with the rough endoplasmic reticulum (rER).

Endomembrane System

• Comprises the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and cell membrane.

• Coordinates the processing, modification, and secretion of proteins.

Energy Harvesting in Eukaryotic Cells

Mitochondria

• Sites for cellular respiration, converting food energy into usable cellular energy.

Chloroplasts

• Found in photosynthetic organisms, converting sunlight into chemical energy stored in sugars.

Cytoskeleton

• Network of protein structures that provide cellular support and facilitate movement, transport, and division.

• Includes microfilaments, intermediate filaments, and microtubules.

Cell Communication

• Animal Cells:

  • Use junctions (tight, anchoring, gap) to facilitate communication and structural integrity.

• Plant Cells:

  • Utilize plasmodesmata to transport nutrients and chemical signals between cells.

Specialization of Cells

• Multicellular organisms have specialized cell types to perform distinct functions (e.g., muscle cells, nerve cells).

• Specialized cells adapt to specific roles,