Biology Chapter 1: The Cell and Its Structure

What is a Cell? Unit of Life

• Cells are the basic structural and functional unit of life.
• Vary in size, with prokaryotic cells typically ranging from 0.5 to 8 μm.

Cell Structure

• Animal Cells: Complex and highly compartmentalized with organelles.
• Plant Cells: Similar to animal cells, with added components like a cell wall and chloroplasts.
• Bacteria: Simple structures, lacking membrane-bound organelles; often contain peptidoglycan cell walls.

Bacteria and Archaea

• Prokaryotic Domains: Consist of Bacteria and Archaea.
• Bacteria:
  • Includes true bacteria and cyanobacteria (blue-green algae).
  • Thrive in various environments, typically below 70°C.
  • Exhibit metabolic diversity; can be aerobes or anaerobes.
• Archaea:
  • Live in extreme conditions such as deep-sea vents and hot springs.
  • Mostly anaerobic, thriving in low-oxygen environments.
  • Metabolically distinct pathways support survival.

Differences Between Bacteria and Archaea

• Bacteria have membrane lipids linked by ester bonds; Archaea have ether bonds.
• Both reproduce asexually via budding, fission, and fragmentation.

Bacterial Structure

• Cytoplasm: Contains all cellular components.
• Nucleoid: Region where genetic material is located.
• Cell Membrane: Barrier controlling entry/exit of substances.
• Cell Wall: Composed of polysaccharides, mainly peptidoglycan.
• Additional structures may include an outer membrane, capsule, spores, flagella, and pili.

Eukaryotic Cells

• Highly organized with compartmentalization through membranes.
• Contain various organelles performing distinct functions.

Key Organelles

• Nucleus:

  • Enclosed by double membranes with nuclear pores.
  • Contains the nucleolus and nucleoplasm.
  • Holds the majority of genetic information in chromosomes.

• Ribosomes:

  • Serve as the site for protein synthesis.
  • May be free in the cytoplasm or attached to membranes.

• Endoplasmic Reticulum:

  • Appears as a network of membranes, with incoming vesicles at the cis face and outgoing at the trans face.

• Mitochondria:

  • Site of aerobic respiration, producing most of the cell's energy.
  • Contains two membranes and DNA of bacterial origin, indicative of evolutionary history.

• Chloroplasts:

  • Responsible for photosynthesis and contain chlorophyll.
  • Comprise three membranes: inner, outer, and thylakoid space.

Evolutionary Insights

• Eukaryotic cells evolved to form complex structures with organelles, providing specialization in function and increased efficiency in cellular processes.