Chapter 4

Cells and Life

  • Cells are independent, self-contained units that sustain life.

  • They are considered the fundamental unit of life.

Characteristics of Life

  • Growth and Development: Ability to grow larger and change in various ways.

  • Metabolism: Chemical and physical processes that sustain life, including the conversion of amino acids into proteins and the breakdown of proteins back into amino acids.

  • Response to Stimuli: Cells must be able to respond to their environment (movement and irritability).

  • Cellular Organization: Cells are composed of structures like cell walls, which provide protection and support.

  • Nutrient and Waste Management: Cells need mechanisms to take in nutrients and expel waste.

  • Reproduction and Heredity: Capability to produce offspring that inherit traits from parent organisms.

  • Note: Viruses can reproduce and have heredity but cannot perform metabolism independently and require host cells.

Macromolecular Structures in Cells

  • Cells comprise macromolecular polymers:

    • Proteins

    • Nucleic acids (DNA, RNA)

    • Polysaccharides

    • Lipids

The Cell Theory

  • All cells arise from pre-existing cells.

Phylogenetic Relationships

  • Luca (Last Universal Common Ancestor):

    • A cell from which all life on Earth is descended; it had basic capabilities including a rod shape and phospholipid cell membrane.

    • Utilized DNA, had DNA polymerase, and was capable of processing glucose, nitrate, sulfate, and phosphate for life-sustaining reactions.

    • Had some but not all amino acids and was involved in ATP production and metabolic pathways.

Cellular Structures

  • Nucleoid: Contains chromosomal DNA, represents where genetic content is stored in a prokaryotic cell.

  • Cytoplasm: The gel-like substance within the cell where metabolic processes occur.

  • Ribosomes: Sites of protein synthesis, made from RNA.

  • Extra Chromosomal DNA: DNA that exists in addition to the chromosomal DNA, often in separate loops.

  • Capsules: Protective layers around some bacteria, can be composed of carbohydrates or proteins.

Bacterial Morphology

  • Bacteria can be classified based on shape:

    • Coccus: Spherical

    • Bacillus: Rod-shaped

    • Vibrio: Comma-shaped

    • Spirillum: Spiral-shaped

  • Reproduction: Bacterial spores can remain dormant and germinate in favorable conditions; the process of forming a spore is called sporulation.

Membrane Structure

  • Cell Membrane Composition:

    • Formed by a phospholipid bilayer containing hydrophilic heads and hydrophobic tails which allows for selective permeability and signaling capabilities.

Nutrient Transport Mechanisms

  • Facilitated diffusion: Uses protein channels to allow specific substances like glucose to cross membranes down their concentration gradient without energy.

  • Active transport: Moves substances against their concentration gradient using energy (ATP).

Bacterial Movement and Chemotaxis

  • Flagella: Structures that enable bacterial movement, rotating to propel the cell forward or causing it to tumble based on directional stimuli.

  • Chemotaxis: Bacteria can move towards attractants (e.g., sugar) or away from repellents by altering their movement patterns (runs and tumbles).

  • Cells sense gradients and adjust movements accordingly to optimize their environment.