Cells, the basis of life

Lecture Aims and Overview

  • Understand the connections between lectures, practicals, and assessments in Biology 1A course.

  • Importance of scale in biology, especially SI units and log scales.

  • Biological pressures related to body mass variations.

  • Components of life, from organelles to multicellular organisms.

  • Distinguish between prokaryotic and eukaryotic cells.

  • Methods of motility in unicellular organisms linked to written assessments.

Key Concepts in Cell Biology

Fundamental Understanding of Cells

  • Cells are the basic units that compose organisms.

  • Increase in cell number occurs via cell division, specifically mitosis.

  • Cell Theory: All living things are composed of cells, and cells originate from pre-existing cells.

Microscopy and Cell Visualization

  • Light microscopy enables visibility of animal, plant, and large bacterial cells.

  • Common sizes: 1 m, 1 mm, 1 µm, 1 nm.

    • Bacterial cell approx. 0.5 µm (prokaryote).

    • Mammalian cell approx. 2.0 µm (eukaryote), containing a nucleus.

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic Cells:

    • DNA without a nuclear membrane (nucleoid region).

  • Eukaryotic Cells:

    • DNA enclosed within a nuclear membrane.

    • Contain membrane-bound organelles (e.g., mitochondria, Golgi apparatus).

Organelles and Their Functions

Key Organelles in Eukaryotic Cells

  • Mitochondria:

    • ATP generation from metabolic products.

  • Endoplasmic Reticulum:

    • Rough ER: Ribosome-studded for protein synthesis.

    • Smooth ER: Synthesizes lipids/membranes.

  • Golgi Apparatus:

    • Protein sorting and secretion.

  • Lysosomes:

    • Digests cellular waste (low pH).

  • Plasma Membrane:

    • Encloses the cell, regulating transport.

  • Nucleus:

    • Contains genetic material in eukaryotic cells.

The Endosymbiotic Theory

  • Proposed by Lynn Margulis:

    • Eukaryotic cells evolved via a symbiotic relationship between different prokaryotes (e.g., engulfing aerobic bacteria).

    • Evidence includes similarities between mitochondria and certain bacteria.

Size Limiting Factors in Cells

  • Key reasons cells maintain similar sizes include:

    • Surface Area/Volume Ratio: Influences nutrient uptake and waste elimination.

    • Diffusion Rate: Larger cell size increases distance, complicating material exchange.

Diffusion Mechanics

  • Diffusion efficiency decreases with distance:

    • Time to diffuse increases with the square of the distance (Time ∝ Distance²).

    • Critical for multicellular organisms; average diffusion time calculated for distances (e.g., synapse).

Unicellular Motility

Mechanisms of Movement

  • Distinctions in flagellar movement methods between prokaryotes (e.g., bacteria) and eukaryotes (e.g., protists).

  • Assessment focuses on understanding these differences with references to examples of unicellular organisms.