Cell Biology Lecture 1: Cell Size, Type and Cycle

Overview of Cell Biology

• Key Focus Areas:
  • Diversity of Cellular Shapes and Functions: Understanding how different cell types arise and their functions.
  • Scale and Measurement: Importance of measuring cellular components to comprehend biological processes.
  • Microscopy Techniques: Familiarity with various microscopes, their capabilities, and limitations particularly in 2D vs. 3D representation.
  • Cell Cycle and Mitosis Basics: Understanding the phases of the cell cycle and the processes involved in mitosis.

The Cell as a Basic Unit

• Definition:
  • The cell is the structural and functional unit of all living organisms.
• Origin of Human Cells:
  • All human cells derive from a single fertilized egg, emphasizing the importance of replication and specialization in development.

Types of Human Tissues

• Four Major Tissue Types:
  1. Epithelium
  • Epithelial cells form layers covering body surfaces, internal organs, and systems such as the skin and digestive tract.
  1. Muscle
  2. Connective Tissue
  3. Nervous Tissue
• Role of Tissues:
  • Tissues consist of groups of cells working together for common functions.

Cellular Diversity

• Visual Diversity:
  • Common cell shapes include spheroid, squamous, polygonal, discoid, cuboidal, fusiform, columnar, fibrous, and stellate.
• Determinants of Cell Shape:
  • Cell structures are dictated by genes and protein expression, where each cell type expresses a unique subset of genes.

Number of Cell Types in Humans

• Current Estimates:
  • Textbooks state around 200 distinct cell types, but ongoing research continually uncovers new types and cellular states.
  • Example: Discovery of the "pulmonary ionocyte" in the lungs, crucial in cystic fibrosis gene expression (CFTR).

Measurements in Cell Biology

• Size of Cells:
  • Average cell sizes range from 5 to 20 µm (micrometres), with some sizes like red blood cells benchmarked at about 8 µm in diameter.
• Conversions:
  • 1 µm = 1/1000 of mm
  • 1 nm (nanometre) = 1/1000 of µm
  • 100 µm = useful cellular ruler for references.

Microscopy Techniques

• Resolution Capacities:
  • Human Eye: 0.2 mm
  • Light Microscope: 0.2 µm
  • Electron Microscope: 0.2 nm
  • Super-resolution microscopy: 20 nm
• Electron Microscopes:
  • Transmission Electron Microscopes (TEM):
  • Allow viewing of internal cell structures as electrons pass through the sample.
  • Scanning Electron Microscopes (SEM):
  • Provide high-resolution images of surface morphology by bouncing electrons off the sample.

3D to 2D Imaging Challenges

• Cells seen under light microscopy appear as 2D slices; hence, 3D visualization is constructed through interpretation.
• Example: Viewing neurons can provide insights on how structure relates to function.

The Cell Cycle

• **Phases of the Cell Cycle:
  • G1 Phase (Gap 1):** Growth and normal cellular activities
  • S Phase (Synthesis):** DNA replication occurring over 6-8 hours
  • G2 Phase (Gap 2):** Preparation for mitosis lasting about 3-4 hours
  • Mitotic Phase (M): Includes stages of mitosis such as prophase, metaphase, anaphase, and telophase.

Mitosis Stages Explained

• Prophase:
  • Chromosomes condense, and the nuclear membrane disappears.
• Metaphase:
  • Chromosomes align at the equator of the cell; spindle fibers fully form.
• Anaphase:
  • Chromatids split at the centromere and move to opposite poles.
• Telophase:
  • Chromatin decondenses, nuclear envelope reforms, and cytokinesis begins, finalizing cell division.

Fun Fact

• For a deeper understanding of cell structures and innovative techniques, explore resources such as videos on specific cell structures (e.g., paraspeckles).