BIO 150 Forensic Biology - Cellular Structure and Function

A cell is defined as the smallest unit of life.
Many cells are microscopic and cannot be observed without the aid of microscopes, which gained prominence in the 1600s.
Antony van Leeuwenhoek (Dutch lens-maker) was among the first to observe microorganisms, which he referred to as "animalcules."
He used handmade lenses to discern movements of protista and sperm.
Robert Hooke (1665) introduced the term "cell" after observing cork tissue under a microscope, noting box-like structures.
In the 1670s, van Leeuwenhoek discovered bacteria and protozoa, enhancing our understanding of cellular life.
Technological advancements in lens crafting, microscope development, and staining techniques contributed to clearer cell observations.
By the 1830s, Matthias Schleiden (botanist) and Theodor Schwann (zoologist) formulated the unified cell theory, which includes three key principles:
1. All living organisms are composed of one or more cells.
2. The cell is the basic structural and functional unit of life.
3. All cells arise from existing cells.
Rudolf Virchow further substantiated these foundational concepts.

Modern microscopes significantly surpass the early models in complexity and capability.
Two primary types of modern microscopes include:
- Light Microscopes: Suitable for viewing living cells but have limitations in magnification and resolution.
- Electron Microscopes: Provide higher magnification and resolution, but samples must be dead due to preparation methods.

Cells are broadly categorized into prokaryotic and eukaryotic.
Prokaryotic Cells:
- Dominantly unicellular organisms from Bacteria and Archaea domains.
- Prokaryotes are characterized by:
- Lacking a nucleus and membrane-bound organelles.
- Composed of four common components:
  1. Plasma Membrane: Outer covering separating cell interior from the environment.
  2. Cytoplasm: A jelly-like region suspending cellular components.
  3. DNA: Genetic material found in a region called the nucleoid.
  4. Ribosomes: Sites for protein synthesis.
Eukaryotic Cells:
- Includes animal cells, plant cells, fungi, and protists and have:
- Membrane-bound nucleus and organelles with distinct functions.
- Eukaryotic cells are generally larger than prokaryotic cells (10 to 100 times) and exhibit compartmentalization for varied biological processes.

Organisms are classified into three groups: Archaea, Bacteria, and Eukarya.
Fossil Record:
- The fossil record is scant, but deduced histories of Eukarya suggest all extant eukaryotes descend from a common ancestor.
Characteristics of Eukaryotes include:
- Cells containing nuclei surrounded by nuclear envelopes with pores.
- Presence of mitochondria and various organelles.
- A cytoskeleton comprising actin microfilaments and microtubules.
- Flagella and cilia for motility; ancestral traits seen across lineages.
- Linear chromosomes associated with histones, observed universally during the mitosis process.
- Organisms undergo sexual reproduction and can possess walls (originally characteristic).

Endosymbiotic Theory (Lynn Margulis, 1960s):
- Explains eukaryotic cell origins as an integration of ancestral prokaryotes engulfing aerobic bacteria.
- Indications show aerobic prokaryotes formed mitochondria while cyanobacteria evolved into chloroplasts.
Prokaryotic Metabolism:
- Prokaryotes perform essential metabolic functions, like nitrogen fixation and aerobic respiration within the mitochondria.
- Progressive aerobic activity and photosynthesis led to oxygen accumulation, enabling the evolution of aerobic organisms.

Mitochondria:
- Present in varying quantities to meet energy needs (1 to several thousand per cell).
- ATP production through cellular respiration, has double membranes, and replicates independently (binary fission).
Chloroplasts:
- Essential for photosynthesis in plants and a few protists, characterized by double membranes and thylakoids where chlorophyll resides.
- Originates from primary endosymbiosis involving cyanobacteria.