Cells are the Fundamental Units of Life

Overview of Cells

  • Focus on cells as fundamental units of life.

  • Discussion of prokaryotic and eukaryotic cells.

  • Overview of components within the cell.

What Makes a Cell?

  • Information

    • Possessed in DNA, the hereditary material of genes.

    • All cells contain DNA.

    • DNA’s structure: double stranded antiparallel strands that allow for transcription into RNA.

    • RNA provides the information necessary to synthesize proteins (enzymes, channels, receptors).

  • Central Dogma of Molecular Biology

    • Flow of genetic information: DNA → RNA → Protein.

    • Transcription:

    • DNA is transcribed into mRNA (messenger RNA) in the nucleus (in eukaryotes).

    • Translation:

    • mRNA is translated into proteins at the ribosome.

    • Importance:

    • Controls cellular processes (e.g., enzyme activity, cell communication).

    • Mitosis:

    • Precedes cell division; involves DNA replication, ensuring genetic consistency in daughter cells.

Exception to Central Dogma - Red Blood Cells

  • Mature Red Blood Cells:

    • Lack a nucleus and organelles, hence cannot synthesize RNA or proteins.

    • Adaptation for enhanced oxygen transport.

    • Enucleation:

    • Process where maturing red blood cells eject their nucleus to maximize hemoglobin capacity.

Differentiation

  • Definition:

    • Process of cell specialization, allowing cells to develop functions unique to specific tissues.

  • Stem Cells: cells with the potential to differentiate into any cell type if given the appropriate signals.

  • After differentiation, genes responsible for other cell types are permanently turned off.

  • Crucial for:

    • Proper development.

    • Tissue repair.

    • Maintaining organ systems.

Chemistry in Cell Formation

  • Primitive Earth had inorganic molecules leading to the formation of organic molecules (amino acids, lipids, nucleic acids).

  • Miller-Urey Experiment (1952):

    • Attempted to recreate early Earth conditions.

    • Resulted in the formation of organic compounds from inorganic materials.

    • Support for abiogenesis: The idea that life originates from nonliving chemical matter through natural processes.

Components of Cells: Compartmentalization

  • Definition:

    • Defined membranes (single or double lipid layer) organize cell functions.

  • Organelles like mitochondria and chloroplasts increase efficiency of biochemical processes by maintaining separate environments.

    • Importance:

    • Prevent interference, regulate timing and location of reactions.

Discovery of Cells

  • Robert Hooke (1665):

    • Coined the term "cell" while examining cork.

  • Cell Theory Contributions:

    • Matthijs Jacob Schleiden and Theodor Schwann:

    • Proposed all living organisms are composed of cells.

    • Rudolf Virchow (1855):

    • Added that all cells arise from preexisting cells, refuting the idea of spontaneous generation.

Basic Properties of Cells

  • Complexity and Organization:

    • Cells contain specialized structures (organelles) working efficiently.

  • Genetic Control:

    • DNA directs cellular functions, passed to next generations.

  • Reproduction:

    • Cells reproduce through division (mitosis/binary fission).

  • Energy Utilization:

    • Cells assimilate nutrients, convert them to usable energy (ATP).

  • Metabolism:

    • Biochemical processes (e.g., respiration, photosynthesis).

Mechanical Activities of Cells

  • Example - Killer T Cells:

    • Immune cells that recognize and destroy harmful cells (e.g., cancer cells).

    • Preprogrammed through DNA, which allows efficient immune responses.

Self-Regulation and Evolution of Cells

  • Self-Regulation:

    • Stem cells control their differentiation and proliferation regulated by environmental signals.

  • Cell Cycle Regulation:

    • Ensures proper growth, repair, and responses to environmental signals.

  • Evolution:

    • Cells adapt over time leading to changes in structure/function;

    • Epigenetics:

    • Modifications affecting gene expression without changing DNA sequences, influenced by environment (diet, stress, chemicals).

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic Cells:

    • Smaller, simpler, no nucleus:

    • DNA is circular and found in cytoplasm (nucleoid).

    • Examples: bacteria, archaea.

    • Asexual reproduction (binary fission).

  • Eukaryotic Cells:

    • Larger, complex with nucleus and organelles:

    • DNA within nucleus. Examples include plants, animals, fungi.

    • Organelles like mitochondria, endoplasmic reticulum, Golgi apparatus.

Distinctions between Animal and Plant Cells

  • Plant Cells:

    • Have a cell wall, chloroplasts, large vacuoles.

  • Animal Cells:

    • Lack cell wall and chloroplasts; have lysosomes.

  • Cell Communication:

    • Plasmodesmata in plant cells vs. no such structures in animal cells.

Conclusion

  • Important to remember the roles of information, chemistry, and compartments in cell makeup.

  • The cell theory emphasizes that all living organisms are made of cells and emphasizes the continuity of life.