Cell Biology: Scientists and Microscopy

Notable People and Their Works

• Robert Hooke (1635-1703) proposed Micrographia (1665), the first book devoted to microscopic observations like fruiting structures of molds.
• Antonie van Leeuwenhoek (1632-1723) constructed a simple/small microscope and discovered bacteria, which he called "Wee Animacules".
• Matthias Schleidein (1838) found that plant parts are made of cells and generalized that all plants consist of cells.
• Theodore Schwann made microscopic investigations of animal parts, generalizing that all animals are made of cells.
• Rudolf Virchow disputed spontaneous generation, stating "All living cells come from pre-existing living cells," or "Omnis cellula e cellula," meaning "Each cell comes from another cell."

Microscopy and Types of Microscopes

• Magnification can effectively magnify up to 100 times the actual size.
• Contrast accentuates differences in parts of a sample.
• Resolution measures the clarity of an image.
• A light microscope passes visible light through a specimen and glass lenses (e.g., Simple, Bright Field, Phase-Contrast, Fluorescence, Confocal, Super-Resolution).
• An electron microscope focuses a beam of electrons through/onto the surface of a specimen (e.g., Scanning EM and Transmission of EM).

Basic Properties of Cells

• Cells are capable of growth and reproduction in culture over extended periods.
• Cells are highly complex and organized.
• Cells possess a genetic program with the means to use it.
• Cells can produce more of themselves.
• Cells carry out diverse chemical reactions and mechanical activities.
• Cells are able to acquire and utilize energy.
• Cells respond to stimuli.
• Cells can self-regulate and evolve.

Prokaryotic and Eukaryotic Cells

• Prokaryotic cells contain DNA in the cytoplasm.
• Eukaryotic cells contain DNA in the nucleus.
• Prokaryotic cells range from 0.1 to 5 micrometers in diameter.
• Eukaryotic cells range from 10 to 100 micrometers in diameter.
• Prokaryotic cells reproduce asexually through binary fission.

Binary Fission

• DNA replicates, the cell elongates, and splits into two identical daughter cells.
• Binary fission is faster than mitosis, facilitating rapid population growth.
• An example is seen in Escherichia coli (E. coli) reproducing in the intestines.

Eukaryotic Reproduction

• Eukaryotic cells reproduce through mitosis (for growth and asexual reproduction) and meiosis (for sexual reproduction).

Mitosis (Asexual Reproduction)

• Mitosis produces two identical daughter cells.
• The steps include interphase, prophase, metaphase, anaphase, telophase, and cytokinesis.
• An example is skin cell regeneration in humans.

Meiosis (Sexual Reproduction)

• Meiosis produces four genetically different haploid cells (gametes).
• It occurs in two stages: meiosis I and meiosis II.
• An example is the formation of sperm and egg cells in animals.

Difference between Prokaryotic and Eukaryotic Cells

Prokaryotic

• Prokaryotic cells are smaller and lack membrane-bound organelles.
• DNA is located in the nucleoid region (no nucleus).
• Transcription and translation occur simultaneously in the cytoplasm.
• Energy conversion occurs in the cytoplasmic membrane.
• Prokaryotes reproduce by binary fission (asexually).

Eukaryotic

• Eukaryotic cells are larger and more complex, containing membrane-bound organelles.
• DNA is enclosed in a nucleus, and genetic processes occur separately.
• Eukaryotic cells have specialized organelles for respiration (mitochondria) and photosynthesis (chloroplasts in plants).
• Eukaryotes use mitosis or meiosis for reproduction.

Key Differences

• Nucleus vs. Cytoplasm in cell division
• Chromosome size and location
• Cytoplasmic organelles
• Cytoplasmic organelles for respiration and photosynthesis
• Cytoskeleton and appendages
• Cell wall composition

Endosymbiotic Theory

• Organelles like mitochondria and chloroplasts of eukaryotic cells evolved from smaller prokaryotic cells.
• Primary and secondary endosymbiosis are key aspects.

Endosymbiotic Theory Evidences

• Organelles of eukaryotic cells contain their own DNA.
• Nucleotide sequences of rRNAs from eukaryotic organelles resemble those of prokaryotes.
• Organelles duplicate independently of the nucleus.

Domains of Life and Examples

Domain Bacteria

• Proteobacteria include nitrogen-fixing bacteria (Azotobacter) and toxic organic compound metabolizers (Pseudomonas).
• Proteobacteria include pathogens like Salmonella, Rickettsia, and Neisseria.
• Cyanobacteria were the first oxygen phototrophs to evolve on Earth.
• Some cyanobacteria form filaments and show morphological forms: unicellular, colonial, and heterocyst.
• Gram-positive bacteria include endospore-forming Bacillus.
• Other phyla include planctomycetes (cells with stalks), spirochetes (helically shaped cells), phototrophic and autotrophic bacteria, and Chlamydia (intercellular parasites).

Domain Archaea

Euryarchaeota

• Euryarchaeota include methanogens, extreme halophiles, thermoacidophiles, and hyperthermophiles.

Crenarchaeota

• Crenarchaeota grow in acidic and hot environments like hot springs and hydrothermal vents.
• They are anaerobes; many use H2 as an energy source.

Domain Eukarya

• Algae
• Protozoa
• Yeasts
• Slime Molds
• Lichens

Organelles and Functions

Animal Cell

• Plasma Membrane: Surrounds the cell and organelles within the cells, a thin sheet or membrane.
• Cytoplasm: Includes the material or protoplasm within a living cell (excluding the nucleus).
• Nucleus: "Commander" or "brain" of the cell, controlling eating, movement, and reproduction.
• Mitochondria: "Powerhouse" of the cell, keeps the cell full of energy.
• Ribosomes: A "protein construction team" to build proteins.
• Endoplasmic Reticulum: Manufacturing and packaging system, works with the Golgi Apparatus and Ribosomes, makes and transports lipids, and also packages proteins.
• Golgi Apparatus: Packages vesicles (also known as the Golgi Complex or Golgi Body).
• Lysosomes: "Digestion machines" for absorbing food particles, wastes, and foreign substances.
• Centrioles: Two organelles that help the cell divide (cell division).

Plant Cell

• Cell Wall: Made of cellulose, found around the plant cell and some other organisms.
• Vacuoles: "Storage Bins" found in both animal and plant cells, but are larger in plant cells, may store food or nutrients.
• Chloroplasts: "Food producers" found in plant cells and some protists, such as algae.