Biology Chapter: Cell Study and Theory

How Were Cells Studied?

• Cell study spanned generations
• Zacharias Janssen, a spectacle maker, produced the first compound microscope (two lenses).
• Robert Hooke used a light microscope to examine thin slices of plant tissue (cork).
• Antonie van Leeuwenhoek first observed living microorganisms.
• Robert Brown identified the central structure of plant cells.
• Matthias Schleiden determined all plants consist of cells.
• Theodore Schwann postulated that all animals are made of cells.

Disproving Spontaneous Generation

• Francesco Redi's experiments disproved spontaneous generation.
• Rudolf Virchow's work revised the cell theory, stating that all cells originate from preexisting cells.

Updated Cell Theory

• A cell is the basic unit of life.
• All organisms are made up of cells.
• All cells come from preexisting cells.
• To be considered alive, an entity needs information, metabolism, and a membrane.
• Viruses contain genetic material but lack metabolism and are, therefore, not considered living.

Parts of the Cell

• Plasma membrane, also called plasmalemma, is a lipid bilayer that selectively regulates passage between internal and external environments.
• The plasma membrane controls movement of materials in and out of the cell.

Cell Membrane: Structure and Fluidity

• The cell membrane is a lipid bilayer composed of phospholipids.
• Phospholipids have hydrophilic heads and hydrophobic tails that arrange to form a bilayer with tails facing inward.
• Cholesterol and proteins are also embedded in the membrane, affecting fluidity.
• The cell membrane's fluidity depends on the hydrocarbon tails (saturated or unsaturated) and cholesterol content.

Cell Membrane: Protein Structures

• Some proteins span the entire membrane (transmembrane) and some sit on one side (peripheral).
• Transmembrane proteins help transport substances across the membrane.

Nucleus and Nuclear Envelope

• The nucleus is the cell's control center, containing DNA.
• The nuclear envelope is a double membrane enclosing the nucleus, perforated by pores that allow RNA to exit.
• The nucleolus is a nonmembranous structure that produces ribosomes.

Cell Composition: DNA/ Chromosomes

• DNA is found within the nucleus, organized into chromosomes.
• Chromosomes contain genetic information.
• Chromosomes carry genetic instructions for building and maintaining cells.

Endomembrane System: Smooth and Rough Endoplasmic Reticulum (ER)

• Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.
• Rough ER has ribosomes and is involved in protein synthesis and modification.

Ribosomes

• Ribosomes are responsible for protein synthesis.
• They are not membrane-bound organelles and are made up of small and large subunits.

Cell Composition: Endomembrane System: Golgi Bodies

• The Golgi body modifies and packages proteins.
• Golgi bodies are involved in vesicle formation and transportation.

Cell Composition: Endomembrane System: Lysosomes

• Lysosomes contain enzymes that digest cellular waste and invaders.
• They function in recycling and breakdown of cellular components.

Cell Composition: Endomembrane System: Vacuoles

• Vacuoles are membrane-bound sacs used for storage and maintaining the shape of the cell.

Cell Composition: Cytoskeleton

• The cytoskeleton gives structure and shape to the cell.
• It supports cell movement and organelle movement.
• It is made up of microtubules, intermediate filaments and actin filaments.

Cell Composition: Extracellular Components: Cilia and Flagella

• Cilia and flagella facilitate movement.
• Cilia are short, hair-like extensions used for moving substances on cell surfaces.
• Flagella are whip-like structures found in sperm cells, used for movement.

Cell Composition: Extracellular Components: Cell Walls

• Cell walls are found in plants, fungi, and some protists.
• They provide support and protection to the cell.
• Plant cell walls are made of cellulose.

Cell Composition: Organelle: Mitochondria

• Mitochondria are the powerhouses of the cell (energy production).
• They are surrounded by a double membrane, with inner folds called cristae.
• The matrix is the fluid-filled space inside the inner membrane.

Cell Composition: Organelle: Plastids

• Plastids are organelles involved in storage and synthesis.
• Chloroplasts are the site of photosynthesis.
• Common examples are chloroplasts, amyloplasts, chromaoplasts, and elaioplasts.

Cell Composition: Organelle: Ribosomes

• Ribosomes are involved in protein synthesis.
• They are not membrane-bound organelles.
• They consist of two subunits

Prokaryotes vs. Eukaryotes

• Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles.
• Eukaryotic cells have a nucleus and membrane-bound organelles.
• These differences relate to complexity and size.

Volume and Surface Area

• Cells have a limited size because a larger volume requires a larger surface area to function efficiently.
• If the volume increases beyond the surface area capacity, the cell will not be able to function and will likely burst.