Cell Theory: Structure and Function

Cell Theory & Its Importance

• Cell theory is a fundamental principle in biology, developed over time by multiple scientists.
• Robert Hooke (1600s) observed cork cells and coined the term "cell".
• Matthias Schleiden and Theodor Schwann (1839) stated that all living organisms are made of cells.
• Rudolf Virchow (1850s) refined the theory, stating that all cells come from preexisting cells, disproving spontaneous generation.
• Spontaneous generation was the idea that life could arise from non-living matter.
• Cell theory unifies biology by showing that the cell is the fundamental unit of life for all organisms.
• Cell theory has practical applications in medicine, biotechnology, and genetics.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells possess both.
• Prokaryotic cells are smaller (1-10 µm) and simpler than eukaryotic cells (10-100 µm).
• Bacteria and Archaea are examples of prokaryotic organisms.
• Plants, Animals, Fungi, and Protists are examples of eukaryotic organisms.
• Prokaryotic cells divide via binary fission, while eukaryotic cells divide through mitosis or meiosis.
• Prokaryotic cells are considered primitive because they evolved first, are simple, and lack a nucleus and organelles.
• Prokaryotic cells survive because they reproduce quickly and adapt easily.

Why Antibiotics Work on Bacteria and Not Humans

• Antibiotics target specific features of prokaryotic cells that are absent in eukaryotic cells.
• Penicillin blocks cell wall formation, effective against bacteria because human cells lack cell walls.
• Some antibiotics target prokaryotic ribosomes, which differ from eukaryotic ribosomes.

Organelles & Their Functions

• Organelles have specialized functions but work interdependently to keep the cell functioning.
• The Nucleus contains DNA, storing instructions for making proteins.
• Ribosomes read the DNA instructions and synthesize proteins.
• The Endoplasmic Reticulum (ER) modifies and transports proteins:
• Rough ER has ribosomes and packages proteins into vesicles.
• Smooth ER makes lipids and detoxifies harmful substances.
• The Golgi Apparatus receives proteins from the ER, modifies them, and sends them where needed.
• Lysosomes break down waste and old cell parts.
• Mitochondria perform cellular respiration, providing ATP (energy).
• Chloroplasts perform photosynthesis to create glucose.
• The nucleus, ribosomes, ER, and Golgi work together to produce proteins.
• Mitochondria and chloroplasts provide energy to power cellular activities.
• Muscle cells have more mitochondria than skin cells because they need more energy (ATP) for movement.

Proteins

• Proteins are large, complex molecules made up of amino acids.
• Proteins are essential for the structure, function, and regulation of the body’s cells, tissues, and organs.
• Proteins are polymers made of amino acids (monomers).
• There are 20 different amino acids.
• The sequence of amino acids determines the protein’s structure and function.