Cellular Organization: Eukaryotic vs. Prokaryotic Cells
Cellular Organization: Eukaryotic vs. Prokaryotic
Types of Cellular Organization
Eukaryotic Cell Organization: Possesses cytoplasmic compartments surrounded by membranes, producing specific chemical reactions.
Prokaryotic Cell Organization: Lacks internal compartments surrounded by membranes and a true nucleus.
Prokaryotic Cells
Plasma Membrane: The cell boundary between the cell’s interior and the external environment.
Nucleoid: The region inside the cell containing hereditary material, typically a single DNA molecule.
Cytoplasm: The rest of the cell’s contents within the plasma membrane, including:
- Cytosol (or Hyaloplasm): Water containing dissolved salts and organic molecules.
- Ribosomes: Granules composed of RNA and protein that manufacture proteins.
Animal Cells
Plasma Membrane: Forms the cell’s outer boundary and controls the exchange of substances.
Cytoplasm: Contains a wide variety of membrane-bound compartments:
- Cytoskeleton: A network of protein filaments responsible for cell movement.
- Smooth Endoplasmic Reticulum: Lacks ribosomes, composed of lipid tubules, and manufactures membrane components.
- Rough Endoplasmic Reticulum: Consists of flattened sacs covered externally by ribosomes and manufactures proteins.
- Golgi Apparatus: Processes and stores macromolecules synthesized in the endoplasmic reticulum, packaging them into vesicles for export from the cell.
- Lysosomes: Responsible for intracellular digestion.
- Mitochondria: Produce energy through the combustion of organic molecules with oxygen, providing the energy cells need for maintenance.
- Nucleus: Separated from the cytoplasm by a double membrane, containing chromatin and nucleoli (where ribosomes are formed).
Plant Cells
Plant cells are similar to animal cells but lack centrioles. Some have exclusive organelles like chloroplasts (where photosynthesis occurs), a cell wall (a rigid wall surrounding the cell, primarily composed of cellulose), and vacuoles (for storage functions).
Cells as Functional Units
A cell is a dynamic entity constantly changing due to chemical reactions occurring within it. This is called metabolism.
- Anabolism: The process by which a cell produces its components from incorporated substances.
- Catabolism: The process by which chemicals are transformed into simpler components, releasing energy stored in their bonds. This energy is used for movement, nutrient transport, etc.
ATP (Adenosine Triphosphate): The most common intermediary between energy-releasing and energy-requiring processes. An ATP molecule consists of an adenine base, a ribose sugar, and three phosphate groups.
Types of Cellular Nutrition
- Heterotrophic Cells: Incorporate organic matter produced by other organisms.
- Autotrophic Cells: Capable of manufacturing organic nutrients from inorganic substances like H2O or CO2. For example, photosynthesis, an anabolic process, occurs in chloroplasts within autotrophic eukaryotic cells in two phases:
Photosynthesis Phases
- Light Phase: Occurs in the thylakoid membranes, synthesizing ATP molecules in the presence of light. Water molecules are broken down, releasing oxygen.
- Dark Phase (Calvin Cycle): Occurs in the stroma and does not require light.