Cell Biology: Structure and Organelles

Cell Theory: All living organisms are composed of cells; the cell is the basic unit of life; all cells arise from pre-existing cells.
Types of Cells:
- Prokaryotic Cells: Lack a nucleus; smaller; examples include bacteria and archaea.
- Eukaryotic Cells: Have a nucleus; larger; examples include plant and animal cells.

Nucleus: Contains genetic material (DNA); controls cellular activities.
Mitochondria: Powerhouse of the cell; site of ATP (energy) production via cellular respiration.
Ribosomes: Synthesize proteins; can be free in the cytoplasm or attached to the rough endoplasmic reticulum (ER).
Endoplasmic Reticulum (ER):
- Rough ER: Studded with ribosomes; involved in protein synthesis and processing.
- Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes: Contain digestive enzymes; break down waste materials and cellular debris.
Peroxisomes: Break down fatty acids and detoxify harmful substances.
Cytoskeleton: Provides structural support; composed of microfilaments, intermediate filaments, and microtubules.

Structure: Composed of a phospholipid bilayer with embedded proteins; selectively permeable.
Functions:
- Regulates the movement of substances in and out of the cell.
- Facilitates cell communication and signaling.

Cell Division:
- Mitosis: Process of somatic cell division resulting in two identical daughter cells.
- Meiosis: Specialized cell division for producing gametes (sperm and eggs); results in four genetically diverse cells.
Cellular Respiration: Process by which cells convert glucose and oxygen into ATP, carbon dioxide, and water.
Photosynthesis (in plant cells): Process of converting light energy into chemical energy (glucose) using sunlight, carbon dioxide, and water.

Signal Transduction: Process by which a cell responds to signals from outside the cell, often involving receptors on the cell membrane.
Types of Signaling:
- Autocrine: Signals affect the same cell that produces them.
- Paracrine: Signals affect nearby cells.
- Endocrine: Signals (hormones) are released into the bloodstream to affect distant cells.

Phases of the Cell Cycle:
- Interphase: Cell growth and DNA replication (G1, S, G2 phases).
- M Phase: Mitosis and cytokinesis.
Regulation: Checkpoints control progression through the cell cycle; proteins like cyclins and cyclin-dependent kinases (CDKs) are key regulators.

Homeostasis: Cells maintain a stable internal environment despite external changes.
Apoptosis: Programmed cell death, crucial for development and maintaining health by eliminating damaged cells.
Stem Cells: Undifferentiated cells with the potential to develop into various cell types; vital for growth and repair.

Cell Theory: The foundational concept in biology that states all living organisms are made of cells, the cell is the fundamental unit of life, and cells arise from pre-existing cells.
Prokaryotic Cells: Characterized by the absence of a nucleus, these smaller cells include bacteria and archaea.
Eukaryotic Cells: Larger cells that contain a nucleus; examples are plant and animal cells.

Nucleus: Houses genetic material (DNA) and orchestrates cellular activities.
Mitochondria: Known as the powerhouse of the cell, responsible for ATP production through cellular respiration.
Ribosomes: Responsible for protein synthesis, existing as free units in the cytoplasm or attached to the rough endoplasmic reticulum (ER).
Endoplasmic Reticulum (ER):
- Rough ER: Covered with ribosomes, key for protein synthesis and processing.
- Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification processes.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes: Contain digestive enzymes for breaking down waste and cellular debris.
Peroxisomes: Function to degrade fatty acids and detoxify harmful substances.
Cytoskeleton: Composed of microfilaments, intermediate filaments, and microtubules, providing structural support to the cell.

Structure: Formed by a phospholipid bilayer with embedded proteins, making it selectively permeable to substances.
Functions:
- Regulates entry and exit of substances.
- Facilitates cell communication and signaling.

Cell Division:
- Mitosis: A process resulting in two genetically identical daughter cells through somatic cell division.
- Meiosis: A specialized division yielding four genetically diverse gametes (sperm and eggs).
Cellular Respiration: Conversion of glucose and oxygen into ATP, producing carbon dioxide and water as byproducts.
Photosynthesis: In plants, this process transforms light energy into chemical energy (glucose) using sunlight, carbon dioxide, and water.

Signal Transduction: Mechanism by which cells respond to external signals, often via membrane receptors.
Types of Signaling:
- Autocrine: Signals impact the producing cell itself.
- Paracrine: Signals affect neighboring cells.
- Endocrine: Hormones are released into the bloodstream to influence distant cells.

Phases of the Cell Cycle:
- Interphase: Comprises cell growth and DNA replication (G1, S, G2 phases).
- M Phase: Involves mitosis and cytokinesis.
Regulation: Controlled by checkpoints that determine progress; cyclins and cyclin-dependent kinases (CDKs) are key regulators.

Homeostasis: Cells maintain a balanced internal environment even when external conditions fluctuate.
Apoptosis: Programmed cell death vital for development and maintaining health by removing damaged cells.
Stem Cells: Undifferentiated cells capable of developing into various types, essential for growth and tissue repair.