Cell Biology: Cell Theory and Types

Prokaryotic Cells
- Lack a nucleus and membrane-bound organelles.
- DNA is circular and located in the nucleoid.
- Examples: Bacteria and Archaea.
Eukaryotic Cells
- Contain a nucleus and membrane-bound organelles.
- DNA is linear and organized into chromosomes.
- Examples: Plant cells, animal cells, fungi, and protists.

Plasma Membrane
- Semi-permeable barrier that regulates what enters and exits the cell.
- Composed of a phospholipid bilayer with embedded proteins.
Nucleus
- Contains genetic material (DNA).
- Surrounded by the nuclear envelope.
Cytoplasm
- Jelly-like fluid where cellular processes occur.
- Contains organelles.
Organelles
- Mitochondria: Powerhouse of the cell; site of ATP (energy) production.
- Ribosomes: Sites of protein synthesis.
- 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 use within the cell.
- Lysosomes: Contain digestive enzymes to break down waste and cellular debris.
- Chloroplasts: Site of photosynthesis in plant cells; contains chlorophyll.

Mitosis: Process of cell division resulting in two identical daughter cells.
- Phases: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
Meiosis: Specialized cell division that produces gametes (sex cells) with half the number of chromosomes.

Signal Transduction: Process by which a cell responds to signals from its environment.
Types of signaling:
- Autocrine: Signals affect the same cell that releases them.
- Paracrine: Signals affect nearby cells.
- Endocrine: Signals (hormones) travel through the bloodstream to distant cells.

Passive Transport: Movement of substances across the membrane without energy (e.g., diffusion, osmosis).
Active Transport: Movement of substances against their concentration gradient, requiring energy (e.g., ion pumps).

Undifferentiated cells with the potential to develop into various cell types.
Two main types:
- Embryonic Stem Cells: Pluripotent; can differentiate into any cell type.
- Adult Stem Cells: Multipotent; limited differentiation potential.

Living organisms are made entirely of cells, which are the fundamental units of life.
All cells originate from existing cells, ensuring continuity in cellular structure and function.

Prokaryotic Cells:
- Do not have a nucleus or membrane-bound organelles.
- DNA is circular, located in a region called the nucleoid.
- Examples include Bacteria and Archaea.
Eukaryotic Cells:
- Feature a nucleus and membrane-bound organelles.
- DNA is linear and organized into chromosomes.
- Examples include plant cells, animal cells, fungi, and protists.

Plasma Membrane:
- Acts as a semi-permeable barrier controlling substance entry and exit.
- Composed of a phospholipid bilayer with embedded proteins.
Nucleus:
- Houses genetic material (DNA) and is surrounded by a nuclear envelope.
Cytoplasm:
- Gel-like fluid where cellular activities occur, containing various organelles.
Organelles:
- Mitochondria: Known as the powerhouse, these structures are essential for ATP production.
- Ribosomes: Sites dedicated to protein synthesis.
- Endoplasmic Reticulum (ER):
  - Rough ER: Ribosome-studded, involved in protein synthesis.
  - Smooth ER: Lacks ribosomes, serves lipid synthesis and detoxification.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for use or secretion.
- Lysosomes: Contain enzymes for digesting waste and cellular debris.
- Chloroplasts: Present in plant cells, responsible for photosynthesis and contain chlorophyll.

Mitosis: A process creating two identical daughter cells composed of several phases: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
Meiosis: Specialized cell division that produces gametes (sex cells), resulting in half the chromosome number.

Catabolism: Involves breaking down molecules to release energy.
Anabolism: Refers to the synthesis of compounds necessary for cellular functions.

Signal Transduction: The mechanism allowing cells to respond to environmental signals.
- Autocrine Signaling: Signals affecting the releasing cell itself.
- Paracrine Signaling: Signals impacting nearby cells.
- Endocrine Signaling: Hormones traveling through the bloodstream to distant targets.

Passive Transport: Movement of substances across cell membranes without energy expenditure, via processes like diffusion and osmosis.
Active Transport: Utilizes energy to move substances against their concentration gradient, such as through ion pumps.

Undifferentiated cells capable of developing into various cell types.
Embryonic Stem Cells: Pluripotent, having the ability to differentiate into any cell type.
Adult Stem Cells: Multipotent, offering limited differentiation options compared to embryonic counterparts.