Cell Biology Overview

Prokaryotic Cells:
- Lack a nucleus and membrane-bound organelles.
- Typically smaller (e.g., bacteria).
- DNA is circular and located in the nucleoid region.
Eukaryotic Cells:
- Have a nucleus and membrane-bound organelles.
- Generally larger (e.g., plant and animal cells).
- DNA is linear and organized into chromosomes.

Cell Membrane:
- Phospholipid bilayer that regulates entry and exit of substances.
Nucleus:
- Contains genetic material (DNA).
- Surrounded by a nuclear envelope with pores.
Cytoplasm:
- Jelly-like substance where cellular processes occur.
Organelles:
- Mitochondria: Powerhouse of the cell; site of ATP production.
- Ribosomes: Sites of protein synthesis; can be free or bound.
- Endoplasmic Reticulum (ER):
  - Rough ER: Studded with ribosomes; synthesizes proteins.
  - Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
- Lysosomes: Contains digestive enzymes to break down waste.
- Chloroplasts: Site of photosynthesis in plant cells (eukaryotic).
- Cell Wall: Provides structure and protection (in plants and some prokaryotes).

Cell Division:
- Mitosis: Process of cell replication for growth and repair (produces two identical daughter cells).
- Meiosis: Process for gamete formation (produces four genetically diverse cells).
Cellular Respiration:
- Process of converting glucose and oxygen into ATP, carbon dioxide, and water.
- Occurs in mitochondria.
Photosynthesis:
- Process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen.
- Takes place in chloroplasts.

Passive Transport:
- Movement of substances across the cell membrane without energy (e.g., diffusion, osmosis).
Active Transport:
- Movement of substances against the concentration gradient, requiring energy (e.g., sodium-potassium pump).
Endocytosis and Exocytosis:
- Endocytosis: Cells engulf materials (e.g., phagocytosis, pinocytosis).
- Exocytosis: Cells expel materials.

Cells communicate through chemical signals such as hormones and neurotransmitters.
Signal transduction pathways convert external signals into cellular responses.

In multicellular organisms, cells differentiate to perform specific functions (e.g., muscle cells, nerve cells).

All living organisms are made up of cells, which serve as the fundamental unit of life.
Cells originate from pre-existing cells, emphasizing the continuity of life.

Prokaryotic Cells:
- Characterized by the absence of a nucleus and membrane-bound organelles.
- Generally smaller in size, exemplified by bacteria.
- DNA is circular and located in a nucleoid area.
Eukaryotic Cells:
- Contain a nucleus and have membrane-bound organelles.
- Larger in size, including types like plant and animal cells.
- DNA is linear and organized into distinct chromosomes.

Cell Membrane:
- Composed of a phospholipid bilayer, regulates the movement of substances into and out of the cell.
Nucleus:
- Houses genetic material (DNA) and is surrounded by a nuclear envelope with pores for material exchange.
Cytoplasm:
- A jelly-like fluid where various cellular processes transpire.
Organelles:
- Mitochondria: Known as the powerhouse of the cell where ATP production occurs.
- Ribosomes: Sites of protein synthesis, found either free in the cytoplasm or bound to the rough endoplasmic reticulum.
- Endoplasmic Reticulum (ER):
  - Rough ER: Has ribosomes on its surface, synthesizes proteins.
  - Smooth ER: Lacks ribosomes, synthesizes lipids and assists in detoxification.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport.
- Lysosomes: Contain digestive enzymes to degrade waste materials.
- Chloroplasts: Present in plant cells, responsible for photosynthesis.
- Cell Wall: Offers structural support and protection, found in plants and some prokaryotes.

Cell Division:
- Mitosis: A type of cell division that results in two identical daughter cells, crucial for growth and repair.
- Meiosis: A specialized form of cell division for producing gametes, resulting in four genetically varied cells.
Cellular Respiration:
- Converts glucose and oxygen into ATP, with byproducts of carbon dioxide and water; primarily occurs in mitochondria.
Photosynthesis:
- A process in which plants convert sunlight, carbon dioxide, and water into glucose and oxygen, taking place in chloroplasts.

Passive Transport:
- Involves the movement of substances across a cell membrane without the use of energy (e.g., diffusion, osmosis).
Active Transport:
- Requires energy to move substances against their concentration gradient (e.g., sodium-potassium pump).
Endocytosis and Exocytosis:
- Endocytosis: Cellular mechanism for engulfing materials, includes phagocytosis (cell eating) and pinocytosis (cell drinking).
- Exocytosis: Process by which cells expel substances.

Chemical signaling through hormones and neurotransmitters facilitates intercellular communication.
Signal transduction pathways convert external signals into appropriate cellular responses.