Cell Biology Overview

Prokaryotic Cells
- No nucleus; DNA is in the nucleoid.
- Lack membrane-bound organelles.
- Typically smaller and simpler (e.g., bacteria).
Eukaryotic Cells
- Have a nucleus containing DNA.
- Contain membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).
- Generally larger and more complex (e.g., plant and animal cells).

Cell Membrane
- Phospholipid bilayer that regulates transport in and out of the cell.
Nucleus
- Control center containing genetic material (DNA).
Cytoplasm
- Jelly-like substance where organelles are suspended.
Organelles
- Mitochondria: Energy production (ATP synthesis).
- Ribosomes: Protein synthesis.
- Endoplasmic Reticulum (ER):
  - Rough ER: Studded with ribosomes; synthesizes proteins.
  - Smooth ER: Lacks ribosomes; synthesizes lipids.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
- Lysosomes: Digestive organelles that break down waste.
- Chloroplasts (in plant cells): Site of photosynthesis.

Mitosis
- Process of cell division resulting in two identical daughter cells.
- Stages: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.
Meiosis
- Specialized cell division that reduces chromosome number by half, producing gametes (sperm and egg).
- Involves two rounds of division: Meiosis I and Meiosis II.

Cellular Respiration
- Process of converting glucose and oxygen into ATP, carbon dioxide, and water.
- Stages: Glycolysis, Krebs cycle, Electron transport chain.
Photosynthesis
- Process by which plants (and some bacteria) convert light energy into chemical energy (glucose).
- Occurs in chloroplasts; involves light-dependent and light-independent reactions (Calvin cycle).

Passive Transport
- Movement of molecules across the cell membrane without energy input (e.g., diffusion, osmosis).
Active Transport
- Movement of molecules against their concentration gradient, requiring energy (e.g., sodium-potassium pump).
Endocytosis and Exocytosis
- Endocytosis: Process of taking substances into the cell via vesicles.
- Exocytosis: Process of expelling substances from the cell via vesicles.

Cells communicate through:
- Chemical signals (hormones, neurotransmitters).
- Cell surface receptors that bind to signaling molecules.
- Gap junctions in animal cells allowing direct cytoplasmic transfer.

Prokaryotic Cells
- No true nucleus; genetic material is located in a nucleoid region.
- Absence of membrane-bound organelles, making them simpler and smaller.
- Common examples include bacteria.
Eukaryotic Cells
- Organized nucleus housing genetic material (DNA).
- Numerous membrane-bound organelles enhance functionality.
- Generally larger and more complex, examples include plant and animal cells.

Cell Membrane
- Composed of a phospholipid bilayer, controlling ingress and egress of substances.
Nucleus
- Acts as the control center, containing cellular genetic material.
Cytoplasm
- A viscous medium in which organelles are suspended, facilitating biochemical reactions.
Organelles
- Mitochondria: Central to energy production through ATP synthesis.
- Ribosomes: Sites for protein synthesis, either free-floating or attached to rough ER.
- Endoplasmic Reticulum (ER):
  - Rough ER: Ribosome-studded, responsible for protein synthesis.
  - Smooth ER: Lacks ribosomes, involved in lipid production.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport.
- Lysosomes: Contain digestive enzymes to degrade waste materials.
- Chloroplasts (in plants): Execute photosynthesis, converting light energy into glucose.

Mitosis
- Involves stages: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis, yielding two identical daughter cells.
Meiosis
- Reduces chromosome count by half, producing gametes (sperm and egg).
- Comprises two rounds of division: Meiosis I and Meiosis II.

Cellular Respiration
- Converts glucose and oxygen into ATP, alongside carbon dioxide and water.
- Involves stages: Glycolysis, Krebs cycle, and Electron transport chain.
Photosynthesis
- Plants and certain bacteria transform light energy into chemical energy.
- Takes place in chloroplasts and includes light-dependent and light-independent reactions (Calvin cycle).

Passive Transport
- Involves molecular movement across the membrane without energy use (e.g., diffusion, osmosis).
Active Transport
- Requires energy to move molecules against their concentration gradient (e.g., sodium-potassium pump).
Endocytosis and Exocytosis
- Endocytosis: Mechanism for internalizing substances via vesicles.
- Exocytosis: Process for expelling substances from the cell, also utilizing vesicles.

Cells utilize chemical signals, including hormones and neurotransmitters, for communication.
Signaling molecules bind to cell surface receptors, triggering responses.
Gap junctions in animal cells allow cytoplasmic exchanges between neighboring cells.