Cell Biology Fundamentals

Two major classes: Prokaryotes and Eukaryotes.
Prokaryotes: no membrane-bound nucleus, no subcellular organelles, only infoldings of the plasma membrane called mesosomes.
Eukaryotes: have a membrane-bound nucleus and membrane-bound subcellular organelles.

A cell is the basic structural and functional unit of living organisms.
The activity of an organism depends on the collective activities of its cells.
The principle of complementarity states that the activities of cells are dictated by their structure, which determines function.

Eukaryotes:
- DNA is found in the nucleus of the cell.
- Contain membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum, and Golgi complex).
- Cell division involves mitosis.
Prokaryotes:
- DNA is not enclosed within a membrane.
- Lack membrane-enclosed organelles.
- Usually divide by binary fission.

Water accounts for about 70-75% of the cell's weight.
Organic compounds (nucleic acids, proteins, polysaccharides, and lipids) account for 25-30% of the cell's weight.
Proteins account for 10-20% of the cell's weight.
Inorganic compounds account for the rest of the cell's weight.

Plasma membrane:
- Structure: phospholipid bilayer containing cholesterol and proteins, and some carbohydrates.
- Functions: acts as a physical barrier, regulates material movement, and functions in cell communication.
Nucleus:
- Structure: enclosed within a double membrane called the nuclear envelope, contains nucleolus.
- Function: contains DNA that serves as the genetic material for directing protein synthesis.
Cytoplasm:
- Structure: contains organelles and provides support for organelles.
- Function: responsible for various cellular processes.
Mitochondria:
- Structure: double-membrane-bound organelles containing a circular strand of DNA.
- Function: responsible for the production of energy in the form of ATP.
Lysosomes:
- Structure: spherical-shaped membrane-bound organelles formed from the Golgi apparatus.
- Function: digest microbes or materials by the cell.
Endoplasmic reticulum:
- Structure: extensive interconnected membrane network.
- Function: modifies, transports, and stores proteins produced by attached ribosomes.
Golgi apparatus:
- Structure: series of several elongated, flattened sac-like membranous structures.
- Function: modifies, packages, and sorts materials, and transports them in vesicles.
Peroxisomes:
- Structure: similar to lysosomes.
- Function: contains enzymes involved in the metabolism of hydrogen peroxide.
Cytoskeleton:
- Structure: organized network of protein filaments.
- Function: maintains integral structural support and organization of cells.

Passive transport:
- Diffusion: movement of a substance from an area of higher concentration to an area of lower concentration.
- Facilitated diffusion: requires a protein carrier.
- Osmosis: diffusion of water across a selectively permeable membrane.
Active transport:
- Uses energy (ATP) provided by the cell.
- Example: sodium-potassium activated ATPase (sodium pump).
Exocytosis and endocytosis:
- Exocytosis: bulk movement of substances out of the cell by fusion of secretory vesicles with the plasma membrane.
- Endocytosis: bulk movement of substances into the cell by vesicles forming at the plasma membrane.

Interphase:
- Longer phase of the cell cycle where the cell is active and preparing for cell division.
- DNA molecule is duplicated exactly in a process called DNA replication.
Cell division:
- Mitosis consists of four stages: prophase, metaphase, anaphase, and telophase.
- Result: two daughter nuclei, each identical to the mother nucleus.