Cell Structure, Transport, Effects of Osmosis

Nucleus (Primary Function)

Serves as the repository of genetic information and acts as the "brain" or control center of the cell.

Nucleolus

Produces and assembles the ribosomes.

Nuclear Envelope

Separates the contents of the nucleus from the cytoplasm and provides structural framework.

Nuclear Pore

Allows proteins, RNA complexes, and ions to freely pass or diffuse into/out of the nucleus.

Chromatin (General Function)

Packages DNA into a unit capable of fitting within the tight space of a nucleus.

Euchromatin

DNA segments involved in replication and transcription.

Heterochromatin

DNA segments that constrain DNA replication and repair.

Histones

Proteins looped with DNA.

Cytosol

Platform for cellular metabolic processes and reactions.

Plasma (Cell) Membrane

Selectively permeable membrane that regulates the transport of materials.

Fluid Mosaic Model

Describes the cell membrane as a phospholipid bilayer with embedded proteins.

Ribosome

Site of protein synthesis (mRNA translation to protein).

Lysosome

Contains enzymes to break down biological polymers; acts as the "stomach" of the cell for intracellular digestion.

Peroxisome (Primary Function)

Participates in the oxidation of long-chain fatty acids and biosynthesis of bile acids, cholesterol, and ether phospholipids.

Peroxisome vs. Lysosome Key Difference

Peroxisomes contain a different form of enzyme: hydrogen peroxidase.

Smooth ER

Responsible for the synthesis of essential lipids such as phospholipids and cholesterol.

Rough ER

Embedded with ribosomes; responsible for the synthesis and secretion of proteins.

Vesicle

Containers that move molecules and secrete substances.

Golgi Apparatus

Sorts and packages proteins received from the ER.

Centrosome (Microtubule Organizing Center)

Organizes microtubules or spindle fibers; active during cell division.

Centrioles

Microtubules found in pairs inside the centrosome.

Cytoskeleton

Organizes cell contents and connects the cell physically and biochemically to external environments.

Mitochondria

Site of ATP synthesis (Krebs cycle and Electron Transport Chain).

Chloroplast

Site of photosynthesis (Light and Dark Reactions).

Central Vacuole

Maintains pressure, provides structure and support for plant cells, and is used for storage.

Cell Wall

Provides structural support and rigidity in plant, fungal, and bacterial cells.

Passive Transport Energy Requirement

No ATP required.

Active Transport Energy Requirement

Requires ATP.

Passive Transport Direction

Along concentration gradient (high $\rightarrow$ low).

Active Transport Direction

Against concentration gradient (low $\rightarrow$ high).

Passive Transport Mechanism Types

Diffusion (simple and facilitated), Osmosis.

Active Transport Mechanism Types

Pumping of ions (e.g., $\text{Na}^+/\text{K}^+$ pump), Endocytosis (pinocytosis, phagocytosis).

Substances Transported Passively

Micromolecules, ions, water, gases.

Substances Transported Actively

Ions, nutrients, macromolecules.

Phagocytosis vs. Pinocytosis

Phagocytosis: Uptake of solids; Pinocytosis: Uptake of fluids.

$\text{Na}^+/\text{K}^+$ ATPase Pump Gradient Baseline

Sodium concentration is higher outside; Potassium concentration is higher inside.

$\text{Na}^+/\text{K}^+$ ATPase Pump Ratio & Movement

Transports $3\text{ Na}^+$ OUT and $2\text{ K}^+$ IN per $1\text{ ATP}$ used.

Osmosis Definition

Movement of solvent molecules (typically water) across a semipermeable membrane from lower solute concentration to higher solute concentration.

Hypotonic Solution Water Movement

Water enters the cell.

Isotonic Solution Water Movement

No net movement of water.

Hypertonic Solution Water Movement

Water leaves the cell.

Effect of Hypotonic Solution on Animal Cells

Swells and may burst (lysis).

Effect of Hypertonic Solution on Animal Cells

Shrinks/shrivels (crenation).

Effect of Isotonic Solution on Animal Cells

No change; remains normal.

Witty Tip for Animal Cell Osmosis

"Hyper-cren, Hypo-lyse".

Effect of Hypotonic Solution on Plant Cells

Becomes turgid (firm due to increased turgor pressure).

Effect of Isotonic Solution on Plant Cells

No change; becomes flaccid.

Effect of Hypertonic Solution on Plant Cells

Plasmolysis (membrane pulls away from the cell wall).