Cell Structure and Function

• The cell is the basic unit of life.

Nucleus

• Stores genetic material (DNA).
• Controls cell activities.
• Nuclear envelope: A double membrane that protects DNA
• Nucleolus: Produces ribosomes.
• Chromatin: DNA and protein complex.

Plasma Membrane

• Regulates entry and exit of substances.
• Structure: Phospholipid bilayer with embedded proteins.

Cytoplasm

• Jelly-like fluid that holds organelles.
• Facilitates biochemical reactions.

Organelles in Eukaryotic Cells

Energy Related Organelles

• Mitochondria: Powerhouse of the cell; produces ATP through cellular respiration.
• Double membrane with inner folds (cristae).
• Chloroplasts (in plant cells): Site of photosynthesis, contains chlorophyll, thylakoids, and a double membrane.

Endomembrane System

• Endoplasmic Reticulum (ER):
• Rough ER: Has ribosomes, involved in protein synthesis.
• Smooth ER: No ribosomes; synthesizes lipids and detoxifies chemicals.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport.
• Lysosomes (mainly in animal cells): Contains digestive enzymes to break down waste and cellular debris.
• Peroxisomes: Breaks down fatty acids and neutralizes toxins.

Cytoskeletal Components

• Microtubules: Provide structure, help in cell division (spindle fibers).
• Microfilaments: Assist in movement and shape maintenance.
• Intermediate filaments: Provide mechanical strength.

Vacuoles

• Storage of nutrients, water, and waste.
• In plants: Large central vacuole helps maintain turgor pressure.
• In animals: Smaller and involved in transport.

Ribosomes

• Protein synthesis.
• Made of RNA and proteins.
• Found in the cytoplasm or attached to the rough ER.

Centrioles (in animal cells)

• Helps in cell division by forming spindle fibers.
• Viruses are NOT cells
• Cell theory: Every living organism is composed of one or more cells, from preexisting cells
• Prokaryotes: Bacteria, simple and single celled.
• Eukaryotes: Plants, animals, fungi, and protists, larger and more complex, double membraned enclosed nucleus.
• Both prokaryotes and eukaryotes: Dna, Cytoplasm, Ribsomes, Plasma Membrane

Diffusion

• The process by which molecules or particles move from an area of higher concentration to an area of lower concentration.

Passive transport

• NO ENERGY REQUIRED
• Simple diffusion: Movement of molecules directly across a membrane or through a medium without the need for energy or assistance.
• Example: Oxygen and carbon dioxide diffusing across cell membranes.
• Movement of molecules across a membrane via specific transport proteins (carrier or channel proteins) without using energy.
• Example: Glucose transport through GLUT transporters in cells.
• A special type of diffusion involving the movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to higher solute concentration.
• Example: Water moving into a dehydrated cell.

Active transport

• ENERGY REQUIRED

Types of transport

• Vesicles: Move molecules from place to place and in and out.
• Endocytosis: The process in which materials are transported INTO the cell.
• 3 types of endocytosis

1. Receptor mediated endocytosis: receptor proteins embedded in the membrane recognize specific surface characteristics of substances to be incorporated into the cell. Ex: Human cells use receptor mediated endocytosis to take up cholesterol containing packages.
2. Phagocytosis: cellular eating particles considerably larger than than biomolecules are ingested
3. Pinocytosis: cellular drinking fluids are ingested.

• Exocytosis: The way materials are transported OUT of the cell via vesicles
• Isotonic: solute concentration equal to that of the cell it surrounds
• Hypertonic: a fluid that has a solute concentration HIGHER than that of the cell it surrounds
• Hypotonic:a fluid that has a solute concentration LOWER than that of the solute it surrounds
• Hosts: an organism that provides a home for another organism, called a parasite
• Viruses: a microscopic, infectious particle that contains genetic material and a protective protein coating