Cell Biology Basics

Cells and Organelles

• Cells are the basic living units of all organisms, highly organized and specialized.
• Organelles are specialized structures within cells that perform specific functions.
• Cytoplasm is a jelly-like substance that holds organelles and is enclosed by the cell membrane.

Cell Membrane/Plasma Membrane

• The cell membrane is the outermost component of the cell, forming a selective barrier between intracellular and extracellular substances.
• It is composed of phospholipids, proteins, cholesterol, and carbohydrates.
• Phospholipids form a double layer with polar (hydrophilic) and nonpolar (hydrophobic) regions.
• Proteins float among phospholipid molecules, functioning as membrane channels, carrier molecules, receptor molecules, enzymes, or structural supports.
• Cholesterol provides added strength and stability by limiting phospholipid movement.
• Carbohydrates may be bound to some molecules, modifying their functions.

Organelles and Their Functions

• Nucleus contains genetic material (DNA) and nucleoli, and is the site of RNA synthesis and ribosomal subunit assembly.
• Ribosomes are the site of protein synthesis.
• Rough Endoplasmic Reticulum has many ribosomes attached and is the site of protein synthesis.
• Smooth Endoplasmic Reticulum is the site of lipid synthesis and participates in detoxification.
• Golgi Apparatus modifies CHON structure and packages CHON in secretory vesicles.
• Secretory Vesicle contains materials produced in the cell and is formed by the Golgi Apparatus.
• Lysosome contains enzymes that digest material taken into the cell.
• Peroxisome breaks down fatty acids, amino acids, and hydrogen peroxide.
• Mitochondria is the site of aerobic respiration and the major site of ATP synthesis.
• Microtubule supports cytoplasm, assists in cell division, and forms components of cilia and flagella.
• Centrioles facilitate the movement of chromosomes during cell division.
• Cilia are located on the cell surface and move substances over certain cells.
• Flagella are found on proper sperm cells.
• Microvilli increase the surface area of certain cells.

Cell Transport

• Movement through the cell membrane can be passive or active.
• Passive Membrane Transport does not require energy and includes diffusion, osmosis, and facilitated diffusion.
• Active Membrane Transport requires energy, usually in the form of ATP, and includes active transport, secondary active transport, endocytosis, and exocytosis.
• Diffusion is the movement of a solute from an area of higher concentration to an area of lower concentration within a solvent.
• Osmosis is the diffusion of water across a selectively permeable membrane.
• Osmotic pressure is the force required to prevent movement of water across a selectively permeable membrane.