The Cell Membrane
Main Functions The main goal is to maintain homeostasis. Regulates materials moving in and out of the cell. Provides a large surface area on which specific chemical reactions can occur. Site for receptors containing specific cell identification markers that differentiate one cell from another. Separates cells from one another. Protects the inside of the cell. The membrane doesn t completely protect the cell because many substances that aren t beneficial to the cell can still enter through diffusion. Membranes allow cells to create and maintain internal environments that differ from external environments.
Selectively Permeable Some materials can pass through and others cannot. Permeability depends on: 1. Lipid solubility 2. Size 3. Charge (ions) 4. Presence of channels and transporters Think of it like a strainer
Fluid Mosaic Model A membrane that is a fluid (can move easily) structure, with a mosaic of various proteins and carbohydrates embedded in it.
General Structure Phospholipids are made up of a hydrophilic phosphate and glycerol head and two hydrophobic fatty-acid tails The head makes up the outside of the lipid bilayer and the hydrophobic tails make up the inside. Proteins that extend through the entire membrane are called amphipathic, they have both hydrophilic and hydrophobic regions. Along the membrane, many proteins and lipids are attached to carbohydrates. Together they function in cell recognition and communication.
Coloring Instructions Hydrophilic heads yellow. Hydrophobic fatty acid tails green. Carbohydrate chains red. Outline the glycolipid in light blue. Outline the glycoprotein in pink. All membrane proteins orange. Peripheral proteins purple. Cholesterols dark blue. Transport protein yellow. Receptor & enzymatic (ATP synthase) proteins pink. Attachment / Recognition dark green.
1) Phospholipid- label the structures on your foldable! Made up of polar phosphate and glycerol heads, and nonpolar fatty acid tails.
2) Phospholipid Bilayer Allows some substances to diffuse through, such as small and nonpolar (O 2 ) or small and polar (H 2 O). Substances can t pass the membrane if they are charged ions or large (sodium ions and glucose).
3) Integral Protein A protein partially or fully embedded in the membrane. Serve as transport channels for particles to enter and leave the cell. Some can move around the membrane.
4) Peripheral Protein Proteins loosely bound on the surface of the membrane or to an integral protein May help regulate cell signaling.
5) Cholesterol Secure proteins in the membrane, prevents the cell from becoming too fluid, and gives cells the ability to communicate with each other. Holds the bilayer together.
6) Glycolipid Carbohydrate bonded to a lipid. Function as identification markers for cell recognition, and may provide energy.
7)Oligosaccharide / Carbohydrate Chain ID tags that allow cells to distinguish one cell from another.
8) Glycoprotein Carbohydrates bound to proteins on the membrane. Brings other cells together; act as receptors on cell surfaces, and offers strength and support.
9. Transport Protein Help substances that can t cross the bilayer. They can t cross because they are charged (ion), too large (glucose), or both (amino acids).
10. Attachment and Recognition Attachment sites for different elements on either side of the membrane. Intracellular & Extracellular
Receptor for Signaling / Receptor Proteins Proteins that bind to hormones or growth factors. When bound they can trigger a signal that begins a cascade of reactions.
Enzymatic Activity Some proteins are involved in catalyzing biochemical reactions. Example: ATP Synthase in the inner membrane of the mitochondria. Hey, it ends in ase what am I?