The Plasma Membrane and Cellular Transport

Maintaining a Balance Maintain HOMEOSTASIS: internal balance Selective permeability: allows some materials to pass through membrane while rejecting others.

Fluid-Mosaic Model This description is of a plasma membrane that is made up of molecules that are free to flow among one another. The kinds and arrangements of proteins and lipids vary from one membrane to another and give each type of membrane specific permeability properties.

Structure of the Plasma Membrane Two-layered structure: Lipid bilayer Made of lipid molecules with protein molecules in the lipid layer. PROTEINS aid in the movement of materials through the membrane.

Structure of the Plasma Membrane The Lipids have two fatty acids attached to glycerol and a phosphate group (phospholipid). The Polar “head” of a Phospholipid molecule contains a polar phosphorus group, and two “tails” are long, nonpolar carbon chains.

Structure of the Plasma Membrane

Structure of the Plasma Membrane F = Phospholipid bilayer Phospholipid D = Hydrophilic head E = Hydrophobic tails I = Cholesterol Proteins J = transport G = Cytoskeletal filaments A = Carbohydrate chain C = Carbohydrate Glycolipid Glycoprotein

Proteins of the Plasma Membrane 1) Transport Proteins 2) Receptor Proteins

1) Transport Proteins Channel Proteins – channel for lipid insoluble molecules and ions to pass freely through Carrier Proteins – bind to a substance and carry it across membrane, change shape in process

2) Receptor Proteins – Bind to chemical messengers (Ex. hormones) which sends a message into the cell causing cellular reaction

How do materials move into and out of the cell? Materials must move in and out of the cell through the plasma membrane. Some materials move between the phospholipids. Some materials move through the proteins.

Plasma Membrane Transport Molecules move across the plasma membrane by: Active Transport Passive Transport

What are three types of passive transport? Diffusion Facilitated Diffusion Osmosis ATP energy is not needed to move the molecules through.

Passive Transport 1: Diffusion Also called Brownian Motion: random motion of molecules. Molecules can move directly through the phospholipids of the plasma membrane

What is Diffusion? Diffusion is the net movement of molecules from a high concentration to a low concentration until equally distributed. Diffusion rate is related to temperature, pressure, state of matter, size of concentration gradient, and surface area of membrane. Dynamic Equilibrium: a continuous movement of molecules, but no change in concentration.

Concentration Gradient The difference in concentration of a substance across a space.

Passive Transport 2: Facilitated Diffusion Molecules can move through the plasma membrane with the aid of transport proteins This is called … FACILITATED DIFFUSION

What is Facilitated Diffusion? Facilitated diffusion is the net movement of molecules from a high concentration to a low concentration with the aid of channel or carrier proteins.

Passive Transport 3: Osmosis Water Molecules can move directly through the phospholipids of the plasma membrane This is called … OSMOSIS

What is Osmosis? Osmosis: diffusion of WATER molecules through a membrane from an area of higher water concentration to lower water concentration.

Osmosis in action What will happen in the U-tube if water freely moves through the membrane but glucose can not pass? Water moves from side with high concentration of water to side with lower concentration of water. Movement stops when osmotic pressure equals hydrostatic pressure.

Osmosis and Tonicity Tonicity refers to the total solute concentration of the solution outside the cell. What are the three types of tonicity? Isotonic Hypotonic Hypertonic

Isotonic Solution in which the concentration of water (solvent) outside the cell is the same as the concentration inside the cell. What will happen to a cell placed in an Isotonic solution? The cell will have no net movement of water and will stay the same size. Ex. Blood plasma has high concentration of albumin molecules to make it isotonic to tissues.

Hypotonic (Less Concentration) Solution in where concentration of water (solvent) outside the cell is higher than the concentration inside the cell. What will happen to a cell placed in a Hypotonic solution? The cell will gain water and swell. If the cell bursts, then we call this lysis. (Red blood cells = hemolysis) In plant cells with rigid cell walls, this creates turgor pressure.

Hypertonic (More Concentrated) Solution in which concentration of water (solvent) outside the cell is lower than the concentration inside the cell. What will happen to a cell placed in a Hypertonic solution? The cell will lose water and shrink. In plant cells, the central vacuole will shrink and the plasma membrane will pull away from the cell wall causing the cytoplasm to shrink called plasmolysis.

Review Tonicity What will happen to a red blood cell in a hypertonic solution? What will happen to a red blood cell in an isotonic solution? What will happen to a red blood cell in a hypotonic solution?

What are three types of Active transport? 2) Exocytosis 3) Endocytosis Phagocytosis Pinocytosis Active Transport ATP energy is required to move the molecules through.

Active Transport Molecules move from areas of low concentration to areas of high concentration with the aid of ATP energy.

The Importance of Active Transport Bring in essential molecules Rid cell of unwanted molecules (Ex. sodium from urine in kidneys) Maintain internal conditions different from the environment Regulate the volume of cells by controlling osmotic potential Control cellular pH Re-establish concentration gradients to run facilitated diffusion. (Ex. Sodium-Potassium pump and Proton pumps)

Active Transport 2: Exocytosis (Exo – out) Movement of large molecules bound in vesicles out of the cell with the aid of ATP energy. Vesicle fuses with the plasma membrane to eject macromolecules. Ex. Proteins, polysaccharides, polynucleotides, whole cells, hormones, mucus, neurotransmitters, waste

Active Transport 3: Endocytosis (Endo – In) Movement of large molecules into the cell by engulfing them in vesicles, using ATP energy. Two types of Endocytosis: Phagocytosis Pinocytosis