Cell Membrane Structure and Function Chapter 3 Cell Membrane Structure and Function

Figure 3.12 Phospholipases in venoms can destroy cells

3.1 What Does The Plasma Membrane Do? The cell plasma membrane separates the cell contents from the ________ environment. The membrane acts as a______________, regulating the passage of molecules into and out of the cell. Cell membranes are complex structures that contain many different components.

3.2 What Is The Structure Of The Plasma Membrane? Plasma membranes are “___________”. Membranes are composed of a _________________ that is highly fluid without breaking. _______________ are embedded in this double lipid layer and give the membrane its mosaic character . ________________________ Stronger, flexible, less soluble to water soluble substances

3.2 What Is The Structure Of The Plasma Membrane? The plasma membrane is a fluid mosaic. extracellular fluid (outside) binding site phospholipid bilayer carbohydrate cholesterol phospholipid receptor protein transport protein protein filaments recognition protein cytoplasm (inside) Fig. 3-1

3.2 What Is The Structure Of The Plasma Membrane? The phospholipid bilayer is the _________ portion of the membrane. Phospholipid molecules have a polar head group and a______________________. CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3 – O + CH2 H3C N CH2 CH2 O P O CH2 O CH CH3 O HC O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH O H2C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 tails (hydrophobic): separate interior from surrounding head (hydrophilic) Fig. 3-2

3.2 What Is The Structure Of The Plasma Membrane? The head groups are ________ and point toward the aqueous environment on both sides of the membranes. The tail groups are ____________ and point away from the aqueous environments and toward each other. extracellular fluid (watery environment) phospholipid hydrophilic heads hydrophobic tails bilayer hydrophilic heads cytoplasm (watery environment) Fig. 3-3

3.2 What Is The Structure Of The Plasma Membrane? A mosaic of proteins is embedded in the membrane. Some of the membrane proteins are anchored to a network of ______________ within the cytoplasm. Other proteins are free to move around in the lipid matrix. Many proteins have _____________ groups that stick outside of the cell.

3.3 How Does The Plasma Membrane Play Its Gatekeeper Role? The phospholipid bilayer blocks the passage of_________________. The embedded proteins selectively transport (hydrophilic molecules), respond to, and recognize molecules. There are three types of membrane proteins— ____________proteins, receptor proteins, and ______________ proteins.

Membrane Proteins Fig. 3-1 extracellular fluid (outside) binding site phospholipid bilayer carbohydrate cholesterol phospholipid receptor protein transport protein protein filaments recognition protein cytoplasm (inside) Fig. 3-1

Phospholipid bilayer blocks passage to most molecules Polar H20 soluble: Salts, ________, __________ Pass freely: Small molecules: H20, uncharged _____________ molecules

3.3 How Does The Plasma Membrane Play Its Gatekeeper Role? Membrane proteins Transport proteins: allow the movement of ___________ molecules through the plasma membrane by forming channels or by carrying them across Receptor proteins: possess a binding site on the outer surface for binding specific chemicals that may alter______________ Recognition proteins: with sugar groups attached to the exterior of the cell, are used by the ________________ to identify cells as belonging to “self”

3.3 How Does The Plasma Membrane Play Its Gatekeeper Role? Animation—Plasma Membrane Structure

Characteristics of molecules in fluids 3.4 What Is Diffusion? Characteristics of molecules in fluids _______________ : the number of molecules in a given unit of volume _____________: a physical difference (concentration, pressure, electrical charge) between two regions of space that causes molecules to move from one region to another

Molecules in fluids move in response to gradients. 3.4 What Is Diffusion? Molecules in fluids move in response to gradients. Diffusion: the movement of ___________ from regions of ______________ molecular concentration to low molecular concentration A drop of dye in water illustrates diffusion.

Diffusion of a dye in water 3.4 What Is Diffusion? Diffusion of a dye in water The dye molecules diffuse into the water; the water molecules diffuse into the dye 2 Both dye molecules and water molecules are evenly dispersed 3 A drop of dye is placed in water 1 drop of dye water molecule Fig. 3-4

Summing up: the principles of diffusion 3.4 What Is Diffusion? Summing up: the principles of diffusion Diffusion is the movement of molecules ___________ a gradient from high concentration to low concentration. The greater the concentration gradient, the __________ the rate of diffusion. If no other processes intervene, diffusion will continue until the concentration gradient is________________.

3.5 What Is Osmosis? Osmosis: the diffusion of water molecules from a high water concentration to a ________ water concentration across a biological membrane Pure _________ has the highest water concentration. The addition of dissolved solutes to pure water ____________ the number of water molecules and thus lowers the water concentration.

3.5 What Is Osmosis? Osmotic water flow across a membrane takes place across __________________________ that allow water to pass, but not certain small impermeable molecules, such as sugars.

A selectively permeable membrane 3.5 What Is Osmosis? A selectively permeable membrane water selectively permeable membrane Water molecule: can fit through the pore sugar pore Sugar with water molecules clustered around it: cannot fit through the pore Fig. 3-5

3.5 What Is Osmosis? Example of osmosis: a water-permeable bag that is impermeable to sugar and has sugar inside of it Water flows into the bag, down a water concentration gradient. The bag swells and eventually bursts from the additional water.

3.5 What Is Osmosis? Osmosis selectively permeable membrane Bag bursts sugar molecule Water flows in water molecule Fig. 3-6

3.5 What Is Osmosis? PLAY Animation—Osmosis

Summing up: the principles of osmosis 3.5 What Is Osmosis? Summing up: the principles of osmosis Osmosis is the ______________ of water across a selectively permeable membrane. Dissolved substances reduce the ______________ molecules in a solution. Water moves across a membrane ________ its concentration gradient from a ________ concentration of water molecules to a ___________ concentration of water molecules.

There are two kinds of transport across cell membranes: 3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane? There are two kinds of transport across cell membranes: __________ transport _____________ transport

3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?