1 CELL MEMBRANES and TRANSPORT

2 The Cell

3 Cell Membrane  All living things are surrounded by a membrane.  A cell membrane is also known as plasma membrane.  Controls exchange of materials such as nutrients and waste between cells and their environment.  Has other important functions  for example to enable cells to receive hormones.

4 Cell Membrane  Fluid Mosaic Model - proteins embedded in a phospholipid bilayer.

5 Fluid mosaic model FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

6  HYDROPHILIC heads (water liking) -Attracted to the water  HYDROPHOBIC tails (water fearing) -repel water Cell membranes are made of PHOSPHOLIPIDS A Phospholipid

7 A Phospholipid Bilayer Phospholipids can form: BILAYERS -2 layers of phospholipids with hydrophobic tails protected inside by the hydrophilic heads. The PHOSPHOLIPID BILAYER is the basic structure of membranes.

8  Bilayer: 2 layers of phospholipids The heads stay on the outside and the tails stay on the inside. The heads stay on the outside and the tails stay on the inside.

9 Cell Membrane  Cell surface proteins a. Channel proteins - transport food and other molecules into the cell and transport wastes out of the cells. a. Channel proteins - transport food and other molecules into the cell and transport wastes out of the cells. b. Receptor proteins - gather information about the cell’s surroundings. b. Receptor proteins - gather information about the cell’s surroundings. c. Cell surface markers - identify the type of cell, important for cell recognition. c. Cell surface markers - identify the type of cell, important for cell recognition.

10 Movement of selected molecules across the cell membrane

11 Cell Membrane  Permeability of the cell membrane 1. Semi permeable/selectively permeable - only certain substances can pass across the membrane. 1. Semi permeable/selectively permeable - only certain substances can pass across the membrane. 2. Factors that determine whether a molecule can pass through a membrane or not: 2. Factors that determine whether a molecule can pass through a membrane or not: a. sizea. size b. typeb. type

12 Transport Mechanisms  Transport Mechanisms - moving material in and out of the cell  Concentration gradient - the difference in the amount of a substance inside and outside of the cell 1. Going “with the gradient”-moving from high to low concentration 1. Going “with the gradient”-moving from high to low concentration 2. Going “against the gradient”-moving from low to high concentration 2. Going “against the gradient”-moving from low to high concentration 3. Equilibrium exists when the concentration of molecules is the same throughout a space (inside and outside the cell) 3. Equilibrium exists when the concentration of molecules is the same throughout a space (inside and outside the cell)

13 Transport Mechanisms  Two categories of transport based on concentration gradient and the need for energy 1. Passive transport does not require energy 1. Passive transport does not require energy goes with the gradient.goes with the gradient. 2. Active transport requires energy 2. Active transport requires energy goes against the gradient.goes against the gradient.

14 Methods of Transport Across Membranes 1. Diffusion 2. Osmosis 3. Facilitated Diffusion 4. Active Transport

15 Methods of Transport Across Membranes 1. Diffusion -passive transport - no energy expended energy expended 2. Osmosis - Passive transport of water across membrane 3. Facilitated Diffusion - Use of proteins to carry molecules or ions across carry molecules or ions across 4. Active Transport- requires energy to transport molecules against a transport molecules against a concentration gradient – energy is concentration gradient – energy is in the form of ATP in the form of ATP

16 Types of Transport

17 Passive Transport Mechanisms Diffusion  Movement of molecules from an area of high concentration to an area of low concentration.  Movement from one side of a membrane to another Example: smoke across a room, food coloring dropped into water, oxygen in lungs Example: smoke across a room, food coloring dropped into water, oxygen in lungs

18 Diffusion in action Diffusion in action

19 Passive Transport Mechanisms Osmosis  Diffusion of water Direction of osmosis-the direction of water flow depends upon the concentration of solute and solvent (water) Direction of osmosis-the direction of water flow depends upon the concentration of solute and solvent (water) Tonicity-term used to compare 2 solutions (usually the inside and the outside of the cell) Tonicity-term used to compare 2 solutions (usually the inside and the outside of the cell) a. Hypotonic - less solute (more water)a. Hypotonic - less solute (more water) b. Hypertonic - more solute (less water)b. Hypertonic - more solute (less water) c. Isotonic - equal amounts of solute and waterc. Isotonic - equal amounts of solute and water

20 Passive Transport Mechanisms Osmosis Water will flow from a hypotonic solution to a hypertonic solution Water will flow from a hypotonic solution to a hypertonic solution Will water move in an isotonic solution? Will water move in an isotonic solution? Yes, but it won’t be noticeable- equilibrium is establishedYes, but it won’t be noticeable- equilibrium is established

21 Osmosis How Osmosis works How Osmosis works

22 Solutions  Solutions are made of solute and a solvent  Solvent - the liquid into which the solute is poured and dissolved.  Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes. Salt and sucrose are solutes.

23 Passive Transport Mechanisms Turgor pressure/osmotic pressure- pressure due to water in cell. Turgor pressure/osmotic pressure- pressure due to water in cell. Analogy: air pressure in a tire.Analogy: air pressure in a tire. When a cell has high turgor pressure, it is bigger and stiffer. When a cell has high turgor pressure, it is bigger and stiffer. When a cell has low turgor pressure, it is smaller and flimsy. When a cell has low turgor pressure, it is smaller and flimsy.

24 Passive Transport Mechanisms  Plasmolysis - wilting of a cell due to loss of turgor pressure  Cytolysis - bursting of a cell due to an increase in turgor pressure. How do plant cells avoid cytolysis? Cell walls How do plant cells avoid cytolysis? Cell walls How do unicellular freshwater organisms avoid bursting? Contractile vacuoles. How do unicellular freshwater organisms avoid bursting? Contractile vacuoles.

25 Plant and Animal Cells put into various solutions

26 Passive Transport Mechanisms

27 Passive Transport Mechanisms

28 Passive Transport Mechanisms  Facilitated diffusion - transport of specific molecules across a membrane with the help of a channel protein An example of a molecule that is often transported in this manner is glucose An example of a molecule that is often transported in this manner is glucose How Facilitated Diffusion Works How Facilitated Diffusion Works

29 Active Transport Mechanism  Active Transport Mechanism (requires energy in the form of ATP)  Ex. Sodium-potassium pump - pumps sodium ions out and forces potassium ions in. Sodium-potassium pump - pumps sodium ions out and forces potassium ions in. Sodium-potassium pump Sodium-potassium pump Important for conducting nerve impulses and muscle contraction.Important for conducting nerve impulses and muscle contraction. Proton pump-transport protons through membranes of chloroplasts and mitochondria Proton pump-transport protons through membranes of chloroplasts and mitochondria

30 Active Transport Mechanism  Endocytosis - process of bringing larger molecules into the cell by engulfing them. 1. Pinocytosis – liquids 1. Pinocytosis – liquids 2. Phagocytosis - solids 2. Phagocytosis - solidsPhagocytosis amoebas eat this wayamoebas eat this way white blood cell engulf bacteriawhite blood cell engulf bacteria