Chapter 4 Cell Membranes Chapter 4 Phospholipids Polar

Chapter 4 Cell Membranes

Chapter 4 Phospholipids Polar Glycerol Head Hydrophilic OUT Fatty Acid Tails Hydrophobic IN 2

Chapter 4 Lipid bilayers Hydrophilic OUT Hydrophobic IN Hydrophobic. IN Hydrophilic OUT Phospholipids form membranes as lipid bilayers. (Liposomes. ) 3

Chapter 4 BORDER OF THE CELL OUTSIDE INSIDE 4

Chapter 4 Plasma or Cell Membrane OUTSIDE INSIDE 5

Chapter 4 Plasma or Cell Membrane OUTSIDE LIPID BILAYER INSIDE 6

Fluid Mosaic Model of Membrane Structure Chapter 4 7 Oligosaccharides Membrane Proteins Cholesterol. Cytoplasm Outer Surface

Proteins in the plasma Chapter 4 membrane Transmembrane or Integral Proteins Peripheral Proteins 8

Chapter 4 Diffusion 1 3 2 9

Chapter 4 Diffusion across a membrane Plasma membrane SIMPLE DIFFUSION - no extra energy 10

Chapter 4 11 Diffusion across a membrane channel Plasma membrane FACILITATED DIFFUSION hannel proteins shuttle molecules down the concentration gradient - no extra energy

Chapter 4 Diffusion Molecules are always vibrating. Molecules in gas and liquid move randomly. If there is a concentration gradient to start with, over time it will become uniform. Molecules move from [HIGH] to [LOW]. 12

PASSIVE Transport across a membrane p. 61 Chapter 4 13 Simple diffusion • down the concentration gradient • no extra energy Facilitated diffusion • down the concentration gradient • no extra energy • uses Channel proteins. Osmosis • • • Water down the concentration gradient no extra energy special membrane, such as plasma membrane: lets only water go across

Chapter 4 14 Memory aides Hyper = more “A hyper person” Hypo = less A “hypodermic needle” goes under the dermis.

Chapter 4 Osmosis If environment is: • Hypertonic: – MORE WATER IN CELL, less solutes in cell. – over time, cell loses water • Isotonic: – “Iso-” means environment “=” cell – No change in cell volume • Hypotonic: – LESS WATER IN CELL, more solutes in cell. – over time, cell gains water 15

OSMOSI S Chapter 4 HYPERTON ISOTONICHYPOTONIC IC 16

OSMOSI S Chapter 4 HYPERTON ISOTONICHYPOTONIC IC 17

Chapter 4 18 Osmosis Shriveled RBCs Normal RBCs Swollen RBCs Hypertonic Solution. Isotonic Solution. Hypotonic Solution Net movement of water out of cells Equal movement of water into and out of cells Net movement of water into cells

Chapter 4 Active Transport UP a concentration gradient Requires energy from ATP Protein PUMPS 19

Chapter 4 Active Transport Steps Transported Molecule 1 Energy Provider Outside Cell 2 Inside Cell 3 4 Spent Energy Provider 20

Chapter 4 21 Key concepts and words Plasma membrane includes: - Lipid bilayer made of phospholipids (which have hydrophobic and hydrophilic parts) - Integral and peripheral membrane proteins - Cholesterol (wedges!) Transport across a membrane: Passive: simple or facilitated diffusion (channels), down a concentration gradient, no energy. Active transport (pumps), up a concentration gradient, requires energy.