Chapter 4 Skeleton Notes: Membrane Structure & Function

Transcription

1 Chapter 4 Skeleton Notes: Membrane Structure & Function Overview/Objectives 4.1 Plasma Membrane Structure & Function o Structure and Function of the PM o Major functions of proteins 4.2- Permeability of the PM o Types of transport and their requirements o Diffusion vs. osmosis o Facilitated vs. active transport o Exocytosis vs. endocytosis 4.1 Plasma Membrane What is the plasma membrane? -The that separates the internal environment from the external environment - the entrance and exit of molecules Phospholipid Bilayer: The plasma membrane is composed mainly of There are two layers: (water loving) polar heads of the phospholipids face the outside and inside of the cell (water hating) non-polar tails face each other Fluid Mosaic Model: What does Fluid Mosaic Model mean? - = consistency of light oil - = contains embedded proteins scattered throughout Page 1 of 9

2 The Fluidity of Membranes: (another type of lipid) Has different effects on membrane at different Attached to the membrane: (sugar) chains can be found attached to phospholipids and proteins on the outer surface of the membrane - on phospholipids = - on proteins = Two Types of Membrane Proteins 1. -Penetrate the hydrophobic core of the lipid bilayer -Are often proteins, completely spanning the membrane -Can move around laterally 2. - Are attached to one side of the membrane Page 2 of 9

3 Five Major Functions of Membrane Proteins 1. Provides a channel for molecules to pass through (energy is not required) 2. Combine with a substance and help it pass through the membrane. Energy is required ( ) 3. Some serve as identification tags that are specifically recognized by other cells 4. Has a with a that fits the shape of a, such as a hormone. The external messenger (signal) may cause a change in shape of the protein (receptor) relaying the message to the inside of the cell 5. Protein is an with an a metabolic reaction In some cases, several enzymes in a membrane are organized as a team that carries out sequential steps of a metabolic pathway. Page 3 of 9

4 4.2 Membrane Permeability (selectively permeable) = certain substances can move across the membrane while others cannot Some substances can pass freely though the membrane ( ) and others require energy ( ) Part 1: Passive Transport A) -Moves down the (goes from high to low concentration) -H 2 O and small, noncharged molecules(co 2, O 2, glycerol, alcohol) easily diffuse across plasma membranes -Diffusion of water is known as = the tendency for molecules of any substance to spread out evenly into the available space Some material can t diffuse through the membrane instead they need Allow passage of hydrophilic substances across the membrane Needed for facilitated and active transport B) or proteins and a are needed (no energy required) Some sugars and amino acids Transport proteins speed the movement of molecules across the plasma membrane Page 4 of 9

5 Effects of Osmosis on Water Balance: = Is the movement of water across a semipermeable membrane o Is affected by the of dissolved substances called the solution s Water Balance of Cells Without Cell Walls =Is the ability of a solution to cause a cell to gain or lose water o Has a great impact on - Three States of Tonicity: Isotonic Solution: The concentration of solutes is the as it is inside the cell There will be movement of WATER Hypertonic Solution: The concentration of solutes is than it is inside the cell The cell will lose water Hypotonic Solution: The concentration of solutes is than it is inside the cell The cell will Water Balance in Cells Without Walls An animal cell fares best in an environment unless it has special adaptations to offset the osmotic uptake or loss of water. Page 5 of 9

6 Water Balance in Cells With Cells Walls = Help maintain water balance = Is the pressure of water inside a plant cell pushing outward against the cell membrane If a plant cell is o It is in a environment o It is very, a healthy state in most plants If a plant cell is o It is in an environment How Will Water Move Across Semi-Permeable Membrane? 1) Solution A has 100 molecules of glucose per ml Solution B has 100 molecules of fructose per ml How will the water molecules move? There will be movement of water since the concentration of solute in each solution is equal 2) Solution A has 100 molecules of glucose per ml Solution B has 75 molecules of fructose per ml How will the water molecules move? There will be a until both solutions have equal concentrations of solute Page 6 of 9

7 Part 2: Active Transport Uses to move solutes their concentration gradients Requires energy, usually in the form of The pump Is one type of active transport system Page 7 of 9

8 Comparison of Passive and Active Transport: Substances diffuse down their concentration gradients no energy required The rate of diffusion can be greatly increased by transport proteins Against concentration gradient Energy for this work is usually supplied by ATP Sodium-potassium pump. Cotransport: Occurs when of a specific solute indirectly drives the active transport of another solute Involves transport by a Driven by a - Page 8 of 9

9 Bulk Transport Bulk transport across the plasma membrane occurs by 1.Exocytosis 2.Endocytosis a) phagocytosis b) pinocytosis c) receptor-mediated endocytosis 1. migrate to the plasma membrane, fuse with it, and release their contents 2. The cell takes in macromolecules by forming new from the Three Types of Endocytosis 1) - large particles like food is taken into the cell - - Seen in ameobas and human white blood cells 2) - Liquid or very small particles are brought into the cell - cell drinking - Seen in blood cells and plant roots 3) - Specific type of pinocytosis which uses receptor proteins shaped for specific molecules - Selective and more efficient - Seen in genetic disorders Page 9 of 9