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Biology Membranes 2015 10 28 www.njctl.org 2
Vocabulary active transport carrier protein channel protein concentration gradient diffusion enzymatic activity facilitated diffusion fluid mosaic hypertonic hypotonic integral protein isotonic molarity osmosis passive transport peripheral protein phospholipid bilayer selectively permeable signal transduction 3
Membranes Unit Topics Click on the topic to go to that section Membranes, Diffusion Osmosis Plasma Membranes Transport through Proteins 4
Membranes, Diffusion Return to Table of Contents 5
Membranes Membranes are an arrangement of phospholipids that gather together to enclose a volume. Membranes act as a wall or a barrier separating the outside and the inside of that enclosed volume. 6
Membranes Remember we learned that a phospholipid has a hydrophilic and a hydrophobic end. When these phospholipids arrange to form a membrane that separates the inside and the outside of the shape, both the inside and the outside of the shape usually include water (think of a water balloon in a bathtub). So how can these phospholipids arrange themselves so that their hydrophobic ends are not near the water? Move them into a bilayer. 7
Phospholipid Bilayer The phospholipids do not form a single line, but instead form two parallel lines with their hydrophobic ends in between. Now the hydrophobic ends are protected from the water by the hydrophilic ends. Phospholipids are amphiphilic molecules: meaning they contain both hydrophobic and hydrophilic regions. We call this a phospholipid bilayer. 8
1 The section labelled A is: A amphiphilic B hydrophobic C hydrophilic A Answer 9
2 The sections labelled B are: A amphiphilic B B hydrophobic C hydrophilic B Answer 10
Selective Permeability Membranes allow for the intake of nutrients and the elimination of waste because they are selectively permeable. This means they can let some molecules pass through and not others. 11
Homeostasis The formation of a membrane was one of the first steps in evolution of cells. The membrane separated the inside world and outside world but still allowed for the intake of nutrients and the elimination of waste. Regulating the amount of nutrients and waste passing through the membrane is called maintaining homeostasis. 12
3 The basic component of all membranes is A B C D proteins fats starches phospholipids Answer 13
4 How many layers do plasma membranes have? A B C D one two three four Answer 14
5 Phospholipids arrange themselves so that their A B C D hydrophilic ends contact each other hydrophobic ends ends contact each other hydrophilic end of one layer meets the hydrophobic end of the other layer hydrophobic ends contact the enclosed volume of fluid Answer 15
6 Plasma membranes allow all types of molecules to pass through. True False Answer 16
7 A cell's regulation of its internal environment is called A selective permeability B plasma membranes C phospholipids D maintaining homeostasis Answer 17
Passive Transport Some molecules pass through the membrane without the use of energy, this is called passive transport. These molecules always move from areas of high concentration to areas of low concentration. This is referred to as moving "with the concentration gradient." Which direction with the molecules move? 18
Solutions Review Solutions are defined as homogeneous mixtures of two or more pure substances. The is the substance present in the greatest abundance. Answer All other substances are. dissolves the. In biology, the solvent is almost always. 19
Expressing Concentrations of Solutions Molarity (M) Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution. Molarity (M) = moles of the solute volume of solution in liters 20
Concentration Practice Calculate the concentrations below. Mass of Solute 5g C 10g C 20g NaCl 20g NaCl Volume of Solvent 100ml 100ml 100ml 200ml Concentration 21
Three Types of Passive Transport Diffusion Osmosis Facilitated Diffusion 22
Diffusion Diffusion is the process where solute molecules move from areas of high concentration to areas of low concentration. Membranes act as the barrier between these two areas. Molecules will continue to diffuse across the membrane until an equilibrium is reached. 23
Diffusion No energy is required to move molecules with their concentration gradient. 8.3mM O 2 9.5mM O 2 Which way will the O 2 move? 24
Diffusion Concentration gradients are specific to each type of molecule meaning each type of molecule can diffuse in a different direction, some in and some out. Diffusion is a spontaneous process and each type of molecule diffuses at its own rate. 7.2mM O 2 7.2mM CO 2 9 mm O 2 6 mm CO 2 Which way will the O 2 move? Which way will the CO 2 move? 25
8 Diffusion is the movement of molecules A against their concentration gradient B with their concentration gradient C in their concentration gradient D outside their concentration gradient Answer 26
9 All molecules diffuse from the inside of the membrane to the outside of the membrane. True False Answer 27
10 Each type of molecule diffuses at a different rate. True False Answer 28
11 The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to the sucrose. Which solute(s) will exhibit a net diffusion into the cell? A B C D sucrose glucose fructose sucrose, glucose, and fructose Cell: 0.05M sucrose 0.02M glucose environment 0.01M sucrose 0.01M glucose 0.01M fructose Answer E sucrose and glucose 29
12 Which solute(s) will exhibit a net diffusion out of the cell? A B C D sucrose glucose fructose sucrose, glucose, and fructose Cell: 0.05M sucrose 0.02M glucose environment 0.01M sucrose 0.01M glucose 0.01M fructose Answer E sucrose and glucose 30
13 When diffusion has occurred until there is no longer a concentration gradient, then has been reached. A B C D equilibrium selective permeability phospholipid bilayer homeostasis Answer 31
14 When equilibrium is reached, what is the concentration of fructose outside the cell? Cell: 0.05M sucrose 0.02M glucose environment 0.01M sucrose 0.01M glucose 0.01M fructose Answer 32
Osmosis Return to Table of Contents 33
Osmosis Osmosis is the diffusion of free water molecules across a selectively permeable membrane. 34
Two ways to Describe Osmosis The water is moving with its concentration gradient from an area with lots of free water molecules to an area with fewer free water molecules. OR The water moves from areas of low solute concentration to areas of high solute concentration until the solute concentrations are in equilibrium. 35
Osmosis solute molecule water molecule If the solution on the outside of the membrane has a higher solute concentration than the solution inside, we say that the outside solution is hypertonic. This means that water will diffuse from the inside solution to the outside solution. H 2 O 36
Osmosis If too much water leaves the cell, due to its being in a hypertonic solution, it can shrink or shrivel up. solute molecule water molecule H 2 O 37
Osmosis If the solution on the outside of the membrane has a lower solute concentration than the solution inside the membrane we say that the outside solution is hypotonic. This means that water will diffuse from the outside solution to the inside solution. solute molecule water molecule H 2 O 38
Osmosis solute molecule water molecule If too much water enters a cell due to its being in a hypotonic solution it can swell, and if it swells too much it can, or burst. H 2 O 39
Osmosis solute molecule water molecule If the solution on the outside of the membrane has an equal solute concentration to the solution inside the membrane we say that the outside solution is isotonic to the inside solution. H 2 O This means that water will diffuse equally across the membrane in either direction. 40
15 The diffusion of water molecules across a selectively permeable membrane is called what? A B C D diffusion isotonic osmosis hypotonic Answer 41
16 Water molecules diffuse from A B C D inside the plasma membrane to outside only outside the plasma membrane to inside only from areas of high solute concentration to areas of low solute concentration from areas of low solute concentration to areas of high solute concentration Answer 42
17 Diffusion and osmosis are both types of active transport. True False Answer 43
18 What type of environment has a higher concentration of solutes outside the plasma membrane than inside the plasma membrane? A B C D hypertonic isotonic normal hypotonic Answer 44
19 What type of environment has an equal amount of solute on the inside and outside of the plasma membrane? A B C D hypertonic isotonic normal hypotonic Answer 45
20 What type of solution has a greater flow of water to the inside of the plasma membrane? A B C D hypertonic isotonic normal hypotonic Answer 46
21 The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to the sucrose. Is the solution outside the cell isotonic, hypotonic, or hypertonic? A B Hypertonic Hypotonic C Isotonic Cell: 0.03M sucrose 0.03M glucose environment 0.02M sucrose 0.04M glucose 0.01M fructose Answer 47
22 In which direction will there be a net osmotic movement of water? A In B Out C No net osmosis Cell: 0.05M sucrose 0.03M glucose environment 0.02M sucrose 0.04M glucose 0.01M fructose Answer 48
Plasma Membrane of Cells, Transport through Proteins Return to Table of Contents 49
Plasma Membrane of Cells Early cells were simple lipid bilayers, relying only on passive transport. Later cells developed more complex membranes that included proteins. These proteins act as doorways to allow for more molecules to enter and leave the cell. Most small molecules can diffuse without membrane proteins. Larger molecules need to be facilitated (helped) to diffuse across a membrane by these proteins. 50
Phospholipid Bilayer Remember that membranes are made up mostly of phospholipids. Phospholipids are molecules, containing hydrophobic and hydrophilic regions. 51
2 Types of Membrane Proteins The plasma membrane also contains two types of proteins: Peripheral proteins are not embedded in the membrane, but instead stay on only one side of the membrane. Integral proteins pass through the hydrophobic core and often span the membrane from one end to the other, also called transmembrane proteins. 52
Fluid Mosaic The plasma membrane is sometimes referred to as a fluid mosaic. Fluid because the phospholipids can move sideways within the membrane and do not stay in one stationary position. Proteins can also move around in the membrane but they are much larger than lipids and move more slowly. 53
Fluid Mosaic The plasma membrane is sometimes referred to as a fluid mosaic. Mosaic means the membrane contains many different proteins spread throughout. 54
23 Which of the following statements about the role of phospholipids in forming membranes is correct? A B C D They are completely insoluble in water. They form a single sheet in water. They form a structure in which the hydrophobic portion faces outward. They form a selectively permeable structure. Answer 55
24 Which best describes the structure of a cell's plasma membrane? A proteins sandwiched betweeen two layers of phospholipids B C D proteins embedded in two layers of phospholipids phospholipids sandwiched between two layers of proteins a layer of protein coating two layers of phospholipids Answer 56
25 The fluid mosaic model of membrane structure refers to. A B C D the fluidity of phospholipids and the pattern of proteins in the membrane the fluidity of proteins and the pattern of phospholipids in the membrane the ability of proteins to switch sides in the membranes the fluidity of hydrophobic regions, proteins, and the mosaic pattern of hydrophillic regions Answer 57
Membrane Protein Functions Proteins serve several important functions in the cell membrane. Transport Signal transduction Cell cell recognition Enzymatic activity 58
Transport Proteins can act as doorways for nutrients and waste. There are two types of transport which require proteins: Facilitated Diffusion (a type of passive transport) Active Transport (requires energy) 59
Facilitated Diffusion Small molecules like O 2 and CO 2 readily diffuse through all plasma membranes because they are small and non polar; they can squeeze between the phospholipids. However... Larger molecules and ions, charged particles, cannot squeeze between the phospholipids, they need the help of a transport protein. This is called Facilitated Diffusion. 60
Facilitated Diffusion Just like regular diffusion, particles in Facilitated Diffusion move from an area of high to low concentration. Unlike regular diffusion these particles move through the membrane with the help of a integral protein. Since the substances are going with their concentration gradient, this is a type of Passive Transport: no energy is needed. 61
Examples of Transport Proteins Channel proteins are one type of transmembrane transport protein that provide corridors that allow a specific molecule or ion to cross the membrane. Carrier proteins are another type of transmembrane transport protein that change shape slightly when a specific molecule binds to it in order to help move that molecule across the membrane. 62
Examples of Transport Proteins 63
26 Which of the following molecules is most likely to diffuse freely across the lipid bilayer of the plasma membrane without the involvement of a transport protein? A B C D E carbon dioxide glucose sodium ion DNA all of the above Answer 64
27 Which of the following processes includes all others? A B C D osmosis diffusion of a solute across a membrane facilitated diffusion passive transport Answer 65
28 Facilitated diffusion moves molecules. A B against their concentration gradients using energy against their concentration gradients without the use of energy C D with their concentration gradients using energy with their concentration gradients without the use of energy Answer 66
29 Carrier proteins are an example of integral proteins. True False Answer 67
Active Transport Active Transport uses energy to move solutes through a transport protein against their concentration gradients. Carrier proteins can be used in active transport for specific molecules. energy 68
Comparing Facilitated Diffusion and ActiveTransport Passive Transport Active Transport (REQUIRES ENERGY) Click here for a comparison of the different forms of membrane transport 69
30 Which one of the following is not in some way involved in facilitated diffusion? A B C D E a concentration gradient a membrane a protein an energy source all of the above are components of facilitated diffusion Answer 70
31 Active transport moves molecule. A against their concentration gradients using energy B C D against their concentration gradients without the use of energy with their concentration gradients using energy with their concentration gradients without the use of energy Answer 71
32 Which protein can be used for both active and passive transport? A B C D carrier protein channel protein any integral protein any transmembrane protein Answer 72
Membrane Protein Functions Proteins serve several important functions in the cell membrane. Transport Signal transduction Some proteins are used to gather information about the cell's surrounding environment. Cell cell recognition Some proteins are used to recognize viruses, bacteria, or other cells that have attached to the cell they are in. Enzymatic activity Some proteins are used to catalyze (speed up) reactions. Click here for an animation about Membrane Proteins 73
Diffusion Facilitated Diffusion Active Transport No Energy Carrier Protein Transmembrane Protein Channel Protein High Low Energy Required Low High 74