6 Membrane

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans? Permeability Amphipathic nature Solubility in water Hydrophobic nature

Amphipathic nature Detergents form micelles around the grease, which are then washed away because the polar head groups facing outward on the micelle are water-soluble.

Carrier Proteins

Carrier proteins do not have a pore. Binding of the transported solute to the carrier protein on one side of the membrane induces a conformational change in the protein that exposes the solute binding site to the opposite side of the membrane, where the solute is released. Carriers transport small polar solutes such as sugars and amino acids.

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell? Hints Hypotonic Osmotic Isotonic Hypertonic

Hypotonic

T or F Osmosis is a type of diffusion

true

1. A phospholipid has a "head" made up of a glycerol molecule attached to a single _______________, which is attached to another small molecule. 2. Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a _________ attached to phosphate. 3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is ___________ which means it has an affinity for water. 4. A phospholipid also has two "tails" made up of two ___________ molecules, which consist of a carboxyl group with a long hydrocarbon chain attached. 5. Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are ___________, which means they are excluded from water. Fill in the Blank: glycerol Choline group Hydrophilic Hydrophobic Phosphate group Fatty acid

1. phosphate group 2. Choline group 3. Hydrophilic 4. Fatty acid 5. Hydrophobic

Carrier proteins & Channels

Carrier proteins and channels are both transport proteins involved in facilitated diffusion, the passive transport of solutes across a membrane down their concentration or electrochemical gradient. As integral membrane proteins, both carriers and channels protect polar or charged solutes from coming into contact with the hydrophobic interior of the lipid bilayer. Furthermore, all transport proteins are specific for the solutes they transport, owing to the specificity of the interactions between the solute and the transport protein.

Channels

Channels are protein-lined pores across the membrane. A channel may be open at all times (non-gated), or may be gated such that the channel opens and closes under specific conditions. Channels transport inorganic ions or water.

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur. Solution A: 3.21% (m/v) NaCl Solution B: 1.65% (m/v) glucose Solution C: distilled H2O Solution D: 6.97% (m/v) glucose Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl Separate into three groups: Crenation Hemolysis Neither

Crenation: ADE Hemolysis: BC Niether: This activity shows why it is very important to use solutions that are isotonic to body fluids in intravenous solutions (IVs). If an IV solution were hypertonic to the body fluids, cells in the body would shrink. If an IV solution were hypotonic to the body fluids, cells in the body would swell.

Ions Ex? Hydrophobic/Hydrophilic? Transport Proteins required?

Ex. Na+, K+, Ca2+ Cl- Hydrophilic Have difficulty crossing the hydrophobic part transport proteins required to cross efficiency

Polar Molecules Ex? Hydrophobic/Hydrophilic? Transport Proteins required?

Ex. water, sugars Hydrophilic Have difficulty crossing the hydrophobic part transport proteins required to cross efficiency

How can a lipid be distinguished from a sugar? Lipids are mostly nonpolar. Lipids are mostly saturated. A lipid dissolves in water. A lipid is made up of only hydrocarbons.

Lipids are mostly nonpolar

Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers. -Allow water molecules and small ions to flow quickly across the membrane -undergo a change in shape to transport solutes across the membrane - are integral membrane proteins -transport solutes down a concentration or electrochemical gradient -provide a continuous path across the membrane -transport primarily small polar organic molecules -provide a hydrophilic path across the membrane

Only Channels: -Allow water molecules and small ions to flow quickly across the membrane -provide a continuous path across the membrane Only Carriers: -undergo a change in shape to transport solutes across the membrane -transport primarily small polar organic molecules Both channels and carriers: - are integral membrane proteins -transport solutes down a concentration or electrochemical gradient -provide a hydrophilic path across the membrane

Which of the following particles could diffuse easily through a cell membrane? Hints Hydrogen ion (H+) Oxygen (O2) Sodium ion (Na+) Glucose

Oxygen Small nonpolar molecules such as oxygen can diffuse across cell membranes.

How does it pass thru the phospholipids bilayer? small nonpolar (hydrophobic) molecules Small polar molecules Polar molecules Large molecules Ions and charged particles

Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer. Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer. Polar molecules such as glucose and sucrose have very limited permeability. Large molecules such as proteins cannot pass through the lipid bilayer. Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane.

A semipermeable membrane is placed between the following solutions. Which solution will decrease in volume? Solution A: 1.4% (m/v) starch Solution B: 7.62% (m/v) starch

Solution A: 1.4% (m/v) starch The water molecules actually move in both directions, but they move to a greater extent toward Solution B because it has a higher solute concentration than Solution A. The net movement of water molecules causes Solution A to decrease in volume and Solution B to increase in volume.

Which statement is correct? A solution of seawater is hypertonic. A solution of distilled water is hypotonic. The contents of a red blood cell are hyperosmotic to distilled water.

The contents of a red blood cell are hyperosmotic to distilled water. The red blood cell has a greater solute concentration than distilled water, which means that its contents are hypertonic to distilled water.

Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply. Hints The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. The diffusion of Na+ ions into the cell is impeded by the electrical gradient across the plasma membrane. The diffusion of K+ ions out of the cell is impeded by the K+ concentration gradient across the plasma membrane. The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. The electrochemical gradient is larger for Na+ than for K+.

The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. The electrochemical gradient is larger for Na+ than for K+.

A semipermeable membrane is placed between the following solutions. Which solution will increase in volume? Solution C: 9% (m/v) NaCl Solution D: 12.4% (m/v) NaCl

The water molecules actually move in both directions, but they move to a greater extent toward Solution D because it has a higher solute concentration than Solution C. This net movement of water molecules causes Solution D to increase in volume and Solution C to decrease in volume.

Structure B is a _____. solvent transport protein water molecule solute phospholipid **pointing at the purple structure**

Transport protein The transport protein facilitates the movement of solute across the plasma membrane..

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group. Hints True False

True The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.

Which of the following molecular movements is due to diffusion or osmosis? When a plant cell is placed in concentrated salt water, water moves out of the cell. Cells of the pancreas secrete insulin into the bloodstream. The sodium-potassium pump pumps three sodium ions out of a neuron for every two potassium ions it pumps in.

When a plant cell is placed in concentrated salt water, water moves out of the cell. If the salt water is hypertonic to the plant cell's contents, water moves out of the cell by osmosis, a form of diffusion.

Facilitated diffusion is a type of _______. pinocytosis active transport passive transport phagocytosis

passive transport

Which of the following factors does not affect membrane permeability? Hints Temperature The amount of cholesterol in the membrane The polarity of membrane phospholipids The saturation of hydrocarbon tails in membrane phospholipids

the polarity of membrane phospholipids

Non polar molecules Ex? Hydrophobic/Hydrophilic? Transport Proteins required?

Ex: hydrocarbons, O2, CO2 Hydrophobic Can cross easily No transport protein required

Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both. -secretes large molecules out of the cell -requires cellular energy -forms vesicles from inward folding of the plasma membrane -decreases the surface area of the plasma membrane -increases the surface area of teh plasma membrane -transported substances never physically cross the plasma membrane -requires fusion of vesicles with the plasma membrane

Exocytosis: -secretes large molecules out of the cell -increases the surface area of the plasma membrane -requires fusion of vesicles with the plasma membrane Endocytosis: -decreases the surface area of the plasma membrane -forms vesicles from inward folding of the plasma membrane Both: -requires cellular energy -transported substances never physically cross the plasma membrane

A red blood cell has been placed into three different solutions. One solution is isotonic to the cell, one solution is hypotonic to the cell, and one solution is hypertonic to the cell. Determine which type of solution is in each beaker based on the cell's reaction. What does it look like: Hypertonic Isotonic Hypotonic

For a cell in an isotonic solution, water flows into the cell to the same extent that it flows out of the cell. If a cell is in a hypotonic solution, water flows into the cell, which causes it to swell and potentially burst. For a cell in a hypertonic solution, water flows out of the cell, which causes it to shrink.

Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply oxygen ions sucrose water carbon dioxide lipids proteins

Oxygen Water Carbon Dioxide Lipids

The structure of the plasma membrane makes it selectively permeable, enabling it to regulate the transport of substances into and out of the cell.

Small, nonpolar molecules are hydrophobic, so they can easily cross the phospholipid bilayer of the plasma membrane. Polar molecules and ions are hydrophilic, so they cannot very easily cross the hydrophobic portion of the plasma membrane (formed by the phospholipid tails). Water is an unusual molecule because, despite the fact that it is polar, it is small enough to pass directly through the hydrophobic interior of the lipid bilayer, albeit slowly. Polar molecules and ions generally cross the plasma membrane with the help of transport proteins. For example, water crosses the bilayer rapidly via transport proteins called aquaporins.