Biology 120: Chapter 7

Ions (examples: Na+, K+, Ca2+, Cl-)

- hydrophilic, have difficulty crossing the hydrophobic part, transport protein required to cross efficiently

Polar molecules (exapmles: water, sugars)

- hydrophilic, have difficulty crossing the hydrophobic part, transport protein required to cross efficiently

Facilitated diffusion via channels and carrier proteins. Both:

- provide a hydrophilic path across the membrane - transport solutes down a concentration or electrochemical gradient - are integral membrane proteins

The plasma membrane

extracellular fluid: hydrophillic Plasma membrane: hydrophoblic cytoplasm: hydrophillic

Active transport by the sodium-potassium pump follows this cycle:

-Three Na+ ions from the cytosol bind to the pump. -The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. -Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. -The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. -Release of the phosphate group causes another conformational change in the pump. -The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.

Endocytosis

-decreases the surface area of the plasma membrane -forms vesicles from inward folding or the plasma membrane

Membrane structure: Identify Structure A.

-glycoprotein Structure A is composed of both a carbohydrate and a protein.

Nonpolar molecules (examples: hydrocarbons, O2, CO2)

-hydrophobic, can cross easily, no transport protein required

Exocytosis

-increases the surface area of the plasma membrane -requires fusion of vesicles with the plasma membrane -secretes large molecules out of the cell

Membrane protein

E) hydrophillic F) hydrophobic G) hydrophillic

Selective Permeability of Membranes: Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?

-B,C, and D Ions, such as hydrogen ions, and hydrophilic molecules, such as water and glucose, cannot rapidly pass directly through the phospholipids of a plasma membrane. To move rapidly through the membrane, they must pass through membrane transport proteins.

Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels?

-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.

Membrane structure: Identify Structure D.

-phospholipid bilayer of membrane Phospholipids can be recognized by the presence of a head and two tails.

Facilitated diffusion via channels and carrier proteins. Only channels:

-provide a continuous path across the membrane -allow water molecules and small ions to flow quickly across the membrane

Exocytosis and endocytosis

-requires cellular energy - transported substances never physically cross the plasma membrane

Membrane structure: What is the function of structure E?

-stabilization of the phospholipids Cholesterol helps to stabilize the structure of the plasma membrane.

Selective Permeability of Membranes: Structure A in this animation is a(n)

-transport protein The protein is allowing solute molecules to enter the cell.

Facilitated diffusion via channels and carrier proteins. Only carriers:

-undergo a change in shape to transport solutes across the membrane -transport primarily small polar organic molecules

Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism?

-water, lipids, oxygen, carbon dioxide

Diffusion

1) orange dye moves independently of purple dye? Always 2) Concentration gradients exist that drive diffusion of both dyes. Only before equilibrium is reached 3) There is a net movement of orange dye from side A to side B. Only before equilibrium is reached 4) purple dye moves only from side B to side A. Never 5) There is no net movement of the purple dye. Only at equilibrium

Reviewing phospholipid structure

1. A phospholipid has a "head" made up of a glycerol molecule attached to a single phosphate group, 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 choline group attached to phosphate. 3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is hydrophilic, which means it has an affinity for water. 4. A phospholipid also has two "tails" made up of two fatty acid 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 hydrophobic, which means they are excluded from water.