BIO 48_Lecture 4 and 5 (Cell: Membrane Transport / Potentials)

14. Describe the different forms of passive membrane transport.

1. Diffusion- see below i.) Simple-the net movement of molecules from a region of HIGH concentration to a region of LOW concentration until equilibrium is reached. ii). Facilitated -a protein carrier is needed to carry the molecule across a membrane

4. What does the term "gradient" mean?

A concentration gradient occurs when the concentration of particles is higher in one area than another. In passive transport, particles will diffuse down a concentration gradient, from areas of higher concentration to areas of lower concentration, until they are evenly spaced.

20. Explain how "hypertonic", "isotonic" and "hypotonic" solutions will affect the cell.

A hypertonic solution has increased solute, and a net movement of water outside causing the cell to shrink. A hypotonic solution has decreased solute concentration, and a net movement of water inside the cell, causing swelling or breakage.

10. What is the overall function of the cell membrane?

A plasma membrane acts as a selectively permeable barrier that regulates what may cross into or out of the cell.

Endocytosis

A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane. Three Forms of Endocytosis. Endocytosis is a form of active transport in which a cell envelopes extracellular materials using its cell membrane. (a) In phagocytosis, which is relatively nonselective, the cell takes in a large particle. (b) In pinocytosis, the cell takes in small particles in fluid. (c) In contrast, receptor-mediated endocytosis is quite selective. When external receptors bind a specific ligand, the cell responds by endocytosing the ligand.

2. What is a solvent? What is a solute?

A solvent is able to dissolve other substances (liquids). A solute is the minor component in a solution, dissolved in the solvent. A solvent is a liquid that dissolves a solid, liquid or gaseous solute. A solute is a substance dissolved in another substance. A solute and a solvent make up a solution

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

23. Briefly describe primary and secondary active transport. How are they similar, how are they different?

Active transport mechanisms can be divided into two categories. Primary active transport directly uses a source of chemical energy (e.g., ATP) to move molecules across a membrane against their gradient. One of the most important pumps in animal cells is the sodium-potassium pump, which moves Na+ out of cells, and K+ into them. Because the transport process uses ATP as an energy source, it is considered an example of primary active transport. Secondary active transport (cotransport), on the other hand, uses an electrochemical gradient - generated by active transport - as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP. The electrochemical gradients set up by primary active transport store energy, which can be released as the ions move back down their gradients. Secondary active transport uses the energy stored in these gradients to move other substances against their own gradients.

21. What is filtration? How is filtration similar to diffusion and osmosis? What is the driving force for molecular movement?

Filtration is the passage of materials through a membrane by a physical force such as gravity. Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluid—and the solutes within it—from a higher pressure area to a lower pressure area. Filtration is an extremely important process in the body. For example, the circulatory system uses filtration to move plasma and substances across the endothelial lining of capillaries and into surrounding tissues, supplying cells with the nutrients. Filtration pressure in the kidneys provides the mechanism to remove wastes from the bloodstream. In the body filtration is also achieved by means of a physical pump, the heart, which effects the rate of filtration by effecting the pressure of the blood through the blood vessels. It is similar to diffusion and osmosis in that it involves the movement of molecules and water from higher concentration to lower concentration. Hydrostatic Pressure is the driving force for molecular movement for filtration.

19. Define "hypertonic", "isotonic" and "hypotonic".

Hypertonic- having a higher osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid. Isotonic-denoting or relating to a solution having the same osmotic pressure as some other solution, especially one in a cell or a body fluid. Hypotonic-having a lower osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid.

8. List and describe the different functional types of membrane proteins. What do they do?

Intergral Protein- integrated into the membrane(expands edge to edge on membrane) Peripheral Protein- On the outside of the membrane Lipid bound-protein- RARE- stuck on the inside (does not reach outside of membrane) The difference between intergral and peripheral is one is stuck in the membrane(difficult to remove) and the other lays on the outside (there for cell processes)

11. Compare and contrast "passive" and "active" membrane transport.

Passive membrane transport- Composed of simple and facilitated diffusion. Molecules move from high energy to lower concentration 1. Diffusion- see below Simple- the net movement of molecules from a region of HIGH concentration to a region of LOW concentration until equilibrium is reached. Facilitated- a protein carrier is needed to carry the molecule across a membrane 2. Osmosis- the net movement of water across a selectively permeable membrane from a region of LOW solute concentration to a region of HIGH solute concentration until equilibrium is reached. Active membrane transport- This type of transporter pump requires ATP. 1. Protein "PUMPS" 2. Bulk Transport i). Exocytosis ii.) Endocytosis

27. What is the Goldman-Hodgkin-Katz (GHK) equation is used to determine?

The Goldman-Hodgkin-Katz (GHK) equation can be used to determine the membrane potential at any given time. The Goldman-Hodgkin-Katz voltage equation, more commonly known as the Goldman equation, is used in cell membrane physiology to determine the reversal potential across a cell's membrane, taking into account all of the ions that are permeant through that membrane.

28. According to the GHK equation what is the significance of membrane permeability of an ion?

The Goldman-Hodgkin-Katz (GHK) equation is used to describe the effect of the membrane permeability to different ions on membrane potential. The GHK equation includes membrane permeability values because the per- meability of an ion influences its contribution to the membrane potential. If the membrane is not permeable to a particular ion, that ion does not affect the membrane potential.

29. The Nernst equation is a simplification of the GHK equation - what is the Nernst equation used to determine?

The Nernst equation is derived from the Goldman-Hodgkin-Katz equation and indicates the effect of permeability of one ion alone. The Nernst equation can be used to determine the equilibrium potential that could be reached if the membrane became permeable to the given ion, which inturn indicates the driving force (both chemical and electrical) influencing ion movement. The Nernst equation describes the membrane potential that would result if the membrane were permeable to only one ion [p. 153]. For any given ion concentration gradient, this membrane potential is called the equilibrium potential of the ion (Eion): Eion (in mV) = 61 log [ion]out z / [ion]in

31. When is the sodium-potassium pump actively pumping?

The Sodium-Potassium Pumps are always at work. One can think of them as a continuous process that maintains the equilibrium potential for the individual ions. They always are grabbing internal sodium and exchanging it with external potassium at the cost of ATP.

electrochemical gradient

The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

26. What is an "equilibrium potential"?

The electrical potential difference across the cell membrane that exactly balances the concentration gradient for an ion is known as the equilibrium potential. Because the system is in equilibrium, the membrane potential will tend to stay at the equilibrium potential. e.g. Potassium (K+); positively charged ions attracted inside the cell . This is why it is -90 mV.

30. The Nernst potential for sodium is +65mv and for potassium it is -90mv. At rest cells are not very permeable to sodium and have a membrane potential of -70mv. What does this tell you about potassium permeability?

The plasma membrane at rest has greater permeability for K+, thus the membrane potential will lean closer in equilibrium for K+.

32. What is the significance of the sodium-potassium pump?

The sodium potassium pump (NaK pump) is vital to numerous bodily processes, such as nerve cell signaling, heart contractions, and kidney functions. The NaK pump is a specialized type of transport protein found in your cell membranes. NaK pumps function to create a gradient between Na and K ions. The Sodium-Potassium Pump. The sodium-potassium pump is found in many cell (plasma) membranes. Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, three sodium ions are extruded from and two potassium ions are imported into the cell.

16. How do cells regulate the diffusion of ions & molecules?

They are selectively permeable

15. Describe the different characteristics of protein transporters (the same characteristics apply to enzymes).

They can be blocked by competitors, they can exhibit saturation, slower & have more limitations on how many can move across the membrane at a given time

7. Describe how membrane proteins fit into the membrane.

They fit by being selectively permeable

Crenation

This happens when a cell shrinks and shrivels; can result in cell death if severe.

5. Describe the structure and characteristics of phospholipids. How do phospholipids interact with water and each other?

When phospholipids are mixed with water, they spontaneously rearrange themselves to form the lowest free-energy configuration. This means that the hydrophobic regions find ways to remove themselves from water, while the hydrophilic regions interact with water. The resulting structure is called a lipid bilayer.

1. Define "solution".

a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent) A solution is a homogeneous mixture of solvent and solute molecules. A solvent is a substance that dissolves another substance by pulling the molecules apart through electrochemical interactions.

Exocytosis

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.

-lysis

destruction

ATPase

enzyme that hydrolyzes ATP to ADP

17. Define "osmosis".

net movement of water from a region of low solute concentration to a region of high solute concentration across a selectively permeable membrane towards equilibrium. Influenced by: conc. gradient (osmolarity), solute permeability, water permeability (aquaporins), temp., size (MW), surface area... a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane.

Brownian motion

the chaotic movement of colloidal particles, caused by collision with particles of the solvent in which they are dispersed

milliequivalent

the chemical combining power of the ion, or the capacity of cations to combine with anions to form molecules

12. Define "diffusion".

the net movement of molecules from a region of HIGH concentration to a region of LOW concentration until equialibrium is reached.

18. What is osmotic pressure?

the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution.

22. Define "active transport". What do cells use active transport for?

Active transport- the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy. Active transport requires energy from the cell (carrier mediated) Cells use active transport to expend energy (ATP) to maintain the right concentrations of ions and molecules in the living cells Active transport usually happens across the cell membrane. There are thousands of proteins embedded in the cell's lipid bilayer. Those proteins do much of the work in active transport. They are positioned to cross the membrane so one part is on the inside of the cell and one part is on the outside. Only when they cross the bilayer are they able to move molecules and ions in and out of the cell. The membrane proteins are very specific. One protein that moves glucose will not move calcium (Ca) ions. There are hundreds of types of these membrane proteins in the many cells of your body.

25. In terms of molecular movement, what does "equilibrium" mean?

At equilibrium, movement of molecules does not stop. At equilibrium, there is equal movement of materials in both directions. If a molecule can pass freely through a cell membrane, it will cross the membrane by diffusion

9. What other components make up the cell membrane? Describe the overall structure of the cell membrane. Identify all of the components and their orientation in the membrane.

Bilipid Layer (phospholipids), Proteins (Transport, receptors, enzymes, attachment, recognition), Carbohydrates, Cholesterol

6. Describe the relationship between phospholipids and the structure of cell membranes.

Cell membranes are an essential component of the cell, providing separation between the intracellular and extracellular environment. They head group is hydrophilic, while the tail is hydrophobic. Cell membranes are vital for the normal functioning of all the cells in our bodies. Their main functions consist of: Forming a continuous, highly selectively permeable barrier - both around cells and intracellular compartments. Allowing the control of an enclosed chemical environment - important to maintain ion gradients. Communication - both with the extracellular and extra-organelle space. Recognition - including recognition of signalling molecules, adhesion proteins and other host cells (very important in the immune system). Signal generation - in response to a stimulus creating a change in membrane potential.

13. Describe the factors that influence the rate of diffusion and the different forces that cause the movement?

Concentration gradient, size of the particles that are diffusing, and temperature of the system affect the rate of diffusion. Some materials diffuse readily through the membrane, but others require specialized proteins, such as channels and transporters, to carry them into or out of the cell. The forces include osmotic pressure (measures the potential driving the movement), tonicity, isotonic, hypertonic, hypotonic.

3. Define "Potential".

Describes the differences between the two solutions that can impart movement onto solute or solvent molecules or can impart movement due to charge differences between the two environments today. Potential is the measuring of gradient or measuring of a difference in electrical charges

24. Name the different forms of bulk transport. Why is this sometimes NOT described as membrane transport?

Different forms include: phagocytosis, pinocytosis, receptor-mediated endocytosis, and exocytosis It is NOT described as membrane transport because this involves large particles (or large quantities of smaller particles) are moved across the cell membrane. These mechanisms involve enclosing the substances to be transported in their own small globes of membrane, which can then bud from or fuse with the membrane to move the substance across.