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What physical characteristics of a solute and the structure of a cell help determine whether the solute is able to enter or exit the cell?
(Note: concentration difference is NOT a physical characteristic of a solute or membrane.)
Some of the physical characteristics that can help determine whether a solute can enter or exit a cell are the size versus the protein channel pore (the bigger the solute, the smaller the chance of it fitting in the protein), the temperature (the higher the temp, the faster the diffusion), solute charge versus local membrane charge (opposite charges attract), solubility in lipids, and the presence of specific carrier molecules.
How are facilitated diffusion and active transport different? How are they similar?
- Facilitated Diffusion is different from Active Transport in that it DOES NOT require ATP and goes from High to Low on the concentration gradient, whereas AT requires some form of ATP and it goes against the gradient (Low to High).
- However, they are similar because both of them are specifically carrier-mediated.
Write Fick's equation for simple diffusion and define each of the variables.
- Flux is the rate of diffusion (how quickly/slowly the solutes are passing over the concentration gradiant)
- D is the diffusion coefficient for the solute in a particular medium at a particular temperature.
- A is the surface area over which diffusion is taking place.
- Delta C is the concentration difference and L is the length over which diffusion is occurring.
A 300 mOsm/l solution of urea is both iso-osmotic and hypotonic to a human red blood cell (solute concentration = 300 mOsm/l). Describe how this is possible.
- It is iso-osmotic due to the fact that the concentration of solutes inside and outside of the cell are at equilibrium.
- Also, it is hypotonic due to the fact that water is flowing from the urea concentration to the inside of the human red blood cell, where the salt content is larger, and so the cell swells.
How would a decrease in the concentration of oxygen in the lungs affect the diffusion of oxygen into the blood?
Diffusion is driven by a concentration gradient. The larger the concentration gradient, the faster the rate of diffusion, and the smaller the concentration gradient, the slower the rate of diffusion. If the concentration of oxygen in the lungs and oxygen in the blood would decrease (as long as the oxygen level in the blood remained constant). Thus, oxygen would diffuse more slowly into the blood stream.
Some pediatricians recommend using a 10% salt solution as a nasal spray to relieve congestion in infants with stuffy noses. What effect would such a solution have on the cells lining the nasal cavity? Why?
The 10% salt solution is hypertonic with respect to the cells lining the nasal cavity, because it contains a higher salt (solute) concentration than do the cells. The hypertonic solution would draw water out of the cells, causing the cells to shrink and adding water to the mucus , thereby diluting it and relieving congestion.
Write an equation for diffusion of a substance across a semi-permeable membrane and define each of the variables.
- Flux (the diffusion rate) depends on the permeability (P) of the solute and the solute's concentration (Delta C) across the membrane.
During digestion in the stomach, the concentration of hydrogen ions (H+) rises to many times that in the cells lining the stomach. Which transport process must be operating?
An active transport process must be involved because it takes energy expenditure to move the hydrogen ions against their concentration gradient - that is, from a region where they are less concentrated (the cells lining the stomach) to a region where they are less concentrated (the interior of the stomach).
- A VERY cold temperature, at which all atoms and molecules completely stopped moving. Scientists have yet been able to reach it.
- O K
- -273 Degrees Celsius
- -459 Degrees Fahrenheit
- Requires ATP.
- Goes AGAINST the concentration gradient (Low to High).
- Primary Active Transport, Secondary Active Transport, and Vesicular Transport.
- The movement of large particles in a fluid (air or liquid) in response to a pressure gradient.
- More solute movement than would occur due to simple diffusion or osmosis.
- ATP is not used at the site of transport.
- A facilitated diffusion that is apart of passive transport.
- High to Low concentration gradient.
- No ATP is used.
- Contains a receptor site where a molecule can attach and if it fits, it can be released in/out of the cell.
Cell (Plasma) Membrane
- Made up of lipids that contain different channels/pores through which solutes can pass through.
- Lipid soluble molecules can pass directly through the plasma membrane.
- Small water soluble molecules can diffuse through the channels, but the larger molecules cannot cross unless they are transported by a carrier mechanism.
The state of which different factors are at an equal amount.
The state of which different solutes are at an equal amount. For example, the solute concentration of water outside of a cell is the same as the concentration of water inside of the cell.
- A form of passive transport in which a carrier molecule is involved.
- High to Low concentration gradient.
- No ATP is used.
- VERY specific (carrier-mediated).
Flux (Across a Semipermeable Membrane)
Flux = PxΔC
- Part of Osmosis and Passive Transport
- This can OPPOSE osmotic pressure.
- Part of Osmosis
- Water moves OUT of the cell and it shrinks.
- Crenation occurs.
- Part of Osmosis
- Water moves INTO the cell and it swells.
- Hemolysis may occur.
- Part of Osmosis
- No osmotic flow occurs, no change in volume.
- The diffusion of water down its concentration gradient across a semipermeable membrane.
- Osmotic Pressure can stop this from taking place.
- Water follows Salt (solute).
- Water moves from Higher [H2O] to lower [H2O].
- This is the pressure required to stop Osmosis from happening.
- Nothing is able to pass through the semipermeable membrane.
- Does NOT use ATP.
- Energy required for transport provided by random molecular motion due to heat.
- Solutes move from a HIGH to LOW concentration.
- Examples: Simple Diffusion, Facilitated Diffusion, Osmosis
- The ease at which substances are able to cross the cell membrane.
- Nothing can pass through an impermeable barrier, but anything can pass through a freely permeable barrier.
- Cell membranes are selectively permeable.
Transporter (Carrier Molecule)
These are very specific molecules which only allow certain types of solutes to attach to go through the semi-permeable membrane.
The ability for a cell membrane to allow different solutes/molecules/proteins to pass in and out of the cell.
- Part of Passive Transport.
- All molecules are in constant random motion if the environmental temperature is above absolute zero.
- Net diffusion keeps occurring until equilibrium is reached.
- The time in which the cell prepares for cell division. There are 4 different parts.
- G1 Phase: First "gap" after mitosis (growth, metabolism, everyday activities)
- S Phase: Synthesis (synthesis of DNA, histone synthesis)
- G2 Phase: Second "gap" after mitosis (growth, getting prepared for mitosis)
- G0 Phase: Withdraws from the cell cycle (such as nerve cells, heart muscle cells)
One of the factors affecting the permeability of a solute through a membrane.
M-Phase (Maturation) Promoting Factor
- A growth factor that affects the cells life cycle.
- Chemically important
- Cdc2: cell division cycle protein 2
- Cyclin: concentration changing with time
Na+/K+ ATPase Pump (Primary Active Transport)
- Part of Primary Active Transport.
- ATP used at the site of transport.
- Both Na+ and K+ are pumped against the concentration gradient
- Requires a carrier molecule
- Net loss of cations (+)
- Helps make inside of cell membrane negatively charged compared to outside of membrane.
- Movement into the cell.
- Ligands bind to the receptor sites and end up forming deep pockets in the cell membrane. It ends up being pinched off and forming a coated vesicle which then dumps out the ligands, and then reattaches to the cell membrane.
Saturation (of Transporters and Enzymes)
- Transporters and Enzymes both relate to each other in saturation.
- The amount of solvent/solute needed to reach a state of equilibrium in which it is saturated and no more can flow in.
- The number of Mitotic Divisions depends on how long the telomeres are.
- DNA + proteins at the ends of chromosomes which are formed by telomerase.
- Contains multiple TTAGGG that form caps on the ends of chromosomes.
- Protects the ends during mitosis.
- These wear out during cell division and when it gets to short, it signals a repressor gene to stop cell division altogether.
Secondary Active Transport
- ATP NOT used at the site of transport.
- Glucose Carrier
- ONLY changes shaped if both Glucose and Na+ are binded.
- Only works if there is a higher concentration of Na+ outside of the cell.
- Also depends on the Sodium/Potassium Pump for the extra cation that is released so a state of equilibrium can be reached.