Osmoregulation
What is osmoregulation?
Regulation of solute concentrations and water balance in cells
What is passive transport and why is it named as such?
Diffusion of a substance across a biological membrane. Called "passive" because no energy is required.
What supplies the energy needed for active transport?
ATP
What two biomolecular components primarily contribute to the structure of cell membranes? How does this relate to the name given to the model of biological membranes?
Lipids and Proteins; "Fluid-mosaic" model --> fluid part represents the fluid phospholipid bilayer, while "mosaic" part represents the collection of proteins in the cell membrane.
Can polar molecules such as glucose pass through the bilayer?
YES. However, they do so SO slowly that it is ineffective for transport without assistance of membrane proteins.
What type of environment would most accurately maintain proper water balance in plant cells?
Hypotonic environments
When a particular substance moves down its concentration gradient, is it affected by other substances?
No--each substance diffuses down its OWN concentration gradient, unaffected by other substances.
What kinds of proteins are involved in active transport and why?
Carrier proteins--only carrier proteins are involved in active transport because they physically transport their substance from one side of the membrane to the other.
(Channel proteins on the other hand only provide a tunnel for substances to pass through, they don't actually provide any help in moving the substance)
What does the term "amphipathic" mean and how does it relate to biological membranes?
Means it contains both a hydrophilic region and hydrophobic region. This describes the phospholipids in the bilayer and why they are able to spontaneously orient themselves into this formation.
What is a channel protein and which specific one transports water across a membrane?
Protein with hydrophilic channel that certain molecules/ions use as a tunnel through the membrane. Aquaporins are channel proteins that facilitate water movement.
How does the unicellular protist p. caudatum osmoregulate in its environment?
P. caudatum lives in a hypotonic environment. In order to osmoregulate, the organism makes use of contractile vacuoles, which pump water out of the cell as fast as it enters.
Is facilitated diffusion a type of passive transport? Why or why not?
Yes--Large / polar molecules that have trouble crossing the bilayer use transport proteins to facilitate movement down their concentration gradients. Because they are still moving down their gradients and no energy is required, this is a method of passive transport.
Is ATP a part of the cotransport process? Why or why not?
No--although ATP can power proton pumps which can be used to generate concentration gradients, it is not involved with the cotransporter protein itself in actively transporting substances in or out of the cell.
Is the Na+/K+ pump a transport protein or a transmembrane protein? Why/why not?
Both
Selective permeability of a membrane depends on what two key factors?
1. Discriminating barrier of lipid bilayer
2. Specific transport proteins of membrane
The sodium concentration in blood plasma is typically around 137-145mEq/L. If RBCs were isolated and placed in a 5M KCl solution, what would likely happen to the cells after a brief period of time and why?
Cell would probably shrink and become non-functional. Intracellular [K+] is high relative to outside of cell. If we dramatically increase extracellular concentration of [K+], it would reverse the direction of diffusion (and free water movement) across the cell membrane. Higher solute concentration outside cell would mean lower free water concentration relative to inside cell --> water would rush out of cell.
What are the two main types of channel proteins involved in facilitated diffusion? Are they interchangeable?
Ion channels and gated channels. Ion channels transport specifically ions, while gated channels open and close in response to a stimulus. Stimulus can be binding of an ion or allow for the passage of ions.
What type of pump is a proton pump and how does it act as a dual energy source for the cell?
An electrogenic pump (generates a voltage across the membrane) -- Translocates ( + ) charge in the form of protons. That voltage as well as the proton gradient generated both act as energy sources to drive other processes in the cell.
How do cholesterol and saturation of hydrocarbon tails affect membrane fluidity?
Cholesterol - at moderate (warmer) temps, C decreases membrane fluidity. At colder temps, C increases fluidity.
Saturation -- Increasing saturation decreases membrane fluidity.
500 mL of a 1M sucrose solution and 250mL of a 2M sucrose solution are placed on either side of a selectively permeable membrane. The membrane is permeable to water, but not to the larger sucrose molecules. After 5 minutes have passed, what will the two sides of the membrane look like?
The volumes of solution on each side of the membrane would be relatively equal.
How do certain cells of the renal system make use of passive transport to osmoregulate?
Contain aquaporins to reclaim water from urine. Concentration of water is high in tubules/vessles of renal system, so aquaporins allow diffusion out into extracellular fluid so that it may be taken up by cells.
What are the two forces that drive ions across a membrane? Explain how Na+ movement across animal cell membranes relates to these forces in establishing membrane potential.
Chemical (concentration gradient of ions) and electrical (attraction of ions/charged particles to oppositely charged side of membrane). Na+ "falls" down its electrochemical gradient. [Na+] is higher outside the cell, so it wants to diffuse in. The inside of cells are negatively charged relative to the outside, so Na+ also naturally is attracted inward because of its positive charge.
How does the Na+/K+ pump demonstrate active transport? Explain what occurs during the process of one "pump."
Cytoplasmic Na+ binds to pump. Binding stimulates phosphorylation by ATP. Phosphoryllation causes protein shape change (reducing affinity for Na+). New shape allows binding of K+ on extracellular side. Binding triggers release of phosphate group. Loss of phosphate restores original protein shape.
Name/describe 4 of the 6 functions of membrane proteins.
Transport-
Enzyme-
Signal transduction-
Cell-cell recognition-
Intercellular joining-
Attachment to ECM/cytoskeleton-