Lab 6: Membrane Permeability Flashcards
Lipid membranes are made up of _____
phospholipids
“Mosaic” part of the fluid mosaic model
due to proteins, cholesterol and other molecules that are a part of the membrane surface
“Fluid” part of the fluid mosaic model
phospholipids can diffuse rapidly through the membrane. proteins can also diffuse, but are slower due to larger sizes.
A protein that spans the entire membrane and often as a hydrophobic core but hydrophillic end is aka ______
integral protein
a loosely attached protein on one face of the membrane is known as a ____
peripheral protein
how is a peripheral protein anchored onto the lipid membrane face?
by non-covalent forces, can be easily stripped with detergent.
Oligosaccharide
chain of 3-7 sugars. Often used for cell recognition and communication
Glycoprotein
protein with an oligosaccharide linkage
glycolipid
lipid with oligosaccharide linked to phosphate head.
Membranes are semi permeable. What does this mean?
they are permeable to lipid soluble, uncharged, and small molecules, but are impermeable to larger molecules.
2 properties about a molecule that dictates how it can pass through a membrane
1) the size of the molecule
2) the ability to enter the hydrophobic interior of the membrane
osmosis
the movement of water across a SEMIPERMEABLE membrane down it’s concentration gradient
three ways solutes can be moved
1) diffusion
2) facilitated diffusion
3) active transport
how is water moved across a membrane
osmosis
3 cellular functions that rely on membrane transport
1) acquiring nutrients
2) disposing of waste
3) maintaining cell volume
Why are red onions good specimans to analyze H2O movement?
- has large and translucent cells, easily defined cell wall
- cell is mostly comprised of the central vacuole, which can be easily seen due to red and purple pigment
central vacuole membrane of a plant cell is also known as a
tonoplast
vacuoles in onion cells contain _____ that accounts for the red and purple pigments
anthocyanins
Effects of a hypotonic solution on a cell
cell is more salty than the hypotonic solution. Water will enter the cell via osmosis. If cell has a cell wall, the wall will provide support for the water pressure and the cell will become turgid. if there is no cell wall, the cell may burst if water rushes into it too fast.
How does a cell become turgid?
when water enters the central vacuole of the cell, and the tonoplast (membrane surrounding the vacuole) presses up against the cell wall.
Effects of a hypertonic solution on a cell?
the cell is in a salty solution. Water will LEAVE the cell via osmosis and the central vacuole will shrink away from the cell wall, resulting in PLASMOLYSIS
what is deplasmolysis
when a plasmolyzed cell is returned back to a hypotonic solution (or isotonic) and the vacuoles swell up again to full turgidity.
How can you trigger deplasmolysis?
place the cells in a HYPERTONIC solution with DIFFUSABLE SOLUTES.
- first, water will rush out of vacuole into the hypertonic solution and the cell will plasmolyze
- solutes will begin to slowly diffuse across the membrane into the cell, making the cell more “salty”
- when solutes enter the cells,water will follow, resulting in more water in the cell, allowing it to regain its turgidity.
what is the iso-osmotic threshold
the concentration of solute in solution required for the cell to remain in a normal turgid or isotonic state
how would you find a more specific isoosmotic threshold?
use smaller increments of solute
Why is the NaCl isoosmotic threshold lower than the sucrose threshold?
NaCl will dissociate into 2 ions (Na+, Cl-), contributing to 2x the amount of solute particles present in the water than that of a sucrose solution, which does not dissociate.
- ideally, the NCl solution would have an isoosmotic threshold thats 1/2 that of sucrose.
would sucrose or NaCl solution create a faster rate of deplasmolysis? Why?
Nacl.
Recall: deplasmolysis occurs when diffusable solutes move into the cell and then water follows. The rate of deplasmolysis is reliant on the ability for the solute to first enter the cell:
- both Nacl and sucrose are polar. therefor, the polarity will cause both of them to move slow
- Nacl dissociates into two ions,there for there is 2x the solute concentration and a steeper concentration gradient, NaCl is more likely to enter the cell at a faster rate because of the steeper gradient.
- molecular size will play a role on the rate of deplasmolysis
- NaCl is smaller than sucrose and could diffuse into the membrane faster
How is the rate of de-plasmolysis affected by biological mechanisms
affected by osmoregulation
specific example of how osmoregulation regulates the rate of de-plasmolysis
how the stomata of plants can open and close in order to prevent water loss. the stomata is reliant on the Absicsic Acid hormone, causing stomata closing and stimulates root growth so that water can be absorbed, aiding in WATER CONSERVATION. surplus of water would allow water to flow back into the cells, deplasmolyzing them and preventing wilting.
