LEC 3-Introduction to Membranes Flashcards
What are biological membranes made up of?
A phospholipid bilayer
Why do phospholipids spontaneously form a bilayer when they are added to water?
Phospholipids are amphipathic. When they are placed in water, the lipid tails are subject to the hydrophobic effect. The highly polar water molecules do not interact readily with the hydrophobic lipids and so force them to clump together to avoid the water. The hydrophilic heads can remain in contact with the water. A bilayer will result, with the hydrophobic lipids packed into the centre and with the hydrophilic phosphates facing the water on the edges of the membrane.
Which of the following are not considered a major factor to influence membrane fluidity?
A. Cholesterol B. Fatty acid saturation C. Osmotic pressure D. Temperature E. B and C
C. Osmotic pressure!
Cholesterol is used to maintain membrane fluidity in hot/cold environment
Temperature does effect membrane fluidity
What is the difference in formation between a bilayer and micelle?
A bilayer is formed when double-tailed phospholipid are put into water (It forms a bilayer).
A micelle is formed when single-tailed phospholipids are placed into water. These are formed because single-tailed phospholipids are conical.
The phospholipid bilayer can move freely. What direction do they move around?
The phospholipid can move around laterally RAPIDLY within the same plane.
Why is flip-flop movement in membranes very rare?
Flip-flop movement is rare because the polar head of a phospholipid is not stable in the hydrophobic core.
What does it mean to be amphipathic?
Amphipathic means for a substance to have both a hydrophilic and hydrophobic ends
What are the most permeable substance? What is the least permeable?
Least- ions
Most- gases (like oxygen and carbon dioxide)
What occurs when a cell is placed in a hypertonic environment?
Lots of salt on the outside; therefore, the water rushes out (lots of girls outside, boys rush out).
The cell would undergo plasmolysis
What occurs when a cell is placed in a hypotonic environment?
Lots of salt on the INSIDE of the cell; therefore, the water rushes IN (“There are no girls outside, so let’s go in,” the boys’ said).
When a plant cell is placed in a hypotonic environment, what prevents it from bursting?
The cell wall prevents the plant cell from osmotic lysis.
What are the channels that allow water to diffuse into the cell? What type of diffusion is this?
Aquaporins
This is an example of facilitated diffusion.
What occurs when a membrane is in high temperatures?
The phospholipid increases in kinetic energy; therefore, it moves faster. The gap between the membranes increases which increases permeability.
What are some adaptations to high heat some membranes have?
1) Increase the hydrocarbon tail length (increase hydrophobicity)
2) Decrease the # of double-bonded carbons
3) Increase cholesterol content (which increases hydrophobicity and slows down phospholipids)
What occurs when a membrane is in cold temperatures?
The gaps between phospholipids decreases; therefore, reduces permeability & flexibility.
