L5: Membrane Lipids - Membrane Structure and Self-Assembly Flashcards
What is the primary subunit of the cell membrane?
phospholipid
What is the purpose of the cell membrane?
- defines the cell’s boundary
- barrier to the environment
- wall to hold stuff in
- gateway for things that need to move in and out of the cell
What are the two important regions of a phospholipid
- head
- tails
Describe the phospholipid’s head
- contains a number of polar bonds and ionic charges
- polar head
Describe the phospholipid’s tails
- carbon and hydrogen bonds
- non-polar tails
What is an amphipathic molecule?
a molecule that contains both polar (hydrophilic) and non-polar (hydrophobic) components.
What happens to phospholipids when added to water?
They spontaneously form a bilayer
Describe the non-covalent interactions in terms of the non-polar tails
interact with each other with ID-ID interactions
Describe the non-covalent interactions in terms of the polar heads
interact with each other and surrounding water with:
- PD-PD interactions
- PD-ion interactions
- H-bond interactions
What is an important aspect of the cell membrane?
It is largely held together by non-covalent interactions
Describe the concept of the fluid mosaic model
- “fluid”: membranes are dynamic. the lipids and proteins are not covalently linked and can move freely in the plane of the membrane
- mosaic: diverse components. Membranes are made up of phospholipids embedded with proteins.
Which molecules can easily pass through the membrane?
- small, non-polar molecules
- CO2, O2, and H2O (even though they’re polar)
What does the direction of net movement depend on?
the concentration gradient
Which molecules CANNOT easily pass through the membrane?
- large, polar molecules
- ex: glucose
What are non-covalent interactions?
- weak bonds that are less permanent
- interactions between other molecules
What is macromolecular assembly?
When macromolecules assemble into higher-order structures.
- ex: DNA Helix, Lipid Bilayer
What are some examples of an INTRAmoleculer interaction?
Covalent, Ionic interactions
What are the TWO key ideas in regards to phospholipids/membrane structure?
- Phospholipid structure interact via non-covalent interactions
- Membrane formation is spontaneous due to thermodynamics and hydrophobic effect
Define and explain “hydrophilic”
- molecules (or molecular groups that are part of that molecule) that interact with water
- typically, polar, charged, make H-bonds and ionic interactions
Define and explain “hydrophobic”
- molecules (or molecular groups that are part of a larger molecule) that tend to have weak or little interactions with water
- typically non-polar bonds
What type of bond is present between water and water
PD-PD
What types of bond(s) are present between water and a lipid head group?
- PD-PD
- PD-Ion
- PD-ID
What types of bond(s) are present between water and lipid tails?
- PD-ID
What types of bond(s) are present between lipid tails and lipid tails?
- ID-ID
What contributes to the enthalpy of the system?
Covalent (between atoms in the phospholipids) and non-covalent interactions contribute to the enthalpy (bondedness) of the system
In an aqueous environment, what happens when a lipid bilayer forms?
- Hydrophobic part of lipid molecules make many non-covalent interactions between each other
- hydrophilic part of lipid molecules make many non-covalent interactions with water
- water molecules make many non-covalent interactions with the hydrophilic parts and between themselves
What does a system’s stability depend on?
- enthalpy
- entropy
In regards to phospholipid assembly in water, what happens to the stability of the system?
- it moves from less stable to more stable
Describe phospholipid assembly in water in terms of spontaneity
- spontaneous and energetically favourable (delta g < 0)
What is the hydrophobic effect?
- The observation that burying non-polar groups away from water increases the system stability
- Water molecules have increased entropy (motional freedom) when tails come together
Describe SPONTANEOUS state of thermodynamics.
- Energetically favourable
- likely to happen in this direction
- less stable to more stable
Describe NON-SPONTANEOUS state of thermodynamics.
- Energetically unfavourable
- requires energy to happen in this direction
- more stable to less stable
