Lecture 3: Intro to membranes Flashcards
why are membranes composed of a phospholipid bilayer?
b/c of their geometry (cylindrical) and their chemistry (amphipathic)
- Amphipathic nature allows phospholipids to spontaneously form membranes
Define a micelle and describe differences b/t micelle and bilayer
Micelle= forms an aggregate with the hydrophilic “head” regions in contact with surrounding solvent, with the hydrophobic single-tail regions in the micelle centre.
- Micelles are single tailed phospholipids, bilayers are double
- phospholipids spontaneously form a bilayer because they’re cylindrical
- micelles form (a circle) because phospholipids are conical (cones)
Phospholipids can move freely laterally because they’re only associated based on hydrophobicity, and no ____ bonds
covalent
What’s the effect of high temp of membrane fluidity? Name the 3 adaptations
more kinetic energy at high temps = move faster, gap increases between them
1) increase HC tailing (increases hydrophobicity)
2) decrease C=C bonds (double)- the kink prevents close packing
3) increase cholesterol content (increases hydrophobicity and acts as a pylon to slow them)
What’s the effect of low temp of membrane fluidity? Name the 3 adaptations
less kinetic energy at low temps = move slower, gap decreases between them
- increase C=C (double) b/c kink physically pushes them apart
- decrease tail length (decrease hydrophobicity)
- increase cholesterol: acts as a spacer b/w phospholipids
What are the 2 types of membrane associated proteins
integral membrane proteins and peripheral membrane proteins
many protein-protein interactions in membranes are hydro____
hydrophobic
How can you tell the difference b/w an animal and plant membrane?
animal membrane contains cholesterol
The fluid mosaic model states that:
the membrane is a fluid structure (phospholipids) with a mosaic of different proteins embedded in or attached to a double bilayer of phospholipids
____ have different functions within the bilayer; for every role of the membrane there’s a ___ involved
protein
protein
name 6 of the different types of proteins in a membrane
- transporter
- enzymes
- cell-cell recognition
- cell-cell attachment
- signal receptors
- attachment to extracellular matrix
what substances are permeable to the membrane?
small, uncharged molecules
Impermeable substances cannot cross the hydrophobic core because they’re either too ___ or too ___
large
polar
____ are the least permeable to the membrane. Why?
Ions
- b/c whenever there’s a proton, there’s an entourage of water, making a big, polar molecule
Water is polar but diffuses readily by osmosis (is permeable). why?
it undergoes a dipole moment: the unequal charge distribution disappears long enough to cross the membrane
*but water diffuses by osmosis very slowly
osmosis is the ___ diffusion of water
passive
Passive transport (for ____ (permeable/impermeable) substances) is diffusion that’s not active or involved in any way. Define diffusion
permeable
- diffusion= movement of molecules from an area of high concentration to an area of [low] until an equilibrium is reached
- molecules have thermal motion and can diffuse
water follows ___
solute
what’s the risk in an animal cell if too much water rushes in?
the cell can burst! = osmotic lysis
describe a hypotonic enviro in an animal and plant cell
H20 rushes into the cell (increase [solute] inside the cell)
- animal cell may burst (b/c no cell wall)
- in a plant cell, the cell wall prevents bursting
describe a isotonic enviro in an animal and plant cell
no net water movement
[solute] inside cell = [solute] outside cell
-“perfect” enviro
describe a hypertonic enviro in an animal and plant cell
H20 rushes out of the cell (increase [solute] outside the cell)
risk= cell shrinks
- in plant cells, plasmolysis can occur (pulling away of membrane from cell wall)
____ are a protein that’s a transmembrane water channel. This speeds up osmosis
aquaporins
Facilitated diffusion involves
- ____ energy input
- transport __(up/down) concentration gradient
example?
no
down
example= aquaporin
2 types of facilitated transporters
- Channel protein
2. Carrier protein
Describe channel proteins
- used to move molecules down their conc. gradient
- it’s an integral membrane protein
- allows transport of a specific solute without changing the shape
- can tell difference b/w different molecules, so very specific with what molecules are allowed across
Describe carrier proteins
- used to move molecules down their conc. gradient
- spans bilayer (integral membrane protein)
- allows transport of a specific solute by changing shape
transport proteins are ____ and can be ____ (open or close in response to a stimuli)
specific
gated
active transport requires ___
- solute moves __(up/down) gradient
energy
up
why perform active transport? list 3 reasons
- to concentrate nutrients in the cell
- to expel waste
- to maintain a voltage and/or [gradient] across membrane
an example of active transport is the ____/___ ___
sodium/ potassium pump
what’s an example of cotransport?
cotransport= 2 molecules use the same transporter example = Na/ K pump
explain the Na/K pump
SOPI PONI (sodium out, potassium in; positive out, negative in) 3Na+ out and 2 K+ in net negative charge inside the cell (resting membrane potential)
symport vs antiport
(in cotransport)
symport= 2 molecules moved in same direction
antiport= 2 molecules moved in different directions
molecule that need to pass the membrane but are too large must be transported using a _____ transport mechanism.
This involves the formation of ____
bulk
vesicles
bulk transport can either undergo ____ (secretion) or _____(“bringing into cell”)
exocytosis
endocytosis
receptor mediated endocytosis is the ____ of a specific ligand (anything that binds a receptor).
- receptor = ______
- receptors congregate at ____-____ pits
endocytosis
receptor= integral membrane protein that recognizes and binds a specific ligand
clathrin- coated pits (clathrin recruits receptors)
