Topic 3: Membranes Flashcards
What is the most abundant lipid in the plasma membrane?
Phospholipids
Phospholipids are _________ _________, containing hydrophobic and hydrophilic regions.
amphipathic molecules
Characteristics of phospholipids
- spontaneously form membrane bilayers
- hydrophobic core
- which creates selectively permeable barrier
Fluid Mosaic Model
A membrane is a fluid structure with a “mosaic” of proteins embedded in it
True or False: in the fluid mosaic model, there are no covalent bonds; only hydrophobic/hydrophilic interactions
True
Factors that affect the fluidity of a membrane:
- Temperature: cold=viscous
hot=fluid
- Fatty acid tail saturation:
- sat = viscous
- unsat = fluid
- tail length: long=viscous
short=fluid
- Presence of sterols -> act of stabilize fluidityWhat regulates membrane fluidity?
Sterols
Cholesterol is found in:
Animals
Animal cells insert cholesterol into bilayer to:
- Prevent freezing by stopping phospholipids from packing too tightly
- Prevent melting by restraining phospholipid movement and filling gaps
Membrane composition is an ________ _____ and is also ________.
adaptive trait, plastic (changeable, mouldable)
Peripheral proteins
- bound to surface of membrane
- polar amino acids on outside, non-polar inside
Integral proteins
- penetrate the hydrophobic core and are embedded in membrane
- non-polar regions interact with core of membrane
6 major functions of membrane proteins
- transport across membrane
- enzymatic
- signalling
- cell-cell recognition
- joining
- Anchoring
What is the permeability of the lipid bilayer?
selectively permeable
- small and uncharged molecules let through
- large and charged blocked
What is passed through lipid bilayer most easily?
Nonpolar molecules
- O2, CO2, N2
What passes through lipid bilayer but passes slowly?
small, uncharged polar molecules
- H2O, indole, glycerol
What can’t pass through lipid bilayer because it is too big?
large, uncharged polar molecules
- glucose, sucrose
What is totally blocked from lipid bilayer?
Ions
- CI-, K+, Na+
Two types of transport:
Active: requires energy, moves against/up concentration gradient
Passive: based on diffusion, moves with/down concentration gradient
What is osmosis?
the diffusion of water across a selectively permeable membrane
osmotic pressure
the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semi permeable membrane
Tonicity
the ability of a surrounding solution to cause cells to gain or lose water - osmosis
Isotonic solution
solute concentration is the same as that inside the cell; no net water movement across palm membrane
Hypertonic solution
solute concentration is greater than that inside the cell; cell loses water
Hypotonic solution
solute concentration is less than that inside the cell; cell gains water
Channel Proteins
provide corridors that allow a specific molecule or ion to cross
- acts like a tunnel
Carrier proteins
undergo subtle change inshore that translocate the solute-binding site across the membrane
- acts like revolving door
Aquaporins
allow water to move across the membrane at rates that can sustain life
- makes tunnel that is hydrophilic
- allows cells to quickly adjust water balance
Facilitated diffusion (requires transport protein)
the solute moves down its concentration gradient, and transport requires no energy
Characteristics of transport proteins
- specific: work only with specific molecules
- can become saturated: all available proteins in use
- can be gated: open/close
When does cotransport occur?
when active transport of a solute indirectly drives transport of other solutes
(two transports working together)
Bulk transport
- requires energy
- both directions involve formation of vesicle
- 2 processes : endo/exocytosis
Endocytosis
moving things in
- cell takes in macromolecules by forming vesicle from palm membrane
Exocytosis
moving things out
- transport vesicles migrate to membrane, fuse with it, release contents to outside cell
