intracellular trafficking and membrane transport Flashcards
what is the organelle type in eukaryotic cells
membrane bound organelles
what is the membrane composed of in eukaryotic cells & name x2 characteristics if it
= phospholipid bilayer
- hydrophilic polar heads = interact with the aqueous environment both inside and outside of a cell
- hydrophobic hydrocarbon tails that interact to exclude water
what is the role of the cell membrane x1
what are the roles of organelle membrane x2
- prevent contents of the cell from escaping & mixing with its surrounding environment
- lipid membranes enclosing organelles act as containers for proteins & other soluble molecules = preventing them from freely mixing with proteins & molecules within the cytoplasm
- organelle in membrane enables the cell & individual organelles to maintain different conditions (e.g., concentration gradients or different pH)
define ectoplasmic face
faces outward environment
define cytosolic face
faces into the cell
what does transport of molecules inside & outside of cell depend on
size, charge, polarity & permeability of the membrane
why do cells need access from the outside environment x3
- need materials for biosynthesis
- need materials for energy production
- excrete waste
characteristic of the interior & exterior of cell membrane
- hydrophobic interior
2. hydrophilic exterior
can hydrophilic molecules cross the hydrophobic membrane interior without help
no
what facilitates the transport of the hydrophilic substances into membrane & out
= highly selective transporter & channel proteins that span the bilayer and allow these substances (e.g. proteins, molecules, ions) to be imported or exported
2 types of diffusion across membrane
- simple diffusion
2. facilitated diffusion
what does the rate of simple diffusion rely on
depends on its relative hydrophobicity and the size of the molecule
can ions cross with simple diffusion
no
order in terms of the rate of speed that these substances cross via simple diffusion:
- large uncharged polar molecules
- small uncharged polar molecules
- hydrophobic molecules
- ions
- hydrophobic molecules travel the fastest through
- next small uncharged polar molecules but some can’t get in
- slowest is large uncharged polar molecules and some can’t get in
- ions can’t travel through via simple diffusion at all
define facilitated diffusion
membrane transport proteins facilitate the movement of hydrophilic solutes across the bilayer membrane without them needing to interact with the hydrophobic interior
what are the two types of facilitated diffusion
protein transporters & channels
two types of transport through the membrane transporters & channels
passive or active (input of energy) transport
define passive transport
All channels and many transporters allow solutes to spontaneously cross the membrane bilayer and travel down a concentration gradient
define active transport
pumping of substances against the concentration gradient
does active transport occur in channels and transporter proteins?
no only transporter proteins
3 types of binding sites on a transporter
- Outward open: the binding sites for the solute are exposed to the outside
- Occluded: the sites are not accessible from either side
- Inward open: the binding sites are exposed on the inside of the bilayer
how does the transition between outward & inward states in transporter proteins occur & what’s it called?
when solute concentrations are higher outside of the cell, more solute will bind to the transporter in the outward conformation, when the transporter switches conformation, there will be a net transport of solute down its concentration gradient into cell
= spontaneous
how is the energy supplied in active transport
supplied via the hydrolysis of ATP, or through coupled pumps
define coupled transporters (type of active transport)
combine the movement of one solute to that of another.
= electrochemical gradient of one solute moving down its concentration gradient, is used to drive the active transport of another solute that is moving against its concentration gradient (e.g. sodium molecule travelling down concentration gradient drags glucose molecule with it)
define symporter
transporter pump moves both solutes in the same direction
define antiporter
two solutes are transported in opposite directions e.g. sodium potassium channel
example of a coupled transporter
Sodium-Glucose Symporter
where is a Sodium-Glucose Symporter found
= found on the apical membrane of the epithelial cells of the small intestine
what is transported in Sodium-Glucose Symporter
- as sodium moves into the epithelial cells, it travels down its electrochemical gradient (sodium concentration lower inside)
- energy stored within sodium electrochemical gradient is used to drag glucose into the epithelial cell against its concentration gradient (glucose concentration higher inside cell)
The greater the electrochemical gradient for Na+ the…. (Sodium-Glucose Symporter)
the more Na+ moves into the epithelial cell, simultaneously bringing more glucose into the cell
how does it transition between states in Sodium-Glucose Symporter
When Na+ binds to the pump in the outward open state, glucose will also bind. The occluded intermediate state will only be formed when both substrates are bound, before transitioning to the inward open state
what drives movement in ATPase pumps active transport)
hydrolyse ATP to drive the transport of a solute against an electrochemical gradient
what are the four types of ATPase (active transport)
- P-type pumps = phosphorylate themselves during the pumping cycle –> transports Na+, K+, H+, and Ca2+
- ABC transporters = pump small molecules across cell membranes = largest fam
- V-type pumps = turbine-like protein, multiple subunits, pump H+ into organelles e.g. lysosomes, to acidify the interior of these organelles.
- F-type ATPases (ATP synthases) similar to V pumps structurally
- found in mitochondria
- They work in reverse by using a H+ gradient across the membrane to drive the synthesis of ATP from ADP and phosphate
what does ABC transporters stand for
ATP-Binding Cassette transporters
example of P-type (active transport)
Sodium-Potassium ATPase Pump
how does the Sodium-Potassium ATPase Pump work & where is it found
- found on the plasma membrane of a cell
1. the hydrolysis of ATP induces a conformational change in the transporter
2. drives the exchange of 3x Na+ out of the cell, against its concentration gradient, with the pumping of 2x K+ into the cell, against its concentration
= action creates a negative environment within the cell and contributes to the membrane potential.
define channel proteins
form transmembrane pores across the bilayer and allow the passive movement of small water soluble molecules
what do channels facilitate the transport of
inorganic ions e.g. Na+, K+, Ca2+, or Cl–
are ion channels selective
yes & dependent on the diameter, shape of the ion channel & distribution of the charged amino acids which line the inner surface of the channel
types of ion channels x4
- voltage-gated
- ligand-gated (extracellular ligand)
- ligand-gated (intracellular ligand)
- mechanically gated
what is faster: ion channels or transporter proteins
ion channels because they don’t need to undergo any conformational changes
when do voltage gated ion channels open
they open when there is a change in voltage across the membrane
when do ligand-gated ion channels open
when a molecule binds to it
when do mechanical gated channels open
opens in response to vibrations or pressure
what creates a membrane potential
Differences in ion concentration inside and outside of the cell creates a membrane potential, with the inside of the cell being more negatively charged than the exterior
what makes a resting membrane potential
when the exchange of cations (+ ions) and anions (- ions) across the membrane is balanced and the voltage difference remains unchanged
what changes membrane potential
when ions flow through open ion channels is the basis of electrical signalling in many cells, particularly nerve & muscle cells
what charge are channels at resting potential & why
negative
potassium concentration higher inside the cell = slowly moves outside