Cell Transport Processes Part 1 Flashcards
Format of Phospholipid Bilayer
Energetically Unfavourable- Planar phospholipid bilayer with edges exposed to water
Energetically Favourable- Sealed
(Spherical liposomes) compartment formed by phospholipid bilayer
Diffusion
Diffusion is the movement of
molecules in a fluid from
areas of high concentration to
areas of low concentration
Osmosis
A process by which molecules
of a solvent tend to pass
through a semipermeable
membrane from a less
concentrated solution into a
more concentrated one.
Cell Membrane
the semipermeable membrane
surrounding the cytoplasm of a cell
Rate of Simple Diffusion
Small, non polar molecules (O2,CO2, N2 and steroid hormones—-> Go through straight away
Small, uncharged polar molecules (H20, ethanol and glycerol)—–> Most rejected by lipid bilayer, some pass through
Larger, uncharged polar molecules (AAs, glucose and nucleotides)—–> Most rejected by lipid bilayer, some pass through
Ions (Na+, Ca2+, K+, Cl-)—–>All rejected
Passive Transport
-Simple Diffusion
-Channel Mediated
-Transporter Mediated
Active Transport
Active transport against concentration gradient using energy and ATP
Aquaporins
Water Channels
Example of Passve Transport
1)Glucose from extracellular space binds to glucose transporter at the glucose binding site
2) Binding occurs
3) Glucose released to cytosol
Active Transport Example
Ca2+ pump in sarcoplasmic reticulum is an ATP driven ion pump
2Ca2+from cytosol attaches to the calcium-binding cavity. Aspartic Acid remains in the nucleotide binding domain. ATP is used for active transport, therefore, ATP becomes ADP and Pi is released
2Ca2+ is released to the lumen of the sarcoplasmic reticulum. Aspartic Acid is phosphorylated via phosphorylation domain.
Antiporter (Active Transport) Na+-K+ pump
3 Na+ out
2 K+ in
Charge difference = -1
Binding of Ions:
3 sodium ions (Na⁺) from inside the cell bind to the pump.
ATP Binding:
ATP attaches to the pump and is hydrolyzed, providing energy. A phosphate group stays attached to the pump, causing it to change shape.
Sodium Release:
The shape change moves the 3 Na⁺ ions out of the cell and releases them into the extracellular space.
Potassium Binding:
2 potassium ions (K⁺) from outside the cell bind to the pump.
Phosphate Release:
The phosphate group is released, causing the pump to return to its original shape.
Potassium Release:
The 2 K⁺ ions are released inside the cell, resetting the pump for the next cycle
Channels
Closed Conformation- flow of ions controlled by a gate
Opened Conformation- allows rapid influx of ions through channel
Pore- Controls what enters channel based on size, proportion and charge
Transporters- Glucose transport via facilitated diffusion:
Binding:
Glucose binds to a specific glucose transporter protein (e.g., GLUT) embedded in the cell membrane.
Conformational Change:
The transporter undergoes a shape change, allowing glucose to pass through the membrane.
Release:
Glucose is released into the cell’s interior (or exterior), following its concentration gradient (high to low).
This process doesn’t require energy (ATP).
