Membrane Transport Flashcards
Active Transport Features
Substances move from low to high concentration
Substances move against concentration gradient
Requires ATP and a protein pump
Equilibrium is NOT reached
Examples include endocytosis, exocytosis, and active transport
Glycolipid Protein Location and Function
Location: Phospholipids with carbohydrates attached, hydrophilic
Function: Cell recognition, identifies self and non-self cells, forms a layer with glycoprotein called glycocalyx which binds cells together and prevents the tissue from falling apart
Peripheral Protein Location and Function
Location: Bound on the membrane surface, hydrophilic
Function: Cell to cell communication
Protein Pumps
The carrier has two sides, with one to recognize the substance to carry and one to release ATP to provide energy for the protein carriers
As a result, the protein molecule changes its shape so the target substance can be carried across the membrane
After that, the phosphate molecule is released from the protein molecule and combines with ADP to form ATP in the mitochondria
The protein then reverts back to its original shape
Components of Plasma Membrane
Phospholipid and Cholesterol
Cholesterol
An amphipathic molecule that is needed for membrane fluidity and stability
Disrupts the regular packing of the tails which increases flexibility as it prevents the tails from crystalizing and solidifying
Allows membranes to function at a wider range of temperatures
Integral Protein Location and Function
Location: Penetrate the phospholipid bilayer, amphipathic
Function: Pumps for active transport and channels for facilitated diffusion
Differences with Simple and Facilitated Diffusion
Simple Diffusion moves directly through the phospholipid bilayer while facilitated diffusion doesn’t move directly through
Simple diffusion doesn’t involve a channel protein while facilitated diffusion uses channel proteins
Simple diffusion transports hydrophobic molecules while facilitated diffusion transports hydrophilic molecules
Simple diffusion is slower and facilitated diffusion is faster
Function of Phospholipids in Cell Membrane
Allow lipid-soluble and polar substances to enter and exit the cell
Prevents water-soluble substances from entering and exiting the cell, acts as a hydrophobic barrier
Allows membrane fluidity and stability
Functions of the Plasma Membrane
Structural (keeps cell contents together)
Serves as the boundary between the cytoplasm and the external environment
Maintains stability and fluidity of the cell
Provides cell-to-cell communication by different mechanisms
Controls what enters and exits the cell
Simple Diffusion
The passive movement of particles across a partially permeable membrane and concentration gradient from high to low concentration
Components of Phospholipid
Hydrophilic Head: Made of glycerol and phosphate group and faces outwards into both the cytoplasm and external environment
Hydrophobic Tail: Made of 2 fatty acids facing each other
Phospholipid bilayer is amphipathic
Facilitated Diffusion
The passive movement of molecules across the partially permeable membrane and the concentration gradient through the aid of a membrane channel
Types of Active Transport
Protein Pumps
Exocytosis
Endocytosis
Fluid Mosaic Model
FMM was first suggested to describe the arrangement of molecules in the plasma membrane
Fluid: Always changing shape and flexible
Mosaic: The pattern of the scattered proteins when seen from above
Model: No one knows how plasma membrane looks like, so this was constructed based off experiments on the behaviour of the membrane
Cotransport
The coupled movement of substances across a cell membrane via a carrier protein
A combination of facilitated diffusion and active transport
Endocytosis
The process by which macromolecules enter the cell
The membrane pulls inwards and seals back on itself forming a vesicle
The vesicle pinches off the plasma membrane
Inside of plasma membrane becomes outside of vesicle membrane, and vice versa
The vesicle enters the cytoplasm and carries the content anywhere in the cell
Fatty Acids in High and Low Temperatures
High: Stabilizes the membrane and raises the melting point
Low: Intercalates between the phospholipids by disrupting the packing of tails
Function of CAMs
Help cells stick to each other
Crucial components in maintaining tissue structure
Play important roles in the cell’s growth
Factors Affecting Fluidity of Membrane
Fatty Acid Saturation: The more saturated the fatty acid, the less movement, therefore the less fluid the membrane is
Tail Length: The longer the tail, the less fluid the membrane
Temperature: The lower the temperature, the more the membrane solidifies. Solidified membranes do not function well
Cell Adhesion Molecules (CAMs)
Cell surface proteins that are involved in the binding of cells with other cells through cell adhesion
Glycoprotein / Conjugated Protein Location and Function
Location: Peripheral proteins but with carbohydrates called oligosaccharides attached, hydrophilic
Function: Cell recognition, identifies self and non-self cells, forms a layer with glycolipid called glycocalyx which binds cells together and prevents the tissue from falling apart
The 2 Types of Integral Proteins
Channel Proteins: Transports most of the ions and hydrophilic molecules through facilitated diffusion
Carrier Proteins / Protein Pumps: Transport molecules by active transport using ATP
Importance of Selective Permeability
Helps maintain and regulate a cell’s internal environment and conditions
Permeability depends on size, charge, and polarity of molecule
Osmosis
The passive movement of water molecules across a partially permeable membrane through aquaporin protein channels from low solute to high solute concentration until equilibrium
Active Transport
The movement of substances through the membrane against their concentration gradient from low to high concentration through the use of ATP and carrier molecules
Passive Transport Features
Moves from high to low concentration
Substances move across a concentration gradient
Doesn’t require ATP or a protein pump
Equilibrium is reached
Examples include simple diffusion, facilitated diffusion, and osmosis
What Determines How Easily Substances can pass Membranes
Size: Smaller substances can enter easier
Polarity: Non-polar (hydrophobic) molecules can pass easier than polar (hydrophilic)
Exocytosis
The process by which macromolecules leave the cell
Vesicles from RER transport proteins to Golgi apparatus
These Vesicles undergo modification from the Golgi and get repackaged and sent into the plasma membrane
The vesicles carrying the protein fuse with the membrane expelling the content outside the cell
The membrane then goes back to its original state
Gated Ion Channels
Three sodium ions bind on the sodium potassium pump in the intracellular space
ATP attaches to the protein and a phosphate group is transferred to the pump via hydrolysis
This causes a change in shape for the sodium pump, thus releasing the sodium ions into the exterior
Two potassium ions bind to different regions of the protein in the exterior surface which causes the release of the phosphate group
The loss of phosphate makes the pump revert back to its original shape and releases the potassium ions into the intracellular space
