Lecture 2 Membrane Transport Mechanisms Flashcards
Kinetic Energy
Molecules will have movement until it encounters another particle and change direction.
Don’t have to put E into system
Osmosis
Movement of water across membrane without putting E into system
High conc to low conc
Only water can cross
Osmotic Pressure
Semipermeable membrane - only some things can get through, allowing water through the diphram
Dynamic Equilibrium
molecules will be entering and leaving at same rate
3 critical parts of cell fluid
Sodium, Potassium and Chloride
Sodium highest
outside cell
142 conc
Potassium highest
inside cell
140 conc
Chloride highest
outside cell
103 conc
3 Energy independent mechanism for crossing cell membrane
- Diffusion
- Osmosis
- Facilitated Diffusion
Diffusion
High conc to low conc. No membrane required, but can be.
Ex. Perfume, high conc (on you) to low conc (person walking by)
Osmosis
Movement of water molecules across semi-permeable membrane
Facilitated Diffusion
Requires carrier proteins
No Energy required
Low conc to high
4 Types of Mechanisms to cross cell membranes that require channels
- Aquaporins
- Ion channels
- Ligand gated
- Voltage gated
Channels
are proteins that create pathways through cell membrane
Ex. Channel proteins
Very transient, depends on need of cell
Non-gated channels
Always open
2 types 1. Aquaporins 2. Ion channels
Gated channels
May open or close at any time, voltage required
2 types 1. Ligand 2. Voltage
Ligand gated
Requires a signal molecule to open
Voltage gated
When voltage changes, they open. Critical for membrane potentials
Mechanisms for Crossing cell membranes Energy dependent
- Active transport
- Primary - requires ATP
- Secondary - requires multiporters
Active Transport
Energy typically comes from ATP
Defying entropy
Primary and Secondary
Primary Active Transport
Requires ATP at site of transportation
ATPases have enzyme that can split ATP to get E
Many types of ATPases, each responsible for something different. This happens first, then secondary
Secondary Active Transport
Requires multiporters
2 types 1. Symporters - cotransporters
2. Antiporters - countertransporters or exchangers
Multiporters
Proteins that will transport more than one solute at a time
2 Types of Multiporters
- Symporters
2. Antiporters
Symporters
2 sometimes 3 in the same direction at the same time
Antiporters
Transports 2 or 3 different in different directions
Diffusion
Movement of particles from area of high conc to low conc
Depends on kinetic energy of particles rather than external energy
Difussion across biphospholipid layer
Particles that diffuse across biphospholipid layer
Oxygen, carbon dioxide, nitrogen, alcohols can diffuse readily across biphospholipid layer
3 Factors affecting rate of diffusion
- proportional to concentration difference across membrane
- Membrane electric potential (Nernst potential)
- Pressure difference
Osmosis
Diffusion of solvent (water) across a semipermeable membrane
Facilitated Diffusion
Requires uniporter carrier protein
Vmax
Used by glucose, amino acids
Uniporter carrier protein
Used in facilitated diffusion
Carry one type of particle with the diffusion gradient
Vmax
Limits the transporter, can be overwhelmed
Ex. If you eat 15 donuts, will be sugar in urine
2 things that use Facilitated diffusion
Glucose, amino acids
3 Types Non-gated channels
- Aquaporins
- Potassium channels with selectivity filters with carbonyl oxygens
- Sodium channels
Why can’t sodium use potassium’s channel
Potassium is larger, so it would fit. But there is a selective filter that doesn’t let it through
Active transport
Movement of particles against concentration gradient Requires energy 2 types Primary Secondary
Primary active transport
Energy is derived directly from breakdown of ATP
Utilizes ATPase transporters
Secondary transport
Energy is derived secondarily from concentration differences of molecular or ionic substances created originally by primary active transport
Utilizes multiporters
Na+ K+ pump uses
Primary active transport
Most common in nerve cells
