Membrane Transport Flashcards
Examples
Gases
small Hydrophobic Molecules
Small polar molecules
Large Polar molecules
Charged molecules
Gases
= O₂, CO₂ , N₂
small Hydrophobic Molecules
= Lipids: fatty acids/Triglycerides
= Hydrocarbons: Benzene, octane, methane
Small polar molecules
= H₂O ,ethanol, Methanol, Glycerol, Ammonia
Large Polar molecules
= Glucose, sucrose, amino acids, proteins , DNA/RNA (do not fit)
Charged molecules
= H+, Cl-, Na+ and Ca2+
Order these from Most permeable to LEAS permeable.
small non polar molecules
large polar molecules
charged molecules
gases
small A polar molecules
Proteins
Gases
Small, nonpolar molecules (e.g., lipids, benzene)
Small polar molecules (e.g., water, ethanol):
Large polar molecules (e.g., glucose, amino acids)
Charged molecules (e.g., ions like Na⁺, Cl⁻, Ca²⁺): These are the least permeable and require ion channels or transporters to move across the membrane.
Proteins
How does glucose move across membranes?
cannot pass through the cell membrane via simple diffusion (CHANNEL PROTEINS), instead, it requires specific transport proteins, such as glucose transporters (GLUTs),
What facilitates transport across membranes.
Transmembrane Proteins- These proteins can function as either Channels or Transporter/carriers.
BE ABLE TO IDENTIFY WHICH ONE IS WHICH?
Channel Proteins
- Function
- Mechanism
- Selectivity
- examples
Function: Channel proteins create aqueous pores (channels) that allow specific ions or molecules to pass through the membrane.
Mechanism: Channels operate through passive transport (facilitated diffusion).
Selectivity: Channel proteins are highly selective, allowing only certain ions or molecules to pass through based on:
- size = only small molecules and ions
- polarity= only polar molecules and ions
Examples:
small Ions - (Na⁺), (K⁺), (Cl⁻), (Ca2+)
small polar molecules= water
Transporter/Carrier Proteins
- Function
- Mechanism
- Selectivity
Function: Transporter proteins bind to specific substrates and undergo conformational changes (shape/structure) to transport them across the membrane.
Mechanism: Transporters can mediate both passive transport (facilitated diffusion) and active transport.
Selectivity: Like channels, transporter proteins are highly selective for particular substrates, :
size- both small and large molecules
ions - both small and large ions
polarity: both polar and a polar
large molecules- amino acids ad glucose
small ions- Na⁺), (K⁺), (Ca²⁺), (Cl⁻), (H⁺)
Type of transport examples
active transport=
facilitated diffusion=
sodium potassium pump/ calcium OR proton pump/ sodium-glucose linked transporters(SGLTs) = requires ATP
most glucose OR amino acid transporter/ ion channels / Aquaporins = no energy
What is chemical potential.
A difference in concentration (a gradient).
which side is open in:
- channel proteins
- transporter proteins/carriers
Channel proteins
-trigger causes channel to open, when open, both sides are open- extracellular and intracellular.
However in carrier proteins, when one is side is open( extracellular), the other side (intracellular) is closed, and vice versa.
what is potential gradient? why?
The concentration gradient of a
substance across a membrane
represents potential energy because it drives diffusion.
When the bow is pulled back, this gives the bow potential energy. When the string is released, the potential energy is converted to kinetic energy in movement of the arrow. The string pushes the arrow out and is the driving force behind the motion.
Key characteristics of passive transport:
-Energy (WHY?)
- movement
- equilibrium
Types: Osmosis, Diffusion, Facilitated Diffusion
No energy required: It does not require cellular energy (ATP) because the concentration gradient is the driving force.
Movement from high to low concentration: Molecules NATURALLY (spontaneous process) move from areas where they are more concentrated to areas where they are less concentrated.
Equilibrium: The process continues (Net Flow) until equilibrium is achieved, where the concentration of molecules inside the cell is equal to the concentration outside the cell.
Transporting Molecules Against their Concentration gradient via what mechanism?
Via Active Transport.
Unlike passive transport, which relies on concentration gradients, active transport works uphill, meaning substances are moved from areas of lower concentration to areas of higher concentration.
key Characteristics of Active Transport?
- Energy
- mediated
- equilibrium
- selectivity
Requires energy- provided by ATP (adenosine triphosphate), but other forms of energy such as electrochemical gradients (e.g., ion gradients) may also be used in certain types of active transport.
Active transport is mediated by specific INTEGRAL membrane proteins, known as pumps- use energy to actively move molecules across the membrane. E.g. sodium-potassium pump.
Equilibrium= maintains a state of dynamic equilibrium, where the concentration of molecules or ions is kept at different levels on either side of the membrane. e.g. sodium-potassium pump.
Selectivity- The transport proteins or pumps have binding sites that are highly selective for the substances they move e.g. glucose transporter or proton pumps.
key factors of :
Channel proteins (5)
Transport Proteins (3).
Channels:
Open/close (“all-or-none”)
Highly selective
Gated (open/close triggered by
stimulus)
Open to both environments (sides) at the SAME time
FASTER ! >106 ions/sec
Transporters/carriers:
Binding sites to solutes
Can be highly selective
Conformational change
what are key facts about membrane transport?
ALL membrane transport proteins are multipass transmembrane proteins (Go through the lipid bilayer multiple times = have multiple transmembrane domains)
30-70% of total ATP is used by pumps to establish and maintain Na+ and K+ gradients
what are aquaporins
Aquaporins are specialized water channels in cell membrane= They facilitate the rapid transport of water molecules in and out of cells= efficient water balance and homeostasis.
TABLE on word - differences’ between primary and secondary Active transport.
Primary vs Secondary Active Transport - ENERGY SOURCE.
PRIMARY :
Direct use of ATP.
The energy is provided directly from the hydrolysis of ATP (or sometimes another energy-rich molecule like GTP).
SECONDARY:
Indirect use of ATP.
Relies on the ion gradients created by primary active transport. These gradients represent potential energy, and this energy is used to move other molecules across the membrane.
Primary Vs Secondary Active Transport- MECHANISM
PRIMARY:
ATPase pumps - These proteins have an ATP-binding site and are involved in the direct consumption of energy.
SECONDARY:
movement of ions or molecules is driven by the electrochemical gradient of ions (such as Na⁺ or H⁺), which is created by primary active transport.
As ions flow down their gradient, they provide the energy needed to transport other molecules against their gradient.
Primary vs Secondary Active Transporter- FUNCTION
PRIMARY
Maintaining electrochemical gradients of ions across membranes.
It is essential for processes like nerve impulse transmission, muscle contraction, and maintaining osmotic balance in cells.
SECONDARY:
Essential for the co-transport of ions and other molecules, such as nutrients (glucose, amino acids) or waste products.
It allows cells to use energy stored in ion gradients for processes that require the import or export of different molecules.
Primary Active Transport- EXAMPLES (4)
P-type Pumps:
- Use ATP to transport ions while undergoing phosphorylation.
Example: Sodium-Potassium Pump (Na+/K+ ATPase), which pumps Na⁺ out and K⁺ in to maintain cellular function.
F-type and V-type Proton Pumps:
F-type pumps (e.g., ATP synthase) use the proton gradient to synthesize ATP in mitochondria and chloroplasts.
V-type pumps (e.g., vacuolar H+-ATPase) pump protons into vacuoles or lysosomes to create acidic environments for cellular processes.
ABC Transporters:
Large family of ATP-powered transporters that move a variety of molecules (like ions, lipids, or drugs) across membranes.
Example: CFTR transporter, which moves chloride ions.
Secondary Active Transport- EXAMPLES
Uniport, Symport, Antiport
TABLE ON WORD.
Symport and Antiport = ?
transport?
Symport and Antiport= Coupled Transport
They transport one solute down the concentration gradient and
other against the concentration gradient (SECONDARY ACTIVE TRANSPORT)
what powers Transport? EXAMPLE
ATP Binding: Transport proteins, such as ATP-binding cassette (ABC) transporters, bind ATP molecules.
Hydrolysis: The energy from ATP hydrolysis (breaking down ATP into ADP and inorganic phosphate) powers the transport process.
EXAMPLE : removal of toxins and drugs from the cells by the ABC transporter P-glycoprotein.
