Membrane Transport Flashcards
Examples
Gases=2
Hydrophobic Molecules=1
Small polar molecules=2
Large Polar molecules=2
Charged molecules=4
Gases= CO2 / O2
Hydrophobic Molecules= Benzene
Small polar molecules= H2Oand ethanol
Do Not Fit!
Large Polar molecules= Glucose
Charged molecules= H+, Cl-, Na+ and Ca2+
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
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), meaning they allow substances to move along their concentration gradient without requiring energy.
Selectivity: Channel proteins are highly selective, typically allowing only certain ions or molecules to pass through based on size, charge, or other chemical properties. For example, ion channels are selective for specific ions like sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), etc.
Transporter/Carrier Proteins
- Function
- Mechanism
- Selectivity
Function: Transporter proteins bind to specific substrates and undergo conformational changes to transport them across the membrane.
Mechanism: Transporters can mediate both passive transport (facilitated diffusion) and active transport, the latter requiring energy (usually ATP) to move substances against their concentration gradient.
Selectivity: Like channels, transporter proteins are highly selective for particular substrates, ensuring that only specific molecules (such as glucose, amino acids, or ions) are transported into or out of the cell or organelle.
What is chemical potential.
A difference in concentration (a gradient)
represents a chemical potential.
which side is open ?
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?
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:
Types: Osmosis, Diffusion, Facilitated Diffusion
No energy required: It does not require cellular energy (ATP) because the driving force is the concentration gradient.
Movement from high to low concentration: Molecules naturally 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?
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.
Selectivity- highly specific for the molecules it transports. The transport proteins or pumps have binding sites that are highly selective for the substances they move-
This ensures only correct molecule is transported, e.g. glucose transporter or proton pumps.
Active transport is mediated by specific membrane proteins, known as pumps. These are integral membrane proteins that use energy to actively move molecules across the membrane. E.g. sodium-potassium pump (Na+/K+ pump), which moves sodium ions (Na⁺) out of the cell and potassium ions (K⁺) into the cell, both against their concentration gradients.
Channel vs Transport Proteins
Channels:
Open/close (“all-or-none”)
Highly selective
Gated (open/close triggered by
stimulus)
Open to both environments at the
same time
>106 ions/sec
Transporters/carriers:
Binding sites to solutes
Can be highly selective
Conformational change
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:
Direct use of ATP to fuel the movement of ions or molecules through membrane-bound transporters, usually known as pumps. ATPase pumps are the main type of transporter in primary active transport. These proteins have an ATP-binding site and are involved in the direct consumption of energy.
SECONDARY:
In secondary active transport, the 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
P-type Pumps:
- Use ATP to transport ions while undergoing phosphorylation during the process.
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 and is associated with cystic fibrosis.
