Transport across Membranes Flashcards
Which type of molecules are able to pass through the cell membrane easily and which are not?
Small, nonpolar, uncharged molecules can pass right through (Ex. O2, CO2, Glycerol).
Large, polar, or charged molecules cannot (Ex. Glucose, Cl-, Na+).
What are the 3 categories of membrane transportation?
Passive membrane transportation: Movement of substances from high concentration to low concentration.
Does not require energy.
Active membrane transport: Movement of substances from low concentration to high concentration.
Requires energy (ATP) + proteins.
Vesicle Formation: A form of ACTIVE TRANSPORT, Movement of molecules into and out of the cell using vesicles.
What are the 3 types of passive transport?
Simple diffusion.
Osmosis.
Facilitated diffusion.
What is simple diffusion?
A form of passive transport. The free movement of small, nonpolar, uncharged molecules through the plasma membrane without the assistance of proteins.
Will move into or out of the cell based on concentration (high to low) in order to reach equilibrium.
What is osmosis?
A form of passive transport. The movement of specifically water molecules across the plasma membrane.
Heavily depends on the solute concentration on the internal vs external side of the cell.
What is tonicity?
Tonicity refers to the concentration of solutes inside of the cell relative to outside the cell. It determines how water in a cell will move when placed in the solution.
Hypertonic solutions are solutions that have a greater solute concentration _____ the cell.
Outside.
Does water move into or out of the cell in a hypertonic solution?
Water moves out of the cell to balance the high solute concentration out of the cell. This causes the cell to shrink.
Hypotonic solutions are solutions that have greater concentration of solute ____ the cell.
Inside.
Does water move into or out of the cell in a hypotonic solution?
Water moves into the cell to balance the high solute concentration inside the cell. This causes the cell to swell.
What is an isotonic solution?
A solution where there is no net movement of water, therefore the cell maintains it’s current structural shape.
What is crenation?
It refers to when animal cells lose water and shrivel up due to hypertonic solutions. This causes the cytoplasm and therefore the cell to shrink.
This process affects the shape of the cell, and may damage the cell membrane. This then impairs the cells ability to properly diffuse substances into and out of the cell.
What is plasmolysis?
The shrinking of the cytoplasm in plant cells due to hypertonic solutions.
This heavily affects the structure of a plant cell, as the plasma membrane will begin to seperate from the cell wall. This will cause the cell wall to buckle.
What is lysis?
Lysis is when animal cells split due to damaged cell membrane. This can be caused by hypotonic solutions.
This causes a cell to lose it’s integrity and leak out its contents to surrounding cells. This compromises it’s ability to perform it’s necessary function in the body.
Why do plant cells react better to hypotonic solutions than hypertonic?
Plant cells prefer to be in a hypotonic state, due to it’s large vacuole. Plant cells are capable of carrying a large amount of water at any given time. While a hypotonic state increases turgor pressure, it’s cell wall prevents it from bursting.
A hypertonic state is very harmful to a plant cell, as it’s large vacuole is important in maintaining it’s shape. When the vacuole shrivels, that causes the membrane to shrivel and then damages the cell wall.
What is facilitated diffusion?
A form of passive transport. Facilitated diffusion is the movement of substances from high concentration to low concentration with the assistance of a channel or carrier protein. specifically for larger/ polar molecules.
This does not require energy.
The proteins merely facilitate this movement, they do not cause it (would require energy). However, they are able to regulate the movement of molecules.
What are channel proteins?
Channel proteins are tubular-shaped integral proteins (all the way through the membrane).
The external portion is hydrophobic so the cell membrane can hold the protein in place. The internal portion is hydrophilic/ charged so that polar/ charged molecules can pass through.
Channel proteins can be opened or closed to regulate the movement of substances. Movement of the substance does not change the shape of the protein.
What is a carrier protein?
A protein that binds to specific molecules (Ex. Glucose).
This bind causes the protein to make a conformational change, moving from a high affinity shape to the molecule to a low affinity shape. This then releases the molecule on the other side of the membrane.
What are GLUT carrier proteins?
A family of proteins that carry glucose into the cell.
Examples:
GLUT 1: Brings glucose in (Faulty GLUT 1 associated with diabetes).
GLUT 4: Stimulated by insulin to work.
What are the two types of active transport?
Primary active transport.
Secondary active transport.
What is primary active transport?
Primary transport uses ATP directly to move molecules/ ions across the membrane.
Carrier proteins are involved in active transport are called pumps.
What happens to ATP after being used in primary transport?
ATP (Adenosine Triphosphate) becomes ADP (Adenosine Diphosphate) + Pi (Inorganic phosphate).
ADP + Pi will then go on to react to make ATP again.
How does the sodium/ potassium pump work?
The pump begins by binding to 3 Na+ ions. ATP will then be used on the protein, releasing ADP and creating Pi.
The protein will react to this energy by making a conformational change. This causes the 3 Na+ ions to be released on outside the cell. This then allows 2 K+ ions to bind to the cell.
Once the protein uses the energy, it will return to its orignal shape. Releasing the 2 K+ ions and the Pi into the cell. the ADP and Pi will go to become ATP once more, and the Sodium/ potassium pump will repeat.
What is secondary active transport?
Secondary transport uses an existing active transport system to drive the transport of another molecule.
An ion pump creates a difference in charge/ electric potential across a membrane so that one side is more postive/ negative than the other.
A concentration gradient will build across the membrane, increasing the concentration on one side. This then creates an electrochemical gradient that stores potential energy for the cell to use.
