2.5 - Biological Membranes Flashcards
What is a plasma membrane?
It is a barrier between the cell and the environment, that controls what goes in and out of the cell.
What is the permeability of plasma membranes like?
It is partially permeable, meaning it allows certain molecules to pass through.
What does the plasma membrane do?
- Separates the cell contents from the outside environment
- Compartmentalise organelles from the cytoplasm
- Regulates the movement of substances in and out of the cell
- Allows cell recognition
- Holds the components of the metabolic pathway in place
What does the plasma membrane have a role in?
- Barrier/exchange
- Communication
- Transport
- Metabolic reactions
- Separation
How does the cell membrane play a role in exchange?
It is partially permeable so it controls what passes through them
Example:
It allows uncharged particles to pass through
What role does the cell membrane play in communication?
It is involved in cell signalling
Example:
Substances from one cell cause something to happen in another cell
What role does the cell membrane play in transport?
It allows signals to pass along them
Example:
Action potentials transmitted in the nervous system
What role does the cell membrane play in metabolic reactions?
It is the attachment site for enzymes and other molecules involved in metabolism
Example:
The inner membrane of chloroplasts contain chlorophyll for photosynthesis
What role does the cell membrane play in separation?
It produces different compartments inside the cell
Example:
Mitochondria is surrounded by 2 membranes which isolates reactions in the cytoplasm
What do phospholipids do in the cell membrane?
They are the basic structural component of all cell membranes forming a bilayer. This acts as a barrier to ions and large polar molecules
What does cholesterol do in the cell membrane?
Increases mechanical stability and regulates the fluidity of the membrane
What do channel proteins do in the cell membrane?
It allows the movement of substances across the membrane such as ions and large polar hydrophilic molecules
What do carrier proteins do in the cell membrane?
Actively moves substances across the membrane using ATP for energy
What do intrinsic proteins do in the plasma membrane?
The span the membrane and may function as enzymes or receptors for drugs and hormones
What do extrinsic proteins do in the plasma membrane?
They are partially embedded in the membrane but they do the same thing as intrinsic proteins
What do glycoproteins do in the plasma membrane?
- They are proteins with carbohydrates attached.
- They act as receptors for drugs and hormones
- They are involved in cell signalling
- They act as antigens
- They bind cells together to form tissues
What do glycolipids do in the cell membrane?
- They are phospholipids with carbohydrates attached
- They can act as receptors
- They are involved in immune recognition and cell signalling
What is simple diffusion?
The net movement of particles (molecules and ions) from an area of high concentration to an area of low concentration
Is diffusion passive or not?
Yes it is a passive process
What is able to diffuse using simple diffusion?
Small non polar molecules like oxygen and carbon dioxide
What are the factors effecting the rate of diffusion?
- The higher the ** concentration gradient** the the faster the rate of diffusion
- The shorter the diffusion pathway the faster the rate of diffusion
- The larger the surface area the faster the rate of diffusion
- The higher the temperature the faster the rate of diffusion (particles have more kinetic energy
What is facilitated diffusion?
The movement of polar molecules from an area of high concentration to an area of low concentration, across a partially permeable membrane via channel proteins or carrier proteins
What do carrier proteins do in facilitated diffusion?
A large molecule attaches to the binding site in the protein causing it to change shape. This then releases the molecule on the opposite side of the membrane
What do channel proteins do in facilitated diffusion?
The charged particle diffuses through the embedded protein
What is osmosis?
The passage of water molecules down there water potential gradient through a partially permeable membrane. It moves from an area of high water potential to and area of low water potential.
How is low water potential measured?
It is measured by the tendency of water molecules to diffuse through osmosis
What is the water potential of pure water?
0kPa (highest)
What happens when solute molecules are added to water?
It changes the relative number of water molecules
What happens to an animal cell when to solution has a higher water potential?
The water molecules move into the cell causing it to burst (cytolysis)
What happens to a plant cell when the solution has a higher water potential?
The water molecules move into the cell causing the vacuole to swell, this makes the cell turgid
What happens to and animal cell when the solution has a lower water potential?
The water molecules move out of the cell causing it to shrink
What happens to a plant cell when the solution has a lower water potential?
The water molecules move out of the cell making the flaccid (the cytoplasm and membrane pull away from the cell wall)
What is active transport?
The movement of substances (potassium ions) against there concentration gradient (low —> high) across the cell membrane, using protein carriers
Is active transport passive or not?
It is not a passive process, it use ATP
How does active transport work?
The molecules attach to the carrier proteins and they change shape and move to the other side of the membrane
How does the carrier proteins get ATP to move the molecule?
It gets energy from a hydrolysis reaction that takes place when the ATP molecule binds to a specific part of the protein
What is endocytosis?
It is the bulk transport of molecules that are too large to pass through the cell membrane into the cell
How does endocytosis work?
- A section of the plasma membrane surrounds the substances
- The membrane then pinches off to form a vesicle inside the cell containing the ingested substance
Does endocytosis require ATP?
Yes
What does endocytosis move?
Proteins and lipids
What is exocytosis?
The bulk transport of large molecules out of a cell
How does exocytosis work?
- Vesicles containing the substance pinch off the Golgi body and move to the plasma membrane
- The vesicle fuses to the membrane and the contents are released out of the cell
- Things like proteins are just absorbed straight into the membrane and don’t leave the cell
Does exocytosis require ATP?
Yes it uses it as an energy store
What is hydrostatic pressure?
It is the pressure that water creates on the surface when it goes into a closed cell
What does hypotonic mean?
There is a lower water potential inside the cell
What does hypertonic mean?
There is a higher water potential in the cell
What does isotonic mean?
There is an equal water potential both inside and outside of the cell
Why do organs and organelles communicate?
To control processes in the body and respond to environmental changes
How does basic cell signalling work?
- The cell releases a messenger molecule (hormones)
- The messenger molecule travels around the body to another cell
- Receptors at the surface of the cell interact with the messenger molecule
- A response is triggered
What are the 3 types of cell signalling?
- Receptor activates a G-protein
- Receptor as an enzyme
- Receptor as an ion channel
How does a receptor as an ion channel work?
The signalling molecule binds to the ion channel causing the channel to open so that the ions can go through
How does a receptor activating a G-protein work?
- A G-protein is inside the CSM which interacts with a receptor
- The messenger molecule attaches to the receptor which activates the protein
- The protein the starts a chemical reaction in the cell
How does a receptor as an enzyme work?
- The receptor is in 2 parts which are joined together by a messenger molecule
- This activates the enzymes that control reactions in the cell
How does aspirin work after an injury?
- It blocks the receptor
- This inhibits the production of prostaglandins in cox-12 cells
- This stops the sending of pain signals and swelling
How does aspirin prevent blood clots?
- Aspirin prevents the production of cox-12
- This then stops the production of thromboxane
- Thromboxane cause blood to clot so if it isn’t produced the blood can’t clot
