2.3 TRANSPORT ACROSS CELL MEMBRANES Flashcards
What is a cell membrane primarily made up of?
A barrier of phospholipids
How are phospholipid arranged in the membrane?
- Hydrophilic phosphate heads point out towards the water.
- Hydrophobic tails point inwards, away from the water.
- This creates a double layer of phospholipids, with the heads protecting the tails from the water.
What other things are in the phospholipid bilayer (except phospholipids)?
- Glycolipids
- Glycoproteins
- Cholesterol
- Intrinsic & Extrinsic proteins
What is the function of cholesterol in the bilayer?
- Provides strength.
- Extremely hydrophobic so prevents water loss.
- Reduces fluidity and lateral movements at high temperatures.
What is the function of glycolipids in the bilayer?
- A carb bonded to a lipid
- Acts as a recognition site for other molecules.
- Helps keep the membrane strong and stable.
- Acts as an attachment site for other cells, to form tissues.
What is the function of glycoproteins in the bilayer?
- A carb bonded to extrinsic proteins.
- Act as recognition sites for other molecules.
- Acts as an attachment site for other cells, to form tissues.
- Has receptors for hormones and neurotransmitter.
What is the function of extrinsic proteins in the bilayer?
Provide mechanical support
What is the function of intrinsic proteins in the bilayer?
Span across the bilayer, and are used in facilitated diffusion and active transport.
What type of molecules can pass directly through the phospholipid bilayer?
- Small
- Non-polar
- Lipid soluble
What are the main functions of the cell membrane?
- Separate cell contents from outside environments.
- Separate organelles from cytoplasm.
- Regulate transport of materials in and out of cell/ organelles.
- Involved in cell recognition and signalling
Why is the phospholipid bilayer called ‘fluid’?
Phospholipids can move around in relation to one another as the membrane is flexible.
Why is the phospholipid bilayer called ‘mosaic’?
The proteins in the bilayer are different shapes and sizes, like tiles in a mosaic.
What is simple diffusion?
The net passive movement of molecules down the concentration gradient through a partially permeable membrane, until equilibrium is reached.
Which molecules can diffuse simply across the bilayer?
- Small
- Non-polar
- Lipid soluble
What is facilitated diffusion?
The net passive movement of molecules down the concentration gradient, through protein channels or carrier proteins, until equilibrium is reached.
How do carrier proteins work in facilitated diffusion?
- A specific molecule bonds to the carrier protein.
- This causes it to change shape so the molecule can be passed through the bilayer.
- Once the molecule is released, the carrier protein returns to its original shape.
How do protein channels work in facilitated diffusion?
- A specific water soluble ion binds to the channel.
- This causes it to change shape and open up.
- Once the molecule is released, the carrier protein returns to its original shape.
Which molecules travel across the bilayer by facilitated diffusion?
- Polar
- Large
- Non-lipid soluble
What is osmosis?
The net passive movement of water molecules down the water potential gradient, through a partially permeable membrane (aquaporin channels), until equilibrium has been reached.
What is water potential?
The pressure created by water molecules.
What is the water potential of pure water (highest WP)
0 kPa
What symbol denotes water potential?
ᴪ (psi)
What will the water potential always be if it has some solute dissolved in it?
<0 kPa
What happens if the ᴪ outside an animal cell is greater than inside?
Water moves in, cell swells and bursts.
