Module 2: Plasma membranes Flashcards
What is the difference between simple diffusion and facilitated diffusion in biological membranes?
Simple diffusion does not require proteins, while facilitated diffusion does.
What is the term for the engulfing of liquids by the cell membrane in biological membranes?
Pinocytosis
What is the term for the specific uptake of macromolecules by the cell membrane in biological membranes?
Receptor-mediated endocytosis
What is the term for the transport of substances across channel proteins?
Facilitated diffusion
What is the phospholipid bilayer?
Hydrophilic phosphate heads on the outside which can interact with water, and the hydrophobic fatty acid tails on the inside. Hydrophobic core.
What is the fluid mosaic model? Why is it called this?
Components of the plasma membrane with glycoproteins, cholesterol etc.
Fluid - phospholipids are free to move within the layer next to each other which gives the membrane flexibility.
Mosaic - proteins embedded in the bilayer vary in size.
What are the 2 types of protein in the cell surface membrane?
- Intrinsic proteins are embedded through both layers of the membrane. They have amino acids with hydrophobic R groups on the external surface which interact with the hydrophobic core of the membrane, keeping them in place.
- Extrinsic proteins are embedded in one side of the bilayer, held by weak hydrophilic interactions with the phosphate heads.
Describe the function of the 2 types of intrinsic proteins.
- Channel proteins - hydrophilic channel that allows the PASSIVE movement of POLAR molecules/ions down a concentration gradient through the bilayer. Allows water and SMALL ion through quickly.
- Carrier proteins - used in diffusion but mainly active transport where ATP changes the shape of the protein allowing LARGE molecules to pass through.
What are glycoproteins and what is their function?
Extrinsic protein that has a carbohydrate chain attached.
Cell adhesion (where cells join together to form tight junctions in certain tissues) and acts as receptors for chemical signals. When a chemical binds to the receptor, it causes a response inside the cell known as CELL SIGNALLING.
Define cell signalling.
Cells communicating with each other by sending and receiving signals.
Give an example of cell signalling.
Receptors for neurotransmitters such as acetylcholine at nerve cell synapses that triggers an impulse on the next neurone.
3 roles of glycoproteins in membranes?
- Cell signalling
- Act as antigens
- Cell adhesion
What are glycolipids and what is their function?
Lipids with a carbohydrate chain attached. They are cell markers + antigens which can be recognised by cells in the immune system as self or non-self.
What molecules can pass through the phospholipid bilayer?
Small, uncharged or lipid-soluble molecules can pass through.
Water soluble molecules cannot pass through.
Function of cholesterol?
Cholesterol is a sterol that has a hydrophilic end (interacts with the heads) and a hydrophobic end (interact with tails)
Cholesterol is positioned between the fatty acids and regulates fluidity. It also restricts the movement of phospholipids and also avoids the phospholipids grouping too closely together, making the membrane more rigid. Stability/flexibility.
What happens to the phospholipid bilayer as temperature increases?
They’ll have more KE and move more, so the membrane becomes more fluid and increases the permeability as this disrupts the structure. More molecules can pass through it.
Carrier and channel proteins will denature at higher temps.
Impact of water on the phospholipid bilayer?
Water, a polar solvent, keeps the non-polar tails away from water to form the hydrophobic core. The polar phosphate heads interact with water, keeping the bilayer intact.
Impact of less/non-polar organic solvents on the phospholipid bilayer?
Organic solvents will dissolve bilayer as they are lipid-soluble, disrupting bilayer and reduces the transport of materials. This is why alcohol is used in antiseptic wipes.
What is diffusion?
Net movement of particles from an area of their high conc to area of low conc. It is a passive process. Equilibrium doesn’t mean the particles stop moving but the movements are equal in both directions.
Why is diffusion a passive process?
It doesn’t require an external energy source. Diffusion relies on the KE from the natural rando movement of particles.
4 factors that affect the rate of diffusion?
- Conc gradient
- Temperature
- SA:Volume
- Diffusion distance
Do non-polar molecules pass through the phospholipid bilayer?
Yes, non-polar molecules like O2 can diffuse through it as the interior of the membrane is primarily composed of hydrophobic lipids, which readily interact with nonpolar substances, allowing them to diffuse across the membrane freely.
Do polar molecules pass through the phospholipid bilayer?
Some small, slightly polar molecules like water and ethanol can cross the cell membrane by passive diffusion (very slowly), but it depends on the size and polarity of the molecule.
Large polar molecules, like glucose, cannot pass through the cell membrane by passive diffusion. This is because they are too large and charged to pass through the nonpolar region of the cell membrane.The cell membrane’s interior is hydrophobic, meaning it repels polar molecules.
To cross the cell membrane, large polar molecules and IONS require the help of transport proteins.
How do micelles form?
When one phospholipid layer is exposed to water, the hydrophilic heads face the water and the hydrophobic tails point inwards away from water.
Active transport
What is the function of cholesterol?
Fits between the hydrophobic tails of the phospholipids, causing them to pack more closely so the membrane becomes less fluid and more rigid.
Cholesterol also has hydrophobic regions, so they create a further barrier to polar substances moving through the membrane.
Channel proteins
Allow small charged particles through.
Carrier proteins.
Transport larger molecules and charged particles across the membrane by active transport and facilitated diffusion.
Glycolipids and glycoproteins.
Both of these form hydrogen bonds with surrounding water molecules to stabilise the membrane. They also act as receptors for messenger molecules in cell signalling and where antibodies bind.
