Transport Across Membranes Flashcards
(33 cards)
What is a cell-surface membrane?
They surround cells and regulates the movement of substances into and out of the cell. They also contain receptors, which can act as antigens or respond to chemicals like hormones
What does partially permeable mean?
They let some molecule through but other cannot get through. This can depend on the molecules size, charge, lipid solubility etc…
Why is the structure of a cell-surface membrane described as ‘Fluid-Mosaic’?
The phospholipid molecules cause the membrane fluidity as it constantly moving. The mosaic part refers to the large proteins and lipids which are scattered in the bilateral like tiles in a mosaic. These proteins and lipids include: transport proteins, glycoproteins, glycolipids and cholesterol.
Name the molecules that make up the cell surface membrane.
Phospholipids, cholesterol, glycolipids, glycoproteins, channel proteins and proteins carriers, co-transporters.
What part of the phospholipid is hydrophilic?
Phosphate Head.
What part of the phospholipid is the fatty acids?
The hydrophobic tails.
What does a phospholipid bilayer mean?
Continuous phospholipid double layer with the phosphate heads facing out and the fatty acid tails facing inward.
Why can’t water soluble substances (ions) diffuse osmotically through the phospholipid bilayer?
The centre hydrophobic tails prevents water-soluble substances through, acting as a barrier.
What’s the function of cholesterol?
Type of lipid which fit between phospholipids and bind to the hydrophobic tails, causing them to pack more closely together. This increases the membrane rigidity. They maintain the Membranes shape in animal cells.
What is an extrinsic proteins?
A membrane protein that partially span the membrane and is attached to either the outer or inner phospholipid layer. Glycolipids and glycoproteins are two examples.
What is the function of glycoproteins and glycolipids?
Both act as cell surface receptors for specific chemicals and they act as recognition sites. Glycolipids also help maintain membrane stability and glycoproteins allow cells to recognise one another.
What effect does temperature have on membrane permeability?
Increasing the temperature, increases the membrane permeability.
What’s the affect of temperatures below 0 degrees on membrane permeability.
Phospholipids don’t have much energy, so can’t move very much. Rigid. Transport deform, allowing more molecules to come through.
Above what temperature does the bilayer start to melt and so becomes permeable?
Above about 45 degrees Celsius.
Define diffusion.
The net movement of molecules from an area of high concentration to an area of lower concentration.
Is diffusion passive or active?
Passive - No energy required.
What does a concentration gradient mean?
Path from high concentration to low concentration.
Name two molecules that can pass through the phospholipid bilayer freely by simple diffusion.
Oxygen and carbon dioxide.
Can a small, non-polar and lipid soluble molecule get through the phospholipid bilayer?
Yes.
What is simple diffusion?
Molecules move directly through the phospholipid bilayer.
Name the two transport proteins that facilitated diffusion happens through.
Protein channel and carrier proteins.
Why are Channel and carrier proteins needed?
To carry large, polar molecules across the membrane.
How does a carrier protein transport molecules?
A molecule attaches to carrier protein in membrane. Protein changes shape and releases its content on the opposite end of the membrane.
What are Channel proteins?
Pores in the membrane for charged particles to diffuse through. Different proteins cater for different molecules (specific).
