B2.1 Membranes and Transport Flashcards
Describe the Composition of a Phospholipid.
Each phospholipid is composed of a three-carbon compound called glycerol. Two of the glycerol carbon are combined with fatty acids, and the third is attached to a highly polar organic alcohol that bonds to a phospholipid group.
Define Hydrophilic.
Substances attracted to water.
Define Hydrophobic.
Substances that are not attracted to water.
Why Are Phospholipids Unusual?
They are unusual because part of the phospholipid is hydrophilic and part is hydrophobic. Therefore, it possesses the property of being amphipathic.
What Part of the Phospholipid is Hydrophilic?
The phosphorylated alcohol side is hydrophilic. It is water soluble and polar.
What Part of the Phospholipid is Hydrophobic?
The glycerol-carbon side is hydrophobic. It is not water soluble and non-polar.
When Mixed With Water:
- Phosphate heads are attracted to water molecules in the cytoplasm or extracellular fluids (as they are hydrophilic).
- Hydrocarbon tails are attracted more to each other than to water (as they are hydrophobic).
Due to this, the phospholipids become arranged in a double layer.
Describe the Arrangement of Components in Phospholipids.
- The hydrophobic hydrocarbon tails face inwards.
- The hydrophilic phosphate heads face outwards to the water (on each side).
These double layers are called phospholipid bilayers.
What are Phospholipid Bilayers?
Stables structures that form the basis of cell membranes.
What Factors Influence Membrane Permeability?
- Size
- Charge
Membrane Permeability:
- Small, non-polar substances move easily.
- Large, polar, (or both) substances do not cross easily.
Recall, the membrane core has low permeability to all hydrophilic particles, including ions with (+) or (-) charges and polar molecules (as it is composed of hydrophobic tails).
Define Diffusion.
When particles move from a region of high concentration to a region of low concentration.
Diffusion can only occur if the bilayer is permeable to the particle.
Which Particles Can Diffuse Easily/Not Easily?
- Non-polar particles can (such as oxygen) diffuse through easily.
- Ions with (+) or (-) charges cannot diffuse easily thorugh (due to the hydrophobic, non-polar centre of the membrane).
- Polar molecules (which have partial (+) and (-) charges over their surface) can diffuse at low rates between the phospholipids of the membrane.
- Small polar particles pass through more easily than large molecules.
If the concentration of oxygen inside the cell is reduced (due to aerobic respiration) and the concentration of oxygen outside the cell is higher, oxygen will pass through the plasma membrane by passive diffusion.
Define Integral Proteins.
They have amphipathic properties. Their hydrophobic regions lay in the midsection of the phospholipid backbone, and the hydrophilic regions is exposed to water molecules on either side.
See Diagram on Page 220 of the Textbook for a Visual.
Define Peripheral Proteins.
They do not protrude the middle hydrophobic region and remain bound to the surface. They can be found on both the inner and outer sides of the membrane. They are often anchored to an integral protein.
See Diagram on Page 220 of the Textbook for a Visual.
