M2 - Chapter 5 - Plasma membrane Flashcards
what is compartmentalisation
The formation of separate membrane- bound areas
Why is compartmentalisation good
It allows specific conditions to be maintained within each molecule (like chemical gradient)
What are the 4 main things needed in a membrane
- phospholipid bilayer
- cholesterol
- proteins
- carbohydrates
Explain the bilayer
2 lipids come together to create a bilayer. This is when the hydrophilic polar heads are on the outside and the hydrophobic sides are on the inside.
Explain cholesterol
They are also lipids and they stay in between the hydrophobic tails. They help to regulate the fluidity of the membrane. Make sure it’s not too fluid or too rigid. It adds stability to the membranes, and stops them from sticking to each other.
Explain proteins
There are 2 types: intrinsic and extrinsic.
Intrinsic proteins
They form all around the membrane. They are also called transmembrane proteins. They have amino acids with hydrophobic R-Groups on the external surfaces, so that they can interact with the hydrophobic core.
Extrinsic proteins
Also called the peripheral. They are usually only present on one side, but some can move. They usually have hydrophillic R-groups on the surface so they can interact with the polar heads.
Examples of intrinsic proteins
Channel proteins
they provide a hydrophillic channel for polar molecules to move down a concentration gradient. They are held in position because of the interaction between the R-Groups and the core.
Also Carrier Proteins
Explain carbohydrates
Glycoprotein
This is created when a carbohydrate (sugar chain) can attach themselves onto the proteins.
They help to join together to form junctions as tissues.
They can also act as cell receptors (the process here is called cell signalling and an example is the receptors on neurotransmitters at synapses)
Glyolipids
The same thing just that the sugar chains are on the lipids/ polar heads rather than a protein.
They are often called cell markers or antigens
What are the 2 factors affecting membrane structure
temperature and solvent
How does temperature affect membrane structure
As the temperature increases, the kinetic energy also increases. This means that the phospholipids in the bilayer move around more quickly and lose their structure, becoming more fluid.
The carrier proteins also become denatured by then.
This all affects the permeability, because if the membrane loses its structure, it becomes more permeable.
How do solvents affect membrane structure
Water is a polar solvent, but this polarity actually enables the bilayer to keep its structure.
However, solvents that may be less polar (like alcohols) or non-polar can actually dissolve membranes. The non-polar alcohol molecules can enter the phospholipids and disrupt the structure, making it more permeable
Why are alcohols used in antibacterial wipes
Because they use quite strong alcohols, which kill the cell membranes of the bacteria. Pure alcohols completely kill cells, but wine etc. is a diluted version, however it still is harmful
How can you investigate membrane permeability
Beetroot contains a pigment which is released when the cell membrane is disrupted.
- cut up cells the same size
- wash thoroughly and put them in 100ml of distilled water in a water bath
- every 5 minutes, take samples of the pigment by using a colorimeter. It will measure the absorbance of light. If there is more light being absorbed, there is less pigmentation, therefore less disruption.
- place the sample back in and increase the temperature by 10 degrees and repeat.
What does compartmentalisation include?
Regulation of substances entering and leaving the cell
Isolate organelles so that specific metabolic reactions can take place
Provide an internal transport system
Isolate destructive enzymes (lysosomes)
Provide surfaces on which reactions can occur.
What is the difference between protein channels and carrier proteins
Protein channels move substance through a concentration gradient by diffusion and it doesn’t use up ATP. However, carrier proteins move substance across a membrane by active transport and they require energy so that they can physically move around the membrane.
What’s the difference between active and passive exchange of surfaces
Passive utilises the energy from the natural motion of particles, rather than energy from another source. Whereas, active movement requires metabolic energy
Define diffusion
It is the net or overall movement of particles from a region of higher concentration to a region of lower concentration. It will continue until there is a concentration equilibrium.
