2.5 Flashcards
what is the plasma membrane
the cell surface membrane which separates the cell from it’s external environment
role of membrane at surface of cell (5)
1) site of chemical reactions
2) Release chemicals to communicate with other cells
3) Acts as a partially permeable barrier between cell & it’s environment
4) Regulates transport of material into & out of cell
5) Contains antigens so immune system can recognise it & not attack it
what is the structure of the membrane like
- formed from 2 layers of phospholipid bilayer
- They hydrophobic tails are on the inside facing each other while the hydrophillic heads are on the outside and face away from each other
why is the cell-membrane known as the fluid-mosaic model
- they contents are free to move within the layer relative to each other like fluid
- There are many different components embedded together like a mosaic
what are intrinsic/integeral proteins
are transmembrane proteins that are embedded through both layers of a membrane.
what are 3 types of intergeral proteins
Channel
carrier
what does channel protein do + their structure
- Channel proteins form tubes that fill with water to enable water-soluble + small + polar molecules to passively diffuse through facilitated diffusion.
- Used when certain molecules can’t pass phospholipid bilayer
what do carrier proteins do
important role in passive + active transport into cells and often involved in the changing of protein shape to transport by binding to larger molecules
what are glycoproteins + their role
- proteins attached to carbon chain
- Has antigens for cell recognition
- Has receptor cells for cell-signalling
what are extrensic / peripheral proteins and their role + structure
Present on 1 side of the bilayer They provide mechanical strength + cell recognition as receptors
what are glycoproteins
lipids attached to carb chain
what is their structure + role
- has antigens for cell recognition
- has receptors for cell-signalling
what does cholesterol do
will retsrict lateral movements of other molecules in membrane and making it less liquid at higher temperatures and preventing water + dissolved ions from leaking out of cell
how does a temperature below 0 affect membrane structure
Increase in membrane rigidity. As the temperature drops to below zero, phospholipids lose much of their kinetic energy. Therefore, the membrane loses its fluidity which causes it to become very rigid.
Increase in membrane permeability. Proteins within the membrane become heavily denatured, which increases the permeability of the membrane. Ice crystals can form in the membrane, which can cause the membrane to fracture, especially during thawing, which also increases permeability.
how does a temperature of 0-45 affect membrane permeability
Membranes are fluid. Between 0-45°C, phospholipids can easily move (although their movement is naturally restricted by cholesterol).
Membranes are semi-permeable. At these temperatures, the membrane is also semipermeable. As temperatures increases, the kinetic energy of the phospholipids also increases, which increases their movement. This increase in movement leads to an increase in permeability of the membrane.
how does a temperature of 45+ affect membrane structure
Phospholipid bilayer begins to break down. Increasing kinetic energy allows the phospholipids to move far away from each other, which destroys the structural integrity of the membrane, causing it to “melt”.
Cell Membrane Structure becomes freely permeable. Transport and channel proteins denature, thus making them unable to regulate what gets into and out of cells, which leads to increased membrane permeability.
The membrane may burst. The heat causes water inside of the cells to expand which puts pressure on the membrane, causing it to burst.
how do solvents such as ethanol affect membrane structure
Lipids dissolve in alcohol, therefore, the phospholipids in a cell membrane will easily dissolve in solutions such as ethanol. As a result, the cell membrane becomes more fluid and permeable as it starts to break down.
how does concentration of solvent affect the permability of membrane
increasing solvent concentration increases membrane permeability.
why is this
This is because as the solvent becomes more and more concentrated, it has a greater ability to dissolve phospholipids and disrupt the membrane structure, making it more permeable to external substances