Structure And Function Of Membranes ✅ Flashcards
What functions do membranes have
Physical Barriers (separate intracellular environments from extracellular environments)
Regulate the exchange of substances in and out of cell (partially permeable)
Compartmentalisation (membranes enclose and isolate organelles, enabling them to maintain specific environments for chemical reactions)
Support for the cytoskeleton
Sites of chemical reactions
Sites of cell communication (cell signaling)
Formation of spheres called vesicles (used in bulk transport)
When are channel proteins used
Facilitated diffusion
When are carrier proteins used
Facilitated diffusion and active transport
What is the role of glycoproteins
Receptors (neurotransmitters, peptide hormones and drugs)
What is the role of glycolipids
Cell recognition (act as antigens)
Why can membrane structure be visualized as a fluid mosaic model
Fluid because phospholipids are able to move within the bilayer
Mosaic because proteins are scattered throughout the bilayer, like tiles in mosaic
What is a phospholipid tail and head in relation to water called
Hydrophobic core
Hydrophilic head
Where is Cholesterol what’s it’s purpose
In the bilayer (looks like a darker phospholipid)
Adds strength
Where is a extrinsic protein
Protein molecule lying on the surface
Where is a intrinsic protein what does it contain
Protein molecule spanning the phospholipid layer
Pore
Which way do hydrophobic tails point
Point inwards
Which way do hydrophilic head point
Point outwards
What does an extrinsic protein look like that’s partly embedded
An extrinsic protein that is partly in bilayer and partly outside
What is a glycoprotein what does it look like
Branching carbohydrate portion of a protein which acts as a recognition site for chemicals eg hormones
Like a branch off of a protein
What is a glycolipid what does it look like
Acts as a recognition site eg for cholera toxins
A branch off phospholipid
What factors affect membrane structure
Temperature and solvents
What effect does temperature have on membrane structure
Decreased temp reduces fluidity (phospholipids move less due to lower kinetic energy)
Increased temp causes greater fluidity and therefore increases permeability, but a membrane will lose its structure and break apart if temp continues to rise
What effect does solvents have on membrane structure
Organic, weakly polar (eg ethanol) or non polar (eg benzene) solvents disrupt or dissolve membranes, making them more permeable
Practical investigating membrane permeability, what is the procedure
5 test tubes of alcohol solution (0%=control,10%,20%,30%,40%) are set up. Beetroot cylinders added to each tube, after 5-10mins the colour of each alcohol solution is measured using a colorimeter
A red pigment (betacyanin) leaks from cells into solution when membranes are damaged. The intensity of the colour released is proportional to level of cellular damage
Practical: permeability
3 control variables
Why is procedure repeated 3 times
Control: temperature, volume of alcohol solution, SA:V ratio of beet cylinders, pH
Repeated 3 times: reproducibility is increased, spread of results can be assessed, greater confidence in accuracy of results
What is diffusion
Net (overall) movement of particles from a region of higher concentration to a region of lower concentration. It is a passive process (ie not requiring ATP)
What Diffuses through the bilayer
Some particles can diffuse between phospholipid molecules. Large lipid-soluble molecules (eg steroid hormones), non polar molecules (eg oxygen), very small polar molecules (eg water) are able to pass directly through the bilayer
What is facilitated diffusion
Process of particles passing through transmembrane proteins
Ions and large polar molecules (eg glucose and amino acids) pass through proteins rather then between phospholipids
What are the 2 types of proteins used for facilitated diffusion
Channel proteins: pores, which can be gated (ie open and closed) allowing the diffusion of ions
Carrier proteins: they have shapes that allow only the passage of specific molecules or ions