Chapter 3 : Biomembranes Flashcards
Enzymatic reactions are faster in prokaryotes of in eukaryotes
in eukaryotes
Why are enzymatic reactions faster in eukaryotes ?
bc they have multiple membranes
Between what and what is the plasma membrane a barrier ?
barrier btw the cytoplasm and the extracellular environment
can the cytoplasm of a cell exchange with it’s environment ?
yes
what are erythrocytes ?
blood cells w hemoglobin and no organelles
where are produced erythrocytes ?
in the bone marrow
what is hemoglobin, where can you find it and what’s its function ?
it’s a protein found in eryhtrocyte that carries oxygen
When you lysed eryhtrocyte, what do you obtain ?
erythrocyte ghosts = only their empty PM
How do you obtain eryhtrocyte ghosts ?
by putting erythrocytes in a hypotonic solution, it provokes the swelling (gonflement) and bursting (éclatement) of the cell
What is haemolysis ?
the rupturing of RBC and the release of their content
When put in an essay tube, where do you find the erythrocyte ghosts (PM) and the content of the cell (hemoglobin+cytoplasm) ?
PM = in the pellets Hemoglobin+cytoplasm = supernatants
What’s the difference btw hyaloplasm and cytoplasm ?
Cytoplasm = Hyaloplasm + Organelles
Describe how a lipid is made ?
polar head = hydrophilic
2 polar tails = hydrophobic
= amphiphile molecule
What’s the main type of lipid found in the living organisms ?
phospholipids (with even number of carbon in their FA)
What can be insterted in the lipid bilayer ?
cholesterol
Describe how a cholesterol is made ?
mainly apolar except an OH group n C3
What function does the cholesterol have in the cell ?
it plays a role in the rigidity of the plasma membrane
How many % can represent cholesterol in the plasma membrane ?
15 to 50% of the PM
What are the 4 different functions of proteins ?
- transporters
- anchoring
- receptors
What transporter proteins do?
thay transport molecule to a point to another
What anchoring proteins do ?
they play a role in linkage, junctions of the cells
What receptor proteins do ?
communication of the cell with it’s extracellular environment
What enzymatic proteins do ?
they transform a molecule into another form
What is SDS-PAGE technic used for ?
for separate proteins according to their mass
What does the acronym “SDS” stands for ?
Sodium dodecyl sulfate
on which principle is SDS PAGE based on ?
electrophoresis
What the electrophoresis does ?
the migration of charged particles on an electric field
What’s the role of SDS in SDS PAGE ?
it denaturates the proteins to they bewome linear and are all negatively charged
What’s the impact of SDS in an electrophoresis using proteins ?
it make them all having negative charges, so proteins don’t migrate depending on their charge but on their mass
In a SDS-PAGE technic, where are the lighter proteins: further or closer ?
lighter proteins go further
What is the most used staining in SDS PAGE technic ?
coomassie blue staining
What is the unit used for the mass of the proteins ?
kD = kiloDalton
Talk about the polar/apolar domain of proteins
Proteins are mainly apolar but can have some small apolar part that are inserted in the PM
Describe the molecular organisation of carbohydrates
they are polymer of monosaccharides = oligosaccharides
which type of bond links the carbohydrates to the lipids and proteins ?
covalent bonds
How do we call all the carbohydrates of the PM ?
GLYCOCALYX
What is the function of Glycocalyx ?
communication of the cell with its environment
How do you call carbohydrates+proteins ?
Glycoproteins = proteins that are glycosylated
How do you call carbohydrates+lipids ?
Glycolipids
What does the acronym “PAS” stands for ,
Periodic Acid Schaff
What is PAS ?
a staining method
What does the PAS technic stains ?
it only stains glycosylated proteins (+glycolipids and glycogen)
What are the three main structures lipids can organise themselves ?
- micelles
- bilayer sheet
- liposome
What is the lipids organization closest to the cell ?
the liposome
What can provoke a chemical fixation of the cell ?
It can change its organization and create artefacts (denaturation of proteins)
How do you prepare a sample for freeze fracture/etching ?
the cell is put in the cold so it freezes, and we add cryoprotection so it avoids cristals that will break the sample
What’s the freeze fracture/etching principle ?
bc the cell is freezed, you can breaks in the softer side of the cell (btw the 2 lipid layers) so you can observe the PM structure
For what type of microscopy is freeze fracture/etching used for ?
electron microscopy
For what type of microscopy is shadowing used for ?
electron microscopy
What is the preparation technic shadowing ?
it replicates the sample by spraying heavy metals on it (it will create a replication of our sample that can be observed)
By who the fluid mosaic model was created ?
Siago and Nicholson
When was the fluid mosaic model created ?
1972
In the fluid mosaic model, what is the mosaic ?
the lipids
In the fluid mosaic model, what corresponds to “fluid” ?
the movement of the lipids (that are the mosaic) NOT STATIC
What are the three types of proteins that compose the plasma membrane of a cell ?
- Transmembrane protein
- Integral protein
- Peripheral Protein
What is a transmembrane protein?
a protein that has an apolar part (in a helix) and which is hidden in the lipid bilayer, and has a polar part on each extremity
How long is the apolar part of transmembrane proteins ?
~20amino acids
What is an integral protein ?
a protein that has a small apolar part hidden in the PM
What is a peripheral protein ?
a protein that moves in the membrane and that is bond to an integral protein
How to you characterize a protein of the plasma membrane ?
depending on their side of the PM : internal or external
Do we find cholesterol in prokaryotes ?
no
What do we find in prokaryotes instead of cholesterol ?
haponoïds
What’s the % of proteins in a proakryotes’ PM ?
70%
Why is there so muche proteins in the prokaryotes’ PM ?
because they can’t be allocated on different mb bc prokaryotes only have one mb (contrary to the eukaryotes)
What is protease ?
an enzyme the accessible polar domain of proteins
Can protease cut through the membrane ?
no
What’s the action of protease on a PM ?
desintegration of external part of the proteins :
- peripheral TOTALLY degraded
- transmembrane and integral are PARTIALLy degraded
What’s the action of permeabilization of the PM ?
it cuts through the PM = holes
What’s the action of protease when the PM is permeabilized ?
it degrades the polar part of proteins on the external AND internal part of the PM, but still not degrades the apolar part hidden in the PM
What are the two types of asymetry of the PM ?
lipids asymetry and proteins asymetry
What are the three major phospholipids found in the PM ?
- phosphatidylserine
- phosphatidylethanolamine
- phosphatidylcholine
What are the four major lipids found in the PM ?
- phosphatidylserine
- phosphatidylethanolamine
- phosphatidylcholine
- glycolipids
What are the % of phosphatidylserine found in the internal and external part of the PM ?
0% external
100% internal
What are the % of phosphatidylethanolamine found in the internal and external part of the PM ?
10% external
90% internal
What are the % of phosphatidylcholine found in the internal and external part of the PM ?
90% external
10% internal
What are the % of glycolipids found in the internal and external part of the PM ?
100% external
0% internal
What are the two main lipids found in the external part of the PM ?
glycolipids and phosphatidylcholine
What are the two main lipids found in the internal part of the PM ?
phosphatidylethanolamine and phosphatidylserine