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
Why are glycolipids only external ?
Because they are produced in the endoplasmic reticulum and glycosylated in the golgi apparatus and then it creates vesicles to emanating it, then in fusion with the PM so what was in the lumen of the vesicle is now outside th PM
What are the proteins that are only external ?
glycosylated proteins
Why are glycoproteins only external ?
bc they are produced the same way as glycolipids :
they are produced in the endoplasmic reticulum and glycosylated in the golgi apparatus and then it creates vesicles to emanating it, then in fusion with the PM so what was in the lumen of the vesicle is now outside th PM
What’s the model used to study the plasma membrane (with only lipids) ?
the black membrane model
What is the Black Membrane model ? explain how it works
2 chambers with water separated by a wall with a hole in it
lipids close this hole by forming a bilayer sheet
What do we study with the black membrane model ?
the lipids’ behaviour
What are the three behaviors of lipids ?
- flip flop
- axial rotation
- lateral diffusion
Is lateral diffusion fast or slow ?
very fast 2µm/sec
Is the flip flop movement of lipids very common ?
no, it’s very rare
By what is provoked the flip flop movement of lipids ?
it’s induced by a protein
What’s the flip flop movement of lipids ?
the up ones and the down ones echange their places
What are the three factors that influence the membrane fluidity ?
- temperature
- nature of the FAs
- cholesterol
How the temperature can influence membrane fluidity ?
The higher the temperature is, the more fluid is the membrane
BUT under 4°C the movement of the lipids stop so it’s not fluid anymore
How the nature of the FAs of the cholesterol can influence the membrane fluidity ?
the longer it is, the more stable is the membrane (bc more apolar/hydrophbic)
BUT ABOVE ALL :
+ saturated FA = + fluidity
+ unsaturated FA = + rigidity = - fluidity
How the cholesterol can influence the membrane fluidity ?
it’s a buffer of the membrane fluidity, according to the FA
Do the “flip flop” movement exist in proteins ?
no, proteins can’t change of layer just like that
What is the main behavior of proteins ?
lateral diffusion
What kind of proteins are expressed on the surface of the cell ?
glycosylated proteins
What is a heterokaryon ?
a fusion of two cells so it expresses charaters of both (like proteins)
What are glycosylated proteins ?
proteins with carbohydrates linked by covalent bonds
On a heterokaryon, what technic can you use to mark the glycosylated proteins of both cells ?
immunofluorescent technic :
fluorophore + antibodies that fix to the prots
Thanks to what experiment we discovered the lateral diffusion of proteins ? explain the process
thanks to an experiment using a heterokaryon + a immunofluorescent technic :
ex with a heterokaryon of a human cell and a mouse cell, human’s glycosylated prots are marked with antibodies + FITC (green) and the mouse’s glysolyated prots are marked with antibodies + rhodamin (red)
At first : heterokaryon half green, half red
40 minutes later : red and green mixed
What type of movement is the lateral diffusion of the proteins ? simply explain
the proteins move at the surface of the cell
What does the acronym “FRAP” stands for ?
Restauration After Photobleaching
What type of fluorophore is used for the FRAP technic ?
GFP = fluo proteins expressed by the cell in green
Simply explain the FRAP technic
we use a laser at max power (=bleach), making a hole without proteins on the surface of the cell, and when time passes, the hole without GFP disappear, it’s green again
=> movement of proteins
What is showed by the FRAP experiment ?
the movement of proteins
What is the freeze fracture used for ?
used to study the structure of the membrane layer
Why molecules that can pass through the PM in vivo can’t pass through an artificial PM ?
bc these molecules need something to transport them (active transport)
What are the types of molecule that use passive transport to go through the PM ?
- gaz (O2,CO2)
- small uncharged polar molecules (H2O, glycerol, ethanol)
What are the types of molecule that use active transport to go through the PM ?
- larger uncharged molecules (aa, glucose, nucleotides)
- ions (H+, Na+, K+…)
What is passive transport through the PM ?
- spontaneous
- generates energy
- follow the electro-chemical gradient
What is the electro-chemical gradient ?
gradient of the charges (electro) and of the concentration (chemical)
What are the two types of passive diffusion ?
- simple diffusion
- facilitated diffusion
What are the two types of facilitated diffusion ?
- permease = carrier protein -> uncharged molecules
- protein channel -> ions
According to what the simple diffusion increase/decrease ?
the difference of concentration btw the external and internal part of the cell
(proportional)
What is facilitated diffusion ?
spontaneous movement BUT need another molecule to help go through the PM
What kind of graphic do we obtain with facilitated diffusion ?
a curve that quickly goes up, until it reaches a plateau (= saturation)
What kind of graphic do we obtain with simple diffusion ?
a straight line (proportional)
What kind of molecules are carried by carrierproteins (permease) ?
uncharged molecules
What kind of molecules are carried by protein channels ?
ions (charged molecules)
Thanks to which molecule the glucose is transported ?
GLUT1
What type of transport is GLUT1 for Glucose ?
facilitated transport = carrier protein
How do carrier proteins carry molecules through the PM ?
by a conformational change
open to the ECR and close to the cytosol -> close to the ECR and open to the cytosol
What are the two types of protein channel ?
ion channel
aquaporine (water)
What are the two conformations of protein channels ?
open and close
What can activate protein channels ?
electric or chemical signal
How many molecules can pass at a time thanks to protein channel ?
millions of molecules like ion at a time
What’s the main difference btw active and passive transport ?
passive = no need of energy active = need energy
Through what kind of structure the active transport go through ?
the active transport go through carrier proteins
What is active transport ?
- energy consumed
- not spontaneous
- sometimes against the electrochemical gradient
What are the two types of active transport ?
- primary active transport
- secondary active transport
What are the two types of secondary active transport ?
- symport
- antiport
What is primary active transport ?
it uses ATP as en energy source
What is secondary active transport ?
it uses energy made by passive diffusion
What is a symport ?
goes through a carrier protein against it’s own gradient at the sime time as another molecule that follows its gradient
What is an antiport ?
goes through a carrier protein following its gradient at the same time as another molecule that follows its gradient
By which mean of transport is the osmosis maintain in the cell ?
by simple diffusion (a bit) and by facilitated diffusion (through aquaporines, a lot more)
How are macromolecules and particles transported inside the cell ?
the PM is deformed to circle it and creating a vesicle
What are the two types of transport for macromolecules and particles ?
- endocytosis
- exocytosis
What is endocytosis ?
invagination (vesicles) of macromolecules
What is exocytosis ?
secretion (outside) of macromolecules
What are the two types of endocytosis ?
- pinocytosis = fluid phase endocytosis + receptor mediated endocytosis
- phagocytosis
What is pinocytosis = fluid phase endocytosis ?
internalization of macromolecules in small vesicles
What’s the size of vesicles created by pinocytosis ?
small : >150 µm of diameter
When pinocytosis happens ?
continuously , the cell continuously internalizes its PM (for prots and water)
How fast is pinocytosis ?
as it is continously made, it’s not fast
What’s the specificity of vesicles created by pinocytosis ?
they have a wide contour because of protein called CLATHRIN that assembly by three to form kind of triskels
What is clathrin ?
a protein that is wrapped around the vesicles made by pinocytosis
What is receptor mediated endocytosis ?
a specific receptor induced internalization
How fast is receptor mediated endocytosis ?
its very fast as it’s specific
What are the two types of pinocytosis ?
- fluid phase endocytosis
- receptor mediated endocytosis
What is phagocytosis ?
internalization of big molecules making big vesicles
What’s the size of vesicles created by phagocytosis ?
big vesicles <250µm of diameter
What’s the difference btw phagocytosis and pinocytosis ?
size of vesicles created :
- pino : small vesicles + clathrin
- phago : big vesicles
What are the two types of endoplasmic reticulums ?
- rough (RER)
- smooth (SER)
What synthetize the RER ?
integral protein + secreted proteins
What synthetize the SER ?
lipids
What’s the function of flipase enzyme ?
to flip layer of phosphatidylcholine (or at least lipids, not sure) in the SER
What regulate the action of the enzyme flipase ?
Cytoplasm and the Lumen of SER
What are the two types of exocytosis ?
- constituve exocytosis
- regulated/controled exocytosis
What do the constituve exocytosis transport ?
- extracellular matrix proteins
- newly synthetize proteins + lipids
By what is the regulated cytosis transport activated ?
by a signal
How much does the endoplasmic reticulum represent of membrane of the cell ?
50%
By how many membrane is delimited the ER ?
by only one ; delimited by a simple membrane
How is organized the ER ?
as a labyrinth, a network
it communicates btw them
What’s the difference btw the rough and the smooth ER ?
the rough one is denser
What’s the other name for the rough endoplasmic reticulum ?
granular endoplasmic reticulum (GEM)
What can you find on the cisternae of the RER ?
ribosomes
What type of enzyme can you find on the surface of the SER ?
enzyme for the phospholipids synthesis
Is ther a lipid asymetry on the SER membrane ?
no there isn’t, it’s only on the plasma membrane
How do the SER releases the lipids it produces ?
by releasing budding vesicles, that fuse with the PM so the’re on the external part of the PM
What do you find in the Golgi apparatus ?
lots of cisternae that are not in contact
What are dictyosomes ?
there are a a sum of saccules and cisternae
How many saccules/cisternae is there per dictyosome ?
6
Are distyosomes polarized ?
yes
Where can you find dictyosomes ?
in the golgi apparatus
What does the acronym “LDL” stands for ?
Low Density Lipprotein
What does the acronym “HDL” stands for ?
High Density Lipprotein
What does the LDL transport ?
it transport cholesterol
What’s the structure of LDL ?
micelle
What type of endocytosis is realized for internalizing liganol ?
It’s a recepor mediated endocytosis
Describe the different steps of liganol internalization
1 - Liganol/receptor interaction => clustering of the liganol-receptor complex
2 - formation of a clathrin coated pit => clathrin coated vesicle
3 - Denudation
4 - Fusion with an endosome
5 - Recycling + lysosomal degradation
What are the three phases of the dictyosomes in the golgi appartus ?
1 - Cis phase : receive vesicles of RER and SER (lipids+prots)
2 - Maturation : Modification of proteins
3 - Trans phase : Vesicle budding and free the molecules
What is contained inside Lysosomes ?
contains different enzymes (nuclease …)
lots of acid => acid pH
protease AND proteins
What’s the diameter of a lysosome ?
0,05 to 0,5 µm
What’s the energy used by a lysosome to degrade things ?
the hydrolysis of ATP
What’s the pH inside a lysosome ?
acid = 5
What’s the pH inside the cytosole ?
neutral = 7.2
How are the proteins protected from the protease inside a lysosome ?
by being highly glycosylated
What are the two types of digestion of a lysosome ?
- heterophagy (endo/phagocytosis)
- autophagy (reyccle old organelles)
Does the lysosome degrade everything ?
no, it can store and release some elements in the ECR
How much space can a vacuole take in a plant cell ?
until 95%
What does a vacuole contains ?
enzymes for hydrolysis for auto/heterophagia (just like lysosomes)
How do you call the membrane of the vacuole ?
tonoplast
What are the 3 functions of the vacuole ?
- turgor (=turgescence), it swells to make pressure agaisnt the cell wall = ++ rigidity
- better division of the cell
- stock nutrients
What are the three organelles that are delimited by 2 membranes (=envelope) ?
- nucleus
- mitochondria
- plastid
