Zusammenfassung der Ressource
CELL
- Encompassed in biomembrane
Anmerkungen:
- Up to 50% of the membrane can be proteins
- Fluid
- Dynamic at 37º
Anmerkungen:
- biomembrane as to be able to move things around
- 2 dimensional fluids
- Lateral diffusion
Anmerkungen:
- within the leaflet
Phospholipids in one leaflet can move within that leaflet with ease
common, easy, rapid
- Transverse Diffusion
Anmerkungen:
- Between bilayers is very slow & unlikely
you never get flip-flopping
you rarely get phospholipid from one leaflet going into the other
- Temperature & composition dependent
- Fluidity regulation
- Sterols, cholesterol
- break apart van der waal
interactions = more fluid
- Composition of phospholipids
- # of double bonds
- # of phospholipids
- Proteins
- transmembrane proteins break van der waal
forces = more fluid
- Measuring fluidity
- FRAP
Anmerkungen:
- using fluorescent proteins
proteins in PM are potentially floating around & laterally diffusing in the PM
bleached area cannot be seen on microscope
recovery- does bleached area recover some of it's fluorescence?
- Goal: look for recovery
Anmerkungen:
- only way to look for recovery is if proteins from periphery diffuse into this area & recover fluorescence
protein diffusion related to amount of diffusion in the membrane
more fluid = more recovery
- Graph
Anmerkungen:
- Certain level of fluorescence, which is 100% (starting point)
when you bleach, it drops to 0 (100-0 real quick)
look for recovery, which eventually plateaus
you end up with 50% recovery in this case, which means 50% are motile & 50 are non-motile
50% of the membrane has fluidity
- reason for non-motility
- protein linked to cytoskeleton, which
is tethered to membrane & does not let proteins move
- Closed compartments
- membrane-bound organelles
- Plasma membrane
- Cytosolic face
- Internal
Anmerkungen:
- BUT FOR VESICLE MEMBRANE CYTOSOLIC = EXTERNAL FACE
- Exoplasmic face
- proteins in lumen
- Carbs are found exclusively
here
- Asymmetric
Anmerkungen:
- Present with all proteins, not just lipid bilayer
- Proteins within membrane are same orientation
- Cadherins have binding domain in EC
domain ALWAYS
- ETC
- Membrane proteins
- integral
Anmerkungen:
- Proteins go through PM
sizes of domain vary
- transmembrane domain
Anmerkungen:
- most important domain
inner part of lipid bilayer transmembrane made up of hydrophobic amino acids
it has fatty acid carbon tails
- Spans lipid bilayer, hydrophobic region
- Different structures
- Alpha helix
Anmerkungen:
- chain of amino acids making a simple little helix
20-25 amino acids
- Beta barrel
Anmerkungen:
- complex structure
hydrophobic amino acids make it to span the membrane
- cytosolic side
- Arg & lys
- Help anchor the protein
Anmerkungen:
- if you try to pull protein through membrane, these charged proteins resist going into hydrophobic region
- Exoplasmic side
- glycosylated
Anmerkungen:
- can add sugars to transmembrane proteins on extracellular domain
- Cytosolic &
exoplasmic domain
- peripheral
Anmerkungen:
- Proteins somehow attached to membrane
Does not tell you anything about its function
- Example: Dystrophin is bound to transmembrane protein
You never find dystrophin outside of a cell
- attached non-covalently to
something that is covalently linked
to membrane
Anmerkungen:
- Ionic interactions, hydrogen bonds
protein-protein interactions
van der waals forces
- Attached to transmembrane protein, integral
membrane protein or lipid-linked
- integral protein can be linked to cytoskeleton
via peripheral membrane protein
- ECM can be bound by peripheral membrane protein
- ECM can bind to integrins, which are transmembrane
protein, thus making it a peripheral membrane protein
- Lipid-Linked
Anmerkungen:
- Proteins physically linked to one of the phospholipids on the membrane
- Acylation
Anmerkungen:
- N-term Glycine linked to phosphate
- Prenylation
Anmerkungen:
- C terminal Cysteine or one that is close to C-terminal domain
- GPI linked
Anmerkungen:
- PI (phosphlipd &
phoshoglyceride)
Anmerkungen:
- In order to link protein to membrane you have to link to PI
LINK IS CALLED GPI ANCHOR
- have a signal on their
C-term so they can be
linked to GPI anchor
- Doesn't have to be
transmembrane
domain
- Some NCAM have GPI anchors
Anmerkungen:
- NCAM = IG superfamily molecules have transmembrane domain, others have GPI anchors
remember: both are cell adhesion molecules
but they can do different things
- does not interact with cytoskeleton
Anmerkungen:
- NCAM transmembrane molecules do interact with cytoskeleton
- INSERTION OF PROTEINS
INTO MEMBRANE
- Translation of any protein starts in
cytosol
Anmerkungen:
- Need signal to leave cytosol
Anmerkungen:
- not necessarily sequence specific
- WHENEVER YOU HEAR SIGNAL IT IS BEING TAKEN TO ER
- Topogenic sequences
Anmerkungen:
- found in proteins that can be translated
- Its not the exact amino acids that are signals, its the shapes they form, which are recognized by other proteins such as signal recognition particles
- N terminal Sequence
Anmerkungen:
- found on N-term & is cleaved
Recognized by signal recognition particle- taken to ER
- Signal Anchor Sequence (SA)
Anmerkungen:
- anchored in ER
N-term signal that is NOT cleaved
- Hydrophobic C-terminus
Anmerkungen:
- acts as a signal to get protein to ER
- Tail-anchored protein
- translation starts at N-terminal in the cytoplasm
- after translation finishes, a
Hydrophobic C terminus made
Anmerkungen:
- Occurs in cytosol, which has a hydrophilic environment
- Protein folds to get out of hydrophilic
environment of cytosol
- Forms a structure recognized by GET3
Anmerkungen:
- GET 3 in cytoplasm
GET 1 & 2 - ER MEMBRANE
- GET3 recognizes C terminus
- Docks with Get 1 & 2 and uses
ATP to shove hydropobic tail
into ER membrane
- Result: protein that has
hydrophobic C term tail in the
membrane and N term
domainin cytosol
- DOES NOT HAVE EXTRACELLULAR
DOMAIN BUT HAS TRANSMEMBRANE
DOMAIN
- Stop-transfer/Membrane anchor (STA)
Anmerkungen:
- Where-ever its being transferred, we transfer & stop it
anchor it there
- Type 1, 3, 4B the N terminal are luminal
- Type 2 & 4A N terminal is cytosolic
- TYPES OF PROTEINS
Anmerkungen:
- ALL TYPES OF PROTEINS ARE TRANSMEMBRANE PROTEINS
- Synthesis of Type I
Anmerkungen:
- typical transmembrane proteins
has hydrophobic domain
- N term sign go into lumen
& is cleaved
C term remains in the cytoplasm
- translation occurs in
cytoplasm N terminal
translated first
- N term signal is
hydrophobic & begins to
fold (stops translation)
- Signal recognized by signal
recognition particles (goes to ER)
- N term goes via translocon into ER lumen
- N term sequence cleaved- mature protein does
not have signal
- Translation continues into ER lumen
- hydrophobic domain = STA,
- Synthesis of TYPE II & III
Anmerkungen:
- No n terminal signal
they have integral signal
- translation starts in cytosol with
N term domain
- make N term domain, until you hit SA, which tells
you to go to ER
Anmerkungen:
- signal region = hydrophobic
it becomes the transmembrane domain , but the thing is you already have this N terminal domain translated
- Does the N term domain stay in cytosol, or do you shove it into the
lumen?
Anmerkungen:
- depends on charges around the SA
SA = hydrophobic, its going to be in the membrane
- cytosolic amino acids are often charged, which helps anchor the protein in the membrane & helps get protein to the right side of the matrix
- TYPE II
- Positive charged amino acids on N
term side
- N term stays in cytosol
- translocon flips translation & lets C
term domain go into lumem
- Type III
- No/very little charge on amino acids
on N term domain
- N term goes into lumen
- Charged amino acids on Carboxyl term side of SA thus
it stays in cytosol
- Synthesis of Type IV
- STA means protein stops transferring into ER
- Protein goes back & forth between signal, STA, signal, STA
- in & out of ER
- # of domains varies & position of N term domain can be
cytosolic or luminal
- Transport across Membrane
- Passive Diffusion
- partition coefficient AND
concentration gradient
Anmerkungen:
- membranes are semi permeable & allow small uncharged molecules through
- partition - measures
hydrophobicity of molecule
Anmerkungen:
- How soluble a molecule is VS how soluble it is in an aqueous solution
- how fast a moelcule goes through biomembrane
- relatively high coefficient
Anmerkungen:
- some solubility in membrane
- remember: do not want it too lipid soluble
- K = 0, not cross
- no energy
Anmerkungen:
- driven by existing concentration different across PM or any membrane
HIGH TO LOW
- Active Transport
- Needs energy
- primary active transport
- secondary active transport
Anmerkungen:
- uses a situation that's already arisen using primary transport
- doesn't really require ATP, so not necessarily ATP powered
- Antiporters
- Symporters
- Na/Glucose
Anmerkungen:
- Na high outside cell- (+) charge
Glucose = outside cell
High glucose = inside cell, energy source for cells
- want more glucose inside cell, but you already have a high concentration of it
Glucose moves against its gradient, which requires energy
- Energy is provided by symporter & uses the fact that Na wants to come in (down its gradient)
Glucose uses the energy provided by Na
- 2 free energies
Anmerkungen:
- 1) Concentration gradient of Na
more sodium outside, it wants to get inside
- 2) Charge gradient of cell
positive charge on outside of cell
- Both energies enough to move 2 Na down & 1 glucose against gradient
- Use already established
graident to tranport
themselves
Anmerkungen:
- Use one molecule that goes with concentration gradient & one against gradient
- pumps that use ATP to move molecules against
concentration gradient
Anmerkungen:
- ions are charged, cannot get them across the membrane, need to pump ions
- V & F
Anmerkungen:
- responsible for pumping, they use ATP to pump H+ across membrane
- Important in mitochondria & chloroplasts, that is where a lot of H gets pumped around for ATP synthesis
- ABC type
Anmerkungen:
- Move variety of small molecules
- Have ATP binding cassette
Anmerkungen:
- specific domain that binds ATP in specific way
- Not restricted to ions
- Can flip from one leaf to
other
Anmerkungen:
- CFTR
Anmerkungen:
- P
Anmerkungen:
- move different types of ions
two types
first one is called muscle-calcium ATPase
- Muscle ATPase pumps 2 Ca out of
cytoplasm per ATP
Anmerkungen:
- in this case it pumps it into SR as soon as you trigger muscle contraction
- Calcium release is voltage gated channel, as soon as calcium comes out P-class pump kicks in & gets it back into SR
- END: cystosol has little or no Ca
Anmerkungen:
- pump works against concentration gradient
END: lots of Ca in SR, so when channel opens again Ca can flow out
- Na/K ATPase pumps 3 Na
out per 2 K in per ATP
Anmerkungen:
- working all the time in our cells
- Lots of Na outside of the cell & K inside of cell because pump is always working - pumps ions against concentration gradient
- Antiporter
- Facillitated transport
- pore/channel
Anmerkungen:
- holes in membrane formed by some sort of protein
- Selective
- proteins line at pore,
creating holes through membrane
Anmerkungen:
- keep things out, let things in
- K+ resting channel
- K+ can go through the membrane leaving water molecules behind
Anmerkungen:
- but its bound to water molecules, so it has to have the right driving force
- in this example: bound to 4 oxygen molecules, so it has to break bond with all 4 in order to pass through channel
- Needs concentration gradient
- channel's have oxygen that are same spacing as water shell
- K+ release itself from water & binds to Oxygen lining channel
- goes through channel & once its released to other side it picks up
water molecules again
- Channel specific to K+, because if you look at Na even though it has
hydration shell it is different size & spacing
- Results in creation of membrane potential
- more positive on one side
- Uniporter
Anmerkungen:
- Glucose binds to one side of uniporter (GLUT1)
- conformational change, opens up, allows glucose to enter
- gate
Anmerkungen:
- something that opens & closes
- opened/closed
- GLUT1 is basically a gate
- LIgand gated channel
Anmerkungen:
- still with a concentration gradient
- Voltage gated channels
Anmerkungen:
- opens with change in membrane potential
- EXAMPLE: channel that releases Ca+
from SR in response to nerve impulses
- nerve impulses travel down muscle cell & trigger
voltage chennel on SR
- opens & calcium comes down concentration gradient
- concentration gradient
Anmerkungen:
- HIGH TO LOW
moving through pore/channel such as protein-lined, so they don't come into contact with hydrophobic interior
- faster than passive
- Saturable
Anmerkungen:
- only certain number of molecules can get through in any period of time
- limit to the speed
- uniporter, symporter, antiporter
Anmerkungen:
- do not tell you about type of transport, just the number of molecules & which way they are moving
- uni
- one mole moving
- sym
- two molecules
moving same
direction
- Anti
- two molecules moving
different direction
- Co-transporter In Epithelial Cells
- Leaflets
- Semi-permeable
- Small & uncharged or hydrophobic
- YES YOU CAN ENTER
- Large &/or hydrophilic
- NO. DIPSHIT
- Ions & glucose
- Amphipathic
Anmerkungen:
- main component is phospholipid
- Micelles
- Liposomes
Anmerkungen:
- CELL IS A LARGE LIPOSOME
its a hallow sphere, where all of the tails form a bilayer structure
- lipid bilayer is not just a lipid
- Transmembrane
proteins
Anmerkungen:
- transmembrane receptors such as cadherins & integrins have transmembrane domains
Dystrophin links transmembrane protein to cytoskeleton
- Transmembrane
domain is the most
imporatant domain
- Peripheral
proteins
- EC domains
Anmerkungen:
- integrins have domains outside of the cell to allow it to bind to ECM
- Composed of
two leaflets
Anmerkungen:
- row of phospholipids on each side
hydrophobic tails facing inside
- lipid
composition
varies within
each half of
bilayer
Anmerkungen:
- depending on composition, certain properties arise
- EXAMPL: PC or PE can be
used in the membrane
Anmerkungen:
- If PC is cyclindrical & PE has a comb-like structure, then you get bilayers of different shapes
PC would form a straight bilayer, but as soon as you put in PE (tail wider than head), you introcude curves
- Fatty Acid
Anmerkungen:
- basic building block of phospholipid
Cx:y
x = carbon molecules
y = double bonds
- Phosphoglyceride
- Base = glycerol
Anmerkungen:
- 2 esterified fatty acids attached to glycerol
- different heads
groups, ALL
attached by a
phosphate
Anmerkungen:
- depending on head group you have PE, PC, PS, PI
- Plasmalogen
Anmerkungen:
- One of its fatty is not esterified
- Saturated vs.
unsaturated
- Temperature
Anmerkungen:
- Humans = 37ºC
Palmitate (C16:0)- TM = 63ºC
at 37 it forms a fat (solid)
thus not a good building block
- longer chain = higher TM
Anmerkungen:
- more carbons interact with each other, if you stack them together there are van der waal interactions
TEMPERATURE CANNOT BE TOO HIGH BECAUSE IT BECOMES A SOLID AT 37ºC
- More double bonds = lower TM
Anmerkungen:
- double bonds introduce kinks, you cannot stack them & as a result get less attraction between chains
becomes more liquid
- Cis double bonds
- PM is semi-fluid because it uses
combination of saturate & unsaturated
- Sphingolipids
- base = sphingosine
Anmerkungen:
- 3 carbons that kind of look like glycerol
sphingosine already has this carbon chain, so you are only adding ONE fatty acid
- Glycolipid
Anmerkungen:
- sugar group as polar head
- can/cannot use phosphate group
Anmerkungen:
- can be a phospholipid
if there is no phosphate used to attached head group its just a sphingolipid
- Sterols
Anmerkungen:
- 4 ring hydrocarbons
intercalate themselves into lipid bilayer with polar hydroxyl groups facing same direction as polar head groups
- Cholesterol
- No long carbon chain (tail)
- Thickness may change
- PC + cholesterol = thickens
membrane
- Sphingomylein + cholesterol = does
not change thickness
- made up of lipids, sterols, proteins