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CELL

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CELL

Encompassed in biomembrane
- Up to 50% of the membrane can be proteins
- Fluid
  - Dynamic at 37º
    - biomembrane as to be able to move things around
  - 2 dimensional fluids
    - Lateral diffusion
      - within the leaflet Phospholipids in one leaflet can move within that leaflet with ease common, easy, rapid
    - Transverse Diffusion
      - 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
      - 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
        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
        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
        BUT FOR VESICLE MEMBRANE CYTOSOLIC = EXTERNAL FACE
    - Exoplasmic face
      - proteins in lumen
      - Carbs are found exclusively here
- Asymmetric
  - ASYMMETRY TILL YOU DIE
  - 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
      - Proteins go through PM sizes of domain vary
      - transmembrane domain
        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
        chain of amino acids making a simple little helix 20-25 amino acids
        Beta barrel
        complex structure hydrophobic amino acids make it to span the membrane
        cytosolic side
        Arg & lys
        Help anchor the protein
        if you try to pull protein through membrane, these charged proteins resist going into hydrophobic region
        Exoplasmic side
        glycosylated
        can add sugars to transmembrane proteins on extracellular domain
      - Cytosolic & exoplasmic domain
    - peripheral
      - 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
        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
      - Proteins physically linked to one of the phospholipids on the membrane
      - Acylation
        N-term Glycine linked to phosphate
      - Prenylation
        C terminal Cysteine or one that is close to C-terminal domain
      - GPI linked
        Link to exterior surface
        PI (phosphlipd & phoshoglyceride)
        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
        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
        NCAM transmembrane molecules do interact with cytoskeleton
    - INSERTION OF PROTEINS INTO MEMBRANE
      - Translation of any protein starts in cytosol
        ribosome is in cytosol
        Need signal to leave cytosol
        not necessarily sequence specific
        WHENEVER YOU HEAR SIGNAL IT IS BEING TAKEN TO ER
        Topogenic sequences
        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
        found on N-term & is cleaved Recognized by signal recognition particle- taken to ER
        Signal Anchor Sequence (SA)
        anchored in ER N-term signal that is NOT cleaved
        Hydrophobic C-terminus
        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
        Occurs in cytosol, which has a hydrophilic environment
        Protein folds to get out of hydrophilic environment of cytosol
        Forms a structure recognized by GET3
        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)
        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
        ALL TYPES OF PROTEINS ARE TRANSMEMBRANE PROTEINS
        Synthesis of Type I
        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
        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
        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?
        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
        membranes are semi permeable & allow small uncharged molecules through
        partition - measures hydrophobicity of molecule
        How soluble a molecule is VS how soluble it is in an aqueous solution
        how fast a moelcule goes through biomembrane
        relatively high coefficient
        some solubility in membrane
        remember: do not want it too lipid soluble
        K = 0, not cross
        no energy
        driven by existing concentration different across PM or any membrane HIGH TO LOW
      - Active Transport
        Needs energy
        primary active transport
        secondary active transport
        uses a situation that's already arisen using primary transport
        doesn't really require ATP, so not necessarily ATP powered
        Antiporters
        Symporters
        Na/Glucose
        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
        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
        Use one molecule that goes with concentration gradient & one against gradient
        pumps that use ATP to move molecules against concentration gradient
        ions are charged, cannot get them across the membrane, need to pump ions
        V & F
        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
        Move variety of small molecules
        Have ATP binding cassette
        specific domain that binds ATP in specific way
        Not restricted to ions
        Can flip from one leaf to other
        need ATP
        CFTR
        just pumps Cl-
        P
        move different types of ions two types first one is called muscle-calcium ATPase
        Muscle ATPase pumps 2 Ca out of cytoplasm per ATP
        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
        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
        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
        holes in membrane formed by some sort of protein
        Selective
        proteins line at pore, creating holes through membrane
        keep things out, let things in
        K+ resting channel
        K+ can go through the membrane leaving water molecules behind
        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
        movement of one molecule
        Glucose binds to one side of uniporter (GLUT1)
        conformational change, opens up, allows glucose to enter
        gate
        something that opens & closes
        opened/closed
        GLUT1 is basically a gate
        LIgand gated channel
        still with a concentration gradient
        Voltage gated channels
        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
        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
        only certain number of molecules can get through in any period of time
        limit to the speed
      - uniporter, symporter, antiporter
        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
- main component is phospholipid
- Micelles
- Liposomes
  - 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
      - 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
      - integrins have domains outside of the cell to allow it to bind to ECM
    - Composed of two leaflets
      - row of phospholipids on each side hydrophobic tails facing inside
      - lipid composition varies within each half of bilayer
        depending on composition, certain properties arise
        EXAMPL: PC or PE can be used in the membrane
        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
  - basic building block of phospholipid Cx:y x = carbon molecules y = double bonds
  - Phosphoglyceride
    - Base = glycerol
      - 2 esterified fatty acids attached to glycerol
    - different heads groups, ALL attached by a phosphate
      - depending on head group you have PE, PC, PS, PI
    - Plasmalogen
      - One of its fatty is not esterified
  - Saturated vs. unsaturated
    - Temperature
      - Humans = 37ºC Palmitate (C16:0)- TM = 63ºC at 37 it forms a fat (solid) thus not a good building block
      - longer chain = higher TM
        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
        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
      - 3 carbons that kind of look like glycerol sphingosine already has this carbon chain, so you are only adding ONE fatty acid
    - Glycolipid
      - sugar group as polar head
    - can/cannot use phosphate group
      - can be a phospholipid if there is no phosphate used to attached head group its just a sphingolipid
  - Sterols
    - 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