2.1 Cells Flashcards
what are the parts of the fluid masaic model
* biological membranes are two dimensional liquid where all lipid and protien mol diffuse more or less freely
*PM contains less fluid like structures or domains such as:
- protein peotien complexes (interact w/ proteins on inside, outside or on PM of other cells
- lipid rafts (for signalling)
- pickets and fences formed by actin absed cytoskeleton
- large stbale structures like synapses or desomosmes
what is found on the surface of plasma membranes?
Phospholipids
- 75%
- phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) phosphatidylserine (PS)
- for every one phospholipid there are two lipid chains coming off (polar head interacting with extracellular fluid or intracelular)
Flippases: *act to dsitribute phospholipids
- concentrate PE and PS (carrying negative charge) on inner memmbrane
- does not mean they are EXCLUSIVELY on inner mem, just conc there
Scramblases: *act to dsitribute phospholipids
- Concentrate PC and phingolipid on outermembrane
Glycolipids
- 5%
- only on outer membrane surfaces, role is to provide energy and serve as amrkers fo cell recognition
Cholesterol
- 20%
- increases membrane stability, maintains fluidity, and permeability
what phospholipids are concentrated on the inner membrane?
PS, PI and PE
*only PS and PI have charges associated with them (neg charge contributing to neg inner membrane chage)
what phospholipids are conc on outside cell
PC
- also sphingomyelin, glycolipid, cholesterol
describe transport membrane proteins
- protein spans the membrane and may provide a hydrophilic channel across the membrane that is selective for a particualr solute
- some use ATP to actively pump across membrane
describe membrane proteins involved in enzymatic activity
- rpotein is build into memrbane
- can be an enzyme with an active site, can act w. seveeral ezymes to catalyze sequential steps of matabolic pathway
*onvolec in cell signalling
desrcibe membranes proteins that are receptors for signal transduction
- protein is exposed to outside of cel and can have bindign site with specific shape for specific chem messenger
(ex hormhome)
- external signal can cause conformational change in protein -> initiation of chain of chemical rxns in cell
describe intracellular adhesion membrane proteins
- membrane proteins in adjacent cells can be hoked together in various kinds of intercelular junctions
- some mem proteins (CAMs) provide temporary bindign site that guide cell migration and other cell-cell interactions
*membrane from one cell has membrane protien, and membrane from other cell will bind via membrane protein
describe cell - cell recognition membrane proteins
some glycoproteins serve as identification tags that are specifically recognized by other cells
*see membrane protein on another cell recogonizing glycoprotein
describe membrane proteins involved in attachment to the cytoskeleton and extracellular matrix
- elements of cytoskeleton and ECM can be anchored to membrane proteins
- helps to maintian cell shape and fix location of certain membrane proteins
p others play a role in cell movement or bind adjacent cells together
what are the different types of membrane junctions?
- Anchoring (desmosomes)
- mediate cell-cell and cell-matrix adhesions: linked t cytoskeleton to transmit and distribute stress (skin and heart muscle)
- Occluding Junctions (tight junctions)
- impermeable junction that encircles the cell to form seals between epithelial cells
- Channel-forming (gap junctions)
- allow diffusion of small molecules
- Signal-relaying
- ligands on or released from cell transmit signals to receptors on adjacent cell (ex: synapses)
describe desmosomes
- “disks” of desmosome interact via linker protein, intermedia filaments come off desmosome to interact and proivde strength and resistance to sheer force
*prevents tearing of tissue by interacting & providing strength in and inbetween cells
- adhesion plaque (disk) ex: Plactoglobin and demoplakin
linker proteins between disks: Cadherins (desmocolins and desmogleins)
Intermediate filaments: keratin
Describe tight junctions
- two proteins on different cells interact to make a membrane impermeable
- proteins are within the cell membranes so interact with eachother via membranes in zipperlike format
- proteins interact, pull mem close togethr and tightly close na dmultiple levels so prevents leakage of fluid (ions cant sneak away, liquids etc) want these thigns to go through cell not what leaks between
*tight junctions are assocaited w. actin filaments to help keep them in place/orientation in appropriate area (apical side of cell in GI tract)
Ex of proteins forming tight junction: Occludin and Claudin
Describe a Gap Junction
allow for one cell to communicate or exchange nutrients with another
- can also be called connexons which are made of 12 connexin protein monomers (6 per cll and 2 sets have to interact to form a channel)
- connexons stay closed until they interact w/ connexon of antoher cell
describe simple diffusion
pass directly though phospholipid bilayer
- non polar, lipid soluble substances
ex: oxygen, carbon dioxide, fat soluble vitamins
describe facilitated diffusion
- transport of glucose amino acids and ions
- bind carrier proteins or pass through protein channels
what is channel mediated diffusion
for transport of ions via protein channel
describe osmisis
method of passive membrane transport
- movement of water from high to low conc
- direction of osmosis determined only by a difference in total solute conc
- occurs when conc of solvent is diff on opp sides of mem
isotonic
hyper tonic
hypotonic
isotonic: sol with ssame solute conc as that of cytosol (no effect on cell)
Hypertonic: solutions having greater solute conc than that of cytosol (cell shirnks)
Hypotonic: solutions ahve lesser solute conc than that of cytosol (cell swellsX
Primary active transport vs secondary
Primary: hydrolysis of ATP phosphorylates the transport protein causing conformational change
secondary: use of exchange pump (like Na K pump) to indirectly to drive transport of other solutes
describe steps in primary active transport
- 3 sodiums bind from cytopalsm side
- ATP binds to phosphorylate donating a phosphate ATP -> ADP
- causes conformational change, sodium now in extracellular compartment
- Cannel facing extracellular fluid, takes 2 potassium
- K+ binding triggers release of potassium mol Conformational change to original position
- K released inside cell now have a charge diff
Describe Vesicular transport
- transport of large particles and macromolecules across cell membranes
- exo or endocytosis
- transcytosis = moving substances into, across and then out of cell
vesicular trafficking = moving substances from one area of the cell to another
describe exocytosis
* important parts are V and T snare
T-SNARE: target - Found on where the vesicle needs to go
V-SNARE: Found only on vesicles
- Targeting (V and T snares come together)
- Specific set of t snares that go with plasma membrane, and specific v snoes recognize specific t snares
- Once besicle hits target of interest it docks, uses engery (priming step) to get the vesicle and PM closer together
- Ca not always required but usually, causes a triggering step
- Ex for hormones, visicle is close to membrane but wont release contents and fuse until calcium
- Then fusion
examples of V and T snares
V snares: synaptotagim III and synaptobrevin, work together to form the V snare
T snares: Syntaxin and SNAP-25 are T SNARES
*different types of T snares found on dirrerent target sites
what are the different types of Endocytosis
5 ish ttypes
Phagocytosis (englufing larger mol)
Macropinocytosis (cell drinking
Clathrin dependent (clarthrin is protein)
Caveolin dependent
Other types not as clear: clathrin and caveolin independent, membrane invaginates we don’t know how
Describe phagocytosis of Bacteria
Can take bacteria up into immune cells for distruction (bacteria is yellow)
Actin push the membrane out to surround bacteria to take up
Microtubule depolarization lets actin grow and remodel the membrane
*note: viruses can also undergo phagocytosis, main mechansim is macropincytosis which uses diff rpteins like clarthin, dynamin, caveolin and flotilin
describe Macropinocytosis
cell “ gulps” drops of extracellular fluid containing solutes into tiny vesibles
- no receptors are used, so non specific
most vesicles are protien covered
gives cell a taste of what is out there
describe Clathrin mediated enodcytosis
Adapter protein AP2
Come along the membrane, green structure called clathrin will interact, the interaction causes a membrane invagination (proteins help to bend membrane)
As more AP2 and protein come in need dynamin to go to membrane flask like component to help pinch off the membrane
All associated proteins will break off and vesicle can go where needs to go
describe receptor mediated endocytosis
Clathrin is a membrane bound protein :One way it works is take ligands from cell signalling and turn off cell signalling
Clathrin comes in and interacts with receptors, when receptors have bound ligand some receotors are internalized -> Mechisms to turn off receptors
Bring it inside of the cell its if excessively stim
describe caveolin vesicles
- smaller than calrthin vesicles
- caveolin works in similar manner to clarthin but not just specific to cell signalling, can help with pagocytosis o viruses
- often associated w/ platforms for a variety of signaling molecules,
- cause special memrbane invagination (flask like structure)
*hihg qty of shingolipids and cholesterol in mmebrane helps with stability of caveolae - formed from lipid rafts
what are coatomer protiens
COP1 and COP2
- coate vesicles that are associated with intacellular trafficking
- important for interior movment from ER to golgi
*COP 1 moves from golfi back to ER
COP 2 moves from ER to golgi
describe steps of Caveolin mediated endocytosis
If too much signalling, NT (neurotransmitters) get caveolin medicated endocytosis.
Dynamin will pinch the membrane to save receptor from degredation
what generates electrochemical gradients
- ions moving down conc gradient (potential)
- electrical effects of charges on each side of membrane
*resting memrbane potential is point where K+ potential is balanced by the membrane potential
*potasium rests resulting membrane potential
what ions are primarily outside cell? what ions are primaryil inside?
OutsideL Na, Cl a bit of K
inside: Porteins, lots of K, a bit of Na and Cl
*Chloride is generally high outside the cell because it is repelled out ebcause of neg charge inside cell
how is membrane potential generated and maintained?
* ranges from -20 to -200mV
- Na+/K+ pump pumps more cations out
- conc gradeitn fo K+ and higher permeability of K+
*K is main driver bc ther are potassium lead channels in membrane that are open at all times
- memrbane is impermeable to anionic proteins
What are the 3 roles of membrane receptors
- Contact signaling: important in normal development and immunity
- Electrical signaling: voltage gated ion gates in nerve and muscle tissue
- signaling chemicals (ligands) that bind specifically to membrane bound receptors
ex: ACh neurotransmitter binds to ligan gated ion channgels and G protein coupled receptors
what are the parts of the G rptoein coupled receptor
G protein is made up of 3 kinds of proteins: A, b and gamma
Usually bound to GDP
When ligand is bound, g protein bidns to activated receptor, GDP is displaced by GTP and then alpha subunit separates from beta gamma complex
how are G rptoein coupled receptors activated?
- Protein inactive bc GTP is bound, interacting with alpha subunit, inactive alpha interacts with beta and gamma
- Alpha and gamma have direct interaction with PM but not Beta
- Signal mol binds and signals actiation, recetor protein interacts with alpha, GDP comes off and GTP comes on
- When GTP bound to alpha ( active form) alpha separates from beta and gamma
- Activated alpha with GTP can then go activate other things and cause signaling in the cell
- can use ATP to Convert to cyclic AMP and interact wi. inactive pka to do cell signalling
- To turn off signaling cascade, GTPase on alpha subunit causes cleavage of a phosphate unit and inactivation of alpha and inactivation of taget
* GTP bound alpha subunit can interact and lead to signaling
describe the PKA pathways of GPCR
Example of G protein: alpha S bound GTP
Atp conv to cyclic AMP
Interacts with inactive PKA, binds to regualtroy part, and release activated protein kinase A
describe PLC pathway of GPCR
PLC beta interacts with g protein coupled receptors
When ligand present activation of GQ (type of alpha subunit)
Interacts with PLC beta, the beta goes on and takes lipid in the membrane, PIP2 gets cleaves into IP3 that then can leaved to signaling in cell by an IP3 receptor (present on ER). When bound channel opens and releases calcium inside of the ER
IP3 generated can also use the diacylglycerol to activate protein kinase C, interact with other proteins in the cell
