1
Q
Function of Membranes
A
- membranes are required for life
- 20-30% of all genes encode membrane proteins, across all domains
- big chunk of the genome is dedicated to proteins that are embedded in the plasma membrane
- membranes are essential for creating barriers between different chemical within an organism
- why the fuss?- we dedicate so much of genome to proteins that go into the cell, because we think of this membrane as the gate keeper between one molecule and another
2
Q
Membrane function: cell compartmentalization
A
- plant cells
- not only has membrane around but also all the organelles are surrounded by a membrane
- plays a role in compartmentalizing in different functions and different areas in the cell
3
Q
Membrane function: Anchoring of the cytoskeleton
A
- proteins in the plasma membrane play a role in anchoring the cytoskeleton
- cytoskeleton are protein filaments- stretched from the inside of the cell to the cytoskeleton
- important role of transporter cells
- in cytoskeleton all are anchored or attached to a particular protein, making sure the cytoskeleton is set up the way it is supposed to be
4
Q
Function of membranes: Protein sorting, Golgi complex and ER
A
- Protein synthesis is the making of proteins in cells, must be tagged and sorted and then shipped to the right spot
- ER- site of protein synthesis, sending the proteins that it has made to the Golgi in order to get packaged up the right way
- this is done through vesicles
- this vesicles pinch of from ER and travel to Golgi then fuse with the Golgi and the whole outer area of the ER and vesicles and Golgi is surrounded by a membrane, the phospholipid bilayer
5
Q
function of membranes: Cell adhesion
A
- cells sticking to other cells or to something
- critical role of the membranes and proteins in the membranes to keep things put together
- multicellular organisms appreciate this
6
Q
function of membranes: cell division
A
- cells in the body are all actively dividing right not
- critical role in synthesizing more of the plasma membrane and keeping one cell separate from one another
- altogether they pinch apart and what keeps them separate from each other is the phospholipid bilayer and associated proteins
- neurons for example- one way our neurons conduct signals from one another is by taking up ions and this electrical gradient is moving against the neuron. It maintains the electrical gradient so you have an electrical signal moving through the cell
7
Q
Function of membranes: uptake and export of ions
A
??
8
Q
Function of Membranes: Cell Signaling
A
- how cells communicate with one another
- how cells use the information around them to dictate what is going on inside the nucleus
- this is through a series of chemical signals and messages received on the outside of the cell and then transmitted to the inside of the cell
9
Q
Phospholipid Bilayer
A
- Separates internal and external environments
- amphipathic
- two leaflets??
- main component, a lipid
- head region and two tails
- tail is hydrophobic and head is hydrophilic
- this happens, because of the head and tail, they form together into a bilayer which is 2 layers of phospholipids, the tails in the middle with a hydrophobic region and heads on the outside are hydrophilic
10
Q
Additional Membrane components
A
- other things added in to make the membrane have various properties
- cholesterol is for animals only. has a tail, the amount in the phospholipid bilayer depends on the organism and environmental conditions
- different proteins, embedded within the phospholipid bilayer, like a channel that is open that is allowing material to enter or exit the cell
- some proteins have different carbohydrate chains attached to them, little polymers of glucose and fructose sticking from the outside, this plays a role in cell signaling like a receptors or chemical messenger
- main component is the phospholipid bilayer and theres other stuff stuck in there
11
Q
Fluid- Mosaic Model
A
- a membrane is a mosaic of lipid, protein and carbohydrates
- fluid-like because lipids and proteins can move
- mosaic is a mix match of different things
- has proteins and cholesterol
- mixture of different macromolecules and different types of molecules
- each leaflet has a horizontal movement so the phospholipid can float and not have flip flop movement
12
Q
membrane proteins
A
- integral/intrinsic- get into the PB
1. transmembrane proteins- go all the way through and infiltrate the membrane
2. lipid-anchored protein - Peripheral/Extrinsic- on the peripheral and not actually embedded into the PM, doesn’t go into the PM
-proteins embedded within the PB
13
Q
Integral (intrinsic) proteins
A
- two types
- transmembrane proteins go all the way through and expands both leaflets and goes to the outside and inside membranes
- lipid anchor proteins- has a pink extension which is the chain of lipids coming off of it. Infiltrating membrane but not going all the way across
14
Q
Peripheral (extrinsic) proteins
A
- on the peripheral and not actually bound to the membrane
- does not go into the PM
- phospholipid is attached to the side protein and does not have to be
- does not go into the membrane
15
Q
Semi-Fluidity of Membranes
A
- most lipids can
1. freely rotate around long axes
2. move laterally within leaflet
16
Q
Lipid “flip flopping”
A
- does not occur spontaneously
- flipping is moving from one leaflet to another
- reason they are not spon, is because they are amphipathic, if you have a region of the head that is hydrophilic and you flip it to go to the other portion then you have to break through the hydrophobic region will repel the hydrophilic region
- flippase uses ATP to transport lipids
- flippase physically moves one leaflet to another place, cost cell some ATP energy
- flippase spares the phospholipid from having to go through and breaking through the hydrophobic region
17
Q
Lipid Rafts
A
- high cholesterol concentration
- with unique set of membrane proteins
- lipid group “floats” together as a unit
18
Q
factors affecting fluidity; length of fatty acyl tails
A
- length of fatty acyl tails
- shorter acyl tails are less likely to interact , which makes the membrane more fluid
- semi fluid, some are very rigid
- a lot of fluidity means your integral proteins are all over around the PM and if you have a lot of rigidity they don’t move much
- longer fats are more rigid
19
Q
Factors affecting fluidity; presence of double bonds in the acyl tails
A
- creates a kink, more fluidity
- saturated (single bonds) or unsaturated (double bonds)
- unsaturated fats have a kink by the DB so this creates more fluidity
- depending on how many sat or unsat FA in membrane you may be more or less lipid
- sat is more solid and more rigid
- more fluid the more unsat fats you have, more rigid the more sat fats
20
Q
Factors affecting fluidity: Presence of cholesterol
A
- cholesterol- more rigid than fatty acids
- effects depend on temperature
- at high temps, small amounts of cholesterol increase rigidity
- at low temps, large amounts of cholesterol decrease rigidity
- only in animals
- a molecule to be able to increase and decrease the fluidity of a membrane is due to its cholesterol
21
Q
Factors affecting fluidity; cholesterol affects
A
- small amounts of cholesterol increase van der Waals forces
- large amounts of cholesterol break up polar attraction
- big idea, cholesterol can do both, make a membrane more fluid or rigid depending on the circumstances
22
Q
How would you detect the fluidity of a material?
A
- Larry Frye and Michael Eddin conducted an experiment that verified the lateral movement of membrane proteins
- if membranes are fluid, then stuff should move in them
- freezing membranes should stop the movement of stuff
- not tested very well
- researchers put fluorescent tags on components of the membrane and track and see if the tags float around
- if membranes are fluid then the stuff move around more
23
Q
Experiment: fuse a mouse and human cell
A
- used a mouse and human cell
- tagged the mouse green and human red
- take these two cells and fuse into one big cell
- mouse tags are on one side and human tags on other (one big cell)
- lower temp so they have fluroescently tag, they want to see if these things move
- frozen, they wont move
- this is how they determined that we do have fluidity in our membranes
24
Q
but…not all membrane proteins can move laterally (picture-slide 27)
A
- 10-70% restricted, depending on cell type
- what cells may need fixed protein locations? neurons
- neurons are sending chemical messengers fom one neuron to another, releasing chemical messengers
- end of one neuron is releasing chemical signals and the beginning of the other is receiving the chemical signals
25
anchoring proteins
-association with cytoskeleton
-association with extracellular matrix or other cells
(slide 28 part1)
26
Glycosylation
- carbohydrate attachment to protein or lipid; glycolipid and glycoprotein
- recognition signals; cell surface and for other cellular proteins
- help protect proteins from damage
- protect cover or layer over important things and bind to chemical receptors or signals around environment
27
modifications of membranes
- carbohydrate usually attached on extracellular side
| pictures slide30pt1
28
membrane transport
- plasma membrane is selectively permeable
| - allows passage of some things
29
Active Transport
- trying to get molecules into the cell
- they need to use membrane proteins, the peripheral protein, and to work it needs an input of ATP
- molecules are entering protein part way, if you want them all the way through you want protein to open up and release inside you need ATP
30
Passive Transport
- no energy is required
- diffusion- net movement of molecules down concentration gradient
- net movement is towards the lower side
- once concentration is equal just means as many are leaving are entering
31
Diffusion
-net movement of molecules down concentration gradient
32
Simple Diffusion
-right across the phospholipid bilayer, higher concentration to lower concentration but using a transport protein
33
Facilitated Diffusion
- uses some type of protein to transport molecules
34
cells maintain gradients
-relatively constant internal environment different from their external environment
35
Transmembrane gradient
- solute concentration higher on one side
| - one side of membrane has a really high concentration and other side has a very low concentration
36
Ion electrochemical gradient
- both an electrical gradient and chemical gradient
- different in charge, if inside is more negatively charged then outside or vis versa
- this cell works very hard to keep negative charged particles and tries to pump out the positive charged ones, difference of electrochemical gradient inside to outside of cell
37
Osmosis
- movement of water across a selectively permeable membrane
- water can cross, but solute can not
- net water movement: toward lower water (higher solute) concentration
38
Osmosis
- movement of water across a selectively permeable membrane
- water can cross, but solute can not
- net water movement: toward lower water (higher solute) concentration
- molecules diffuse through a membrane from an area with more molecules to an area with less molecules
39
Hypertonic
- greater solute concentration- net movement of the water will be towards the left because water follows solute
40
Hypotonic
- has a low concentration
| - water leaves the cell and cell shrinks
41
Isotonic
- as much water is entering is also leaving because solute concentrations are equal within and outside the cell
42
Osmosis in Animal Cells
- to maintain size and shape..
- try to keep conditions isotonic
- otherwise at risk for
- osmotic lysis- hypertonic inside the cell than has too much water entering so it experiences osmotic lysis or bursting- water keeps coming in because it tries to even out the solute concentration and cell can burst
- crenation- or shrinking, if you don't have enough solute inside the cell then water will be leaving because it follows solute then you get a shivered or dehydrated looking cell
43
Osmosis in Plant Cells
- cell wall prevents major size changes
- turgor pressure- pushes the plasma membrane against cell wall
- plasmolysis- plants wilt, water leaves cells
44
Osmosis- Cholera
- bacteria release toxin that cause chloride and sodium ions to be released into the gut
- severe diarrhea--> dehydration , shock
45
Transport Proteins
-
46
Transport Proteins
- not everything diffuses but have other molecules that need to get into and out of cell, like large molecules, polar molecules and charged molecules
- TP-getting ready to move from one side to another
- helping with low permeability types of molecules
- these are molecules that need help with transport
47
Transport proteins cont.
- integral membrane proteins
- enable selective permeability
- can be active or passive
- two classes:
1. channels
2. Transporters
48
Channels
- Form an open passageway for the direct diffusion of ions or molecules across membrane
- example: aquaporins
- fast, gated
- 100 million ions/sec
49
methods of gating
- ligand-gated (ion-gated)
- intracellular regulatory proteins
- Phosphorylation
- voltage-gated
- mechanosensitive channels
50
Selectively permeable
- How can we move solutes against the gradient?
- want to get all solutes on same side, does not work for diffusion because diffusion goes down the concentration gradient
- this is active transport, requires input of energy it gets stuck, keeps going as long as its something the cell wants to keep inputing and until the cell runs out of ATP
- once it runs out of ATP it is not able to go further
51
Active Transport; selective permeability
- Transport against concentration gradient
- requires energy input
- continues until the cell runs out of energy-requires a pump
- pumps are known as transporters
- couples conformational changes to an energy source
52
Transporters
- also known as carriers
- conformational change transports solute
- principle pathway for uptake of organic molecules (sugars, aa, nucleotides)
- key role in export
- slower than channels
53
Uniporters
-a single solute moves in one direction
54
Symporter/cotransporter
-two solutes move in the same direction
55
antiporter
-two solutes move in opposite direction
56
ATP- driven Ion pumps
- generate ion electrochemical gradients
- Na+/K+-ATPase
- actively transport Na+ and K+ against their gradients by using the energy from ATP hydrolysis
- 3Na+ exported for 2K+ imported into cell
- antiporter
- electrogenic pump-export 1 net positive charge
57
Exocytosis and Endocytosis
-to transport large molecules such as proteins and polysaccharides
58
Exocytosis
material inside the cell packaged into vesicles and excreted into the extracellular medium
59
Endocytosis
- plasma membrane folds inward to form inward to form a vesicle that brings substances into the cell
- 3 types of endocytosis
1. receptor-mediated endocytosis
2. Pinocytosis
3. Phagocytosis
60
Pinocytosis
- the plasma membrane folds inward to create a kind of harbor
- the harbor then encloses completely, pinches off as a vesicle, and moves into the cell's cytoplasm, carrying with it whatever material was enclosed
61
Phagocytosis
- food particles- or perhaps whole organisms- are taken in by means of "false feet" or pseudopodia that surround the material
- Pseudopodia then fuse together, forming a vesicle that moves into the cell's interior with its catch enclosed
BIO 111
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