Chapter 5 Flashcards
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
