Week 7 Textbook

Question 1

plasma membrane

Answer 1

a protein - fatty - thin, contains components inside
- 2 layers of lipid molecules with proteins inserted inside
- allows import/export, deformation, self-healing,

Question 2

how did scientists find the lipid bilayer

Answer 2

since the layer can dissolve in organic solvents, they used benzene to extract all the lipids from the plasma membrane of RBCs - spread on a film and saw that they formed a continuous sheet which was one molecule thick
- discovered the hydrophilic head and hydrophobic tails

Question 3

definition of lipid bilayer

Answer 3

a pair of sheets composed mainly of phospholipid molecules that forms the structural basis of all cell membranes

Question 4

phospholipids

Answer 4

a major type of lipid molecule in cell membranes
- composed of 2 fatty acid tails and one phosphate group = polar

Question 5

how is phosphatidylcholine a phospholipid

Answer 5

it is the most common bc it has 2 hydrocarbon tails + glycerol + phosphate group + choline on the end (still makes the head polar)

Question 6

what does it mean to be amphipathic and give an example

Answer 6

molecules that are both hydrophilic and hydrophobic
- cholesterol which is the membrane of animal cells - has a hydrocarbon tail and a polar head
- glycolipids - sugar apart of their hydrophilic head

Question 7

explain how hydrophilic molecules interact with water molecules

Answer 7

hydrophilic = polar, ex, acetone which has a dipole.
the positive carbon will interact with the negative end of the water (oxygen) and the oxygen on the acetone will interact with the water-positive hydrogens

Question 8

explain how hydrophobic molecules interact/format themselves in water

Answer 8

they cannot form favourable interactions with water so they have to force water molecules to form a cage-like structure around them
- this cage structure is more highly ordered so it needs Gibbs free energy
- this is why the fats/oils in water form large fat droplets

Question 9

what does a triacylglycerol

Answer 9

glycerol (head) with a hydrocarbon tail - the 2 parts are attached by a C=O
- they are the main constituents of animal fats and plant oils = entirely hydrophobic

Question 10

explain what would happen if there was a tear in the bilayer

Answer 10

hydrophobic tails facing inside the membrane away from the water
hydrophilic heads facing outside the membrane
any tear in the sheet will create a free edge that is exposed to water - this is energetically unfavourable - they will spont rearrange to eliminate the free edge
- if the tear is large, then the sheet may begin to fold in on itself and break up into separate closed vesicles

Question 11

why is a planar amphipathic sheet unfavourable and how can it become favourable

Answer 11

it is unfavourable because it has edges that allow water to be exposed from the hydrophobic tails
- they bend and seal forming a closed space
- makes the cells circular
the circle = energetically favourable

Question 12

t/f the lipid bilayer is flexible and fluid

Answer 12

true
when using laser tweezers, the components do not leak out

Question 13

what is a liposome

Answer 13

pure phospholipids will form closed spherical vesicles

Question 14

what are the 4 movements that the lipid molecules can do in the bilayer

Answer 14

they can rotate, lateral diffusion (switch places with adjacent molecules), flexion (move tails right and left), flip-flop (rarely occurs but moves the top bilayer molecule to the other end of the bilayer)
because of these movements, the bilayer behaves as a 2D fluid

Question 15

t/f the more closely packing the tails and composition of the bilayer is, the more/less viscous/fluid the bilayer will be

Answer 15

true
their length and number of double bonds in the tails affect
and the cholesterol available in the bilayer

Question 16

what are the 2 major properties of hydrocarbon tails

Answer 16

length
- a shorter chain length reduces the tendency of the hydrocarbon tails to interact with each other and form LDFs - short chains = increase the fluidity of the bilayer

number of double bonds
- double bond = not the maximum, number of hydrogen bonds = unsaturated = forms a kink in the tail = this makes it difficult for the tails to pack against one another and form LDFs this makes the membrane more fluid and dynamic
- all single bonds = saturated = more stiff, less molecules can move thru this

Question 17

t/f bacterial and yeast cells are constantly adjusting their tails

Answer 17

true
they do it in different conditions - varying temperatures
at high temps they make tails that are long and have less double bonds

Question 18

what does it mean to hydrogenate

Answer 18

vegetable oils can be turned into margarine by hydrogenation
- it is the addition of hydrogens - this can remove the double bonds and make them more saturated
- this makes the oil solid into butter at room temperature (less fluid/dynamic)

Question 19

what is cholesterol

Answer 19

the membrane fluidity is modulated by the inclusion of the sterol cholesterol
- it can fill in the spaces of phospholipids that have kinks in their tails due to unsaturation
- cholesterol can stiffen the bilayer - making it less flexible and less permeable = stiff

Question 20

what is the use of having fluidity in the membrane

Answer 20

for proteins to go in and out
cell signalling
ensures that membrane molecules are distributed evenly between daughter cells when a cell divide

Question 21

where are new phospholipids manufactured in the cell

Answer 21

made by enzymes in the cytosolic surface of the endoplasmic reticulum
- these enzymes deposit the newly made phospholipids only in the cytosolic half of the bilayer

Question 22

how do new phospholipids make it to the opposite monolayer?

Answer 22

phospholipids are transferred by a protein called scramblase - this is a type of transporter protein that removes randomly selected phospholipids from one half of the lipid bilayer and inserts them in the other

Question 23

what does flippase do

Answer 23

it is apart of the Golgi membrane
- contains flippase which is the phospholipid-handling transporter
- they use ATP to transfer SPECIFIC phospholipids from one side of the bilayer to the other (moving lipids from the exterior monolayer to the interior)
= this maintains the aymmetrc arrangement of phospholipids that is characteristic of the animal cell membranes

Question 24

cytosolic and noncytosolic monolayer

Answer 24

cytosolic layer faces the cytosol
noncytosolic monolayer faces the lumen which is the interior space of the organelle

Question 25

how do glycolipid molecules position themselves in the membrane

Answer 25

they have sugar groups on the ends the sugars are placed only to the exterior of the cell with the extracellular space - glycolipids are distributed asymmetrically in the lipid bilayer of the animal cell plasma membrane

Question 26

what are the functions of membrane proteins

Answer 26

transport certain nutrients (Na+ pump) receptors that detect chemical signals in the cells environment (platelet driver growth factor - PDGF) enzymes to catalyze specific reactions at the membrane anchors (integrins)

Question 27

explain how transmembrane proteins interact with the bilayer

Answer 27

has both hydrophobic/philic regions the phobic regions lie in the interior and the philic are exposed to the aqueous environment

Question 28

what are 4 types of interactions that proteins can have with their bilayer

Answer 28

- transmembrane proteins - proteins that are associated with the systolic half of the bilayer by an amphipathic alpha helix - some lie entirely outside the bilayer on the other side - they are attached to the membrane by covalently attached lipid groups - some proteins are only held in place by their interactions with other membrane proteins nd face only one way

Question 29

what are integral membrane proteins and how can they be removed

Answer 29

they are the proteins that are directly attached to the bilayer - we remove only by disrupting the bilayer with detergents - the rest of the proteins are called peripheral membrane proteins which can be removed with simpler extraction procedures that leave the bilayer intact

Question 30

what is the transmembrane protein's orientation and attachments

Answer 30

connected to the specialized membrane-spanning segments of the polypeptide chain these segments run through the hydrophobic (interior of the bilayer) - composed largely of amino acids with hydrophobic side chains - bc these side chains cannot interact with the water molecules they prefer to interact with the hydrophobic tails of the lipid molecules

Question 31

t/f the peptide bonds that join the amino acids in proteins are normally polar

Answer 31

true making it hydrophilic bc water is absent in the hydrophobic part of the bilayer, the atoms that are part of the polypeptide backbone are thus driven to form h bonds with one another - H bonds are maximized if the polypeptide chain forms a regular alpha helix in the spinning helix, the hydrophobic lipid tails are on the outside (between the phospholipid tails) and the hydrophilic polypeptide backbones form H bonds with one another within the helix

Question 32

how do multipass transmembrane proteins arrange themselves in the membrane

Answer 32

usually amphipathic formed from alpha helices - hydrophobic side chains fall on the inside of the circular arrangement - the hydrophilic side chains are concentrated on the other side - form into a ring structure

Question 33

T/F the most common form that a polypeptide chain crosses the lipid bilayer is beta sheets

Answer 33

false - it is alpha sheets

Question 34

how do beta sheets arrange themselves as transmembrane proteins

Answer 34

beta-sheet is rolled into a cylinder = beta-barrel the amino acid side chains that face the inside of the barrel = aqueous channel = hydrophilic and the outside lining of the beta barrel is in contact with the hydrophobic tails

Question 35

what are porin proteins

Answer 35

they have a lot of beta-barrel structures they form large, water-filled pores in mitochondrial and bacterial outer membranes porins allow the passage of small nutrients, metabolites and inorganic ions across their outer membranes while preventing unwanted larger molecules from crossing

Question 36

how do detergents work to examine the lipid bilayer in detail

Answer 36

it is a soapy substance used to solubilize lipids and membrane proteins - disrupting the hydrophobic associations the detergents are small amphipathic lipid-like molecules that only have a single hydrophobic tail - in water these molecules tend to go into small irregular clusters called micelles - when you mix it, the hydrophobic ends of detergent molecules interact with the membrane-spanning hydrophobic regions of the transmembrane proteins and the phobic tails of the phospholipids (disrupts bilayer)

Question 37

what happened when scientists fused a mouse cell and a human cel together and watched the activity of the plasma membrane?

Answer 37

the 2 cells remained on either side of their halves, but after time, the two sets of proteins became evenly mixed over the entire x2 sized cell

Question 38

what are membrane domains

Answer 38

functionally and structurally specialized regions in the membrane of a cell or organelle - typically characterized by the presence of specific proteins

Question 39

what are the ways lateral mobility of plasma membrane proteins can be restricted

Answer 39

- proteins can be tethered to the cell cortex inside the cell - proteins can be tethered to just the extracellular matrix molecules outside the cell - the proteins on the surface, interact with the adjacent cell - proteins can have diffusion barriers which can restrict proteins to a particular membrane domain

Question 40

what is the basal lamina

Answer 40

it is a mat of extracellular matrix that supports all epithelial sheets

Question 41

how do we measure and study the fluidity of cell membranes

Answer 41

1. FRAP - fluorescence recovery after photobleaching labelled components of the cell membrane with a fluorescent marker - monitored in a fluorescent microscope - measuring the amount of time the proteins take to migrate into the bleached region of the membrane DRAWBACK - monitors the movement of fairly large populations of proteins so there's no way to track the motion of individual molecules - - they have developed methods to label individual molecules = SPT single particle tracking microscopy - tagging the molecules with antibodies - mild detergents can be used to solubilize and reconstitute functional membrane proteins - artificial lipid bilayers generally diffuse more freely and rapidly - it is bc in the real cell membrane they are surrounded by more types of proteins and contain a greater variety of lipids than an artificial lipid bilayer

Question 42

whats the difference between an artificial bilayer and a cell membrane bilayer

Answer 42

the artificial one is protein free = liposome = impermeable to most water soluble molecules the real cell membrane has transport proteins to transfer specific molecules by facilitated transport = those who cannot diffuse on its own

Question 43

what kinds of molecules can diffuse into the membrane easily

Answer 43

small, nonpolar molecules and small uncharged polar molecules = concentration gradient - goes from high to low concentration nonpolar: steroids, horomes, CO2, O2 - simple diffusion all hydrophobic moloecules = faster diffusion uncharged polar: H2O, ethanol, glycerol - the small the better but most of it cant go thru

Question 44

what kinds of molecules need membrane proteins to go into the membrane

Answer 44

larger uncharged polar molecules - amino acids, glucose, nucleosides a very tiny amount can but most cannot large charged polar molecules (ions) - H+, K+, Cl- - none can go thru

Question 45

what are the 2 main classes for membrane transport proteins

Answer 45

1. channel - selective about size and electric charge - transient interactions with the channel - van der waals, h bonds, etc - there is no conformation changes, always stay the same shape = open channel 2. transporter - the solute can be any kind just need to fit inside binding site - conformational changes - can only take one solute at a time so needs to close and open on the other end

Question 46

what falls under passive transport

Answer 46

channel mediated, and transport mediated proteins driven by concentration gradient from high to low

Question 47

what is active transport

Answer 47

pushes solutes against the conc gradient - from low to high needs ATP to open and close and release contents

Question 48

concentration gradient + membrane potential = ____

Answer 48

electrochemical gradient

Question 49

what does the electrochemical gradient induce

Answer 49

passive transport

Question 50

when the voltage (charges on either side) and the concentration gradients work in the same direction, what happens?

Answer 50

theres is a fast diffusion if its + on the outside and - on the inside, and the solute has a + charge it will repel the + on the outside and have a large driving force that pushes to the negative side where the +/- have attraction

Question 51

when the voltage (charges on either side) and the concentration gradients work in the opposite direction, what happens?

Answer 51

if your moving + solutes out of the cell where the + is outside and the - is inside, you will get a smaller net driving force because its going in the unfavourable direction where the + will repel the + on the outside instead of moving TOWARDS the charges that it attracst

Question 52

explain the structure of channel proteins and how they work

Answer 52

hydrophobic core that pinches close together at a certain area to have transient interactions and be selective - this area strips the K+ ion of any other negative charge surrounding it to make sure it only transports the singular K+ = ion channel transport - fastest transport

Question 53

what is an ion channel

Answer 53

it is a type of channel protein found in animals and plants that transports ions only

Question 54

what are the 2 kinds of ion channels

Answer 54

1. non gated ion channels - always open like K+ leak channels - moving K+ out of the cell *leak* - moves in the direction of the gradient - this can generate the resting membrane potential by creating a voltage on one side 2. gated ion channels - some type of signal is required to open the channel and then it stays open - requires specific kind of ion to pass thru as it has the pinching mechanism

Question 55

what are the 4 kinds of gated ion channels

Answer 55

1. mechanically gated - the signal to open the gate would be the stretching or compressing of the membrane 2. ligand-gated extracellular ligand - the signal would be neurotransmitters from outside of the cell binding in its binding spots on the outside 4. ligand-gated intracellular ligand - the signal would be like an ion or nucleotide that binds to the binding site on the inside of the protein to open it 5. voltage-gated - the signal would be a change in voltage across the membrane - making the membrane depolarized (negative charges on the outside0

Question 56

explain the transporter proteins

Answer 56

they can only bind to a specific solute that goes thru a conformational change to move the solutes to the other side - follows the concentration gradient - when there is more of a difference of concentration on either side = more speed in transporting to resolve

Question 57

explain the Vmax of the transporter proteins

Answer 57

the rate of a simple diffusion channel protein is much faster and can increase in speed but the transporter protein can only go up to Vmax bc it carries one solute at a time and gets saturated and cant move any faster

Question 58

explain this type of transporter protein: uniport

Answer 58

one solute moves at a time down its electrochemical gradient works with concentration gradient and it can be reversible depending on the gradient of that solute EX: glucose transporter (GLUT Uniporter) - transports glucose down its gradient - can go in or out of the cell (reversible)

Question 59

what are the 3 types of active transport

Answer 59

1. gradient driven - symport and antiport 2. atp driven - P-type, V-type, ABC transport 3. light driven pump

Question 60

explain the types of gradient driven active transport

Answer 60

1. symport - can move 2 solutes at the same times in the same direction - one goes against the gradient - one goes towards gradient EX; Na+/Glucose symporter 2. antiport - can move two solutes in the opposite direction - one goes against the gradient - one goes towards the gradient EX: Na+/H+ antiporter - both use this principal that the free energy from the 1st solute moving down its gradient is used to transport the 2nd solute AGAINST its gradient (coupling) - the one going against needs more free energy since its unfavourable

Question 61

explain the Na+/Glucose symporter

Answer 61

na+ down the electrochemical gradient (high to low) provides the energy needed to move the glucose against its own concentration gradient - the conformational change only occurs when both solutes are in the binding site occluded empty = closed, no Na+ or glucose in binding site occluded occupied = the brief second that both solutes are in the binding and the open ended closes while the other end is preparing to open occluded empty again

Question 62

explain the Na+/H+ antiporter/exchanger

Answer 62

both solutes have their own unique gradient the na+ moves from high to low - provides free energy the H+ gradient moves against (low to high) - uses free energy in Na+ to move against some reasons why there is high conc of H+ on the outside of the cell is bc lysosomes release H+ and it needs to be maintained for enzyme function to occur in this environment - the transporters maintain the pH inside the cell - so when the pH drops (lots of H+ makes acidic) inside the cell they move H+ outside

Question 63

since the gradient of Na+ drives and gives free energy to alot of other pumps, how does the Na+ gradient remain maintained?

Answer 63

Na+/K+ pump - ATP driven - needed bc the symporter and antiporter proteins wont work without an Na+ gradient givning free energy

Question 64

what are the 3 types of ATP driven pumps

Answer 64

P type - Na+/K+ V type proton pump ABC transporter

Question 65

explain P type pumps

Answer 65

uses ATP hydrolysis to transport solutes - phosphorylated during pumping cycle ATP --> ADP + P the P phosphorylates the transporter protein and changes conformation - flippases that move PL to the other side = P type pump

Question 66

explain the P-type pump using Na+/K+ mechanisms

Answer 66

uses ATP hydrolysis the Na+ moves against the gradient - from low to high ( 3 Na+ out) the K+ moves against the gradient - from low to high ( 2 K+ in) Na+ gradient is useful for transporting nutrients from other pumps like glucose and maintain pH

Question 67

explain in depth the pumping cycle of the Na+ K+ pump (EXAM)

Answer 67

K+ high in cytosol (inside) Na+ high in EXC the pump opens, 3Na+ goes in - ATP --> ADP + P, phosphorylates the pump to change conformation and expels the 3Na+ outside the pump is now exposed and open to the EXC side where 2K+ go inside - ADP + P --> ATP (dephosphorylates - removal of P from pump) turns the pump back to its og conformation to open the pump towards the inside and 2K+ is released

Question 68

what is the use of P-type pumps

Answer 68

generates and maintains the electrochemical gradients the Na+/K+ maintains the Na+ electrochemical gradient for driving antiport and symport also plays a role int he membrane potential (overall + or - charge on one side) H+ pump in plant cells are also P-type maintains the H+ gradient and used to drive symport and antiport like Na+ does also plays a role in the membrane potential

Question 69

explain the ABC transporter

Answer 69

uses 2 ATP to pump small molecules across the cell membrane usually its toxins out of the cell

Question 70

explain the V type proton pump

Answer 70

uses ATp to pump H+ into the organelles to make them acidic (MOVES AGAINST GRADIENT) this is useful for organelles like the lysosome and plant vacuole (digestion)

Question 71

explain the F-type ATP synthase

Answer 71

structurally similar to he V type but uses H+ gradient to drive the SYNTHESIS of ATP moves H+ from high to low so ADP + P --> ATP can occur - this is useful in the mitochondria, chloroplasts and bacteria

Question 72

explain how transporters work together to transfer glucose from the intestine to the blood

Answer 72

in one epithelial cell there is the gut lumen, the apical domain with the microvilli, then you have the lateral domain and then the basal lamina, then EXC of the bloodstream there is a Na+/glucose symport pump on the microvilli to move Na+ and glucose inside (Glucose against gradient) there is a glucose pump (GLUT transporter high to low) attached to the basal lamina to move glucose into the bloodstream but it needs the energy of the Na+/K+ pump also on the basal lamina theres low conc of glucose in the gut lumen and a high concentration of glucose in the lateral domain of the epithelial cell where the Na+/glucose symporter work. then theres low concentration of glucose in the bloodstream

Question 73

how are membrane proteins restricted to particular domains of the plasma membrane of the epithelial cells in the gut

Answer 73

creating boundaries with tight junctions the apical membrane (the surface of the gut lumen) has the Na+/glucose symporter the basolateral plasma membrane (basal lamina and the lateral domain share the same protein) - has the GLUT uniporter (only moves glucose) - also has the Na+/K+ to give energy

Question 74

what is the significance of the tight junctions

Answer 74

without tight junctions the glucose or the molecules of transport wont know where to go

Question 75

what is the membrane potential

Answer 75

it is the difference in electrical charge on both sides of the membrane - used by the gradient driving pumps to carry out active transport like symport and antiport

Question 76

how does the animal cell generate membrane potential

Answer 76

1. K+ leak channels - outward flow of K+ (out of cell) using gated ion channels - the signal to open the gates is when the membrane potential or voltage is off - when the driving force due to K+ gradient = the driving force due to voltage gradient 2. Na+/k+ pump - maintains Na+ low in the cell and K+ high in the cell since 3Na+ and 2K+ there is a net 1+ ion which is pumped out making the membrane potential outside = (+) and inside = (-)

Question 77

explain the 2 pumps that generate the membrane potential in animal cells

Answer 77

the K+ leak channels and the Na+/K+ pump gives the outside of the cell slightly more + the K+ leak channels move the K+ out of the cell from high to low the Na+/K+ has a net of 1+ outside the cell makes the outside + and the inside - bc there are also Cl- fixed anions inside the cell

Question 78

what is the equilibrium resting membrane potential

Answer 78

around -20mV to -200 mV

Question 79

explain the generation of membrane potential in plant cells

Answer 79

the P-type H+ pump generates a H+ electrochemical gradient inside the cell used by gradient driven pumps to carry out active transport - regulates pH and electrical signalling