Cell Biology Membrane Transport and Cell Signaling

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Membranes

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1

Membranes

act as a permeable shield; retain metabolic intermediates, release waste compounds

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2

What kinds of molecules can diffuse across the membrane

size and polarity matter, but you have to ask if it’s charged

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3

Free energy

a measure of the potential energy of a system; a function of enthalpy and entropy

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4

Entropy

a measure of the degree of disorder or randomness in a system; the greater the spots in the room, the greater the entropy

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5

enthalpy

total bond charges present in a chemical reaction

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6

If delta G is -

energetically favorable

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7

if delta G is +

not energetically favorable

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8

Gibb’s Law

all system change in such a way that free energy is minimized

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9

if delta G is -

the reaction will occur spontaneously

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10

if delta G is +

reaction will only occur with an input of energy

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11

if delta G is 0

the reaction is at equilibrium

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12

simple diffusion

does not use any energy to move across the membrane; movement down the concentration gradient

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13

will entropy increase or decrease in diffusion

increase in entropy due to more space

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14

will delta G increase or decrease with diffusion

delta G will decrease due to the increased entropy

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15

whether or not something diffuses is dependent on

it’s partition coefficient

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16

if you are moving something from low concentration to high concentration…

the number of available spaces does down

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17

if you are moving something form high to low concentration…

the number of available spaces goes up

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18

partition coefficient

the measure of a substance’s solubility in lipid

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19

in simple diffusion

rate is linear; partition coefficient is relevant

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20

in simple diffusion, if there is a higher partition coefficient

you have a steeper slope

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21

in simple diffusion, if you have a lower partition coefficient

you have a less steep slope

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22

in simple diffusion

there is no theoretical maximum

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23

what is the rate of simple diffusion dependent upon

concentration

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24

what is the rate like in transporter-mediated diffusion

greater than simple diffusion

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25

the partition coefficient in transporter-mediated diffusion

is irrelevant because it would be so low that you would need a transporter to move the molecule

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26

the max rate in transporter-mediated diffusion

is due to the limited number of transporters

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27

max rate

Vmax

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28

transporter-mediated diffusion is

transporter specific

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29

the rate of transporter mediated diffusion

is dependent on the affinity(Km) of the transporter for the transported molecule

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30

as actual affinity increases,

Km decreases

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31

what is the relationship between Km and affinity

reciprocal

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32

what is the rate in transporter-mediated diffusion dependent on

concentration

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33

for uriporters, we go

down the concentration gradient

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34

the function of uniporters depends on

the number of transporters, the affinity of transporters for substrate, the concentration outside of the cell

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35

in uniport function, what is the function of the partition coefficent(K)

K is irrelevant

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36

what happens to the shape of the curve as affinity increases in simple diffusion

simple diffusion will be a straight line

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37

what happens to the shape of the curve as affinity increases in transporter-mediated diffusion

the slope of the line can be affected by the partition coefficient

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38

the higher the partition coefficient

the higher the curve

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39

in simple diffusion, the higher rate of concentration means

the greater the rate of transport

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40

in transporter-mediate diffusion, the plateau

is due to the limited number of transporters

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41

active transport uses energy because

we are moving something against its concentration gradient, entropy is negative

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42

Why do ions need to use an ion channel

ions are really smal, but they are charged

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43

how do ion channels know what ions to move across the membrane

multipass transmembrane proteins have a selectivity loop

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44

where are ion channels placed within the membrane

within small pockets known as vestibules

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45

how specificity in ion channels determined

by the distance between oxygens within the vestibule

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46

within the vestibule

oxygens are free to move around

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47

how is gating within ion channels regulated

changed in membrane potential or ligand binding

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48

K+ leak channels

are always open even in an unstimulated or resting state

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49

what does it mean when the K+ leak channels are always open

this channel will always be moving ions form an area of high concentration to low concentration

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50

what are the three main sources of energy in active transport

light, ATP-drive pump, coupled transporter

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51

where is light used within active transport

a limited number of places

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52

ATP-driven pump

primary active transport; will use ATP as a source of energy

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53

within a p-type pump, are kinases used

no

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54

within a p-type pump, what is being phosphorylated

aspartic acid

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55

sarcoplasmi reticulum

when the ER contains a high amount of Ca2+

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56

the p-type pump is composed of

ten alpha helices

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57

in a p-type pump what will bind

calcium

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58

within the p-type pump, how many calciums will the binding site accommodate

two

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59

where does the ATP bind in the p-type pump

the nucleotide binding domain

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60

in the p-type pump, where will the phosphate move

to the aspartic acid

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61

what is the movement of the phosphate going to lead to

a conformational change

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62

within the p-type pump ADP is

converted back to ATP, but the P still remains

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63

within the p-type pump, calcium is..

released

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64

what happens to H+ in the p-type pump

2H+ binds

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65

what is the function of H+ and H2O

they stability the empty Ca2+ binding sites

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66

after the Ca2+ binding site is stabilized

P is released from its binding site

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67

under conditions when you don’t have an affinity change

passive transport will be used

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68

a lower concentration of K+ outside the cell and a higher concentration inside the cell is possible with the..

K+ leak channel because there is a mechanism that transports K+ back into the cell

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69

a higher concentration of Ca2+ outside the cell and a lower concentration of Ca2+ inside the cell is possible because…

as Ca2+ moves with its concentration gradient inside the cell there is a mechanism that transports it back outside the cell

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70

Sodium-Potassium ATPase

protein that will move sodium out of the cell and move potassium into cell

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71

within the Sodium-Potassium ATPase

for every three sodium molecules, two molecules of potassium will be pumped inside

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72

how is a gradient created that pulls water into the cell

cells contain a high concentration of solutes including negatively charged organic molecules that are confined inside the cell and their accompanying cations that are required for change balance

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73

how is the gradient pulling water into the cell counteracted

by an opposite osmotic gradient due to high concentration of inorganic ions in the extracellular fluid

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74

the Na+-K+pump helps maintain this balance by

pumping out Na+

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75

coupled transporters

facilitate the transport of one molecule to the energetically favorable

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76

Na+-Glucose symporter

an example of a coupled transporter

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77

Within the Na+-Glucose Symporter

Na+ and glucose binding are cooperative, transition to the occluded state only occurs when both Na+ and glucose are bound

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78

within the Na+-Glucose Symporter what does it mean to say that the binding sites for Na+ and glucose are “cooperative“

Na+ binding increases the affinity for glucose

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79

within the Na+-Glucose Symporter stochastic fluctuations caused by thermal energy

drive the transporter randomly

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80

Signal transduction

the process whereby a cell receives an extracellular signal and converts it to an intracellular signal that alters cell behavior

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81

effector proteins

metabolic enzymes, transcription regulatory proteins, cytoskeletal proteins

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82

How are effector proteins altered

A signaling molecule of some sort is going to engage a receptor on the plasma membrane, which will activate a series of events with intracellular signaling proteins

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83

what is the first messenger molecules

the extracellular signaling molecule

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84

What is the second messenger molecule

small intracellular molecules whose concentration changes in response to binding of an extracellular signal and functions in signal transduction

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85

Contact-dependent signaling

a signaling molecule is directly attached to the target cell via a membrane bound signaling molecule on the signaling cell and a receptor on the target cell

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86

paracrine system signaling

signaling molecules are released from a signaling cell, and the molecules find their way to the receptor adjacent cells

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87

synaptic signaling

combination of paracrine and contact-dependent signaling; involves neurons and synapses

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88

endocrine system

a signaling molecule is dumped into the bloodstream

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89

the response to a specific signaling molecule

is cell type dependent

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90

cross talk

intermediates in one transduction pathway can affect intermediates in another pathway

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91

when can the receptor be inside the cell

if the signaling molecule can cross the cell membrane if the signaling molecule is small and hydrophobic

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92

what moves the cell signal across the membrane

a carrier protein

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93

why are carrier proteins needed

since the signal molecules tend to be non polar, the molecule will aggregate before it can get to the receptor

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94

signaling molecules need to be

something that can alter protein function or gene expression and can be elevated under certain conditions

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95

how many domains do transcription factors have

two; DNA binding domain and activation/repressor domain

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96

what are the classes of surface receptors

ion-channel-coupled receptors, g-protein-coupled receptors, and enzyme-coupled receptors

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97

an ion-channel-coupled receptor

is both an ion channel and a receptor for a signaling molecule

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98

ion channel-coupled receptors interact with chemical signals by

transducing a chemical signal into an electrical signal by allowing an ion to move across the membrane

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99

small monomeric g-proteins

direct effects on effector molecules and relay signals from cell surface receptors

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100

large trimeric g-proteins

bind and are activated by cell surface receptors

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