Week 9(L16-17): Movement across membranes, signal transduction, ECM, & mitochondria

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What is the transmembrane domain (TMD)?

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120 Terms

1

What is the transmembrane domain (TMD)?

  • largely hydrophobic (uncharged) alpha-helical peptide sequence that spans the membrane

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2

What does the TMD consist of?

amino acids with hydrophobic side chains

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3

TMD permanently attaches the protein to what?

Plasma membrane

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4

What interacts with the hydrophobic TMD?

hydrophobic fatty acid tails

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5

The TMD can facilitate what?

protein-protein interactions

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6

What do lipid bilayers NOT allow?

many compounds cannot pass through freely

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7

What type of molecules can cross membranes relative easily?

small, uncharged

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8

What are examples of small and uncharged molecules?

H2O

O2

CO2

NO

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9

What type of compounds cannot easily cross lipid bilayers?

large

polar

charged

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10

What are examples of large, polar, and charged compounds?

Ca+

Na+

K+

glucose

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11

What are the 4 basic mechanisms for moving molecules across membranes?

  1. simple diffusion

  2. diffusion through channel

  3. facilitated diffusion

  4. active transport

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12

What does passive movement of substances across cell membranes rely on?

concentration gradient

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13

What is a concentration gradient?

molecular concentrations of substances across the membrane

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14

Molecular concentrations move from _______ across the membrane

  1. high to low

  2. low to high

  1. high to low

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15

What does simply diffusion only work for?

very small and uncharged molecules (H2O, O2, CO2)

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16

What are aquaporins?

  • specific water channels

  • H2O moves through in single file down the concentration gradient

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17

Channels are formed by what?

integral membrane proteins - multiple subunits that line an aqueous pore

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18

Channels are effective for what?

small charged molecules - ions

(Na+, K+, Ca2+, Cl-)

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19

Ions move ______ concentration gradients

down

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20

Channels are selective

only allow certain types of ions to pass (uniporter)

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21

What are often gated?

ion channels

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22

What does it mean to be gated?

can be turned on/off in response to different signals/stimuli

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23

What are the two types of gated ion channels?

  1. voltage-gated (Na+ & K+)

  2. ligand-gated (neurotransmitters)

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24

Voltage-gated channels respond to what?

changes in charge across membrane

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25

Under non-depolarized conditions, neurons have what?

low [Na+] inside

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26

Ligand-gated channels respond to what?

binding of specific molecule on its surface (ligand)

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27

What does the binding of a ligand produce?

conformational change in structure of the receptor/channel

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28

What is tetrodotoxin (TTX)?

a very potent neurotoxin; Na+ channel blocker

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29

How does TTX work?

  • inhibits firing action potentials in neurons by binding to voltage-gated sodium channels in nerve cell membranes

  • blocks Na+ ion passage into the neuron

  • prevents the nervous system from carrying messages to muscles

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30

What is curare?

competitive antagonist of the nicotinic acetylcholine receptor (nAChR)

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31

What does curare do?

  • occupies same position on receptor as ACh with ≥ affinity

  • elicits no response

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32

What is an example of curare?

non-depolarizing muscle relaxant

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33

What was curare used as?

a paralyzing poison + hunting tool

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34

In facilitated diffusion, compounds bind to integral membrane called a

facilitative transporter

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35

In facilitated diffusion, what allows for a compound to be released on the other side of the membrane?

a change in transporter conformation

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36

Most animal cells import glucose from the blood into cells _____ via _______

down a concentration gradient

facilitative transporter

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37

4 steps of importing glucose

  1. transporter ready to accept glucose molecule

  2. glucose accepted by the transporter

  3. The intracellular side of the transporter opens

  4. glucose released, cycle repeats

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38

What is the solution to moving substances from a LOW concentration to a HIGH concentration? (against the concentration gradient)

chemical gradient of a 2nd molecule that would NOT reach extracellular/intracellular equilibrium

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39

Symporter

both molecules are transported in the same direction

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40

Describe the Na+ Glucose Symporter

  • 2Na+ & 1 glucose bind to outward binding site of transporter

  • conformation change in transporter occurs (occluded conformation)

  • transporter adopts inward-facing conformation

  • 2Na+ dissociate in the cytosol

  • glucose gets pushed in

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41

Antiporter

the concentration gradient of one molecule is used to transfer a 2nd molecule in OPPOSITE directions

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42

What is an example of an antiporter?

Na+/H+ exchanger

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43

Where is the Na+/H+ exchanger located?

in the nephron of the kidney

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44

How does the Na+/H+ exchanger work?

  • transports Na+ into the cell

  • forces H+ out of the cell

  • maintains pH and Na levels in specific kidney cells

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45

Active transporter

an integral membrane protein a compound specifically binds to

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46

What causes a change in conformation of the transporter? (active)

hydrolysis of an ATP molecule

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47

What does the hydrolysis of an ATP molecule allow for in active transportation?

molecule is released on other side of membrane

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48

What does active transport require?

energy input in the form of ATP

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49

What maintains cellular [Na+] and [K+] using ATP?

the Na+/K+ ATPase

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50

Describe the Na+/K+ pump

  • 3Na+ exit cell, 2K+ enter cell

    • important to maintain higher Na+ concentration OUTSIDE than INSIDE the cell

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51

How do cells achieve and sustain the Na+ chemical gradient for non-stop activity of Na+ glucose symporter?

spend energy (ATP)

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52

What are two mechanisms in which molecules move across membranes?

passive

active

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53

What are the passive mechanisms?

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54

What are the active mechanisms?

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55

How are TTX and curare related?

toxins that interfere with movement through ion channels

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56

ECM components are produced and secreted by what?

cells

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57

ECM components are assembled into what?

an extracellular network

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58

What are the major components of the ECM?

proteins - collagen

glycoproteins - laminin, fibronectin

proteoglycans

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59

What are proteoglycans?

proteins with a polysaccharide chain?

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60

What are the functions of the ECM?

  • cell adherence

  • cell communication

  • cell shape

  • mechanical support

  • structural integrity

  • barrier

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61

Anchor membrane proteins - integrins

interact with ECM components

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62

what do anchor proteins assist in?

  • tissue formation

  • coordinated cell function

  • cell communication

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63

What is the ECM abundant in?

connective tissues (tendons, ligaments, dermis)

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64

What cells have walls?

NON-ANIMAL

  • bacteria

  • plants

  • fungi

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65

Plant cell walls = ?

ECM

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66

Plant cell walls are composed of what?

  • cellulose

  • hemicellulose

  • pectin

  • protein

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67

Plant cell walls provide what?

structural support to cell + whole organism

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68

Plant cell walls protect cells from what?

  • mechanical damage

  • pathogen attack

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69

Membrane proteins play a major role in what?

signal transduction

  • converts extracellular signal → intracellular signal(s)

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70

Signal transduction allows cell to do what?

rapidly respond to events happening in their environment

  • grow

  • divide

  • survive

  • move

  • differentiate

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71

What are ligands?

small molecules that bind to receptor

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72

What does ligand binding change?

conformation of receptor protein

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73

What does the ligand not do?

enter the cell

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74

What side of the receptor protein is affected by the conformation change?

cytosolic side

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75

What can conformation changes activate?

other proteins in cytosol/membrane bound

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76

What are the 3 stages to signal transduction?

  1. ligand binds to receptor

  2. signal transduction → 2nd messenger (cAMP, Ca, G-protein)

  3. cellular response: growth, division, glucose→glycogen

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77

What are some diseases caused by signal transduction defects?

  • cancer

  • diabetes

  • brain disorders

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78

Glycogenolysis

how epinephrine activates glycogen→glucose

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79

Where is epinephrine made?

in the adrenal glands

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80

What does epinephrine bind to?

receptor on liver cell (hepatocyte)

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81

___________ will recruit G-protein and allow the binding of GTP to turn it on

active receptor

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82

The yellow subunit of the G-protein dissociates and turns ON what?

Adenyl cyclase → causes accumulation of cAMP inside cells

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83

At the end of glycogenolysis, what enzyme will release glucose units?

phosphorylase-P

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84

Function of mitochondria

  • ATP synthesis

  • apoptosis

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85

Function of chloroplast

  • photosynthesis

  • ATP synthesis

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86

What is the Endosymbiotic Theory?

organelles from eukaryotic cells with two membranes represent formerly free-living prokaryotes taken on inside the other in endosymbiosis

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87

What is the supporting evidence of the Endosymbiotic Theory

  1. binary fission of mitochondria & plastids

  2. circular DNA inside organelles similar to bacteria

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88

Describe aerobic respiration

  • converts in presence of oxygen energy stored in food into chemical energy stored in ATP

  • by-product: CO2

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89

Describe photosynthesis

building carbs using sun energy and CO2

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90

What is the chemical equation for aerobic respiration?

CH2O + O2 → CO2 + H2O + ATP

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91

What is the chemical equation for photosynthesis?

CO2 + H2O → CH2O + O2

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92

What does the Outer mitochondrial membrane - OMM contain?

  • enzymes w/diverse metabolic functions (lipid metabolism)

  • porins → large channels permeable (PASSIVE) to many molecules when opened (ATP, sucrose)

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93

What is the protein:lipid ration in the Inner mitochondrial membrane?

3:1

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94

Cristae

  • double-layered folds in the IMM

  • increase membrane surface area

  • contain machinery for aerobic respiration and ATP formation

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95

What is the IMM rich in?

cardiolipin

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96

What is cardiolipin?

  • phospholipid

  • characteristic of bacterial membranes

  • needed for optimal function of many enzymes

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97

The mitochondria has 2 _________

aqueous compartments

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98

What are the 2 aqueous compartments of the mitochondria?

  1. intermembrane space separates OMM + IMM

  2. matrix → high protein content, gel-like space containing ribosomes and genome (DNA)

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99

What does cellular respiration use to produce ATP?

chemical energy stored in carbs and lipids

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100

What kind of reaction is involved in cellular respiration?

catabolic

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