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BIOL 1101 > Lecture 4: Membranes and Signalling > Flashcards

Lecture 4: Membranes and Signalling Flashcards

1
Q

Structure of membranes: fluid mosaic model

A
  • fluid lipid bilayer in which proteins are embedded and float freely
  • membranes aren’t rigid (dynamic structures)
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2
Q

function of fluid mosaic model

A

1) protection

2) allow selective exchange of molecules between cell and environment: need the exchange of energy and matter

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3
Q

what do peripheral proteins do for communication

A
  • link microtubule to membrane, they sit there to help with communication or transportation
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4
Q

purpose of integral protein

A
  • also called transmembrane protein
  • interact with lipid bilayer/aq environment
  • ex. collagen is an integral component of EC matrix
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5
Q

purpose of cholesterol

A

maintains fluidity (low temp) and rigidity (high temp) of mosaic model

HIGH TEMP
- F.A. chains move freely, cholesterol fits in between to restrict movement

LOW TEMP
- F.A. chains pack tightly, making the membrane rigid

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6
Q

membrane asymmetry

A
  • membranes are asymmetrical
  • membrane proteins of one half of the bilayer are structurally and functionally distinct from the other half

important because: specialization (inner and outer), cell signalling, stability

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7
Q

How can we support the idea that membranes are fluid

A
  • membrane proteins start out segregated
  • proteins move around in the membrane proving that they are fluid
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8
Q

what does freezing do to your cell

A
  • rigidity in the cell
  • slows down processes
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9
Q

how does membrane asymmetry support the fluid mosaic model

A
  • maintains fluid part of the model through the uneven distribution of lipids and proteins
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10
Q

the lipid fabric of a membrane

A

1) phospholipids are the dominant lipids in membranes

2) membrane fluidity

3) organisms can adjust fatty acid composition

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11
Q

How will water behave in a phospholipid bilayer

A

phospholipid bilayers will rearrange to form a hydrophilic outer layer facing the water and a hydrophobic inner layer facing each other

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12
Q

maintaining proper fluidity

A
  • fluidity of lipid bilayer dependent on how densely individual lipid molecules can pack together

BASED ON:
1) temperature
2) composition of lipid molecules
- these will help indicate the fluidity of our membrane

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13
Q

COMPOSITION OF LIPID MOLECULES

viscosity and fluidity

A
  • we want to maintain balance, over fluidity can cause leakage

A) VISCOUS
saturated hydrocarbon tails, made by linear fatty acid chains

B) FLUID
unsaturated hydrocarbon tails with kinks, unsaturated fatty acid are:
- non-linear increases fluid
- can’t fit as many
- less dense, more fluid

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14
Q

TEMPERATURE

relative to fluidity

A

TEMPERATURE DROPS
- phospholipid molecules become closely packed and membrane forms highly viscous semisolid gel

  • fluidity of membrane related to degree to which membrane lipids are unsaturated

alternate: unsaturated fatty acid + saturated fatty acid chains, helps maintain proper fluidity

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15
Q

Adjusting fatty acid composition

A

1) proper fluidity is maintained by adjustment of fatty acid composition

2) DESATURASES: enzymes that produce unsaturated fatty acids during fatty acid synthesis

3) Regulation of desaturates— membrane fluidity

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16
Q

All phospholipids are first

A

made linear

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17
Q

Temperature affects

A

the ratio of unsaturated fatty acids to saturated fatty acids which determine fluidity

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18
Q

DESATURASES

A
  • Desaturases are enzymes that introduce double bonds into fatty acid chains, converting saturated fatty acids into unsaturated fatty acids, which affects membrane fluidity and lipid composition.
  • LINEAR: INCREASE DENSITY, DECREASE FLUIDITY
  • BENT: DECREASE DENSITY, INCREASE FLUIDITY
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19
Q

Increase temperature, decreases…

A

Desaturases

  • as temperature increases, the relative amount of desaturate % likely means there’s too much packing which decreases density and increases fluidity
  • but it will drop to counteract over fluidity, and produce saturated lipids to promote rigidity
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20
Q

Sterols

A

ex. cholesterol
- 4 C ring
- type of lipid, buffers for fluidity
- at high temperature: decreases fluidity
- at low temperatures: increases fluidity

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21
Q

cholesterol

A
  • helps decrease density and increase fluidity
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22
Q

membrane buffer

A

ex. cholesterol
- stabilize membrane fluidity
- maintain structural integrity
- prevents changes in fluidity with temperature variations

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23
Q

Four key functions of membrane proteins

A

1) TRANSPORT:
membrane proteins = transport proteins

2) ENZYMATIC
membrane proteins=enzymes

3) SIGNAL TRANSDUCTION
membrane proteins= send signals

4) ATTACHMENT/RECOGNITION
membrane proteins= adhere to cytoskeleton in the cell and ECM outside of cell
(can be used as recognition proteins)

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24
Q

What are the two structural categories of membrane proteins

A

1) intergral membrane proteins

2) peripheral membrane proteins

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25
Q

1) Integral membrane proteins

A
  • proteins embedded in phospholipid bilayers (interacts with hydrophobic core of the bilayer)

-composed of non polar a.a. coiled into alpha-helices

  • transmembrane proteins (sub category): most integral proteins
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26
Q

what are most integral membrane proteins

A

transmembrane proteins

  • Channels, transporters, or receptors
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27
Q

2) Peripheral membrane proteins

A
  • on the surface of the membrane
  • don’t interact with hydrophobic core
  • held together by hydrogen and ionic bonds via interaction with the lipids or exposed portions of integral membrane proteins
  • most on cytoplasmic side of membrane, they form part of the cytoskeleton helping with anchorage
  • made up of mixture of polar and non polar a.a.
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28
Q

Passive membrane transport

A
  • Based on diffusion
  • SPONTANEOUS
  • Two types: SIMPLE and FACILITATED
    (simple=small molecules can squeeze in)
    (facilitated=use electorchemical gradient)
  • Two groups of transport proteins carry out facilitated diffusion
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29
Q

what is osmosis

A

the passive diffusion of water

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30
Q

passive membrane transport

A
  • hydrophobic nature of membrane restricts free movement of molecules
  • PASSIVE TRANSPORT: movement across a membrane without ATP
  • driven by diffusion
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31
Q

Diffusion

A
  • net movement of substance from region of high to low concentration
  • rate of diffusion depends on the
    1) concentration difference
    2) concentration gradient (on how different the two concentration are)
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32
Q

Simple diffusion

A
  • passive transport of substance across the lipid portion of membranes with concentration gradients
  • small uncharged molecules move rapidly
  • large/charged molecules may be impeded from crossing membranes
  • spontaneous
  • exergonic
    • Gibbs
33
Q

Factors that influence diffusion

A

Size and charge (because some molecules are surrounded by a hydration shell, increase the energy barrier for the ion to pass) of molecules

(lipid solubility) for simple

34
Q

Facilitated diffusion

A
  • passive transport of substances at rates higher than predicted from their lipid solubility

Depends on:
- membrane proteins
- follows concentration gradients
- specific for certain substances
- becomes saturated at high concentrations of transported substance

35
Q

Where are transport proteins found

A
  • on membrane, can help substances get across still no ATP
36
Q

Characteristics of transport mechanisms

A

SIMPLE
- lipids
- no binding of transported substance
- concentration gradient=energy source/transport
- nonspecific molecules get across
- no saturation of high concentrations of transported molecules

FACILITATED
- proteins
- binding of transported substance
- energy source/transport= concentration gradients
- specific molecules get across
- saturated of high concentrations

37
Q

What do transport proteins carry out

which integral membrane protein

A
  • subset of integral membrane proteins (Must span across membrane)
    1) channel proteins: water and ions (ex. K+/Na+)
    2) carrier proteins: specific single solutes (sugars, a.a)
38
Q

Channel proteins

A
  • aquaporin = channel protein
  • the concentration gradient follows the direction of transport=diffusion
  • gated channel or non gated
39
Q

Carrier proteins

A
  • protein and binding site will be open where increased concentration site
  • protein changing 3D Shape= conformational change
40
Q

Movement of molecules through carrier proteins

A

1) conformation so binding site is exposed towards higher concentration

2) solute molecules binds to carrier protein

3) in response to binding, carrier protein changes conformation, binding site is exposed to lower concentration (diffusion=no energy)

4) transported solute is released and carrier protein returns to conformation in step 1

41
Q

Graph of simple vs facilitated diffusion

A

facilitated transport: helps things moves faster, but you will also reach a saturation point

  • F.T: approaches maximum rate when all transporters are occupied
42
Q

Osmosis occurs

A
  • across a selectively permeable membrane
  • in response to differences in concentration of solute molecules
  • selectively permeable membrane must allow water molecules to pass but NOT solute molecules (solute itself cannot cross membrane)
43
Q

tonicity

A

water moves:
- from hypotonic solution (lower concentration of solute molecules) to hypertonic (higher concentrations of solute molecules)

  • when solutions on each side are isotonic: no NET osmotic movement of water in either direction
44
Q

Tonicity and osmotic water movement

A

hypotonic= movement of water into cell increases, can burst

hypertonic=water rushes out of the cell, will kill the cell

isotonic= concentrations are the same, helps maintain integrity
- movement at same rate, net movement=0

45
Q

what are we moving in Primary vs Secondary active transport

A

primary- moves positively charged ions (must occur b4 secondary)

secondary- moves both ions and organic molecules

46
Q

active membrane transport

A

a) active transport requires a direct/indirect input of energy derived from ATP hydrolysis

b) moves substances against concentrations gradients requiring energy (not spontaneous, energy acts as external aid)

c) depends on membrane transport proteins

d) specific certain substance

e) can be saturated

47
Q

What are the differences between primary and secondary active transport

A

a) primary active transport= same protein transport substance also hydrolyzes ATP to power transport directly

b) secondary active transport= transport indirectly driven by ATP hydrolysis (from primary)
- transport proteins don’t break down ATP
- instead use a favourable c.g. of ions as the energy source

48
Q

what are an example of carrier transport proteins

A
  • pumps
  • these pumps allow the charged ion to get through the hydrophobic core (can’t do it themselves)
49
Q

direct hydrolysis of ATP

A

primary active transport, c.g. (Down) and direction of transport (Up) in opposite directions

50
Q

Na+/K+ pump

A
  • REASON FOR AMOUNT: we want a difference in voltage across membranes, creates an electrochemical gradient
  • ATP is split into and phosphate, where 3 Na+ go out and 2 K+ come in

PRIMARY ACTIVE TRANSPORT

51
Q

How do ion pumps maintain membrane potential

A

through membrane potential is the voltage difference across a membrane

electrochemical gradient- concentration difference and an electrical charge difference

This holds potential energy that we can harness for secondary AT to drive endergonic, non-spontaneous reaction

52
Q

Symport vs Antiport

A

both are secondary active transport

a) symport
- cotransport solute moves via channel in same direction
- glucose and a.a.

b) antiport
- provide active transport via channel of another molecule in one direction providing energy for another molecule to go the opposite direction
- also called exchange diffusion
- RBC for coupled movement of Cl-

53
Q

Lap-Chee-Tsui

A
  • channel protein that allows Cl- to pass also lets water pass: important for digestion and respiration
  • genetic mutation: three nucleotide deletion, loss of phenylalanine
  • improper folding and structure improper function, not bringing Cl- and water leads to mucus buildup
  • CYSTIC FIBROSIS
54
Q

exocytosis and endocytosis

Form of transport

A

are active transport
- transport large molceules
- both require energy

55
Q

How do we get functional proteins at the surface

A
  • through exocytosis, where any proteins on the secretory vesicle membrane doesn’t become part of the plasma membrane
56
Q

2 main forms of endocytosis

A

1) bulk phase (pinocytosis)

2) receptor mediated endocytosis: only specific molecules that bind directly to receptor on surface

57
Q

signal transduction pathway

A
  • a signal on a cells surface is converted into a specific cellular response
  • communication is so important because it could mean life/death
57
Q

Clathirin

A

protein that plays a key role in the formation of coated vesicles for endocytosis

  • forms pocket
57
Q

familial hypercholesterolemia

A
  • this is when receptor-mediated endocytosis goes wrong:
  • on the lining of blood cells LDL receptors bring them into the cell where its cleaned up
  • inherited disease: mutation of LDL receptor, the receptor is built improperly so the function is affected, LDL will collect instead forming plaque and clots

result: high cholesterol in blood
- arteriosclerosis (can lead to heart attack)

57
Q

phagocytosis uses

A

pseudopods

58
Q

controlling vs target cell

A

controlling: Makes special molecules that send signals to change what a target cell does.

target: processes signal in 3 steps
1) reception: uses receptor protein on cell surface to read
2) transduction: processing of information (relay)
3) response: change in cell

59
Q

what are surface receptors

A
  • integral membrane proteins
  • recognize and bind signal
60
Q

binding of signal molecule

A
  • induces molecular change in the receptor that activates cytoplasmic end
    transmits signal
61
Q

response of surface receptor

A

1) inactive
2) active

  • when signal molecule is bound a conformational change occurs which causes a change in function
  • the receptor activates when the signal molecule enters the binding site
62
Q

signal transduction pathways

A
  • binding of signal molecule to surface receptor triggers cellular response WITHOUT entering cell
  • relayed through protein kinases
63
Q

protein kinases

A
  • enzymes that transfer phosphate from ATP to target proteins= phosphorylation
  • stimulates/inhibits activates of target protein producing cellular response
64
Q

how do we balance cellular response pathways

A

1) protein phosphatases
- reverse response by pulling off PO4
- turn off signal transduction pathway

65
Q

How do we move from
- active protein to an inactive protein

A

the active protein hydrolyzes ATP in each step for a new PO4 to be added on to an inactive protein to turn it active

  • each step hydrolyzes ATP
66
Q

amplification

A
  • increase in magnitude of each step as signal transduction pathway proceeds

-each enzyme activates hundreds of thousands of proteins that enter the next step in pathway, allowing for FULL response with few signal molecules binding to receptors

Ex. signal enzyme activates 10 of 1st molecules in pathway, which then activate 100 in the 2nd pathway, and then 100 000 in the 3rd…..etc etc

67
Q

what does the mosaic aspect of the fluid mosaic model refer to

A

the assortment of proteins

68
Q

what was the frye-edidin experiment

A

when human and mouse cells were grown in tissue culture, and the cells were fused where they intermixed eahcothers proteins

  • proves the fluidity of the fluid mosaic model, proteins move around
69
Q

freeze fracture technique

A
  • we would freeze cells
  • hit them with a knife to expose the inner/out leaflets of the cell where we observe differences in size, number, shape of cells in both sides
  • proves asymmetry
  • hormones will need to go to the outside, cytoskeleton needs the inside
70
Q

what is a property all phospholipids have

A

amphipathic, allowing them to form micelles, a liposome, or a bilayer in water because of the hydrophobic effect where polar molecules exclude hydrophobic molecules
- acts as a barrier to isolate np from (aq)
-

71
Q

where are sterols found

A

only in membranes of animal cells, not in plants or prokaryotes

  • restrain the movement of lipid molecules
72
Q

the larger the concentration gradient

A

the faster the rate of diffusion

73
Q

gated channels

A
  • type of channel protein found in all eukrayotes
  • switch between open, closed, and intermediate states
  • opened based on voltage change across the membrane or signalling molecules that bind
74
Q

carrier-mediated movement of a solute is also called

A

uniport transport

75
Q

how does an aquapOrin work

A

using a succession of hydrogen bonding sites on the channel in the protein

76
Q

transport pumps

A
  • positively charged ions are moved
  • ex. proton pumps
  • temporarily bind a PO4 from atp as it pumps

BIOL 1101 (4 decks)

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