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Cell Structure and Function > Exam 4 - Lecture 8 > Flashcards

Exam 4 - Lecture 8 Flashcards

1
Q

Membranes define

A

the boundaries of a cell and its internal
compartments

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2
Q

The 5 Functions of Membranes

A
  1. Define boundaries of a cell and organelles and act as
    permeability barriers
  2. Serve as sites for biological functions, such as electron
    transport
  3. Possess transport proteins that regulate the movement of
    substances into and out of cells and organelles
  4. Contain protein molecules that act as receptors to detect
    external signals
  5. Provide mechanisms for cell-to-cell contact, adhesion,
    and communication
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3
Q

Membranes are effective permeability barriers because

A

their interior is hydrophobic

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4
Q

what surrounds the whole cell?

A

the plasma membrane

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5
Q

intracellular membranes do what

A

compartmentalize functions within the cell

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6
Q

Membranes are associated with specific functions
because

A

the molecules responsible for the functions are embedded in or localized on membranes

The specific enzymes associated with particular
membranes can be used to characterize a specific
membrane

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7
Q

Membrane Proteins Regulate

A

the transport of solutes

Membrane proteins carry out and regulate the
transport of substances across the membrane

Cells and organelles take up nutrients, ions, gases,
water, and other substances, and they expel
products and wastes

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8
Q

what are the two ways substances can move into or out of the cell

A

Some substances diffuse directly across
membranes, whereas others must be moved by
specific transporters

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9
Q

Membrane Proteins Detect and Transmit

A

Electrical and Chemical Signals

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10
Q

A cell receives information from its environment as

A

electrical or chemical signals at its surface

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11
Q

Signal transduction describes the mechanisms by which

A

signals are transmitted from the outer
surface to the interior of a cell

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12
Q

Chemical signal molecules usually bind to

A

membrane proteins, known as receptors, on the
outer surface of the plasma membrane

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13
Q

describe signal transduction

A

Binding of signal molecules to their receptors
triggers chemical events on the inner membrane
surface that ultimately lead to changes in cell
function
 Membrane receptors allow cells to recognize,
transmit, and respond to a variety of specific
signals in nearly all types of cells

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14
Q

Membrane Proteins Mediate

A

Cell Adhesion
and Cell-to-Cell Communication

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15
Q

Cell-to-cell contacts, critical in animal development,
are often mediated by

A

cadherins

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16
Q

cadherins

A

mediate cell to cell contact
Cadherins have extracellular sequences of amino
acids that bind calcium and promote adhesion
between similar types of cells in a tissue

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17
Q

4 types of junctions

A

adhesive junctions
tight junctions
gap junctions
plasmodesmata

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18
Q

what do Adhesive junctions do

A

hold cells together

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19
Q

Tight junctions form

A

seals that block the passage of
fluids between cells

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20
Q

Gap junctions allow for

A

communication between
adjacent animal cells

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21
Q

plasmodesmata are present in

A

plants

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22
Q

describe the fluid mosaic model

A

The model envisions a membrane as two fluid
layers of lipids with proteins within and on the
layers

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23
Q

Overton and Langmuir

A

Lipids Are Important
Components of Membranes

Overton: cell surface had some kind
of lipid “coat” on it
 Langmuir: phospholipids
areamphipathic

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24
Q

Gorter and Grendel:

A

The Basis of Membrane
Structure Is a Lipid Bilayer

Structure is a lipid bilayer, with the
nonpolar regions of the lipids facing
inward

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25
Q

Davson and Danielli: Membranes Also Contain

A

Proteins

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26
Q

go look at the research

A

did not make flashcards

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27
Q

Electron microscopy revealed that

A

there was not enough space
on either side of the bilayer for an additional layer of protein ( not ssure of in new slides)

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28
Q

The Davson–Danielli model also did not account for

A

not in updated slides

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29
Q

Membranes are susceptible to digestion by

A

phospholipases, suggesting that membrane lipids
are exposed ( not sure if in new slides)

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30
Q

Scientists were unable to isolate “surface” proteins
from membranes unless

A

organic solvents or
detergents were used

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31
Q

The fluid mosaic bilayer model
accounts

A

or all the
inconsistencies with previous
models

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32
Q

the fluid mosaic model has two key features

A

A fluid lipid bilayer
 A mosaic of proteins attached
to or embedded in the bilayer

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33
Q

Transmembrane Segments

A

Most Membrane
Proteins Contain Transmembrane Segments
 Most integral membrane proteins
have one or more hydrophobic
segments that span the lipid
bilayer
 These transmembrane segments
anchor the protein to the
membrane

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34
Q

the first
membrane protein shown to
possess this structural feature

A

was Bacteriorhodopsin

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35
Q

How are membranes ordered and are the homogenous or heterogenous?

A

Not homogenous, freely mixing structures
 Ordered through dynamic microdomains called lipid rafts

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36
Q

Most cellular processes that involve membranes
depend on

A

structural complexes of specific lipids
and proteins

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37
Q

Membrane lipids are important components of the
“fluid” part of the fluid mosaic model
 Membranes contain several types of lipids
what are the main classes of lipids

A

phospholipids, glycolipids, and sterols

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38
Q

most abundant lipids in membranes

A

phospholipids

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39
Q

what are the two different bases for phospholipids?

A

glycerol-based phosphoglycerides and the
sphingosine-based sphingolipids

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40
Q

Glycolipids are formed by the addition of

A

carbohydrates to lipids

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41
Q

what are two variations of glycerol

A

Some are glycerol based (the glycoglycerolipids),
and some are sphingosine based (the
glycosphingolipids)

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42
Q

The most common glycosphingolipids are

A

cerebrosides and gangliosides

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43
Q

Cerebrosides are

A

are neutral glycolipids; each molecule has an
uncharged sugar as its head group

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44
Q

A ganglioside has

A

an oligosaccharide head group with one or more
negatively charged sialic acid residues

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45
Q

Cerebrosides and gangliosides are especially prominent

A

in brain and nerve cells

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46
Q

The membranes of most eukaryotes contain significant
amounts of

A

sterols

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47
Q

The main sterol in animal cell membranes is

A

cholesterol

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48
Q

cholesterol function

A

needed to stabilize and maintain membranes

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49
Q

Plant cell membranes contain what type of sterol?

A

phytosterols

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50
Q

fungal cell membranes contain

A

ergosterol, similar to
cholesterol

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51
Q

Fatty acids are components of all membrane lipids
except

A

the sterols

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52
Q

the long hydrocarbon tails provide as a

A

barrier to diffusion of polar solutes

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53
Q

The sizes of membrane fatty acids range between

A

12 and 20 carbons long, which is optimal for bilayer
formation and dictates the usual thickness of
membranes (6–8 nm)

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54
Q

Fatty Acids Vary in Degree of

A

saturation

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55
Q

Palmitate has

A

16 carbons

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56
Q

stearate has how many carbons

A

18 carbons

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57
Q

palmitate and stearate are common

A

saturated fatty acids

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58
Q

Oleate has how many double bonds

A

one double bond

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59
Q

linoleate has how many double bonds

A

two double bonds

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60
Q

Oleate (one double bond) and linoleate (two
double bonds) are both

A

18-carbon unsaturated fatty acids

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61
Q

Polyunsaturated fatty acids have more than one

A

double bond

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62
Q

Omega-3 fatty acids are

A

polyunsaturated fatty acids
that are essential for normal human development

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63
Q

Omega-3 fatty acids may also reduce the risk of

A

heart disease

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64
Q

Lipids can be isolated, separated, and studied
using

A

nonpolar solvents such as acetone and
chloroform

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65
Q

Thin-layer chromatography (TLC) is used to

A

separate different kinds of lipids based on their
relative polarities

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66
Q

the bottom of the
TLC plate is called the

A

origin

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67
Q

A nonpolar organic solvent moves up the plate by

A

capillary action taking
different lipids with it to varying degrees

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68
Q

Nonpolar lipids have little affinity for

A

silicic acid on the plate, so they
move readily with the solvent, near the solvent front

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69
Q

in reference to TLC Polar lipids will interact variably (depending on how polar they are) with

A

the
silicic acid, and their movement will be slowed proportionately

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70
Q

Membrane asymmetry describes the difference in degree of what component?

A

is the difference between
the monolayers regarding the kind of lipids present
and the degree of saturation of fatty acids in the
phospholipids

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71
Q

Most of the glycolipids in the plasma membrane of
animal cells are in what layer

A

outer layer

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72
Q

Membrane asymmetry is established during

A

the synthesis of the membrane

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73
Q

does membrane asymmetry change?

A

Once established, membrane asymmetry does not
change much

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74
Q

transverse diffusion

A

The movement of lipids from one monolayer to
another requires their hydrophilic heads to move all
the way through the hydrophobic interior of the
bilayer

This transverse diffusion (or “flip-flop”) is
relatively rare

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75
Q

describe lipid mobility

A

Lipids Move Freely Within Their Monolayer
Lipids are mobile within their monolayer

Movements are rapid and random

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76
Q

types of lipids motion

A

Rotation - Rotation of phospholipids about their axes
can occur
lateral diffusion - Phospholipids can also move within the monolayer, via lateral
diffusion

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77
Q

which membranes tend to have transverse diffusion / flip-flop?

A

Some membranes, in particular the smooth ER
membrane

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78
Q

why are some membranes prone to transverse diffusion?

what is the substance called?

A

because they have proteins that catalyze the flip-flop of
membrane lipids
 These proteins are called phospholipid
translocators, or flippases

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79
Q

proteins catalyze the lip flop

A

phospholipid
translocators, or flippases

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80
Q

The lipid bilayer behaves as a fluid that permits the
movement of both

A

lipids and Proteins

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81
Q

How far can lipids move

A

Lipids can move as much as several μm per
second within the monolayer

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82
Q

Lateral diffusion can be demonstrated using what method

A

Fluorescence recovery after photobleaching
(FRAP)

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83
Q

FRAP measures lipid ______

A

mobility

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84
Q

how does FRAP work

A

Investigators label lipid molecules in a membrane with a fluorescent dye.
 A laser beam is used to bleach the dye in a small area, creating a dark spot
on the membrane.
 The membrane is observed afterward to determine how long it takes for the
dark spot to disappear, a measure of how quickly new fluorescent lipids
move in

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85
Q

Membranes Function Properly Only in the________ state

A

Fluid

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86
Q

what affects membrane fluidity

A

Membrane fluidity changes with temperature,
decreasing as temperature falls and vice versa

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87
Q

what is the transition temperature?

A

a characteristic of every lipid bilayer- the transition
temperature Tm, the temperature at which it
becomes fluid

The Tm is the point of maximum heat absorption as the membrane changes
from the gel to the fluid state

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88
Q

change is state of the membrane is called

A

Phase transition ( solid to liquid)

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89
Q

what happens to memrane functions when the temp is below Tm ?

A

Below the Tm , any functions that rely on membrane
fluidity will be disrupted

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89
Q

The transition temperature can be measured by

A

differential scanning
calorimetry

  • The membrane is placed inside a calorimeter, and the uptake of heat is
    measured as temperature is increased
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90
Q

Fluidity of a membrane depends
mainly on

A

that fatty acids that it contains

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91
Q

what two characteristics about fatty acids affect membrane fluidity

A

The length of fatty acid chains and
the degree of saturation both affect
the fluidity of the membrane

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92
Q

what has a higher Tm? Long chains and saturated fats or short chains and unsaturated?

A

Long-chain and saturated fatty
acids have higher Tm values,
whereas short-chain and
unsaturated fatty acids have lower Tm values

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93
Q

how do saturated farts sit together in the membrane

A

they pack well together in the membrane ( linear)

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94
Q

how do double bonds affect fatty acid shape

A

Fatty acids with one or
more double bonds have
bends in the chains that
prevent them from
packing together neatly

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95
Q

which is more fluid saturated or unsaturated

A

Because saturated bonds pack together and unsaturated bonds have a bend - – unsaturated fatty
acids are more fluid than
saturated fatty acids and
have lower Tm values

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96
Q

Why do Most plasma membrane fatty acids vary in chain length and
degree of saturation?

A

to ensure that membranes are fluid at physiological
temperatures

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97
Q

what type of double bonds do unsaturated fatty acids typically have ? and what type of bonds do trans fats normally have?

A

Most unsaturated fatty acids have cis double bonds

commercially produced trans fats, which pack together like
saturated fats do

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98
Q

how do sterols impact membrane fluidity ?

A

The intercalation of rigid cholesterol
molecules into a membrane decreases its
fluidity and increases the Tm

However, cholesterol also prevents
hydrocarbon chains of phospholipids from
packing together tightly and so reduces the
tendency of membranes to gel upon cooling
 Therefore, cholesterol is a fluidity buffer;
sterols in other organisms may function
similarly
Other Effects of Sterols on Membranes
 Sterols decrease the permeability of membranes to
ions and small polar molecules
 This is likely because they fill spaces between the
hydrocarbon chains of phospholipids
 This effectively blocks the routes that ions and
small molecules would take through the membran

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99
Q

cholesterol’s impact on the membrane gives it the name….

A

fluidity buffer

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100
Q

how do sterols affect permeability of membranes to ions and small polar molecules??? Explain why

A

Sterols decrease the permeability of membranes to
ions and small polar molecules

 This is likely because they fill spaces between the
hydrocarbon chains of phospholipids

 This effectively blocks the routes that ions and
small molecules would take through the membrane

101
Q

How do organisms regulate membrane fluidity?

A

Most organisms can regulate membrane fluidity by
varying the lipid composition of the membranes

102
Q

poikilotherms

A

organisms that cannot regulate their body temperature

use homeoviscous adaptation,
compensating for changes in temperature by
altering the length and degree of saturation of fatty
acids in their membranes

103
Q

desaturase enzyme

A

Some organisms have a desaturase enzyme, which
introduces double bonds into fatty acids as needed

104
Q

In plants and yeasts, temperature-related fluidity
changes are tied to

A

the increased solubility of
oxygen at lower temperatures

More oxygen is available at low temperatures, and
oxygen acts as a substrate for desaturase, allowing
membrane fluidity to be maintained at lower
temperatures

104
Q

Lipid Rafts Are

A

Localized Regions of Membrane
Lipids That Are Involved in Cell Signaling

they are associated with specific proteins

they are also called lipid microdomains

These are dynamic structures,
changing composition as lipids and
proteins move into and out of them

105
Q

how do lipid rafts in the outer membrane compare to those in the rest of the membrane?.

A

Lipid rafts in the outer monolayer of
animal cells have elevated levels of
cholesterol and glycosphingolipids
and are less fluid than the rest of the
membrane

106
Q

Lipid Raft Formation

A

Early models of raft formation proposed that localized regions
of tightly associated cholesterol and glycosphingolipid
molecules attracted particular proteins to them
 Raft-associated proteins sometimes are lipoproteins, with fatty
acids attached to them
 Some of the more than 200 known raft-associated proteins
capture and organize particular lipid rafts
 Lipid rafts contain actin-binding proteins, suggesting that the
cytoskeleton may play a role in their formation and organization

107
Q

Functions of Lipid Rafts

A

Lipid rafts are thought to have roles in detecting
and responding to exracellular signals
 For example, lipid rafts have roles in
 Transporting nutrients and ions across
membranes
 Binding activated immune system cells to their
microbial targets
 Transporting cholera toxin into intestinal cells

108
Q

Receptors in Lipid Rafts

A

When a receptor molecule on the outer surface of
the plasma binds its ligand, it can move into lipid
rafts also located in the outer monolayer

Lipid rafts containing receptors are coupled to lipid
rafts on the inner monolayer

Some lipid rafts contain kinases, enzymes that
generate second messengers in a cell via
phosporylation of target molecules

109
Q

Some lipid rafts contain kinases which are

A

enzymes that
generate second messengers in a cell via
phosporylation of target molecules

110
Q

what is the main component of the “mosaic” part of the mebrane

A

The mosaic part of the fluid mosaic model includes
lipid rafts and other lipid domains

 However, membrane proteins are the main
components

111
Q

Support for the fluid mosaic model came from
studies involving

A

freeze fracturing - a bilayer or membrane is frozen and then hit
sharply with a diamond knife
 The resulting fracture often follows the plane
between the two layers of membrane lipid

112
Q

Freeze-Fracture Analysis of Membranes

(fix)

A

When a fracture plane splits a membrane into its two layers,
particles the size and shape of globular proteins can be seen
 The E surface is the exoplasmic face, and the P surface is the
protoplasmic face
 The protein/lipid ratio varies among cell types

113
Q

Membrane proteins fall into three categories:

A

Integral, peripheral, and lipid anchored

114
Q

Membrane proteins have different _________ and so occupy different positions in or on
membranes

A

hydrophobicites

^ which determines how easily such proteins
can be extracted from membranes

115
Q

Integral membrane proteins

A

are embedded in the lipid bilayer
because of their hydrophobic regions

116
Q

Lipid-anchored proteins are

A

hydrophilic and attached to the bilayer
by covalent attachments to lipid molecules embedded in the bilayer

116
Q

Peripheral proteins are

A

hydrophilic and located on the surface of the
bilayer

117
Q

Integral Membrane Proteins in depth (fix)

A

Most membrane proteins possess one or more hydrophobic regions
with an affinity for the interior of the lipid bilayer
 These are integral membrane proteins, with hydrophobic regions
embedded in the interior membrane bilayer
 They are difficult to remove from membranes by standard isolation
procedures
 Some integral membrane proteins, called integral monotropic
proteins, are embedded in just one side of the bilayer
 However, most are transmembrane proteins that span the membrane
and protrude on both sides
 Transmembrane proteins cross either once (singlepass proteins) or
several times (multipass proteins)

118
Q

Most transmembrane proteins are anchored to the
lipid bilayer by one or more hydrophobic

A

Transmembrane segments

119
Q

conformation and length of transmembrane segments

A

the polypeptide chain appears to
span the membrane in an α-helical conformation
about 20–30 amino acids long
 Some are arranged as a closed β sheet called a
β barrel

120
Q

Singlepass membrane proteins have the______ terminus extending from
one surface of the membrane and the ________ from the other

A

Singlepass membrane proteins have the C-terminus extending from
one surface of the membrane and the N-terminus from the other
 For example, glycophorin is a singlepass protein on the erythrocyte
plasma membrane that is oriented so the C-terminus is on the inner
surface and the N-terminus is on the outer

121
Q

describe Multipass Membrane Proteins

A

Multipass membrane proteins have 2–20 (or more) transmembrane
segments
 For example, bacteriorhodopsin has seven transmembrane
segments positioned to form a channel

122
Q

Membrane proteins that lack discrete hydrophobic
regions do not penetrate the lipid bilayer are called

A

peripheral membranes

123
Q

peripheral membranes lack what ?

A

discrete hydrophobic
regions do not penetrate the lipid bilayer

124
Q

peripheral membrane proteins are bound
to membrane surfaces through

A

weak electrostatic forces and hydrogen bonds

Some hydrophobic residues play a role in
anchoring them to the membrane surface

125
Q

The polypeptide chains of lipid-anchored
membrane proteins are located on the

A

surfaces of
membranes

They are covalently bound to lipid molecules
embedded in the bilayer
 Proteins bound to the inner surface of the plasma
membrane are linked to fatty acids, or isoprenyl
groups

126
Q

Types of Lipid-Anchored Membrane Proteins

A

Fatty acid-anchored membrane proteins

Isoprenylated membrane proteins

GPI-anchored membrane proteins

126
Q

Fatty acid-anchored membrane proteins

A

are
attached to a saturated fatty acid, usually myristic
acid (14C) or palmitic acid (16C)

127
Q

Isoprenylated membrane proteins are
synthesized in the

A

cytosol and then modified by
addition of multiple isoprenyl groups (5C) usually
farnesyl (15C) or geranylgeranyl (20C) groups

128
Q

GPI-anchored membrane proteins are _________ linked to __________

A

are covalently
linked to glycosylphosphatidylinositol

129
Q

Isolation of Membrane Proteins

A

Peripheral membrane proteins are usually easy to
isolate by altering pH or ionic strength
 Chelating (cation-binding) agents are also used to
solubilize peripheral membrane proteins
 Lipid-anchored proteins are isolated by
similar means

130
Q

Isolating Integral Membrane Proteins

A

Integral membrane proteins are difficult to isolate
from membranes
 Often detergents are used that disrupt hydrophobic
interactions and dissolve the lipid bilayer

131
Q

Electrophoresis is a

A

group of techniques that use
an electric field to separate charged molecules
 How quickly a molecule moves during
electrophoresis depends on both charge and size
 Electrophoresis uses various support media, most
commonly polyacrylamide or agarose

131
Q

How does Electrophoresis of Membrane Proteins work?

A

 Membrane fragments are solubilized in sodium
dodecyl sulfate (SDS), which disrupts protein-
protein and protein-lipid associations
 The proteins are thus coated with negatively
charged detergent molecules
 The proteins are loaded onto a polyacrylamide gel
and an electrical potential is applied

132
Q

 Two-dimensional SDS-polyacrylamide gel
electrophoresis (SDS-PAGE) separates….

 Following electrophoresis, polypeptides can be
identified by

A

 Two-dimensional SDS-polyacrylamide gel
electrophoresis (SDS-PAGE) separates proteins in
two dimensions, first by charge and then by size
 Following electrophoresis, polypeptides can be
identified by Western blotting
 In this technique, proteins are transferred to a
membrane and bound by specific antibodies

133
Q

Some integral membrane proteins, called integral monotropic
proteins, are embedded

A

in just one side of the bilayer
 However, most are transmembrane proteins that span the membrane
and protrude on both sides

133
Q

Affinity labeling

A

utilizes radioactive molecules that
bind to certain proteins based on function

For example, cytochalasin B is an inhibitor of
glucose transport

134
Q

membrane reconstitution

A

proteins are extracted
from membranes and separated individually

134
Q

Membranes exposed to radioactive cytochalasin B
will likely have

A

the radioactivity bound to proteins
involved in glucose transport

135
Q

purified proteins

A

are mixed with phospholipids
to form vesicles call liposomes

135
Q

Liposomes can be loaded with

A

particular molecules
and tested for their ability to carry out certain
functions

136
Q

X-ray crystallography

A

an be used to determine the
structure of proteins that can be isolated in
crystalline form
 Membrane proteins are hard to isolate and
crystallize

137
Q

X-ray crystallography is widely used to determine

A

three-dimensional structure of proteins

137
Q

An alternative approach to X-ray crystallography

A

hydropathy analysis

138
Q

Integral membrane proteins are difficult or easy to isolate
and crystallize

A

difficult

139
Q

hydropathy (or hydrophobicity) plot

A

the number and location of transmembrane
segments in a membrane protein can be inferred if
the protein sequence is known

A computer program identifies clusters of
hydrophobic residues, calculating a hydropathy
index for successive “windows” along the protein

139
Q

Site-specific mutagenesis allows determination of

A

how certain amino acids affect protein function

140
Q

hydropathy (or hydrophobicity) plot is used for

A

The number and location of transmembrane segments in a
membrane protein can be inferred if the protein sequence is
known

140
Q

hydropathy index

A

calculating hydrophobic residues

141
Q

protein sequence is hard to determine unlike DNA bc

A

different amino acids are encoded with different codes. Histodine has 6 codes so you have to know which code was responsible

142
Q

Membrane Proteins Are Oriented

A

Asymmetrically Across the Lipid Bilayer

143
Q

Site-specific mutagenesis

A

allows determination of
how certain amino acids affect protein function

144
Q

Once in place, in or on one of the monolayers,
proteins ( can or cannot) move across the membrane from
one surface to the other

A

proteins cannot move across the membrane from
one surface to the other
 All the molecules of a particular protein are oriented
the same way in the membrane

145
Q

The enzyme lactoperoxidase (LP) can be used to

The enzyme galactose oxidase (GO) can be used to

A

attach (125^I) to proteins

label carbohydrate
side chains attached to membrane proteins and lipids

145
Q

Radioactive labeling procedures are used to

A

distinguish between proteins on
inner and outer surfaces of membrane vesicles

146
Q

Glycoproteins

A

are membrane proteins with
carbohydrate chains covalently linked to amino acid
side chains ( covalent = strong)

146
Q

The PROCESS of adding a carbohydrate side chain to a
protein is called

A

glycosylation

147
Q

glycosylation

A

The addition of a carbohydrate side chain to a
protein

148
Q

where does Glycosylation occurs ?

A

ER and Golgi
compartments

149
Q

Glycosylation involves linkage of the
carbohydrate to

A

The nitrogen atom of an amino group
or
The oxygen atom of a hydroxl group

150
Q

N-linked glycosylation

A

Glycosylation involves linkage of the
carbohydrate to The nitrogen atom of an amino group (N-linked glycosylation)
of an asparagine residue

151
Q

O-linked glycosylation

A

Glycosylation involves linkage of the
carbohydrate to The oxygen atom of a hydroxl group (O-linked glycosylation)
of a serine, threonine, or modified lysine or proline residue

152
Q

explain the statement : Membrane Proteins Vary in Their Mobility

A

Membrane proteins are more variable than lipids in
their ability to move freely within the membrane
 Some proteins can move freely, whereas others are
constrained because they are anchored to protein
complexes

153
Q

Experimental Evidence for Protein Mobility

A

Evidence for mobility of some membrane proteins
comes from cell fusion experiments
 These experiments were performed by David Frye
and Michael Edidin

154
Q

The Frye and Edidin Experiments

A

Frye and Edidin fused human and mouse cells and used two fluorescent
antibodies, each with a differently colored dye linked to it
 The anti-mouse antibodies were linked to fluorescein, a green dye; and the
anti-human antibodies were linked to rhodamine, a red dye
 Within a few minutes of fusion, the red and green region proteins began to
intermix

155
Q

Protein distribution on memnbranes are different

A

image on slide 25

When plasma membranes are examined in freeze-fracture
micrographs, the embedded proteins appear to be randomly
distributed
 The same is true for other types of membranes

156
Q

Overcoming the permeability barrier of cell
membranes is crucial to proper functioning of the cell.
What does this mean inte rms on the transports in and out?

A

Specific molecules and ions need to be selectively
moved into and out of the cell or organelle

157
Q

Membranes are protective barriers described as

A

selectively permeable or
semipermeable

158
Q

Homeostasis

A

Cells and cellular compartments are
able to accumulate a variety of substances in
concentrations that are very different from those of the
surroundings

159
Q

solutes

A

Most of the substances that move across membranes
are dissolved gases, ions, and small organic
molecules

160
Q

A central aspect of cell function is selective

A

transport

161
Q

Three quite different mechanisms are involved in
moving solutes across membranes:

A

Simple
Diffusion,

Facilitated Diffusion,

Active
Transport

162
Q

intrinsic directionality

A

opposite direction requirers active transport?

163
Q

The movement of a molecule that
has no net charge is determined
by its

A

concentration gradient

164
Q

Simple diffusion and facilitated
diffusion involves (ender or exergonic?) movement

A

exergonic
movement “down” the
concentration gradient
(negative ΔG)

165
Q

Active transport involves ( ender or exergonic) movement

A

endergonic movement “up” the
concentration gradient
(positive ΔG)

166
Q

The movement of an ion is
determined by its

A

electrochemical potential

167
Q

electrochemical potential

A

the combined effect of its
concentration gradient and the
charge gradient across the
membrane

168
Q

The active transport of ions
across a membrane creates a

A

charge gradient, or
membrane potential (Vm),
across the membrane

169
Q

Simple Diffusion

A

Unassisted Movement
Down the Gradient

170
Q

the unassisted net movement of a
solute from

A

high to lower
concentration

171
Q

Simple Diffusionis only possible for…

A

gases, nonpolar molecules, or
small polar molecules such as
water, glycerol, or ethanol

172
Q

Diffusion always moves solutes
toward

A

equilibrium: solutes will
move toward regions of lower
concentration until the
concentrations are equal

173
Q

Osmosis Is

A

the Diffusion of Water Across a
Selectively Permeable Membrane

174
Q

Water molecules, being
uncharged are not affected by

A

the membrane potential

175
Q

Water concentration is not

A

appreciably different on opposite
sides of a membrane

176
Q

Osmosis: water will move toward the region of

A

higher solute concentration

177
Q

If the solute
concentration is higher
outside the cell, the
SOLUTION is called

A

hypertonic

177
Q

Osmolarity

A

Is the total solute
concentrations inside
versus outside of the cel

178
Q

hypotonic in plants is called ( see figure and know differnet names)

A

turgid

178
Q

If the solute concentration is lower outside the cell, the solution is called

A

hypotonic

179
Q

isotonic solution

A

solute concentration inside and outside the cell is the
same

179
Q

Animal cells vs cells with cell walls (plants, algae, fungi, and many bacteria )

A

act differently

180
Q

Facilitated Diffusion:

A

Protein-Mediated
Movement Down the Gradient

180
Q

Most substances in the cell are too large or too polar to
cross membranes by simple diffusion
 These can move in and out of cells only with the assistance
of

A

Transport proteins

181
Q

movment using transport protein is ( exergonic or endetgonic)

A

This process is exergonic: the solute diffuses as dictated by
its concentration gradient

182
Q

The role of the transport proteins is just to provide

A

a path
through the lipid bilayer, allowing the “downhill” movement
of a polar or charged solute

182
Q

Carrier proteins aka

A

transporters or permeases

183
Q

Carrier proteins bind

A

bind solute
molecules on one side of a membrane, undergo a
conformation change, and release the solute on the other side
of the membrane

184
Q

Channel proteins form

A

form hydrophilic channels through the
membrane to provide a passage route for solutes

185
Q

The alternating conformation model states that

A

a
carrier protein is allosteric protein and alternates
between two conformational states

186
Q

Carrier Proteins Alternate Between

A

Two
Conformational States

187
Q

what are the two conformational states

A

n one state, the solute-binding site of the protein
is accessible on one side of the membrane
 The protein shifts to the alternate conformation,
with the solute-binding site on the other side of
the membrane, triggering solute release

188
Q

Carrier Proteins Are Analogous to Enzymes in
Their

A

Specificity and Kinetics

189
Q

Facilitated diffusion involves binding

A

a substrate
on a specific solute-binding site

190
Q

The carrier protein and solute form an

A

intermediate

191
Q

After conformational change, the “product” is

A

released (the transported solute)

192
Q

Carrier proteins are regulated by

A

external factors

193
Q

Carrier Proteins Transport how many solutes

A

1-2 solutes

194
Q

When a carrier protein transports a
single solute across the membrane, the
process is called

A

uniport

194
Q

uniport

A

When a carrier protein transports a
single solute across the membrane

195
Q

A carrier protein that transports a single
solute is called a

A

uniporter

196
Q

uniporter

A

A carrier protein that transports a single
solute

197
Q

When two solutes are transported
simultaneously, and their transport is
coupled, the process is called

A

coupled transport

198
Q

coupled transport

A

When two solutes are transported
simultaneously, and their transport is
coupled

199
Q

symport (or cotransport)

A

If the two solutes are moved
across a membrane in the same
direction

200
Q

If the two solutes are moved
across a membrane in the same
direction, the process is referred
to as

A

symport (or cotransport)

201
Q

antiport (or
countertransport)

A

the solutes are moved in
opposite directions,

202
Q

If the solutes are moved in
opposite directions, the process
is called

A

antiport (or
countertransport)

203
Q

Transporters that mediate these ( symport and antiport)
processes are

A

symporters and antiporters

204
Q

pores

A

large and
nonspecific channels on the outer membranes of
bacteria, mitochondria, and
chloroplasts

205
Q

Pores are formed by

A

transmembrane proteins called
porins that allow passage of
solutes up to a certain
molecular weight to pass

206
Q

Most channels are

A

smaller and
highly selective

207
Q

Most of the smaller
channels are involved in

A

ion transport and are
called ion channels

208
Q

ion channels are involved in

A

involved in ion transport

209
Q

The movement of solutes
through ion channels is
much ( faster OR SLOWER) than
transport by carrier
proteins

A

faster
because
conformation changes
are not required

210
Q

There are three types of channels: ???

A

ion channels, porins, and aquaporins

210
Q

Channel Proteins Facilitate Diffusion by Forming

A

Hydrophilic
Transmembrane Channels

211
Q

Ion Channels

A

transmembrane proteins that allow rapid passage of
specific ions

typically gated meaning they open and close in response to some stimulus

212
Q

Voltage-gated channels

A

open and close in response to changes in
membrane potential

213
Q

Ligand-gated channels

A

are triggered by the binding of certain substances
to the channel protein

214
Q

Mechanosensitive channels

A

respond to mechanical forces acting on the
membrane

215
Q

porins:

A

transmembrane proteins that allow rapid passage of
various solutes

216
Q

the transmembrane segments of porins cross the membrane
as

A

β barrels

217
Q

Polar side chains line the
inside of the pore, allowing
passage of

A

many hydrophilic
solutes

218
Q

The outside of the barrel
contains many

A

nonpolar side
chains that interact with the
hydrophobic interior of the
membrane

219
Q

Aquaporins (AQPs)

A

transmembrane channels that
allow rapid passage of water

219
Q

All aquaporins are

A

tetrameric integral
membrane proteins

The identical monomers
associate with their 24
transmembrane segments
oriented to form four central
channels
 The channels, lined with
hydrophilic side chains, are
just large enough for water
molecules to pass through
one at a time

220
Q

active transport moves what direction on a gradient

A

protein-mediated movement up the gradient

221
Q

Active transport is used to move

A

solutes up a
concentration gradient, away from equilibrium

222
Q

Active transport couples

A

endergonic transport to an
exergonic process, usually ATP hydrolysis

223
Q

Active transport performs three important cellular functions

A
  1. Uptake of essential nutrients
  2. Removal of wastes
  3. Maintenance of nonequilibrium concentrations of certain
    ions
224
Q

Active Transport Is

A

Unidirectional

225
Q

Active transport differs from diffusion (both simple
and facilitated) in

A

the direction of transport

 Diffusion is nondirectional with respect to the
membrane and proceeds as directed by the
concentrations of the transported substances
 Active transport has an intrinsic directionality

226
Q

The Coupling of Active Transport to an Energy
Source May Be

A

Direct or Indirect

227
Q

describe direct active transport
(reference slide)

A

(primary active transport),
the accumulation of solute
molecules on one side of the
membrane is coupled
directly to an exergonic
chemical reaction
 This is usually hydrolysis of
ATP
 Transport proteins driven by
ATP hydrolysis are called
transport ATPases or
ATPase pumps

228
Q

Indirect active transport

A

depends on the simultaneous
transport of two solutes

Favorable movement of one
solute down its gradient drives
the unfavorable movement of
the other up its gradient

 This can be a symport or an
antiport, depending on
whether the two molecules
are transported in the same or
different directions

229
Q
A

Cell Structure and Function (8 decks)

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