Plasma Membrane Structure and Function

1
Plasma Membrane Structure and Function

• Chapter 7

Image from http//www.biologie.uni-hamburg.de/b-o
nline/ge22/03.gif
Slide show modified fromhttp//www.explorebiolog
y.com/pptAP/2005/http//facstaff.bloomu.edu/gdavi
s/links20100.htm
2
MEMBRANE MODELS

• 1915 Scientists analyzed isolated red blood cell
  membranes, found them made up of proteins and
  lipids
• 10 years later E. Gorter and F. Grendel reasoned
  membranes are made of a phospholipid bilayer
• 1935 Hugh Davson and James Danielli
• proposed membrane was a sandwich
• of proteins and phospholipid bilayer
• with proteins on outside of phopholipids

DAVSON-DANIELLIMODEL
3
FLUID MOSAIC MODEL
Animation from http//www.sp.uconn.edu/terry/ima
ges/anim/fluidmem.gif
Click here to See Fluidity
Click here to SeeFLUIDITY

• 1972- S.J. Singer and G. Nicolson propose
  membrane is a mosaic of proteins and
  phospholipids that are constantly moving and
  changing

4
More than just a barrier

• Expanding our view of cell membrane beyond just a
  phospholipid bilayer barrier
• phospholipids plus

5
A membrane is a collage of different proteins
embedded in the fluid matrix of the lipid bilayer
6
Membrane Proteins

• Proteins determine most of membranes specific
  functions
• cell membrane organelle membranes each have
  unique collections of proteins
• Membrane proteins
• peripheral proteins loosely bound to surface
  of membrane
• integral proteins penetrate into lipid
  bilayer, often completely spanning the membrane
  transmembrane protein

7
Membrane Carbohydrates

• Attached to proteins (glycoproteins) or lipids
  (glycolipids)
• Play a key role in cell-cell recognition
• ability of a cell to distinguish neighboring
  cells from another
• important in organ tissue development
• basis for rejection of foreign cells by immune
  system

http//faculty.southwest.tn.edu/rburkett/GB1-osmos
is.htm
8
Membranes provide a variety of cell functions
9
Molecules need to move across membranes in cells
IN food carbohydrates sugars, proteins amino
acids lipids salts, O2, H2O
OUT waste ammonia salts CO2 H2O products
Image modiified from http//www.accessexcellence.
org/AB/GG/importProt.html
10

• Cell Membranes are made of
• PHOSPHOLIPIDS PROTEINS
• Amphipathic
• Molecules with
• both hydrophilic
• and hydrophobic regions

phosphate
hydrophilic
lipid
hydrophobic
11

• HYDROPHILIC/HYDROPHOBIC areas determine positions
  of molecules in cell membranes
• hydrophobic amino acids
• stick in the lipid membrane
• anchors the protein in membrane
• hydrophilic amino acids
• stick out in the watery fluid in or out of cell

12
Semi-permeable membrane

• Need to allow passage through the membrane
• But need to control what gets in or out
• membrane needs to be semi-permeable

aa
H2O
sugar
lipid
salt
NH3
So what makes a membrane semi permeable?
See a movie
13
PHOBIC TAILS in center determine what can pass
through
14

• What molecules can get through directly?

Small non-polar molar molecules (O2 CO2) and
hydrophobic molecules (fats other lipids) can
slip directly through the phospholipid cell
membrane, but
lipid
O2
salt
What about other stuff?
NH3
aa
H2O
sugar
15
Diffusion

• 2nd Law of Thermodynamics governs biological
  systems
• Universe tends towards disorder

Animatioin from http//www.biologycorner.com/reso
urces/diffusion-animated.gif

• Diffusion
• movement from higher ? lower concentration

16

• Diffusion will also happen across a cell
  membrane as long as there is a difference in
  concentration and the membrane will let the
  molecule pass through.

17
Example DIFFUSION IN CELLS
http//facstaff.bloomu.edu/gdavis/links20100.htm
O2 automatically moves from HIGHER concentration
(in lungs) to LOWER concentration (in blood)
CO2 automatically moves from HIGHER
concentration (in blood) to LOWER concentration
(in lungs)
http//www.le.ac.uk/pa/teach/va/anatomy/case2/2_2.
html
18
Diffusion of 2 solutes

• Each substance diffuses down its own
  concentration gradient, independent of
  concentration gradients of other substances

19
What if cell needs to move a molecule _________
the CONCENTRATION GRADIENT?_______________
AGAINST
(LOWER ? HIGHER)

• Cell example
• Want to put MORE glucose
• into mitochondria when there is
• already glucose in there

Image from http//www.biologyclass.net/mitochondr
ia.jpg
20
What if a cell needs to move _____ or ______
moleculesthat cant getthrough themembrane?
LARGE
POLAR
http//www.d.umn.edu/sdowning/Membranes/membraneI
mages/jpegimages/diffusionmedium.jpg
21
What if cell needs to move molecules really
_______? (cant wait for it to diffuse)
FAST

• Cell example

Movement of Na K ions required to send
nerve signals
http//www.steve.gb.com/images/science/neuron.png
22
Cells need a ____ to ____ molecules across cell
membranes that _______ across by ___________
WAY
HELP

cant go
themselves
23
Kidspiration by Riedell
24
Facilitated diffusion

• Move from HIGH to LOW concentration with aid of
  membrane transport proteins
• passive transport
• no energy needed
• facilitated with help

25
Facilitated Diffusion
Animation from http//bio.winona.edu/berg/ANIMTNS
/facdifan.gif
Carrier Proteins Grab molecule, undergo
conformational change, flip to other side
Channel Proteins Create passageway forsubstances
to pass through May be gated or notopen in
response to chemical or electrical signals
Animation from http//www2.uic.edu/myilma1/ionch
annel.gif
26
Gated channels

• open only in presence of stimulus (signal)
• stimulus usually different from transported
  molecule
• ex ion-gated channelswhen neurotransmitters
  bind to a specific gated channels on a neuron,
  these channels open allows Na ions to
  enter nerve cell
• ex voltage-gated channelschange in electrical
  charge across nerve cell membrane opens Na K
  channels

27
Carriers and Channels are specific
inside cell
sugar
aa
H2O
salt
NH3
outside cell
. . . BUT STILL MOVES FROM HIGHER to LOWER
28
Active transport

• Uses energy from ATP to move molecules against
  concentration gradient
• Moves from lower ? higher
• Uses protein pumps
• OR
• vesicles

Animations from http//academic.brooklyn.cuny.ed
u/biology/bio4fv/page/cell-movement.html http//ww
w.cat.cc.md.us/courses/bio141/lecguide/unit1/eustr
uct/images/sppump.gif
29
PROTON PUMP
Moves Protons (H) across membrane
EXAMPLES - Creates acidic condition inside
lysosomes - Photosynthesis/respiration use H
gradients to generate ATP
See a movie proton pump
30
Active transport

• SODIUM-POTASSIUM PUMP
• Sets up difference in charge across membranes
• Pumps 3 Na outand 2 K in
• Makes cells more outside more - inside

See a movie about Na - K pump
Animation from http//www.cat.cc.md.us/courses/bi
o141/lecguide/unit1/eustruct/images/sppump.gif
31

• All cells have voltages across their membranes
• membrane potential
• Cytoplasm inside cell is more negative
• than extracellular fluid outside
• TWO FORCES drive diffusion
• Concentration gradient
• Electrical force
• Ions move DOWN the electrochemical
  gradient

Favors the passage of cations () into cells
32
MEMBRANE POTENTIAL created by electrogenic pumps
(proteins that generate voltage by pumping ions)
PROTON PUMPMain electrogenic pump in plants,
fungi, and bacteria
Na- K PUMPMain electrogenic pump in animal
cells
http//fig.cox.miami.edu/cmallery/150/memb/electr
ogenic.jpg
Animation from http//www.lionden.com/cell_anima
tions.htm
33
Electrogenic pumps can be coupled to actively
transport other substances
COTRANSPORT Ex Cells pump Hout of cell then
use the diffusion of H back into cell downits
gradient to drivethe uptake of sucrose into
cells
http//faculty.southwest.tn.edu/rburkett/GB1-os29.
jpg
34
Na - K pump sets up MEMBRANE POTENTIAL
http//hyperphysics.phy-astr.gsu.edu/hbase/biology
/nervecell.htmlc2
35
(No Transcript)
36
(No Transcript)
37


38
BULK TRANSPORT

• ACTIVE transport
• Requires energy (ATP)
• Uses vesicles

Watch two video clips aboutendo/exocytosis endo/
exocytosis
Animation from http//www.emc.maricopa.edu/facult
y/farabee/BIOBK/BioBooktransp.html
39
Endocytosis
Cell eating large molecules whole cells
phagocytosis
Cell drinking Fluids Small molecules
pinocytosis
triggered byligand signal
receptor-mediated endocytosis
40
PHAGOCYTOSIS
Animation from http//academic.brooklyn.cuny.ed
u/biology/bio4fv/page/cell-movement.html
Cell eating takes in large molecules whole
cells
See phagocytosis in action
http//www.accs.net/users/kriel/chapter20nine/
41
Example in cellsWHITE BLOOD CELL ENGULFING
BACTERIA using Phagocytosis

• SEE PHAGOCYTOSIS MOVIE

http//fig.cox.miami.edu/cmallery/255/255ion/fig1
4x28.jpg
42
PINOCYTOSIS

• Cell drinking
• Takes in fluids
• Small molecules

http//student.ccbcmd.edu/gkaiser/biotutorials/eu
struct/pinocyt.html
43
Receptor-mediated Endocytosis

• Ligand-any molecule that binds to a receptor site
• Binding of ligands allows uptake of specific
  molecules

44
Receptor-mediated Endocytosis
Example in cells Cholesterol Uptake Low density
lipid proteins (LDLs) bind cholesteroland carry
it in blood LDLs act as ligands
bindingreceptors on cell surfaceand cholesterol
is taken into cell
http//academic.brooklyn.cuny.edu/biology/bio4fv/p
age/rectpr.htm
45
EXOCYTOSIS

• Active transport (requires ATP)
• Uses vesicles
• Releases substances to outside

INSULIN being released by pancreas cells using
exocytosis
46
GOLGI BODIES USE EXOCYTOSIS
Video http//www.southtexascollege.edu/tdehne/BC
_ShockwaveAnimations/07SWF-TourOfTheCell/07-16-End
omembraneSystem.swf

• Animation from http//www.franklincollege.edu/bio
  web/APfiles/week04.html

See a Golgi movie
47
http//fig.cox.miami.edu/cmallery/255/255ion/fig1
4x26.jpg
48
Transport summary
49
The Special Case of WaterMovement of water
across the cell membrane OSMOSIS
50
Osmosis is diffusion of water

• Water is very important, so we talk about water
  separately
• Diffusion of water from high concentration of
  water to low concentration of water
• across a semi-permeable membrane
• Passive
• Uses no energy

51
Aquaporins
1991 2003

• Transport proteins that move water rapidly into
  out of cells
• evidence that there were water channels

Peter Agre John Hopkins
Roderick MacKinnon Rockefeller
52

• TONICITY- ability of a solution to cause a cell
  to lose or gain water
• Refers to the concentration of SOLUTES
• Is a RELATIVE term, comparing two different
  solutions

Solute-substance that is dissolved Solvent-
substance solute in dissolved in Solution
solute solvent
53
What if there is a difference in concentration
but solute molecules cant move across a membrane?
WATER will move until concentrations reach
equilibrium
54
Animation http//www.ouhscphysio.org/humanphys/an
imations/osmosis1.swf
 See an animation Osmosis1
Animation
http//faculty.etsu.edu/currie/images/osmosis1.jpg
55
Concentration of water

• Direction of osmosis is determined by comparing
  total solute concentrations
• Hypertonic - more solute, less water
• Hypotonic - less solute, more water
• Isotonic - equal solute, equal water

water
net movement of water
56
Solute concentration
Greater outside than inside
Lower outside than inside
Equal outside and inside
HYPERTONIC
HYPOTONIC
ISOTONIC
What will happen to an animal cell placed in
different solutions?
57
OSMOSIS
Animation from http//www.ouhscphysio.org/humanph
ys/animations/osmosis3.swf
See an animationOsmosis3
Choose Blood Hypotonic link
Video

• HYPOTONIC Concentration outside cell is
  ________________ inside the cellMore water
  enters than leaves cell so cellwill
  ___________________

LESS THAN
swell and possibly burst
58
OSMOSIS
Animation from http//www.ouhscphysio.org/humanph
ys/animations/osmosis4.swf
See an animation OSMOSIS 4

• HYPERTONIC Concentration outside cell is
  ____________________ inside cell
• More water leaves cell than enters so cell
  ____________

GREATER THAN
shrinks
Choose Blood Hypertonic link
Video
59

• Remember
• Cells try to maintain stable internal conditions
  
• ____________________

HOMEOSTASIS
http//bioweb.wku.edu/courses/biol121/Osmosis/Osmo
sis.asp
So an animal cell in ISOTONIC conditions stays
same size
Water entering water leaving
Video
Choose Blood Isotonic link
60
Animal cells
CYTOLYSIS
CRENATION
http//www.stchs.org/science/courses/sbioa/metener
gy/bloodcells.gif
61
Plant cells
http//www.stchs.org/science/courses/sbioa/metener
gy/aplantturgor.gif
Cell wall keeps plant cell from bursting
PLASMOLYSIS
62
Managing water balance

• Isotonic
• animal cell immersed in isotonic solution
• blood cells in blood
• no net movement of water across plasma membrane
• water flows across membrane, at same rate in both
  directions
• volume of cell is stable

63
Osmosis
.05 M
.03 M
Cell (compared to beaker) ? hypertonic or
hypotonic Beaker (compared to cell) ? hypertonic
or hypotonic Which way does the water flow? ? in
or out of cell
64
http//www.biology4kids.com/files/cell_vacuole.htm
l
Loss of water from central vacuole plants
wilt Vacuole full of water gives plant support
(turgor pressure) Turgid very firm Flaccid
limp
65
HYPOTONICSitting in the bathtub makes your
fingers plump up and get pruny
Grocery stores spray water on their veggies to
plump them up
66
If cells cant maintain stable internal
conditions . . . damage can result and cells can
die.
http//www.the-aps.org/education/lot/cell/Quiz.htm
67
Cell survival depends on balancing water uptake
loss OSMOREGULATION
http//www.microscopy-uk.org.uk/mag/imgjun99/vidju
n1.gif
Paramecium vs. pond water Paramecium is
hypertonic H2O continually enters cell to solve
problem, specialized organelle, contractile
vacuole
68
Drink salt water ACTIVELY pump ions OUTUrinate
less frequently
Gills ACTIVELY pump ions inUrinate frequently