Download The Cell Membrane

Division Ave High School
Ms. Foglia
AP Biology
https://youtu.be/y31DlJ6uGgE
Journal Diagrams
 Shark book pg. 82
The Cell Membrane
 Wolves book pg. 88-89

AP Biology
AP Biology
Fluid Mosaic Model – Cell Membrane
Cell Membrane Proteins
AP Biology
AP Biology
Phospholipids
 Phosphate head

Phosphate
“attracted to water”
hydrophobic
 Arranged as a bilayer
Arranged as a Phospholipid bilayer
 Serves as a cellular barrier / border
sugar
hydrophilic
 Fatty acid tails

Membrane Proteins
 Copy table
Fatty acid
“repelled by water”
H2O
salt
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
impermeable to polar molecules
polar
hydrophilic
heads
waste
AP Biology
lipids
AP Biology
1
Division Ave High School
Ms. Foglia
AP Biology
Cell membrane defines cell
 Cell membrane separates living cell from
aqueous environment


membrane must be fluid & flexible

% unsaturated fatty acids in phospholipids
 about as fluid as thick salad oil
thin barrier = 8nm thick
 Controls traffic in & out of the cell

Membrane fat composition varies
 Fat composition affects flexibility
 keep membrane less viscous
 cold-adapted organisms, like winter wheat
 increase % in autumn
allows some substances to cross more
easily than others
 hydrophobic (nonpolar) vs. hydrophilic (polar)

AP Biology
AP Biology
Permeability to polar molecules?
 Membrane becomes semi-permeable via
specific channels allow specific material
across cell membrane
inside cell
NH
AP
Biology
3
H2O
salt
aa

create semi-permeabe channels
lipid bilayer
membrane
protein channels
in lipid bilyer membrane
sugar
outside cell
Cell membrane must be more than lipids…
 In 1972, S.J. Singer & G. Nicolson
proposed that membrane proteins are
inserted into the phospholipid bilayer
It’s like a fluid…
It’s like a mosaic…
It’s the
Fluid Mosaic Model!
Cell membrane is more than lipids…
 Transmembrane proteins embedded in
phospholipid bilayer
protein channels

cholesterol in membrane
AP Biology
Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
https://youtu.be/Qqsf_UJcfBc
Glycoprotein
Extracellular fluid
Glycolipid
Phospholipids
Cholesterol
Peripheral
protein
AP Biology
Transmembrane
proteins
Cytoplasm
Filaments of
cytoskeleton
AP Biology
1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model
2
Division Ave High School
Ms. Foglia
AP Biology
Classes of amino acids
Why are
proteins the perfect
molecule to build structures
in the cell membrane?
What do these amino acids have in common?
nonpolar & hydrophobic
AP Biology
2007-2008
Classes of amino acids
What do these amino acids have in common?
AP Biology
Protein domains anchor molecule
 Within membrane

Polar areas
of protein
nonpolar amino acids
 hydrophobic
 anchors protein
into membrane
 On outer surfaces of
membrane in fluid

polar amino acids
 hydrophilic
 extend into
AP Biology
polar & hydrophilic
Membrane Proteins
 Proteins determine membrane’s specific functions

cell membrane & organelle membranes each have
unique collections of proteins
 Classes of membrane proteins:

peripheral proteins
 loosely bound to surface of membrane
 ex: cell surface identity marker (antigens)

integral proteins
 penetrate lipid bilayer, usually across whole membrane
 transmembrane protein
 ex: transport proteins
AP Biology
extracellular fluid &
into cytosol
Nonpolar areas of protein
Contains Different Types of Proteins
 Channel proteins
 Protein Pumps
 Adhesion proteins
 Cell-to-Cell Communication
proteins
 Hormone Receptor proteins
 Immobilized Enzymes
 channels, permeases (pumps)
AP Biology
AP Biology
3
Division Ave High School
Ms. Foglia
AP Biology
Channel proteins
Protein Pumps
 Integral protein
 Transports molecules across membranes by
 Integral protein: embedded across bi-layer
 Allows for movement of molecules across
changing shape, requires energy input
cell membrane
AP Biology
AP Biology
Adhesion proteins
 Connects internal

AP Biology
cytoskeleton to
external points of
attachment
Secures cells of
multi-cellular
organisms in place
AP Biology
Cell-to-Cell Communication proteins
Hormone Receptor proteins
 Cells within the
 Hormones bind to cell


same organism use
membrane proteins
to recognize each
other
Often use
glycoproteins
Major importance to
immune system
AP Biology
surface proteins
 Initiates a series of
reactions within cell
 Results in cellular
response such as
gene expression
(making more or less
of a protein)
AP Biology
4
Division Ave High School
Ms. Foglia
AP Biology
Many Functions of Membrane Proteins
Immobilized Enzymes
“Channel”
Outside
 Many enzymes used
Plasma
membrane
by cells are
embedded within
membranes
 Useful in keeping
certain reactions in
specific parts of the
cell
Inside
Transporter
Enzyme
activity
Cell surface
receptor
Cell adhesion
Attachment to the
cytoskeleton
“Antigen”
AP Biology
AP Biology
Cell surface
identity marker
+
H
H+
Examples
Retinal
chromophore
NH2
aquaporin =
water channel in bacteria
Porin monomer
H2O
b-pleated sheets
Bacterial
outer
membrane
Nonpolar
(hydrophobic)
a-helices in the
cell membrane
COOH
H++
H
Cytoplasm
proton pump channel
in photosynthetic bacteria
H O
AP Biology 2
function through
conformational change =
protein changes shape
AP Biology
Membrane carbohydrates
 Play a key role in cell-cell recognition

ability of a cell to distinguish one cell
from another
OSMOSIS
 antigens
important in organ &
tissue development
 basis for rejection of
foreign cells by
immune system

AP Biology
Movement of water across
the cell membrane
AP Biology
2007-2008
5
Division Ave High School
Ms. Foglia
AP Biology
 Movement of WATER (solvent) across a
Osmosis is just diffusion of water
 Water is very important to life,

so we talk about water separately
Diffusion of water from
LOW concentration of solute to
HIGH concentration of solute

across a
semi-permeable
membrane
selectively permeable membrane
Osmosis
Hypertonic
• Above/High
• Solution with the higher
concentration of solute
Isotonic
• Same/Equal
• Solutions have the same
concentration of a solute
Hypotonic
AP Biology
AP Biology
• Below/Low
• Solution with the lower
concentration of solute
Osmosis
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
AP Biology
hypotonic
hypertonic
net movement of water
AP Biology
Managing water balance
 Cell survival depends on balancing
water uptake & loss
AP Biology
AP Biology
freshwater
balanced
saltwater
6
Division Ave High School
Ms. Foglia
AP Biology
1
https://youtu.be/pahUt0RCKYc
Managing water balance
Pumping water out
 Contractile vacuole in Paramecium
 Hypotonic

a cell in fresh water

high concentration of water around cell
 problem: cell gains water,
swells & can burst
 example: Paramecium
KABOOM!
 ex: water continually enters
Paramecium cell
ATP
 solution: contractile vacuole
 pumps water out of cell
ATP
 ATP

No problem,
here
 turgid = full
 cell wall protects from bursting
plant cells
freshwater
AP Biology
2
AP Biology
3
Managing water balance
 Hypertonic
I’m shrinking,
Managing water balance
 Isotonic
a cell in salt water I’m shrinking!
 low concentration of water
around cell

animal cell immersed in
mild salt solution

no difference in concentration of
water between cell & environment
 problem: cell loses water &
 problem: none
can die
 example: shellfish
 solution: take up water or
pump out salt
I

plant cells
 no net movement of water

flows across membrane equally, in
both directions
I could
be better…
 cell in equilibrium
 volume of cell is stable
will
survive!
 example:
 plasmolysis = wilt
 can recover
blood cells in blood plasma
 slightly salty IV solution in hospital
saltwater
AP Biology
That’s
perfect!

AP Biology
balanced
https://youtu.be/JEYv5-8Akgw?t=1m2s
Aquaporins
 Water moves rapidly into & out of cells

Do you understand Osmosis…
evidence that there were water channels
 protein channels allowing flow of water
across cell membrane
.05 M
AP Biology
.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
AP Biology
7
Division Ave High School
Ms. Foglia
AP Biology
Water Potential (Ψ)
Water Potential (Ψ)
Water Potential = Pressure Potential + Solute Potential
Ψ =
Ψp
Ψs
+
 Pressure potential – exertion of pressure on a
solution
 Solute potential AP Biology
AP Biology
https://youtu.be/prfMUwjobo8
Diffusion across cell membrane
 Cell membrane is the boundary between
inside & outside…
DIFFUSION across the
Cell Membrane

separates cell from its environment
Can it be an impenetrable boundary?
OUT
IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
AP Biology
OUT
IN
waste
ammonia
salts
CO2
H2O
products
AP Biology
cell needs materials in & products or waste out
Diffusion
 2nd Law of Thermodynamics
governs biological systems

NO!
universe tends towards disorder (entropy)
Simple Diffusion
 Move from HIGH to LOW concentration


“passive transport”
no energy needed
movement of water
 Diffusion

AP Biology
movement from HIGH  LOW concentration
AP Biology
diffusion
osmosis
8
Division Ave High School
Ms. Foglia
AP Biology
Diffusion through phospholipid bilayer
Diffusion
 What molecules can get through directly?

fats & other lipids
inside cell
NH3
 What molecules can
lipid
salt
NOT get through
directly?

polar molecules

ions (charged)

large molecules
 H2O
outside cell
sugar aa
H2O
 salts, ammonia
 starches, proteins
AP Biology
AP Biology
Facilitated Diffusion
 Diffusion through protein channels


What Affects the Rate of Diffusion?
 Temperature
channels move specific molecules across
cell membrane
facilitated = with help
no energy needed


Warmer = faster
Colder = slower
open channel = fast transport
HIGH
 Concentration gradients
 Molecule size
LOW
AP Biology
“The Bouncer”
Active Transport
Active transport
 Cells may need to move molecules against
concentration gradient



AP Biology
conformational shape change transports solute
from one side of membrane to other
protein “pump”
“costs” energy = ATP LOW conformational change
 Many models & mechanisms
ATP
ATP
ATP
HIGH
AP Biology
“The Doorman”
AP Biology
antiport
symport
9
Division Ave High School
Ms. Foglia
AP Biology
Getting through cell membrane
Transport summary
 Passive Transport

simple
diffusion
Simple diffusion
 diffusion of nonpolar, hydrophobic molecules
 lipids
 HIGH  LOW concentration gradient

facilitated
diffusion
Facilitated transport
 diffusion of polar, hydrophilic molecules
 through a protein channel
 HIGH  LOW concentration gradient
 Active transport

diffusion against concentration gradient

uses a protein pump
requires ATP
 LOW  HIGH

active
transport
ATP
AP Biology
ATP
AP Biology
How about large molecules?
 Moving large molecules into & out of cell
Endocytosis
through vesicles & vacuoles
 endocytosis
phagocytosis

fuse with
lysosome for
digestion
 phagocytosis = “cellular eating”
 pinocytosis = “cellular drinking”

AP Biology
pinocytosis
non-specific
process
receptor-mediated
endocytosis
triggered by
molecular
signal
exocytosis
exocytosis
AP Biology
Videos
 Crash Course
https://youtu.be/dPKvHrD1eS4
 Membrane Transport
https://youtu.be/prfMUwjobo8
 Aquaporins
https://youtu.be/DFu86zguTZA
AP Biology
10