The Cell Membrane & Movement of Materials In & Out of Cells PACKET #11 Sunday, February 26, 2017 1
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
The Cell Membrane &
Movement of Materials In &
Out of CellsPACKET #11
Sun
day, F
ebru
ary
26, 2
017
1
Introduction I
Biological membranes are phospholipid bilayers with associated proteins.
Current data support a fluid mosaic model of the cell membrane.
In 1935, Davson and Daniellastated that phospholipids form a membrane two molecules thick.
Singer and Nicholson developed the fluid mosaic model in 1972.
Furthermore, the membrane is only 10nm thick.
Sunday,
February 26,
2017
2
Introduction II
Biological membranes
fuse and form closed
vesicles.
Endocytosis and
exocytosis are products of
membrane fusion.
More later.
Sunday,
February 26,
2017
3
Cell Membrane
Sunday,
February 26,
2017
4
Properties of
Phospholipids
Sunday, February 26, 20175
Phospholipids are Amphipathic
Molecules with both
hydrophilic and hydrophobic
properties are termed
amphipathic
Other examples
Sterols
Cholesterol
Glycolipids
Hydrophilic (sugar) head
The aqueous environment
inside and outside the cell
prevent membrane lipids from
escaping the bilayerSunday,
February 26,
2017
6
Fluidity of the Membrane
Depends on Two Main Features
Saturated vs. Unsaturated Fatty
Acid tails (phopsholipids)
Unsaturated more fluid
Kinks prevent molecules from
packing together
Cholesterol
Absent in plants, yeast and bacteria
Fill the holes produced by kinks
Stiffens bilayer and makes it less
fluid and permeable.
Sunday,
February 26,
2017
7
Fluidity of the Cell Membrane II
Sunday,
February 26,
2017
8
Proteins of the
Cell Membrane
Sunday, February 26, 20179
Functions of Membrane Proteins
• Cell Membrane
Proteins
• Six different
functions
Sunday,
February 26,
2017
10
Functions of Proteins
Transport
Enzyme Activity
Signal Transduction
Cell to cell Recognition
Intercellular Joining
Attachment to Cytoskeleton
Integral vs. Peripheral Proteins
Integral Proteins
A protein that is firmly
anchored in the plasma
membrane via interactions
between its hydrophobic
domains and the membrane
phospholipids
Directly attached to the
membrane
Sunday,
February 26,
2017
11
Integral vs. Peripheral Proteins
Peripheral Proteins
Not embedded in the lipid
bilayer
Can be released from the
membrane by relatively
gentle extraction
procedures
Possible key player in cell
communication.
Sunday,
February 26,
2017
12
Transmembrane Protein
Protein that spans the entire
membrane
Have both hydrophobic and
hydrophilic regions
Alpha helical secondary
structure is normally the
hydrophobic regions of the
protein
Sunday,
February 26,
2017
13
Diffusion
Sunday,
February 26,
2017
14
Introduction
Atoms and molecules,
above absolute zero,
exhibit motion.
This random motion
allows particles to move
from an area of higher
concentration to an area
of lower concentration in
an attempt to reach
equilibrium. Sunday,
February 26,
2017
15
Introduction
There are 5 ways of transporting materials across the cell
membrane
Diffusion
Regular & Facilitated
Passive Transport
Active transport
Osmosis
Phagocytosis
Pinocytosis
Sunday,
February 26,
2017
16
Categories of Diffusion I
Regular Diffusion
Movement of molecules down the
concentration gradient
High to low
Facilitated Diffusion
Movement of molecules down the
concentration gradient via a channel
In cells, these channels are found in
proteins
More to come later
Active transport
Movement of molecules against the
concentration gradient via channels and
with the use of energy.
Low to high
Categories of Diffusion
Passive Transport
Regular Diffusion
Facilitated Diffusion
Active Transport
OsmosisSpecial type of
diffusion
Phagocytosis
Pinocytosis
Sunday,
February 26,
2017
17
Diffusion
Sunday, February 26, 201718
Diffusion
The movement of a
substance from an area of
high concentration to an area
of low concentration
The difference in
concentration between the two
regions is known as the
concentration gradient
Sunday,
February 26,
2017
19
Rate of Diffusion
The rate of diffusion depends on
The difference in concentration
The greater the concentration gradient, the faster the process
The distance between the two regions
Smaller distance means faster process
The area
If the total “area” is increased, the faster the process
The size of the molecules
Small and fat-soluble molecules will diffuse faster
Sunday,
February 26,
2017
20
Passive Transport
Regular vs. Facilitated Diffusion
“Regular” Diffusion
Movement of molecules is from high concentration to low concentration
No proteins are used
No energy (ATP) is required
Facilitated Diffusion
Movement of molecules is from high concentration to low concentration
Proteins are used
No energy (ATP) is required
Sunday,
February 26,
2017
21
Active Transport
Materials are moved against
the concentration gradient
Molecules move from an area
of low concentration to an
area of high concentration
Proteins are used to move
materials across the
membrane
Energy is also used.
Sunday,
February 26,
2017
22
Active Transport II
Cells carry our active transport in
three ways
ATP driven pumps
Couple uphill transport with
hydrolysis of ATP
Coupled transport (co-transport)*
Light driven pumps
Found mainly in bacterial cells
Input of energy from light
Bacteriohodopsin
Active Transport
ATP PumpsCo-
TransportLight Driven
Pumps
Bacteria Cells
Sunday,
February 26,
2017
23
Active Transport ATP DRIVEN PUMPS
Sunday,
February 26,
201724
Active Transport—ATP Driven Pumps
Energy is used
Because energy is used, cells
carrying out active transport have
A high respiratory rate
Many mitochondria
A high concentration/reserve of
ATP
Any factor which reduces or stops
cell respiration will stop active
transport
Cyanide
Sunday,
February 26,
2017
25
Co-TransportINVOLVES ACTIVE
TRANSPORT
Sunday,
February 26,
201726
Co-Transport I
The Active Transport of H+ ions
Hydrogen gradients are used to
drive membrane transport in
plants, fungi and bacteria
These are not sodium-potassium
pumps
Sunday,
February 26,
2017
27
Co-Transport II
The Active Transport of H+ ions II
Hydrogen pumps, found in the
plasma membrane, pump H+ out
of the cell
This can also be described as
primary active transport
Setting up an electrochemical
gradient
Sunday,
February 26,
2017
28
Co-Transport III
Pump creates an acidic pH in the
medium surrounding the cell
H+ re-enters the cell via a
cotransporter
Usually transports a substance
in addition to the H+
The uptake of sugars and amino
acids, into bacterial cells for
example, are driven by the
presence H+ pumps
Sunday,
February 26,
2017
29
Active
Transport—Light
Driven Pumps
H+ Pumps in
Bacteria
Sunday,
February 26,
201730
Active Transport—Light Driven Pumps
H+ Pumps in Bacteria
In some photosynthetic bacteria, the H+ gradient is created by
the activity of light driven H+ pumps such as
bacteriorhodopsin.
In plants and fungi and many other bacteria, the gradient is set up
by ATPases in their plasma membrane
Sunday,
February 26,
2017
31
Types of Ports
Sunday,
February 26,
2017
32
Types of Ports
Sunday,
February 26,
2017
33
Review so far…
Movement of Materials in/out
of Cells
Passive Transport
Regular Diffusion
Facilitated Diffusion
Active Transport
Sunday,
February 26,
2017
34
Sodium
Potassium Pump
Sunday, February 26, 201735
Electrogenic Pump
These pumps are used to move
electrically charged molecules
Small organic or inorganic ions
MOST cell membranes have a
voltage across them and results in
a difference in electric potential on
each side—i.e. the membrane potential.
Sunday,
February 26,
2017
36
Electrogenic Pump
The membrane potential exerts a force on any molecule that carries an electrical charge
Cytoplasmic side is USUALLYat a negative potential relative to the outside
This tends to pull positively charged solutes into the cell and drive negative charged ones outside the cell
Net driving force = electrochemical gradient
Sunday,
February 26,
2017
37
The Sodium Potassium Pump
For some, ions, voltage
and concentration
gradients work in the
same direction
Sodium Potassium Pump
Sunday,
February 26,
2017
38
Movement of
GlucosePUTTING IT ALL
TOGETHER
Sunday, February 26, 201739
The Movement of Glucose
The Na+ gradient generated by the sodium-potassium pump can be used to driveactive transport of a 2nd
molecule.
The downhill movement of the first solute down provides the energy to drive the uphill transport of the second.
Sunday,
February 26,
2017
40
OsmosisSPECIAL CASE OF
DIFFUSION
Sunday,
February 26,
2017
41
Osmosis
Concise Definition
The diffusion of water (liquid solvent) across a selectively permeable membrane
Detailed Definition
Transfer of a liquid solvent through a semi permeable membrane, that does not allow dissolved solids (solutes) to pass from an area of high concentration to an area of low concentration
Sunday,
February 26,
2017
42
Osmotic Pressure,
Osmotic Potential
& Solute Potential
Sunday,
February 26,
2017
43
Osmotic Pressure
Osmotic Pressure
Is a measure of the tendency of water to move INTO a solution.
The driving force for the water and is the differencein water pressure on both sides of the membrane.
The differences in pressure provides a net pressure that is exerted by the flow of water as it moves through the semi-permeable membrane.
Class Illustration
Sunday,
February 26,
2017
44
Osmotic Potential = Osmotic Pressure
Osmotic Potential
Difference in osmotic pressure that draws water from an area of less osmotic pressure to an area of greater osmotic pressure.
The potential of a solution to pull in water
Value is always negative
The more concentrated the solution, the more negative its osmotic potential
Sunday,
February 26,
2017
45
Osmotic Potential = Osmotic Pressure
= Solute Potential
The presence of solutes, in the solutions, impact the direction of the movement of water.
The ability of a solution to pull in water depends on the number of solute particles present.
The higher the amount of solutes in the solution, the lower the solute potential.
The solution is more concentrated.
Remember, from previous slide, the value is always suppose to be negative.
Sunday,
February 26,
2017
46
Osmotic Potential = Osmotic Pressure
= Solute Potential
All three terms represent a measure of the ability of a solution to pull in water.
The value is always negative.
The more solutes present, the more negative the value.
Represented by s
Sunday,
February 26,
2017
47
Osmotic Potential = Osmotic Pressure
= Solute Potential
When two solutions have the same osmotic potential, they are said to be isotonic.
Where one solution has a greater osmotic potentialcompared to the other, it is described as being hypertonic.
i.e. It is more concentrated.
The solution with the lower osmotic potential is described as being hypotonic.
Less concentrated.
Sunday,
February 26,
2017
48
Pressure Potential
Solutions/Water are also under the influence of external pressures.
These external pressures are measure as pressure potential.
This force (pressure) is not the same as the one caused by the movement of the liquid solvent (water).
Represented by p
Negative or positive depending on conditions.
Sunday,
February 26,
2017
49
Water Potential
Measure of the tendency of water to leave a solution.
Combination of the sumof osmotic potential/solute potential and pressure potential.
= s + p
Sunday,
February 26,
2017
50
Water Potential II
When measuring the
water potential of two
solutions, the solution
with the lower water
potential receives water
from the solution with
higher water potential
Osmosis!
Sunday,
February 26,
2017
51
Cells and Osmosis
Sunday,
February 26,
2017
52
Pressure Potential in Plant Cells
In plant cells, the cell contents
press the plasma membrane
against the cell wall—
producing an external force
called turgor pressure.
Results in a turgid plant cell
Pressure potential is positive
Sunday,
February 26,
2017
53
Pressure Potential in Plant Cells II
Special plant cells that make up
xylem, tissue that conducts
water in plants, undergoes
transpiration.
This transpiration results in a
negative pressure potential.
Sunday,
February 26,
2017
54
Cells & Osmosis
Sunday,
February 26,
2017
55
Cells & Osmosis
Sunday,
February 26,
2017
56
Phagocytosis,
Pinocytosis,
Endocytosis and
Exocytosis
Sunday, February 26, 201757
Phagocytosis
The take up of large particles by cells via vesicles formed
in the plasma membrane
The cell invaginates to form a depression in which
particles are contained
This then pinches off to form a vacuole
White blood cells
Neutrophils
Monocytes
Sunday,
February 26,
2017
58
Pinocytosis
The take up of liquids rather than solids
Vacuoles are smaller than those used during
phagocytosis
Sunday,
February 26,
2017
59
Endocytosis vs. Exocytosis
Both phagocytosis and
pinocytosis involve the
taking of materials into
the cell in bulk.
These are examples of
endocytosis
The removal of materials
from the cell in bulk is
called exocytosis.
Sunday,
February 26,
2017
60
Review
Sunday,
February 26,
2017
61
Related Documents
