Transcript Transport Across Cell Membranes

Transport Across Cell
Membranes
CELL MEMBRANES
I. Cell membranes
A. Function – barrier that separates inside of cell
from the external environment
B. Cell membranes made mainly of:
1. Phospholipids – form bilayer
a. Hydrophilic heads
b. Hydrophobic fatty acid tails
2. Proteins
a. Some have sugar groups bound to them – glycoproteins
3. Cholesterol (animal cells only)
C. Consistency similar to olive oil
MEMBRANE STRUCTURE
Membrane Permeability
D. Permeability - what is
allowed to cross a barrier
1. Impermeable – nothing gets
through
2. Permeable – anything gets
through
3. Cell membranes are
semipermeable a. Some molecules cross freely
b. Some must be transported
across
Membrane Permeability
Membrane Permeability
a. Molecules that pass freely:
1. Small uncharged molecules like glycerol, ethanol
2. Small hydrophobic molecules like oxygen, carbon
dioxide
b. Molecules that must be transported:
1. Water
2. Macromolecules (proteins, sugars, etc..) too large
3. Ions like H+, Na+, Cl-, Ca++
MEMBRANES
• For cells to survive they must be able transport
materials (water, oxygen, food, waste products,
ions) into and out of the cells.
II. Transport mechanisms used by cells include
(handout):
A. Passive mechanisms (require no energy
expenditure)
1. Diffusion
2. Osmosis
3. Facilitated diffusion
B. Active transport (requires energy output)
1. Active transport
2. Endocytosis and exocytosis
Diffusion
A. Passive mechanisms – fueled by
concentration gradient
- Difference in concentration across a given
space
Diffusion
1. Diffusion - movement of a substance from a place of
higher concentration to a place of lower concentration
a. Remember, all molecules in constant, random motion unless
at absolute zero
b. If concentration gradient exists, there will be net movement
of substance in greater concentration until equilibrium (equal
concentration ) is reached.
Diffusion
• Animation
http://www.mhhe.com/biosci/esp/2001_gbi
o/folder_structure/ce/m3/s2/index.htm
Diffusion
c. Example – American pioneers
d. Rate of diffusion is related to kinetic energy and the size
of the gradient
1) Increased kinetic energy…
2) Large concentration gradient…
e. Demonstration
Diffusion
f. Diffusion is one way materials are moved in and
out of cells.
- Cytoplasm is mostly water containing dissolved
solutes (salts)
Diffusion
Gas exchange in the
lungs:
1) Oxygen follows its
concentration
gradient into the
capillary
2) Carbon dioxide
(waste) follows its
concentration
gradient into the
lung, is exhaled
Diffusion
g. Diffusion works very well over short distances
1) As size of cell increases, volume increases faster than
surface area
2) Cells remain relatively small because center of large
cells would not get adequate gas exchange, would die.
3) Multicellular organisms made up of many small cells
because they can be efficiently supplied by circulatory
system, even if deep inside organism.
Osmosis
2. Osmosis - diffusion (movement) of water (only)
across a semipermeable membrane
a. Water moves along its concentration gradient from an
area of high water concentration (less solute) to an
area of lower water concentration (more solute)
• Potato demonstration
Osmosis
a. Animation:
http://www.mhhe.com/biosci/esp/2001_gbio/folde
r_structure/ce/m3/s3/index.htm
b. Can generate significant osmotic pressure
-Turgor pressure in plants
Osmosis
c. 3 possibilities for direction of water movement in living cells:
1) Hypotonic environment: greater concentration of water
outside the cell than inside. Water enters, cell swells.
a) Animal cell bursts (lysis, rupture)
b) Plant cell – water pushes against cell wall, creating
turgor pressure.
- Helps plants stand up against gravity
- Cell wall protects from bursting
Osmosis
2) Hypertonic environment: greater concentration of water
inside cell. Water moves out, cell shrinks
a) Animal cell – shrivels up (crenation)
b) Plant cell – plasmolysis (low turgor pressure). Cell
membrane draws away from cell wall, plant wilts.
Osmosis
3) Isotonic: solute and water concentration is the same
inside and outside cell
a) At equilibrium, molecules continue to move across
membranes evenly (but there is no net movement)
b) Cell size and volume do not change
Osmosis
http://www.mhhe.com/biosci/esp/2001_gbio/folder_s
tructure/ce/m3/s3/index.htm
Osmosis
4) How do organisms that live in water deal with osmosis?
a) Freshwater animals…?
b) Marine (saltwater) organisms…?
c) Plants…?
FACILITATED DIFFUSION
3. Facilitated diffusion - passive
transport of specific substances
down their concentration
gradient by a carrier protein
a. Examples: water, glucose
ACTIVE TRANSPORT
B. Active transport - uses energy
(ATP) and a membrane
protein to move materials
against their concentration
gradient from an area of lower
to higher concentration
1. Used to move ions (Na+, Ca++,
Cl-, K+), amino acids, nucleotides
across the cell membrane
Active Transport
• Animation http://www.mhhe.com/biosci/esp/2001_gbi
o/folder_structure/ce/m3/s5/index.htm
Membrane-Assisted Transport
C. Membrane-assisted transport
uses energy to move large,
complex molecules across the cell
membrane
1. Large molecules like proteins, food,
or fluid droplets are packaged in
vesicles, then sent into or out of the
cell
2. Exocytosis – large products removed
from cell
a) Vesicle from inside cell fuses with
cell membrane to secrete its
contents
b) Examples: insulin, mucus
Membrane-Assisted Transport
3. Endocytosis moves large particles into a cell
a) Phagocytosis – particles
1) Cell membrane extends out, surrounds the material &
pinches off inside the cell making a vesicle
2) Used by amoeba to feed & white blood cells to kill
bacteria
b) Pinocytosis - Cell membrane surrounds fluid droplets
Membrane-Assisted Transport
Animation http://www.mhhe.com/biosci/esp/2001_gbi
o/folder_structure/ce/m3/s6/index.htm
Transport review
Membrane Transport
III. Real world examples:
A. Fresh produce
B. Wrinkled fingers and toes when swimming
C. Lungs
D. Destruction of bacteria, viruses by immune
system
Membrane Transport
Membrane Transport
E. Cystic fibrosis – remember symptoms? Cause?
a. Genetic mutation changes membrane protein controlling
Cl- ion exchange
b. Cl- ions retained in cell, along with water
Membrane Transport
c. Mucus too thick, clogs lungs (infections), pancreas
(trouble with digestion, poor growth), usually fatal by 2040 years old
d. Treatment – antibiotics, physical therapy (vest), diet,
enzymes, transplants
• Membrane-assisted transport activity
Homeostasis
• Homeostasis - maintaining a stable
internal environment even when external
conditions change
– Homes – furnace, a/c
– Cells – membrane transport
– Organisms – have systems that help maintain
relatively constant conditions inside the
organism
• Examples?
Homeostasis
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Temperature (sweat when hot, shiver when cold)
pH (buffers)
Nutrients (maintain level blood sugar)
Blood pressure
O2/CO2 levels (gas exchange, respiratory system)
Concentration of waste products (urinary system)
Homeostasis
– Maintaining homeostasis is critical to survival
of organisms!
– Look at 2 organ systems used by body to
maintain homeostasis
• Respiratory system (gas exchange)
• Excretory system (waste removal)
Respiration
I. Introduction
A. All organisms need constant supply of energy for…
B. Energy from food released through cellular
respiration (in the form of ???)
1. Requires O2
2. Generates CO2.
C. Organisms need a steady supply of O2 and a way to
get rid of CO2.
This is called respiration = breathing = gas exchange
Respiration
II. Water-dwelling organisms
A. Breathing (movement of O2 and CO2)
happens by diffusion across a membrane
B. Some O2 dissolved in water, but
concentration low (<1%), so organisms need
very efficient breathing mechanism
- Large surface area to volume ratio required for
efficient diffusion of O2
Respiration
C. Gills have very large surface area
1. Made of fine, threadlike filaments
2. Allow high rate of water flow and close contact between
water and gill surface
Respiration
3. Constant flow of water over gills + huge surface
area allows O2 to diffuse into extensive blood
supply, while CO2 diffuses out along concentration
gradients.
4. Blood then flows via circulatory system to all cells
in organism
Respiration
II. Land (terrestrial)
organisms
A. Differences/challenges
1. Air has 25-50 times higher
O2 concentration than water
2. But gases (O2 and CO2)
must be dissolved in water
for diffusion to occur
3. Therefore, gas exchange
can occur only on moist
surfaces
4. Land organisms must battle
water loss by evaporation
from moist respiratory
surfaces.
Respiration
B. Human respiratory system
1. To minimize water loss, many
land animals internalize
respiratory surface (lungs)
- Found in thoracic cavity with
heart
- Air is filtered, warmed and
humidified before entering
lungs
Respiration
• www.youtube.com/watch?v=DoSTehS7iq8
Respiration
2. Structures and
functions
a. Trachea (windpipe) –
tube reinforced with
cartilage that carries
air from pharynx to
bronchi.
b. Bronchi – branching
tubes that carry air into
(and out of) the lungs
Respiration
c. Alveoli (folds or pockets)
that maximize respiratory
surface area (thus
diffusion)
- Each lung has hundreds of
million alveoli
- Total surface area of all
alveoli in 1 person’s lungs
would cover a tennis court!
- Respiratory surfaces very thin
with many capillaries to
maximize diffusion of O2 and
CO2
Respiration
d. Diaphragm contracts, rib cage expands to
create larger volume and thus negative pressure
in thoracic cavity. Air rushes in to fill space. As
muscles relax, exhalation occurs.
Respiration
3. Respiratory system
disorder – asthma
a. Airway walls become
irritated, swollen and
very sensitive
b. Exposure to triggers
(allergens, smoke,
perfume, exercise or
illness) causes airways
to react and become
narrower.
c. Lungs get less air,
causing wheezing,
coughing, chest
tightness and difficulty
breathing
Respiration
d. Treatments (often
inhaled medicines)
- Fast acting medicines
that dilate the airways
- Longer acting medicines
like steroids to stabilize
airways, make them
less reactive
Respiration
C. Plants
1. Leaves covered with waxy cuticle to reduce water
loss from evaporation
2. Gases enter leaf through stomates on leaf surface
Respiration
- Stomates controlled by guard cells that are open when water
abundant, closed when water level low.
Waste Removal
I. Introduction
A. Nitrogen wastes
produced from protein
and nucleic acid
metabolism
1. Amino group (NH2)
removed prior to
complete catabolism
2. NH2 combines with a
hydrogen ion (H+) to
form ammonia (NH3).
This is a toxic
substance!
3. Many organisms
convert ammonia to
urea, which is less toxic
Waste Removal
B. Methods of waste removal
1. Diffusion: Simple aquatic organisms (sponge)
excrete wastes through external surfaces
2. Excretory system: Larger, more complex
organisms have specialized organs that:
a. Remove and concentrate wastes from body fluids
b. Return other substances to body fluids as necessary for
homeostasis
c. Eliminate excretory products from the body
Waste Removal
C. Human excretory
system consists of:
1. Kidneys – filter waste
from blood and collect it
as urine.
- Entire blood supply of
human body (about
5.5 L) filtered once
every 5 minutes!
2. Ureters – transport
urine from kidney to
bladder
3. Bladder – stores urine
4. Urethra – conducts
urine out of body
Waste Removal
D. Kidney
1. Nephron is kidney's functional unit
a. 1 million per kidney
b. Components
1) Glomerulus
2) Tubules
3) Loop of Henle
Waste Removal
2. Functions
a. Filtration – fluid part
of blood forced into
nephron by pressure
b. Reabsorption nephron cells process
filtered material,
return valuable
substances (salt,
glucose, amino acids,
water) to blood, send
wastes for excretion
• Kidney animation:
http://www.biologymad.com/resources/kidne
y.swf
Respiration
D. Countercurrent
exchange –
a. Oxygenated water and
blood flow in opposite
directions
b. Allows over 80% of the
initial concentration
difference to be
transferred
C. Maximizes efficiency of
gas exchange