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Membrane Function
– Working cells control the transport of materials to
and from the environment with membranes.
Transport
of materials
Membrane Function
– A closer look at our membranes
How do molecules cross a
cellular membrane?
• Many small non-polar molecules can pass by
diffusion
– Oxygen (O2), Carbon Dioxide (CO2)
– Water (H2O), although polar, is small enough to pass through
• Other charged and larger polar molecules
cannot pass through and need membrane
transport processes to do so.
– Ions: K+, Na+, H+
– Small hydrophilic molecules like glucose, amino acids,
nucleotides
– Macromolecules like proteins and RNA
Passive Transport:
Diffusion Across Membranes
– Molecules contain heat energy.
• They vibrate and wander randomly - Brownian
Motion. http://sv.berkeley.edu/chemicalinteractions/menu.html
– Diffusion is one result of the movement of
molecules.
• Molecules tend to spread into the available space.
• Diffusion is passive transport; no energy is needed.
• Water and small non-polar molecules like O2, CO2
travel across cell membranes through passive
diffusion.
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html
Osmosis and Water Balance
in Cells
– Osmosis is the passive transport of water
across a selectively permeable membrane.
[solute]
[water]
= [solute]
= [water]
[solute]
[water]
–http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
Lab 3 - Osmosis and Diffusion
• Osmosis evidence - the Egg!
–
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
• Hypothesis:
– The solution that is hypertonic relative to the egg will…
– The solution that is hypotonic relative to the egg will…
• Prediction:
– If …[organize what you know and how you are testing your
idea]
– Then …[predict your experimental result - what data will you
actually have?]
– Because …[general principles about osmosis]
Lab 3 - Osmosis and Diffusion
• Constructing a scientific argument
– Re-state your claim/hypothesis
– Support or refute it with evidence or counterevidence from
• Verifiable observations,
• Verifiable measurements, and/or
• Reliable resources, other people’s data
– If claim/hypothesis refuted, state an alternative
hypothesis
Lab 3 - Osmosis and Diffusion
• Plasmolysis
– View of Elodea cells
Plasmolysis
Water Balance in Cells
– Osmoregulation is the control of water balance.
• Sodium-potassium pump essential to regulate cell volume
through control of osmosis in many animal cells.
– Water balance in plant cells is different.
• They have rigid cell walls.
• They are at the mercy of the environment.
Turgid
Flaccid
Passive Transport:
Diffusion Across Membranes
– Molecules contain heat energy.
• They vibrate and wander randomly - Brownian
Motion. http://sv.berkeley.edu/chemicalinteractions/menu.html
– Diffusion is one result of the movement of
molecules.
• Molecules tend to spread into the available space.
• Diffusion is passive transport; no energy is needed.
• Water and small non-polar molecules like O2, CO2
travel across cell membranes through passive
diffusion.
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html
– Another type of passive transport is
facilitated diffusion, the transport of some
substances by specific transport proteins
that act as selective corridors.
– Food molecule monomers like glucose and
amino acids travel across this way.
•Facilitated diffusion
–http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html
Active Transport: The Pumping of
Molecules Across Membranes
– Active transport requires energy to move
molecules across a membrane.
– Ions like Na+, K+, and H+ are often pumped
across membranes against their concentration
gradients. This requires active transport.
•Active Transport
–http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
Other Types of Transport Exocytosis and Endocytosis:
Traffic of Large Molecules
– Exocytosis:
Secretes
substances
outside of the
cell.
– Endocytosis:
Takes
material into
the cell.
– Phagocytosis and
Pinocytosis
– Receptor-mediated endocytosis
• Is triggered by the binding of external
molecules to membrane proteins.
OK, so now we know how
molecules get into and out of
the cell.
How do we obtain energy from
those food molecules once
they are in there????
Flow of Energy through
Cellular Respiration (Ch6)
Cellular Respiration:
Feeling the Burn
– When you exercise,
• Muscles need energy in order to perform work.
• Your cells use oxygen to release energy from
food molecules.
Picture from http://www.camping-field-guide.com/roasted-marshmallow.html
Some Basic Energy Concepts
– What is energy?
– Energy is defined as the capacity to perform work.
• Work is done when an object moves against an opposing
force.
– Kinetic energy is the energy of motion.
– Potential energy is stored energy.
Conservation of Energy
–Energy can be changed from one form to another.
•However, it cannot be created or destroyed.
•This is the conservation of energy principle.
Chemical Energy:
Cellular
Respiration
Combustion
a form of potential energy found in fuels
Living cells and automobile engines use the same basic
process to make chemical energy do work.
Chemical Reactions
– Cells constantly rearrange molecules by
breaking and forming chemical bonds.
• These processes are called chemical reactions.
– Chemical reactions cannot create or destroy
matter,
• They only rearrange it.
Chemical Reactions
Chemical reactions can store energy in or
release energy from chemical bonds
Energy released
all at once
in explosive reaction
Chemical Energy:
Cellular
Respiration
Combustion
a form of potential energy found in fuels
Living cells and automobile engines use the same basic
process to make chemical energy do work.
Heat
• Is a type of kinetic energy.
• Is also a waste product of
all energy conversions.
Heat vs Temperature
-->Heat is the amount of energy in a system
-->Temperature is the average speed of the molecules in
the system
•
http://sv.berkeley.edu/chemicalinteractions/menu.html
Water needs a lot of heat energy to raise its temperature
because it needs to have energy to break the hydrogen
bonds between them so that the molecules can speed
up.
Conservation of Energy
–Energy can be changed from one form to another.
•However, it cannot be created or destroyed.
•This is the conservation of energy principle.
Energy is converted
to heat (air friction,
vibration of
molecules in the
steps)
Energy is
converted to
heat (air friction,
water molecule
movement)
Another example of heat
generated during conversion
of chemical potential energy to
kinetic energy
Energy derived from food
molecules (chemical energy)
is converted to muscle
movement (kinetic energy).
This conversion generates
heat energy as a
waste product.
Food Calories
– A calorie is the amount of energy that raises
the temperature of one gram of water by one
degree Celsius.
– The kilocalorie (or Calorie with capital “C”) is
• 1,000 calories.
• The unit used to measure the energy in food.
Potential (Chemical) Energy
In Foods
Kinetic Energy Used
by Activities
Mitochondria and Cellular Respiration
– The chemical energy of organic molecules
is released in cellular respiration in the
mitochondria. This energy is stored as
another form of chemical energy, ATP.
Chemical Energy:
Cellular
Respiration
Combustion
a form of potential energy found in fuels
Living cells and automobile engines use the same basic
process to make chemical energy do work.
Cellular Respiration: Aerobic Harvest
of Food Energy
– Cellular respiration
• Is the main way that chemical energy is
harvested from food and converted to ATP.
• Is an aerobic process—it requires oxygen.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Relationship between Cellular Respiration and
Breathing
– Cellular respiration
and breathing are
closely related.
• Cellular respiration
requires a cell to
exchange gases
with its
surroundings.
• Breathing
exchanges these
gases between the
blood and outside
air.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
The Overall Equation for Cellular Respiration
– A common fuel molecule for cellular
respiration is glucose.
• The overall equation for what happens to
glucose during cellular respiration
enzymes
Reactants
Products
The Role of Oxygen in
Cellular Respiration
Redox reactions: a transfer of electrons
– Why does electron transfer to oxygen release energy?
• It’s all in the chemical bonds!
– Electrons held more closely to its atomic nucleus have lower
energy than those held further away.
– Oxygen LOVES electrons and keeps them close.
– Thus, C-H and C-C covalent bonds have more energy than an O-H
covalent bond
– Glucose has many C-H and C-C bonds.
– Water has two O-H bonds.
– The energy in the chemical bonds of glucose is greater than the
energy in the chemical bonds of water, therefore….
• When electrons and H+ move from glucose to oxygen to form
water, it is as though they were falling, thus, releasing their
potential energy.
Higher energy bonds
Lower
energy
bonds
– Why does electron transfer to oxygen release energy?
• It’s all in the chemical bonds!
– Electrons held more closely to its atomic nucleus have lower
energy than those held further away.
– Oxygen LOVES electrons and keeps them close.
– Thus, C-H and C-C covalent bonds have more energy than an O-H
covalent bond
– Glucose has many C-H and C-C bonds.
– Water has two O-H bonds.
– The energy in the chemical bonds of glucose is greater than the
energy in the chemical bonds of water, therefore….
• When electrons and H+ move from glucose to oxygen to form
water, it is as though they were falling, thus, releasing their
potential energy.
Higher energy bonds
Lower
energy
bonds
– Why does electron transfer to oxygen release energy?
• It’s all in the chemical bonds!
– Electrons held more closely to its atomic nucleus have lower
energy than those held further away.
– Oxygen LOVES electrons and keeps them close.
– Thus, C-H and C-C covalent bonds have more energy than an O-H
covalent bond
– Glucose has many C-H and C-C bonds.
– Water has two O-H bonds.
– The energy in the chemical bonds of glucose is greater than the
energy in the chemical bonds of water, therefore….
• When electrons and H+ move from glucose to oxygen to form
water, it is as though they were falling, thus, releasing their
potential energy.
Higher energy bonds
Lower
energy
bonds
NADH and Electron Transport Chains
– The path that electrons take on their way down from glucose
to oxygen involves many steps in order to release the energy
a little at a time instead of all at once.
Energy released
all at once
in explosive reaction
Energy released
a little at a time
in cellular respiration
– The first step is an electron
acceptor called NAD+.
• The transfer of electrons from
organic fuel to NAD+ reduces it
(gains electrons) to NADH.
– The rest of the path consists of
an electron transport chain.
• This chain involves a series of
redox reactions (gaining and
losing electrons).
• These lead ultimately to the
production of large amounts of
ATP.
The Metabolic Pathway of Cellular Respiration
– Cellular respiration is an
example of a metabolic
pathway,
• A series of chemical
reactions in cells carried
out by enzymes!
– All of the reactions
involved in cellular
respiration can be
grouped into three main
stages:
• Glycolysis
• The citric acid cycle
• Electron transport
Enzymes
– Metabolism is the sum total of all chemical
reactions that occur in organisms.
– Few metabolic reactions occur without the
assistance of enzymes.
Phospholipase A2
Active site: glsgs
Activation Energy
– Activation energy
• Is the energy that activates the reactants in a
chemical reaction.
• Triggers a chemical reaction to proceed.
– Enzymes
• Lower the activation energy for chemical reactions by
putting stress on the molecules.
Induced Fit
– Each enzyme is very selective.
• It catalyzes specific reactions, or speeds up
reaction rates without being consumed.
– Each enzyme recognizes a specific substrate.
• The active site fits to the substrate, and the enzyme
changes shape slightly.
• This interaction is
called induced fit.
• Enzymes can
function over and
over again.
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html
Chemical Energy:
Cellular
Respiration
Combustion
a form of potential energy found in fuels
Living cells and automobile engines use the same basic
process to make chemical energy do work.
About 60% of your energy generates body heat.
Why are we so inefficient?…Or are we?
What do we need body heat for?….
The Metabolic Pathway of Cellular Respiration
– Cellular respiration is an
example of a metabolic
pathway,
• A series of chemical
reactions in cells carried
out by enzymes!
– All of the reactions
involved in cellular
respiration can be
grouped into three main
stages:
• Glycolysis
• The citric acid cycle
• Electron transport
Stage 1: Glycolysis
– In the cytosol: A molecule of glucose is
split into two molecules of pyruvic acid.
– 2 ATP and 2 NADH are generated
Stage 2: The Citric Acid Cycle
– In the mitochondria: The citric acid cycle
completes the breakdown of sugar into
CO2, high-energy electrons, and H+
– In the mitochondria: For the citric acid
cycle, pyruvic acid from glycolysis is first
“prepped” into a usable form, Acetyl CoA.
– In the mitochondria: The citric acid cycle extracts
the energy of sugar by breaking the acetic acid
molecules all the way down to CO2.
•The cycle uses
some of this
energy to make
ATP.
•High-energy
electrons are
carried away by
NADH and
FADH2.
Stage 3: Electron Transport
– In the mitochondria: Electron transport
releases the energy your cells need to
make most of their ATP.
– The molecules of electron transport chains are
built into the inner membranes of mitochondria.
• The chain functions as a chemical machine that uses
energy released by the “fall” of electrons to pump
hydrogen ions across the inner mitochondrial
membrane.
• These ions store potential energy.
– When the hydrogen ions flow back through
the membrane, they release energy.
• The ions flow through ATP synthase.
• ATP synthase takes the energy from this flow,
and synthesizes ATP.
The Versatility of Cellular Respiration
– Cellular respiration can “burn” all sorts of
food molecules:
Adding Up the ATP from Cellular Respiration
The Structure of ATP
– ATP (adenosine triphosphate)
• Consists of adenosine plus a tail of three
phosphate groups.
• Is broken down to ADP, accompanied by the
release of energy.
Phosphate Transfer
– ATP can energize other molecules by
transferring phosphate groups.
• This energy can be used to drive cellular work.
Chemical potential energy
in ATP is converted to
kinetic energy in order to
a) Move proteins,
b) Transport solutes
against their
concentration
gradient,
c) Rearrange bonds in
chemical reactions.
Heat is released in the
conversion from potential
The ATP Cycle
– Cellular work spends ATP.
– ATP is recycled from ADP and phosphate
through cellular respiration.
Isolated beating rat heart cell
Muscle contraction: Actin-myosin movement
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html
Sodium-potassium pump
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
– Aerobic metabolism
– Anaerobic metabolism
– Aerobic metabolism
• Occurs when enough oxygen reaches cells to support
energy needs.
– Anaerobic metabolism
– Aerobic metabolism
• Occurs when enough oxygen reaches cells to support
energy needs.
– Anaerobic metabolism
• Occurs when the demand for oxygen outstrips the
body’s ability to deliver it.
– Physical conditioning
allows your body to
acclimate to increased
activity.
• The body can increase
its ability to deliver
oxygen to muscles and
utilize it more efficiently.
– If you exceed the ability
of anaerobic
metabolism to provide
you with energy your
muscles will fail.
Fermentation: Anaerobic
Harvest of Food Energy
– Some of your cells can actually work for
short periods without oxygen.
– Fermentation
• Is the anaerobic harvest of food energy.
Fermentation in Human
Muscle Cells
– After functioning anaerobically for about 15
seconds,
• Muscle cells will begin to generate ATP by the
process of fermentation.
– Fermentation relies on glycolysis to
produce ATP.
If fermentation
continues for
some time, H+
from acid will
build up inside
the cell,
causing protein
denaturation!
Fermentation in Microorganisms
– Various types of microorganisms perform
fermentation.
• Yeast cells carry out a slightly different type of
fermentation pathway.
• This pathway produces CO2 and ethyl alcohol.