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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 acellular membrane?

• Many small non-polar molecules can pass bydiffusion– Oxygen (O2), Carbon Dioxide (CO2)– Water (H2O), although polar, is small enough to pass

through

• Other charged and larger polar moleculescannot pass through and need membranetransport 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 ofmolecules.• 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 passivediffusion.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

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Osmosis and Water Balancein Cells

– Osmosis is the passive transport of wateracross a selectively permeable membrane.

–http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

[solute]

[water]

[solute]

[water]= [solute]= [water]

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 counter-

evidence from• Verifiable observations,• Verifiable measurements, and/or• Reliable resources, other people’s data

– If claim/hypothesis refuted, state an alternativehypothesis

Lab 3 - Osmosis and Diffusion

• Plasmolysis– View of Elodea cells

Water Balance in Cells

Pla

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– 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

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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 ofmolecules.• 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 passivediffusion.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

– Another type of passive transport isfacilitated diffusion, the transport of somesubstances by specific transport proteinsthat act as selective corridors.

– Food molecule monomers like glucose andamino 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 ofMolecules Across Membranes

– Active transport requires energy to movemolecules across a membrane.

– Ions like Na+, K+, and H+ are often pumpedacross membranes against their concentrationgradients. 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 thecell.

– Endocytosis:Takesmaterial intothe cell.

– Phagocytosis andPinocytosis

– 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 ofthe cell.

How do we obtain energy fromthose food molecules once

they are in there????

4

Flow of Energy throughCellular 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.

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Chemical Energy:a form of potential energy found in fuels

Living cells and automobile engines use the same basic processto 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 destroymatter,• They only rearrange it.

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Chemical ReactionsChemical reactions can store energy in or release energy from chemical bonds

Energy releasedall at oncein explosive reaction

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Chemical Energy:a form of potential energy found in fuels

Living cells and automobile engines use the same basic processto make chemical energy do work.

• Is a type of kinetic energy.

• Is also a waste product ofall 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 temperaturebecause it needs to have energy to break the hydrogenbonds between them so that the molecules can speedup.

Heat 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 convertedto heat (air friction,vibration ofmolecules in thesteps)

Energy is converted to heat (air friction,water molecule movement)

Another example of heatgenerated during conversion

of chemical potential energy tokinetic 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 onedegree Celsius.

– The kilocalorie (or Calorie with capital “C”) is• 1,000 calories.• The unit used to measure the energy in food.

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Potential (Chemical) EnergyIn Foods

Kinetic Energy Used by Activities Mitochondria and Cellular Respiration

– The chemical energy of organic moleculesis released in cellular respiration in themitochondria. This energy is stored asanother form of chemical energy, ATP.

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Chemical Energy:a form of potential energy found in fuels

Living cells and automobile engines use the same basic processto make chemical energy do work.

Cellular Respiration: Aerobic Harvestof Food Energy

– Cellular respiration

• Is the main way that chemical energy isharvested 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 andBreathing

– Cellular respirationand breathing areclosely related.• Cellular respiration

requires a cell toexchange gaseswith itssurroundings.

• Breathingexchanges thesegases between theblood and outsideair.

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

The Overall Equation for Cellular Respiration

– A common fuel molecule for cellularrespiration is glucose.• The overall equation for what happens to

glucose during cellular respiration

Reactants Products

enzymes

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The Role of Oxygen inCellular 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 formwater, it is as though they were falling, thus, releasing theirpotential energy.

Higher energy bonds

Lowerenergybonds

– 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 formwater, it is as though they were falling, thus, releasing theirpotential energy.

Higher energy bonds

Lowerenergybonds

– 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 formwater, it is as though they were falling, thus, releasing theirpotential energy.

Higher energy bonds

Lowerenergybonds

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 theenergy a little at a time instead of all at once.

Energy releasedall at oncein explosive reaction

Energy releaseda little at a timein cellular respiration

– The first step is an electronacceptor called NAD+.

• The transfer of electrons fromorganic fuel to NAD+ reduces it(gains electrons) to NADH.

– The rest of the path consists ofan electron transport chain.

• This chain involves a series ofredox reactions (gaining andlosing electrons).

• These lead ultimately to theproduction of large amounts ofATP.

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The Metabolic Pathway of Cellular Respiration

– Cellular respiration is anexample of a metabolicpathway,• A series of chemical

reactions in cells carriedout by enzymes!

– All of the reactionsinvolved in cellularrespiration can begrouped into three mainstages:• 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 theassistance of enzymes.

Phospholipase A2 Active site: glsgs

Activation Energy– Activation energy

• Is the energy that activates the reactants in achemical 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 upreaction rates without being consumed.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

– 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 andover again.

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Chemical Energy:a form of potential energy found in fuels

Living cells and automobile engines use the same basic processto 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?….

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The Metabolic Pathway of Cellular Respiration

– Cellular respiration is anexample of a metabolicpathway,• A series of chemical

reactions in cells carriedout by enzymes!

– All of the reactionsinvolved in cellularrespiration can begrouped into three mainstages:• 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 intoCO2, high-energy electrons, and H+

– In the mitochondria: For the citric acidcycle, pyruvic acid from glycolysis is first“prepped” into a usable form, Acetyl CoA.

– In the mitochondria: The citric acid cycle extractsthe energy of sugar by breaking the acetic acidmolecules all the way down to CO2.

•The cycle usessome of thisenergy to makeATP.

•High-energyelectrons arecarried away byNADH andFADH2.

Stage 3: Electron Transport– In the mitochondria: Electron transport

releases the energy your cells need tomake most of their ATP.

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– The molecules of electron transport chains arebuilt into the inner membranes of mitochondria.• The chain functions as a chemical machine that uses

energy released by the “fall” of electrons to pumphydrogen ions across the inner mitochondrialmembrane.

• These ions store potential energy.

– When the hydrogen ions flow back throughthe 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 offood molecules:

Adding Up the ATP from Cellular Respiration

The Structure of ATP– ATP (adenosine triphosphate)

• Consists of adenosine plus a tail of threephosphate groups.

• Is broken down to ADP, accompanied by therelease of energy.

Phosphate Transfer– ATP can energize other molecules by

transferring phosphate groups.• This energy can be used to drive cellular work.

Chemical potential energyin ATP is converted tokinetic energy in order toa) Move proteins,b) Transport solutes

against theirconcentration gradient,

c) Rearrange bonds inchemical reactions.

Heat is released in theconversion from potentialto kinetic energy

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The ATP Cycle– Cellular work spends ATP.– ATP is recycled from ADP and phosphate

through cellular respiration.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html

Muscle contraction: Actin-myosin movement

Sodium-potassium pumphttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Isolated beating rat heart cell

– 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 conditioningallows your body toacclimate to increasedactivity.• The body can increase its

ability to deliver oxygento muscles and utilize itmore efficiently.

– If you exceed the abilityof anaerobic metabolismto provide you withenergy your muscles willfail.

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Fermentation: AnaerobicHarvest of Food Energy

– Some of your cells can actually work forshort periods without oxygen.

– Fermentation• Is the anaerobic harvest of food energy.

Fermentation in HumanMuscle Cells

– After functioning anaerobically for about 15seconds,• Muscle cells will begin to generate ATP by the

process of fermentation.

– Fermentation relies on glycolysis toproduce ATP. If fermentation

continues forsome time, H+from acid willbuild up insidethe cell,causing proteindenaturation!

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.