brownian motion - north seattle...

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Chapter 5: Part 1 Molecules in motion

• Molecules are in constant motion• Even the water molecules in a block of ice

exhibit some movement!

• Molecules rotate, vibrate and move from side to side, spontaneously.

http://www.visionlearning.com/library/module_viewer.php?mid=57&l=&c3=

Brownian Motion

Fat droplets suspended in milk. 40XThe droplets range in size from about 0.5 to 3 µm

• http://www.phy.davidson.edu/brownian.html

http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.html

Demo • From your experience on this planet, do you think that the dye molecules would ever, spontaneously move from evenly spread out, back to a concentrated drop?

• WHY or WHY NOT?

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• On our planet, systems do not become more organized/orderly spontaneously.

• Would you agree that ‘things’ like dye molecules tend to spontaneously become less organized, if prompted to do so?

A Membrane with pores big enough to

allow dye to pass

Remembering that molecules are in constant, random motion, what are the options for the red ‘molecules of dye’ in the left frame?

Looking at the situation on the left, versus the situation on the right, what can you say, if anything about the ENERGY of the two

situations?HIGH POTENTIAL ENERGY LOW POTENTIAL ENERGY

2nd law of thermodynamics

• Energy spontaneously tends to flow only from being concentrated in one place to becoming diffused or dispersed and spread out.

• A hot frying pan cools down when it is taken off the kitchen stove. Its thermal energy ("heat") flows out to the cooler room air. The opposite never happens.

• More examples? compressed air in a tire, loud sounds, water or boulders that are high up on a mountain, your car’s energy when you take your foot off the gas

• All these different kinds of energy spread out if there's a way they can do so

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Energy

• Potential Energy• Kinetic Energy

• Energy is defined as the capacity to perform work.

• Work is done whenever an object is moved against an opposing force (or moved where it would not spontaneously move)

• http://www.wisc-online.com/objects/index_tj.asp?objid=AP1903

Diffusion can lead to a net movement of atoms or molecules when large numbers are present, and when there is an imbalance in the number of particles between one part of a container and another (creating a concentration gradient).

Diffusion

• The spontaneous movement of molecules of any kind, from an area where they are more concentrated to where they are less concentrated

1st Law of Thermodynamics: Conservation of Energy

• Energy can never be destroyed or created, it can only be converted from one form to another. (like from potential to kinetic)

• All energy conversions, though, are inefficient, and produce some heat.

• Heat is a type of ‘not very useful’ kinetic energy. It is the energy contained in the random motion of atoms and molecules. (low quality energy)

• Heat is not ‘useful energy’ because it can’t easily be harnessed to do much work.

HIGH POTENTIAL ENERGY Low POTENTIAL ENERGY

If energy can’t be ‘lost’ where did the energy go as the dye molecules reached equilibrium?

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HIGH POTENTIAL ENERGY

LOW POTENTIAL ENERGY

Energy conversion

Potential Energy converted to Kinetic Energy

What is happening to the energy?

• Systems (or snowboarders on top of a hill) will spontaneously move from a less stable (higher energy) state to a more stable (lower energy) state, if prompted to do so.

• Once started, the process will proceed, without a further input of energy.

• A free ride!

Systems move to more stable statesUnstable systems are rich in free (available) energy and tend tomove toward more stable states, and in doing so, energy is released, or ‘given off’.

fuel

Waste or simpler molecules

Examples in the Cell

Small, uncharged molecules will spontaneously cross the cell membrane from an area of high concentration to an area of low concentration.

DIFFUSION of O2, CO2

FREE RIDE


Ions and water are repelled by the membrane.

To diffuse down their concentration gradient, they need a passageway across the membrane.

oxygen

Na+ or H2O

Facilitated Diffusion

Energetically, still a free ride


Facilitated Diffusion:diffusion of a molecule down its concentration gradient via a membrane protein channel/pore

oxygen

Na+ or H2O

Facilitated Diffusion

Energetically, still a free ride

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Diffusion of Water

• Osmosis- The passive transport of water molecules across a selectively permeable membrane.

Osmosis: Diffusion of Water

• The direction of osmosis (water movement across a membrane) is determined by solute concentration, or tonicity of a solution

• If allowed to do so, water will always move toward the saltier/more sugary/more solute-packed solution!

• This is really water moving from where it is more concentrated to where it is less concentrated!!!

Solute vs. Solution

Note: Solutions can have different levels of tonicity (amount of stuff dissolved in them)

A selectively permeable membrane is used to separate two solutions.

The membrane is selectively permeable only to H2O. (water is free to move, but the sugar molecules may not pass through!!)

When allowed to do so, which way does the water move?

At Time ZERO

• Water diffused to the right.• Water diffused toward the hypertonic solution

(the solution with more sugar)• Water moved down its own concentration gradient

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Tonicity

• When comparing two solutions, the solution with the higher concentration of a solute (say, sugar) is said to be hypertonic to the other.

• Isotonic• Hypertonic• Hypotonic

How could you refer to these solutions?

A CB

1 scoop Gatorade

4 scoops Gatorade

2 scoops Gatorade

Solution A is _____________ to Solution B. Solution B is _____________ to Solution C. Solution C is _____________ to Solution A.

How could you refer to these solutions?

A CB

1 scoop Gatorade

4 scoops Gatorade

2 scoops Gatorade

D

2 scoops Gatorade

Solution C is _______________ to Solution D.

Which way would water move?

A B

1 scoop Gatorade

4 scoops Gatorade

Water would move from __________ to ________.

From the _________solution to the ___________ solution.

Osmosis in Cells without Cell Walls

Isotonic Hypotonic Hypertonic

Osmosis in Cells with Cell Walls

• Osmosis helps a plant cell maintain turgor pressure in a hypotonic environment

• Loss of turgor pressure results in plants becoming flaccid• Plasmolysis: cell membrane pulling away from the cell

wall

www.steve.gb.com

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Net movement of H2O in Hypotonic Isotonic, and Hypertonic Solutions

Isotonic HypertonicHypotonic

What types of things freely cross the lipid bilayer?

cytoplasm

Steroidoxygen

X

What about water?

cytoplasm

Steroidoxygen

Osmosis• The diffusion of water across a selectively

permeable membrane• Just like everybody else, water molecules will

freely diffuse down their concentration gradient from an area of ………….. to …………. concentration.

Osmosis

• Often, biological membranes are selectively permeable to water, but not to a variety of solutes.

• Water is free to go either way across the membrane

• Which way will it move?

Active Transport

• Active transport is used to move ions or molecules against a concentration gradient (from a low concentration to a high concentration)

• Movement against a concentration gradient requires energy. The energy is supplied by ATP

ATP

ENERGY!

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Agenda

• Chapter 5: Part 2• Passive and Active Transport

– Types of active transport• ATP• Energy Coupling• Enzymes• THE CUBE EXPERIMENT

ATP

Passive Transport1. Simple diffusion 2. Facilitated diffusion

Neither of these require any energy to be added to happen.

In both cases, the molecules are simply following the laws of thermodynamics. If the molecules reach equilibrium, they are at a more stable state.

Passive Transport1. Simple diffusion 2. Facilitated diffusion

•In either example, which molecules have the highest potential energy (energy of location)?

•Would you agree that, if left to their own devices, that the molecules would ‘fall’ from a higher energy state to a lower energy state? Energy is actually given off, too, as this happens.

•Energy is REQUIRED for these molecules to move against their concentration gradient

Active Transport

• Active transport is used to move ions or molecules against a concentration gradient (from a low concentration to a high concentration)

• Movement against a concentration gradient requires energy. The energy is supplied by ATP

ATP

ENERGY!

Active Transport-A phenomenon that REQUIRES energy to occur.

To move something (a molecule) AGAINST its concentration gradient, or against WHERE IT WOULD TEND TO END UP IF LEFT ALONE, requires ENERGY!

Energy must be added to the system to make this happen.

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Active Transport-A phenomenon that REQUIRES energy to occur.

•A membrane protein, a transport protein.

•To work, this transport protein requires ENERGY

Active Transport: One example is the Pumping of Molecules Across

MembranesLower solute concentration

Solute

Higher solute concentration

Other Cell Processes That Occur at the Plasma Membrane and Require Energy

• In general, the processes below move larger ‘items’ across the cell membrane

1. Exocytosis (out)2. Endocytosis (in)

-Phagocytosis (eat)-Pinocytosis (drink)-Receptor-mediated endocytosis

– Secretes substances outside of the cell

Outside cell

Plasmamembrane

Cytoplasm

(a) Exocytosis

Exocytosis: An example


muscle

muscle

Motor neuron

synapse

Nerve cell Muscle cells of your arm

ONE Muscle cell

synapse


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– Takes material into the cell

(b) Endocytosis

Endocytosis• In phagocytosis (“cellular eating”) a cell engulfs a

particle and packages it within a food vacuole

• In pinocytosis (“cellular drinking”) a cell “gulps”droplets of fluid by forming tiny vesicles

Food being ingested

Pseudopodof amoeba

Endocytosis

Endocytosis: Receptor Mediated Endocytosis

• Receptor-mediated endocytosis– Is triggered by the binding of external molecules

to membrane proteins; a highly specific process

M

TRANSMEMBRANE RECEPTOR

M M

OPIOID RECEPTOR

Receptor-mediated endocytosis

1.

2. 3

M

M M

This receptor was

‘endocytosed’

• http://www.wisc-online.com/objects/index_tj.asp?objid=AP2904

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The Role of Membranes in Cell Signaling

LDL particlePhospholipid coat

Protein

Cholesterol

Plasmamembrane

Receptor protein

LIVER CELL Cholesterolprocessed

Liver cells remove LDL from circulation by binding to proteins (tags) on the outside of LDL particles and endocytosing them.

BLOOD

Cell Signaling

Muscle cells of your arm

effect

Outside cellInside cell

Receptorprotein

Signal transduction pathway

Nerve cell

RECAP:We have covered a number things that can happen at a cell or in a

cell:

1. PASSIVE TRANSPORT:

diffusion and facilitated diffusion, neither of which require energy

2. ACTIVE TRANSPORT:

movement of molecules/ions AGAINST their concentration gradient, REQUIRES energy

3. SOME CELLULAR PROCESSES (all of which require Energy)

endocytosis, exocytosis, etc.

What is this?

• This is the cartoon version of ATP, the most common form of cellular energy

• We think of carbohydrates and protein as our energy source, but our cells need a simple, tiny and powerful energy source,ATP

• Why do cells need energy?

ATP

Examples of Cell Processes the Require an Input of Energy

ATP

ATP

Vesicle traffic requires the cytoskeleton, motor proteins, and ATP!!!

vesicle

microtubule

motor protein

ATP

And there are lots of other processes that cell undergo that require energy……..

Another example

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Even more examples

Muscle contration: http://www.wisc-online.com/objects/index_tj.asp?objid=AP2904

Adenosine

ATP= Adenosine Triphosphate

The Structure of ATP

– Consists of adenosine plus a tail of three, negatively charged phosphate groups

ATP

---

ATP is Rich in Chemical Energy

• Remember that Chemical Energy is a typeof Potential Energy (energy of position)

Adenosine

---What about the structure

of this molecule,

makes it rich in potential energy, or unstable?

•More potential energy

•Less stable

•Greater work capacity

•Less potential energy

•More stable

•Less work capacity

ATP is Rich in Chemical Energy

Adenosine

---

• The three phosphates are in an unstable arrangement

• Thus the chemical bonds (covalent) are rich in potential energy (unstable)

• If prompted to do so, the phosphates would rearrange themselves into a more stable arrangement

ATP loses a phosphate and becomes ADP

Energy

Adenosine Adenosine

Phosphate transferred to othermolecules

Adenosine Triphosphate Adenosine Diphosphate

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How are ATP and ADP like a spring?

Energy

Adenosine Adenosine


How are ATP and ADP like a spring?

Energy

Adenosine Adenosine


ATP is the compressed spring. (HIGH energy)

ADP is the sprung spring. (Lower energy)Q i kTi ™ d

Q i kTi ™ d

ATP does not do work directly

• ATP transfers phosphate groups to other molecules

• These phosphates energize other molecules, so that they can do work

ATP

ADP

P

Phosphate Transfer or phosphorylation

PADP

ATPclosed transporter

P

Motor protein

Protein moved(a) Mechanical work

(b) Transport workATP

Transport protein Solute

Solute transported

Reactants Product made

(c) Chemical work

How ATP drives cellular work

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‘Cashed’ ADP is recycled to generate ATP

Energy forcellular workIe. giving a phosphate to a transporter so that it can pump molecules against a concentration gradient

P

ATP

ADP

How do we get from ADP to ATP??

Is this likely to be a spontaneous reaction?

‘Cashed’ ADP is recycled to generate ATP

Energy forcellular workIe. giving a phosphate to a transporter so that it can pump molecules against a concentration gradient

P

ATP

ADP

Energy Coupling

Reactions that GIVE OFF ENERGY -The breakdown of organic fuel in cellular respiration

Reactions that REQUIRE ENERGY-Cellular work

Why Recycle?• ATP cycle runs at an astonishing pace. A

working muscle cell recycles all of its ATP about once each minute

• That is about 10 million ATP molecules spent and regenerated per second per cell.

ATP is like a rechargeable battery!

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Enzymes and Chemical Reactions

• Remember monomers and polymers?• Which do you think has more potential

(chemical) energy…monomers or polymers?

Spontaneous??

Enzymes

How is an enzyme like a wrench?

Enzymes

• Enzymes are proteins that speed up chemical reactions.

• Without enzymes, most chemical reactions would still occur, but they would happen much too slowly to sustain life.

• Yes, one time in a trillion, maybe a bolt would randomly plop itself down into a nut.

Enzymes

• How else are enzymes like a wrench?

• IS the wrench used up?

• Sometimes nuts and bolts are put together, sometimes they are taken apart!

Enzymes catalzye chemical reactions

Carbon dioxide and Water

enzyme enzyme

Have you ever observed a potato transform into glucose monomers, or carbon dioxide and water?

Why not…it seems like polymers should break down into lower energy monomers, right??

Activation energy is the barrier that prevents these ‘spontaneous’ reactions from happening in our kitchen!

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Carbon dioxide and Water

enzyme enzyme

What happens if you BURN a potato?

A spark, or fire actually is a catalyst, too. Just a ‘brut force’ type of catalyst.

Enzymes are protein catalysts. One enzyme catalyzes only one chemical reaction!!


• Enzymes lower the activation energy of a specific reaction

• Enzymes bind specific substrate molecules (say starch) and make it easier to break their bonds and start a reaction

• Enzymes can literally ‘twist and turn’ chemical bonds so that they are ‘stressed’ and more likely to break

Enzymes function over and over again

Enzyme(sucrase)

Active site

Fructose

Glucose

Substrate(sucrose)

Enzymeavailable withempty active site

1

2

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Substrate bindsto enzyme

Substrate isconverted toproducts

Productare released

Enzymes– Lower the activation energy for chemical

reactions

Figure 5.8

Activation energybarrier

Reactants

(a) Without enzyme

Products

Enzy

me

(b) With enzyme

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