Membrane Function –Working cells control the transport of materials to and from the environment...

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.

–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 alternative hypothesis

Lab 3 - Osmosis and Diffusion

• Plasmolysis– View of Elodea cells

Water Balance in Cells

Pla

smol

ysis

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

Energy released all at once in 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 process to make chemical energy do work.

• 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.

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 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) EnergyIn 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.

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Chemical Energy: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

Reactants Products

enzymes

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

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 form water, it is as though they were falling, thus, releasing their potential 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 form water, it is as though they were falling, thus, releasing their potential 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 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.

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 and

over again.

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Chemical Energy: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 energyin ATP is converted to kinetic energy in order to a) Move proteins,b) Transport solutes

against their concentration gradient,

c) Rearrange bonds inchemical reactions.

Heat is released in the conversion from potential to kinetic energy

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 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.