1 Chapter 6: pp. 103-116 Metabolism: Energy and Enzymes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. solar.

1

Chapter 6: pp. 103-116

Metabolism: Energy and Enzymes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

solarenergy

heat

heat

heat

heat

Mechanical energy

Chemicalenergy

6.1 Cells and Energy Flow

What is energy?

Ability to do work

Allows LTs to carry out life process

All depend on solar energy

3

A. Forms of Energy

Kinetic:

Energy of motion

Mechanical

Potential:

Stored energy

Chemical

4

Flow of Energy

solarenergy

heat

heat

heat

heat

Mechanical energy

Chemicalenergy


5

B. Laws of Thermodynamics

First law:

Law of conservation of energy

Energy cannot be created or destroyed, but

Energy CAN be changed from one form to another

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Carbohydrate Metabolism


carbohydrate muscle contraction

heat

Second law:

Law of entropy

When energy is changed from one form to another, there is a loss of usable energy

Waste energy goes to increase disorder

8

6.2 Metabolic Reactions and Energy Transformations

Metabolism:

Sum of cellular chemical reactions in cell

Free energy is the amount of energy available after a chemical reaction

FE of reactants – FE of products → If (-) then reaction occurs spontaneously

Endergonic ReactionsEndergonic Reactions Energy input requiredEnergy input required

Product has more free Product has more free

energy than starting energy than starting

substancessubstances

AnabolicAnabolic

Ex: protein synthesis, Ex: protein synthesis,

muscle contractionmuscle contraction

http://bp3.blogger.com/_6ZOUxSfmYeA/R19PgpZQIjI/AAAAAAAAABc/jlaGrT4-W3Y/s320/bio4.jpg

Exergonic ReactionsExergonic Reactions

Energy is releasedEnergy is released Products have Products have

less free energy less free energy than starting than starting substancesubstance

CatabolicCatabolic

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/exergonic.gif

•In which direction is this reaction anabolic? •In which direction is the reaction catabolic?•Where is the energy of the ATP molecule stored?

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A. ATP and Coupled Reactions

Adenosine triphosphate (ATP)High energy compound used to drive metabolic reactionsConstantly being generated

Composed of:Adenine and ribose (together = adenosine), andThree high energy phosphate groups

AdvantagesCommon and universalLittle wasteBreakdown coupled with endergonic

ATP/ADP Cycle

http://www.accessexcellence.org/RC/VL/GG/ecb/ecb_images/03_32_ATP_and_ADP_cycle.jpg

Coupled Reactions

Rxns occur in same time and place so exergonic drives endergonic

Usually exergonic = ATP hydrolysis because more energy released than consumed

2 ways to couple ATP hydrolysisATP used to energize reactant (Cell. Resp)ATP used to change shape of reactant ( muscle contraction)

Drives energetically unfavorable reactions to create order for life

Muscle Contraction

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Work-Related Functions of ATP

Primarily to perform cellular work

Chemical Work - Energy needed to synthesize macromolecules

Transport Work - Energy needed to pump substances across plasma membrane

Mechanical Work - Energy needed to contract muscles, beat flagella, etc

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6.3 Metabolic Pathways

Reactions are usually occur in a sequence

Products of an earlier reaction become reactants of a later reaction

Such linked reactions form a metabolic pathway

Begins with a particular reactant,

Proceeds through several intermediates, and

Terminates with a particular end product

AB C D E FG

“A” is InitialReactant

“G” is EndProduct

B, C, D, E, and Fare Intermediates

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Enzymes

Enzymes

Protein molecules that function as catalysts

The reactants are called substrates

Regulate by eliminating side reactions

Each reaction in a metabolic pathway requires a unique and specific enzyme

End product will not appear unless ALL enzymes present and functional

E1 E2 E3 E4 E5 E6A B C D E F G

Four Features of EnzymesFour Features of Enzymes1) Enzymes do not make anything happen that could 1) Enzymes do not make anything happen that could

not happen on its own. They just make it happen not happen on its own. They just make it happen much faster.much faster.

2) Reactions do not alter or use up enzyme molecules.2) Reactions do not alter or use up enzyme molecules.

3) The same enzyme usually works for both the 3) The same enzyme usually works for both the forward and reverse reactions.forward and reverse reactions.

4) Each type of enzyme recognizes and binds to only certain substrates.


How do enzymes lower the energy of activation?

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A. Energy of Activation

Energy must be added to at least one reactant to initiate the reaction

Enzyme Operation:

Enzymes operate by lowering the energy of activation

Bring the substrates into contact with one another


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B. Enzyme-Substrate Complex

Substrate = reactants

Active site = small part that binds substrate specifically

Induced fit model – active site changes slightly for optimum fit

Sometimes they participate Ex: Trypsin protein digestion

http://www.mun.ca/biology/scarr/F09-20bsmc.jpg


What factors can affect the speed/rate of enzymatic reactions?

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C. Factors Affecting Enzyme Activity

Substrate concentrationIncrease substrate increase collisions until a max rateAmount of enzyme can also limit

TemperatureEnzyme activity increases with temperatureWarmer temperatures cause more effective collisions between enzyme and substrateHowever, hot temperatures destroy enzyme

Optimal pH

Normal configurations

Globular structure dependent on HB between R groups

Change pH will change ionization of side chains

Extreme change will cause inactivity


Temperature

Increase temp, increase activity because of better collisions

Will level out and then decline because of changed shape

Exceptions: prokaryotes in hot springs

Siamese coat color

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Enzyme CoFactors

Molecules required to activate enzymeInorganic = Cu, Zn, Fe

Coenzymes are organic cofactors

Vitamins become part of conenzymes

Phosphorylation – some require addition of a phosphate


Specific Enzyme Inhibition

IrreversibleForms strong

covalent bonds at active site

React with -SH, -OH, or acid groups

Ex: Ag, Hg, Pb

NoncompetitiveReversible

Changes shape, thus changing active site

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Irreversible Inhibition

Materials that irreversibly inhibit an enzyme are known as poisons

Cyanides inhibit enzymes resulting in all ATP production

Penicillin inhibits an enzyme unique to certain bacteria

Heavy metals irreversibly bind with many enzymes

Nerve gas irreversibly inhibits enzymes required by nervous system

Non-CompetitiveOR Allosteric

Binds somewhere other than active site and changes shape of enzyme

Positive FeedbackPositive Feedback

http://www.steve.gb.com/images/science/positive_feedforward.png

Competitive

Inhibitor and substrate both go after active site

Example:Ethanol to

acetaldehyde to acetic acid

2nd rxn fast but Anatabuse block causing side effects

Stop drinking

Negative FeedbackNegative Feedback

http://www.steve.gb.com/images/science/negative_feedback.png


What molecule does grass make available to an herbivore?

What happens to this molecule during cellular respiration?

Carbon dioxide is _____ to produce glucose during PS and glucose is ____ to produce ATP during CR.

6.4 Organelles and Energy Flow

PhotosynthesisChloroplast capture solar

energy

Convert using electron transport chain to ATP

Used to reduce CO2 to glucose

Cellular RespirationH atoms from C are bonded

to O2

Mitochondria breaks down carbs to produce ATP by an electron transport chain

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Electron Transport Chain (ETC)

Membrane-bound carrier proteins that pass e- from one to another

Physically arranged in an ordered series

Starts with high-energy e- and low-energy e- leave

Each carrier is reduced and then oxidized as e- are transferred

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A Metaphor for the Electron Transport Chain


high-energyelectrons

low-energyelectrons

electrontransport chain

ATP

energy forsynthesis of

e

e

ETCs

a. are found in both mitochondria and chloroplasts

b. release energy as e- are transferred

c. are involved in ATP production

d. are located in a membrane

e. all of the above

ATP Production

• Chemosmosis

• Carriers found on thylakoid membrane of chloroplast and cristae of mitochondria

• H+ collects on one side of the membrane

• Establishes an e- gradient

• ATP Synthase complexes

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Chemiosmosis


ATPsynthasecomplex

energy fromelectron transfers

H+ H+

High H + concentration

Low H + concentration

H + pump in electrontransport chain

H+

H+

H+

H+ H+

ATP

ADP + P

Chemiosmosis is dependent on

a. the diffusion of water across a differentially permeable membrane

b. an outside supply of phosphate and other chemicals

c. the establishment of an electrochemical H+ gradient

a. PS

b. CR

c. Both

d. Neither

1. captures solar energy

2. requires enzymes and coenzymes

3. releases CO2 and H2O

4. utilizes an ETC

5. performed by plants

6. transforms one of energy into another form with the release of heat

7. creates energy for the living world

1 Chapter 6: pp. 103-116 Metabolism: Energy and Enzymes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. solar.

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