energy and life ground rules of metabolism l.
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Energy and Life Ground Rules of Metabolism. Chapter 5. Growing Old with Molecular Mayhem. Free radical A molecule that has unpaired electrons Highly reactive, can disrupt structure of molecules. Superoxide Dismutase.

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growing old with molecular mayhem
Growing Old with Molecular Mayhem

Free radical

A molecule that has unpaired electrons

Highly reactive, can disrupt structure of molecules

superoxide dismutase
Superoxide Dismutase
  • Catalyzes the formation of hydrogen peroxide from oxygen free radicals and hydrogen ions
  • Accumulation of hydrogen peroxide can be lethal to cells
catalase
Catalase

Catalyzes the formation of oxygen and water from hydrogen peroxide

2H2O2 ----------> 2H2O + O2

roundworm experiments
Roundworm Experiments
  • Diet supplemented with superoxide dismutase and catalase increased life span of normal worms
  • Diet also allowed worms genetically-engineered for susceptibility to free radicals to live normal life span
what is energy
What is Energy?
  • Capacity to do work
  • Forms of energy
    • Potential energy
    • Kinetic energy
    • Chemical energy
what can cells do with energy
What Can Cells Do with Energy?
  • Energy inputs become coupled to energy-requiring processes
  • Cells use energy for:
    • Chemical work
    • Mechanical work
    • Electrochemical work
first law of thermodynamics
First Law of Thermodynamics
  • The total amount of energy in the universe remains constant
  • Energy can undergo conversions from one form to another, but it cannot be created or destroyed
one way flow of energy
One-Way Flow of Energy
  • The sun is life’s primary energy source
  • Producers trap energy from the sun and convert it into chemical bond energy
  • Allorganisms use the energy stored in the bonds of organic compounds to do work
second law of thermodynamics
Second Law of Thermodynamics
  • No energy conversion is ever 100 percent efficient
  • The total amount of energy is flowing from high-energy forms to forms lower in energy
entropy
Entropy
  • Measure of degree of disorder in a system
  • The world of life can resist the flow toward maximum entropy only because it is resupplied with energy from the sun
energy changes cellular work
Energy Changes & Cellular Work

Energy changes in cells tend to run spontaneously in the direction that results in a decrease in usable energy

endergonic reactions
Endergonic Reactions
  • Energy input required
  • Product has more stored or potential energy than starting substances

product with

more energy

(plus by-products

602 and 6H2O)

ENERGY

IN

6

12

exergonic reactions
Exergonic Reactions
  • Energy is released
  • Products have less energy than starting substance

energy-rich

starting

substance

ENERGY

OUT

+

602

6

6

products with less energy

the role of atp
The Role of ATP
  • Cells “earn” ATP in exergonic reactions
  • Cells “spend” ATP in endergonic reactions

adenine

P

P

P

ribose

electron transfers
Electron Transfers
  • Electrons are transferred in virtually every reaction that harnesses energy for use in the formation of ATP
  • Coenzymes assist in electron transfers
electron transport systems
Electron Transport Systems
  • Arrangement of enzymes, coenzymes, at cell membrane
  • As one molecule is oxidized, next is reduced
  • Function in aerobic respiration and photosynthesis
oxidation and reduction
Oxidation and Reduction
  • Oxidation is the loss of electrons by an atom or molecule
  • Reduction is the gain of electrons by an atom or molecule.
  • Oxidation of molecule A is always accompanied by reduction of a molecule B or vice-versa. (An e- donor requires an e- acceptor or vice-versa)
concentration gradient
Concentration Gradient
  • Means the number of molecules or ions in one region is different than the number in another region
  • In the absence of other forces, a substance moves from a region where it is more concentrated to one one where it’s less concentrated - “down” gradient
diffusion
Diffusion
  • The net movement of like molecules or ions down a concentration gradient
  • Although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient)
factors affecting diffusion rate
Factors Affecting Diffusion Rate
  • Steepness of concentration gradient
    • Steeper gradient, faster diffusion
  • Molecular size
    • Smaller molecules, faster diffusion
  • Temperature
    • Higher temperature, faster diffusion
  • Electrical or pressure gradients
which way will a reaction run
Which Way Will a Reaction Run?
  • Nearly all chemical reactions are reversible
  • Direction reaction runs depends upon
    • Energy content of participants
    • Reactant-to-product ratio
chemical equilibrium
Chemical Equilibrium

RELATIVE

CONCENTRATION

OF REACTANT

RELATIVE

CONCENTRATION

OF PRODUCT

HIGHLY

SPONTANEOUS

EQUILIBRIUM

HIGHLY

SPONTANEOUS

chemical equilibrium24
Chemical Equilibrium
  • At equilibrium, the energy in the reactants equals that in the products
  • Product and reactant molecules usually differ in potential energy content (E > e)
  • Therefore, at equilibrium, the amount (n) of reactant almost never equals the amount (N) of product (n*E= N*e ; where N>n and E>e)
energy relationships
Energy Relationships

large energy-rich molecules

(fats, complex carbohydrates,

proteins, nucleic acids)

ADP + Pi

BIOSYNTHETIC PATHWAYS

(ANABOLIC)

DEGRADATIVE PATHWAYS

(CATABOLIC)

simple organic compounds

(simple sugars, amino acids,

fatty acids, nucleotides)

ATP

energy-poor products

(such as carbon dioxide, water)

ENERGY INPUT

participants in metabolic pathways
Energy Carriers

Enzymes

Cofactors

Participants in Metabolic Pathways
  • Substrates
  • Intermediates
  • End products
types of reaction sequences
Types of Reaction Sequences

LINEARPATHWAY:

CYCLICPATHWAY:

A

B

C

D

E

F

G

K

J

I

N

M

L

H

BRANCHINGPATHWAY:

enzyme structure and function
Enzyme Structure and Function

Enzymes are catalytic molecules

They speed the rate at which reactions approach equilibrium

four features of enzymes
Four Features of Enzymes

1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster

2) Reactions do not alter or use up enzyme molecules

four features of enzymes30
Four Features of Enzymes

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

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

activation energy
Activation Energy
  • For a reaction to occur, an energy barrier must be surmounted
  • Enzymes make the energy barrier smaller

activation energy

without enzyme

starting

substance

activation energy

with enzyme

energy

released

by the

reaction

products

induced fit model

two

substrate

molecules

Induced-Fit Model

substrates

contacting

active site

of enzyme

  • Substrate molecules are brought together
  • Substrates are oriented in ways that favor reaction
  • Active sites may promote acid-base reactions
  • Active sites may shut out water

active sight

TRANSITION

STATE

(tightest

binding but

least stable)

end

product

enzyme

unchanged

by the

reaction

factors influencing enzyme activity
Factors Influencing Enzyme Activity

Temperature

pH

Salt concentration

Allosteric regulators

Coenzymes and cofactors

allosteric activation
Allosteric Activation

enzyme active site

allosteric activator

vacant

allosteric binding site

active site cannot bind substrate

active site altered, can bind substrate

allosteric inhibition
Allosteric Inhibition

allosteric inhibitor

allosteric binding site vacant; active site can bind substrate

active site altered, can’t bind substrate

feedback inhibition
Feedback Inhibition

enzyme 2

enzyme 3

enzyme 4

enzyme 5

A cellular change, caused by a specific activity, shuts down the activity that brought it about

enzyme 1

END PRODUCT (tryptophan)

SUBSTRATE

effect of temperature
Effect of Temperature
  • Small increase in temperature increases molecular collisions, reaction rates
  • High temperatures disrupt bonds and destroy the shape of active site
enzyme helpers
Enzyme Helpers
  • Cofactors
    • Coenzymes
      • NAD+, NADP+, FAD
      • Accept electrons and hydrogen ions; transfer them within cell
      • Derived from vitamins
    • Metal ions
      • Ferrous iron in cytochromes