Energy and Metabolism

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Energy and Metabolism

• Chapter 4
• Part 1

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4.1 Impacts/IssuesA Toast to Alcohol
Dehydrogenase

• Metabolic processes break down organic molecules
  such as ethanol and other toxins binge drinking
  is currently the most serious drug problem on
  college campuses

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Video Alcohol, enzymes, and your liver
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• Alcohol dehydrogenase (ADH) converts ethanol to
  toxic acetaldehyde, which is then converted to
  acetate by ALDH

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4.2 Life Runs on Energy Laws of Thermodynamics

• Energy
• The capacity to do work
• Law 1 Energy can be converted from one form to
  another, but cannot be created or destroyed
• Law 2 Energy disperses spontaneously

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Material Recycle

• Energy inputs drive a cycling of materials among
  producers and consumers
• Producers and then consumers use energy to
  assemble, rearrange, and break down organic
  molecules that cycle among organisms throughout
  ecosystems

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ENERGY IN
Light energy radiating from the sun reaches
Earth. Producers capture some of it by converting
it to chemical energy. They and all other
organisms use chemical energy to drive cellular
work.
PRODUCERS
One way Flow of energy
plants and other self-feeding organisms
nutrient cycling
CONSUMERS
animals, most fungi, many protists, bacteria
ENERGY OUT
With each conversion, there is a one- way ?ow of
a bit of energy back to the environment, mainly
in the form of heat.
Fig. 4-2, p. 63
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Matter recycling and energy flow
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4.3 Energy in the Molecules of Life

• Cells store and retrieve energy by making and
  breaking chemical bonds in metabolic reactions
• Some reactions require a net input of energy
  others end with a net release of energy

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Chemical Reactions

• Reaction
• Process of chemical change
• Reactant
• Molecule that enters a reaction
• Product
• A molecule remaining at the end of a reaction

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A Chemical Reaction
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Energy Inputs and Outputsin Chemical Reactions

• Chemical bonds hold energy the amount depends
  on which elements take part in the bond
• Cells store energy in chemical bonds by running
  energy-requiring reactions, and access energy by
  running energy-releasing reactions

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Energy Inputs and Outputsin Chemical Reactions
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Why the World Doesnt Go Up in Flames

• Molecules of life release energy when combined
  with oxygen but not spontaneously energy is
  required to start even energy-releasing reactions
• Activation energy
• Minimum amount of energy required to start a
  reaction

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Activation Energy
Energy
Time
Stepped Art
Fig. 4-4, p. 65
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Animation Chemical equilibrium
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ATP The Cells Energy Currency

• Energy carriers accept energy from
  energy-releasing reactions and deliver energy to
  energy-requiring reactions
• ATP (Adenosine triphosphate)
• Main energy carrier between reaction sites in
  cells

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Phosphorylation

• Phosphate-group transfers (phosphorylation) to
  and from ATP couple energy-releasing reactions
  with energy-requiring ones

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ATP The Energy Currency of Cells
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4.4 How Enzymes Work

• Enzymes make chemical reactions proceed much
  faster than they would on their own
• Enzyme
• Protein or RNA that speeds a reaction without
  being changed by it

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Substrates

• An enzymes particular substrates bind at its
  active site
• Substrate
• A reactant molecule that is specifically acted
  upon by an enzyme

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Active Sites

• Active site
• Pocket in an enzyme where substrates bind and a
  reaction occurs

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Factors That Influence Enzyme Activity

• Each enzyme works best within a characteristic
  range of temperature, pH, and salt concentration
• When conditions break hydrogen bonds, an enzyme
  changes its characteristic shape (denatures), and
  stops working

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Enzymes, Temperature, and pH
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Fig. 4-6a, p. 66
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Organized, Enzyme-Mediated Reactions

• Cells concentrate, convert, and dispose of most
  substances in enzyme-mediated reaction sequences
• Metabolic pathway
• Series of enzyme-mediated reactions by which
  cells build, remodel, or break down an organic
  molecule

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Linear and Cyclic Metabolic Pathways
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Control of Metabolic Pathways

• Various controls over enzymes allow cells to
  conserve energy and resources by producing only
  what they require
• Concentrations of reactants and products
• Feedback inhibition

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Control of Metabolic Pathways

• Feedback inhibition
• Mechanism by which a change that results from
  some activity decreases or stops the activity

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Feedback Inhibition
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Electron Transfers

• Electron transfer chains allow cells to harvest
  energy in manageable increments
• Electron transfer chain
• An array of membrane-bound enzymes and other
  molecules that accept and give up electrons in
  sequence

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Uncontrolled and Controlled Energy Release
Stepped Art
Fig. 4-9, p. 68