Ground Rules for Metabolism

1
Ground Rules for Metabolism

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 6

2
Key Concepts

• Cells engage in metabolism
• Metabolic reactions lead to energy loss to the
  environment
• Energy losses and energy gains must be balanced
• Cells maintain greater or lesser amounts of
  certain substances as required for metabolism

3
Key Concepts

• Metabolic reactions release usable energy from
  substances to other reactions that require energy
• Action of specific enzymes increase the rate of
  specific chemical reactions
• ATP transports usable energy from one reaction
  site to another by the transfer of a phosphate
  group

4
Energy and the Underlying Organization of Life

• Metabolism
• Cells capacity to
• Acquire energy
• Build
• Break apart
• Release substances

• Defining Energy
• Potential Energy
• Kinetic Energy
• Heat (Thermal) Energy
• Chemical Energy

5
Defining Energy

• First Law of Thermodynamics
• Energy cannot be created or destroyed
• Second Law of Thermodynamics
• Total amount of energy in the universe is flowing
  from higher to lower quality
• Entropy
• Systems disorder

6
Total Energy Content

• Energy content of any system with the environment
  remains constant

7
Energy Inputs Coupled with Outputs

• Exergonic reaction
• Net loss of energy
• Endergonic reaction
• Net increase of energy
• Cells couple reactions

8
Phosphorylation

• Transfer of a phosphate group to a molecule

9
How Does ATP Give Up Energy?

• 5-carbon sugar, base, and triphosphate tail
• Enzymes can break bond between outermost P and
  tail, then attach P to another substance
  energizing it

10
Electron Transfers Oxidation-Reduction Reactions

• Oxidation - removal of electrons
• Reduction - addition of electrons

11
Electron Transport System

• Array of enzymes coenzymes that transfer
  electrons
• In cell membranes
• Mitochondria
• Chloroplasts

12
Which way will a reaction run?

• Nearly all chemical reactions in cells are
  reversible

A B lt----------gt C
Substrates
Product
13
Chemical Equilibrium

• High reactant concentration - runs strongly
  forward
• Equilibrium - rate of forward and back reactions
  the same
• High product concentration - runs strongly in
  reverse

14
Metabolic Pathways

• Ordered
• Enzyme mediated
• Biosynthetic or Degradative

15
Enzyme Structure and Function

• Catalysts speed the rate of chemical reactions
• Not permanently altered or used up
• Reversible reactions
• Selective for the substrates

16
Enzyme - Substrate Interactions

• Activation energy

17
Factors Influencing Enzyme Activity

• Temperature
• pH
• Salinity
• Ranges are specific

18
Control of Enzyme Function

• Allosteric control
• Binding of substances on enzyme other than the
  active site
• Can activate
• Can inhibit

19
Feedback Inhibition

• Shutting down of activity
• Product produced shuts down reaction
• Binds to allosteric site

20
In Conclusion

• Sum of metabolism underlies the survival of
  living things
• The First and Second Laws of Thermodynamics
  affect life
• Energy can be converted from one form to another
  but cannot be destroyed
• Energy flows from higher to lower quality
• Cells balance energy output with input

21
In Conclusion

• Most metabolic reactions proceed in one direction
  but some are reversible
• Reversible reactions tend toward equilibrium
• Metabolic reactions can release or require energy
• Exergonic reactions end with loss of energy
• Endergonic reactions end with a net gain of energy

22
In Conclusion

• Cells couple exergonic and endergonic reactions
• ATP is the main energy carrier in cells
• ATP forms when a phosphate is donated to ADP
• Metabolic pathways are orderly enzymatically
  driven reactions
• Enzymes are catalysts, lower activation energy,
  and bind substrates

23
In Conclusion

• Enzymes are temperature, pH, and salinity
  specific
• Cofactors affect enzymes
• Energy conversions in cells involve a flow of
  electrons
• developed by M. Roig