Transcript Ground Rules for Metabolism Starr/Taggart’s Biology: ,

Ground Rules for Metabolism
Starr/Taggart’s
Biology:
The Unity and Diversity of Life,
Chapter 6
9e
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
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
Energy and the Underlying
Organization of Life
Metabolism
Cell’s capacity to
Acquire energy
Build
Break apart
Release
substances
Defining Energy
Potential Energy
Kinetic Energy
Heat (Thermal)
Energy
Chemical Energy
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
System’s disorder
Total Energy Content
Energy content of any system with the
environment remains constant
Energy Inputs
Coupled with Outputs
Exergonic reaction
Net loss of energy
Endergonic
reaction
Net increase of
energy
Cells couple
reactions
Phosphorylation
Transfer of a phosphate group to a
molecule
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
Electron Transfers: OxidationReduction Reactions
 Oxidation - removal of electrons
Reduction - addition of electrons
Electron Transport System
Array of enzymes &
coenzymes that
transfer electrons
In cell membranes
Mitochondria
Chloroplasts
Which way will a
reaction run?
 Nearly all chemical reactions in cells are
reversible
A + B <----------> C
Substrates
Product
Chemical Equilibrium
 High reactant
concentration - runs
strongly forward
 Equilibrium - rate of
forward and back
reactions the same
 High product
concentration - runs
strongly in reverse
Metabolic Pathways
Ordered
Enzyme mediated
Biosynthetic or Degradative
Enzyme Structure and Function
Catalysts speed the rate of chemical
reactions
Not permanently altered or used up
Reversible reactions
Selective for the substrates
Enzyme - Substrate Interactions
Activation energy
Factors Influencing
Enzyme Activity
Temperature
pH
Salinity
Ranges are
specific
Control of Enzyme Function
Allosteric control
Binding of
substances on
enzyme other
than the active
site
Can activate
Can inhibit
Feedback Inhibition
Shutting down of
activity
Product produced
shuts down
reaction
Binds to allosteric
site
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
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
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
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