Ground Rules of Metabolism

1
Ground Rules of Metabolism

• Chapter 6

2
Free Radicals

• Unbound molecular fragments with the wrong number
  of electrons
• Highly reactive
• Can disrupt structure of molecules

3
Keeping Free Radicals in Check
superoxide dismutase
catalase
Figure 6.1Page 96
4
Superoxide Dismutase

• Catalyzes the formation of hydrogen peroxide from
  oxygen-free radicals and hydrogen ions
• Accumulation of hydrogen peroxide can be lethal
  to cells

5
Catalase

• Catalyzes the formation of oxygen and water from
  hydrogen peroxide
• 2H2O2 ----------gt 2H2O O2

6
What Is Energy?

• Capacity to do work
• Forms of energy
• Potential energy
• Kinetic energy
• Chemical energy

7
What Can Cells Do with Energy?

• Cells use energy for
• Chemical work
• Mechanical work
• Electrochemical work

8
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

9
One-Way Flow of Energy

• The sun is lifes primary energy source
• Producers trap energy from the sun and convert it
  into chemical bond energy
• All organisms use the energy stored in the bonds
  of organic compounds to do work

10
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

11
Entropy

• Measure of degree of disorder in a system

12
Energy Changes Cellular Work

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

13
Endergonic Reaction
glucose - a product with more energy
602 and 6H2O
Energy in
energy-poor starting substances
6
12
Figure 6.5a,bPage 100
14
Exergonic Reaction
glucose - energy-rich starting substance

602
Energy out
6
6
products with less energy
Figure 6.5a,bPage 100
15
Structure of ATP
nucleotide base (adenine)
three phosphate groups
sugar (ribose)
Figure 6.6bPage 101
16
ATP Main Energy Carrier

• ATP/ADP cycle regenerates ATP

ATP
energy output
energy input
ADP Pi
17
Electron Transfers

• Oxidation - lose electron
• Reduction - gain electron
• Central to the formation of ATP during
  photosynthesis and aerobic respiration

18
Participants in Metabolic Pathways

• Energy Carriers
• Enzymes
• Cofactors

• Reactants
• Intermediates
• Products

19
Degradative and Anabolic Pathways
large energy-rich molecules
ADP Pi
BIOSYNTHETIC PATHWAYS (ANABOLIC)
DEGRADATIVE PATHWAYS (CATABOLIC)
ATP
simple organic compounds
energy-poor products
ENERGY INPUT
20
Types of Reaction Sequences
A
B
C
D
E
F
LINEAR PATHWAY
CYCLIC PATHWAY
G
K
J
I
BRANCHING PATHWAY
N
M
L
H
Figure 6.8Page 102
21
Which Way Will a Reaction Run?

• Nearly all chemical reactions are reversible

22
Chemical Equilibrium
RELATIVE CONCENTRATION OF PRODUCT
RELATIVE CONCENTRATION OF REACTANT
HIGHLY SPONTANEOUS
EQUILIBRIUM
HIGHLY SPONTANEOUS
Figure 6.9Page 103
23
Chemical Equilibrium

• Energy in the reactants equals that in the
  products
• Product and reactant molecules usually differ in
  energy content
• Therefore, at equilibrium, the amount of reactant
  almost never equals the amount of product

24
No Vanishing Atoms

• Law of conservation of mass
• Reactions rearrange atoms, but they never destroy
  them
• As many atoms of each element in all the products
  as there were in all the reactants

25
Electron Transfer Chains

• Arrangement of enzymes, coenzymes, at cell
  membrane
• Works like a bucket brigade in fighting fires in
  that electrons are transferred from a carrier to
  the next in the cell membrane.

26
Enzyme Structure and Function

• Enzymes are catalytic molecules
• They speed the rate at which reactions approach
  equilibrium

27
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.

28
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.
29
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
Figure 6.12aPage 105
30
Factors Influencing Enzyme Activity

• Coenzymes and cofactors
• regulators
• Temperature
• pH
• Salt concentration

31
Effect of Temperature

• Small increase in temperature increases molecular
  collisions, reaction rates
• High temperatures disrupt bonds and destroy the
  shape of active site

Figure 6.17bPage 109
32
Effect of pH

Figure 6.17cPage 109
33
Beer, Enzymes, and Your Liver

• Alcohol dehydrogenase
• Acetaldehyde dehydrogenase
• Cytochrome and catalase
• Heavy drinking destroys liver cells and bodys
  ability to detoxify alcohol