Ground Rules of Metabolism

1
Ground Rules of Metabolism

• Chapter 5

2
Growing Old with Molecular Mayhem

• Free radical
• A molecule that has unpaired electrons
• Highly reactive, can disrupt structure of
  molecules

3
Superoxide Dismutase

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

4
Catalase

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

5
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

6
What is Energy?

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

7
What Can Cells Do with Energy?

• Energy inputs become coupled to energy-requiring
  processes
• 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
• The world of life can resist the flow toward
  maximum entropy only because it is resupplied
  with energy from the sun

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 Reactions

• Energy input required
• Product has more energy than starting substances

product with more energy (plus by-products 602
and 6H2O)
ENERGY IN
6
12
14
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
15
The Role of ATP

• Cells earn ATP in exergonic reactions
• Cells spend ATP in endergonic reactions

adenine
P
P
P
ribose
16
Electron Transfers

• Electrons are transferred in virtually every
  reaction that harnesses energy for use in the
  formation of ATP
• Coenzymes assist in electron transfers

17
Electron Transport Systems

• Arrangement of enzymes, coenzymes, at cell
  membrane
• As one molecule is oxidized, next is reduced
• Function in aerobic respiration and
  photosynthesis

18
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 its less concentrated - down
  gradient

19
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)

20
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

21
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

22
Chemical Equilibrium
RELATIVE CONCENTRATION OF PRODUCT
RELATIVE CONCENTRATION OF REACTANT
HIGHLY SPONTANEOUS
EQUILIBRIUM
HIGHLY SPONTANEOUS
23
Chemical Equilibrium

• At equilibrium, the 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
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
25
Participants in Metabolic Pathways

• Energy Carriers
• Enzymes
• Cofactors

• Substrates
• Intermediates
• End products

26
Types of Reaction Sequences
LINEAR PATHWAY
CYCLIC PATHWAY
A
B
C
D
E
F
K
J
I
G
N
M
L
H
BRANCHING PATHWAY
27
Enzyme Structure and Function

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

28
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

29
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
30
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
31
Induced-Fit Model
two substrate molecules
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
32
Factors Influencing Enzyme Activity

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

33
Allosteric Activation
enzyme active site
allosteric activator
vacant allosteric binding site
active site cannot bind substrate
active site altered, can bind substrate
34
Allosteric Inhibition
allosteric inhibitor
allosteric binding site vacant active site can
bind substrate
active site altered, cant bind substrate
35
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
36
Effect of Temperature

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

37
Effect of pH

38
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

39
Cell Membranes Show Selective Permeability
O2, CO2, and other small nonpolar moleculesand
H2O
C6H12O6, and other large, polar (water-soluble)
molecules ions such as H, Na, CI-, Ca plus
H2O hydrogen-bonded to them
X
40
Membrane Crossing Mechanisms

• Diffusion across lipid bilayer
• Passive transport
• Active transport
• Endocytosis
• Exocytosis

41
Transport Proteins

• Span the lipid bilayer
• Interior is able to open to both sides
• Change shape when they interact with solute
• Play roles in active and passive transport

42
Passive Transport

• Flow of solutes through the interior of passive
  transport proteins down their concentration
  gradients
• Passive transport proteins allow solutes to move
  both ways
• Does not require any energy input

43
Passive Transport
solute
44
Active Transport

• Net diffusion of solute is against concentration
  gradient
• Transport protein must be activated
• ATP gives up phosphate to activate protein
• Binding of ATP changes protein shape and affinity
  for solute

45
Active Transport
High solute concentration
Low solute concentration

• ATP gives up phosphate to activate protein
• Binding of ATP changes protein shape and affinity
  for solute

P
ATP
ADP
P
P
P
46
Bulk Transport
Exocytosis
Endocytosis
47
Osmosis

• Diffusion of water molecules across a selectively
  permeable membrane
• Direction of net flow is determined by water
  concentration gradient
• Side with the most solute molecules has the
  lowest water concentration

48
Tonicity

• Refers to relative solute concentration of two
  fluids
• Hypertonic - having more solutes
• Isotonic - having same amount
• Hypotonic - having fewer solutes

49
Tonicity and Osmosis
2 sucrose
water
10 sucrose
2 sucrose
50
Increase in Fluid Volume
compartment 1
compartment 2
membrane permeable to water but not to solutes
fluid volume increases In compartment 2
51
Pressure and Osmosis

• Hydrostatic pressure
• Pressure exerted by fluid on the walls that
  contain it
• The greater the solute concentration of the
  fluid, the greater the hydrostatic pressure
• Osmotic pressure
• Amount of pressure necessary to prevent further
  increase of a solutions volume