Download Metabolism Fansler

Chapter 8
Metabolism
Powerpoint Templates
Page 1
Flow of Energy Through Life
• Life is built on chemical reactions
– Transforming energy from one form to another
sun
Solar Energy  Organic
Compounds + ATP
Organic Compounds 
Organic Compounds+ ATP
Powerpoint Templates
Organic Compounds 
Organic Compounds + ATP
Page 2
Metabolism = all chemical reactions in an
organism
• Catabolic
–
–
–
–
–
Breaking Bonds
Digestion
Hydrolysis
Polymer  Monomer
Releases Energy
• Anabolic
–
–
–
–
Forming Bonds
Dehydration
Monomer  Polymer
Requires EnergyPowerpoint Templates
Page 3
Thermodynamics
• The study of energy transformation
– Energy = the capacity to do work
• 1st Law of Thermodynamics
– Energy is neither created nor destroyed but
transformed (Conservation of Energy)
• 2nd Law of Thermodynamics
– Energy transformation increases entropy (disorder,
randomness)
• Combine the 2 Quantity of Energy is constant,
Quality is not.
Powerpoint Templates
Page 4
Entropy
• Disorder, Randomness
Powerpoint Templates
Page 5
• Living things want LESS entropy
–
–
–
–
They want to be in ORDER
They require ENERGY
This is NOT spontaneous
However, INCREASES the entropy of the universe
Heat
co2
+
H2O
(b) Second law of thermodynamics: Every energy transfer or transformation increases
the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s
surroundings in the form of heat and the small molecules that are the by-products
of metabolism.
Powerpoint Templates
Figure 8.3
Page 6
Free Energy
•
•
•
•
The energy available to do work
∆G
Exergonic Rxns = release free energy, decrease ∆G
Endergonic Rxns = require free energy, increase
∆G
Powerpoint Templates
Page 7
Exergonic
• Reactants have more
energy than products
• More ordered to less
ordered (increase in entropy)
• Unstable to stable (less likely
to transform energy)
•
•
•
•
•
•
Downhill rxn
Free energy released
∆G negative
Spontaneous
Catabolic
Ex: Digestion
Powerpoint Templates
Page 8
Endergonic
• Reactants have less energy
than products
• Less ordered to more
ordered (decrease in entropy)
• Stable to unstable (more likely
to transform energy)
•
•
•
•
•
•
Uphill rxn
Free energy required
∆G positive
Non-Spontaneous
Anabolic
Ex: Polymer synthesis
Powerpoint Templates
Page 9
Equilibrium
• Eventually a closed system (separated from outside)
reaches equilibrium
• ∆G = 0
∆G < 0
Figure 8.7 A
∆G = 0
(a) A closed hydroelectric system. Water flowing downhill turns a turbine
that drives a generator providing electricity to a light bulb, but only until
the system reaches equilibrium.
• Living cells are open systems (materials constantly moving
in and out) – prevented from reaching equilibrium
Powerpoint Templates
Page 10
Where do we get the energy
from?
• Work of life is done by energy coupling
– use exergonic (catabolic) reactions to fuel
endergonic (anabolic) reactions
digestion
+
+
energy
synthesis
+
+
energy
Powerpoint Templates
Page 11
ATP
• Adenosine Triphosphate
• Cellular energy
• Modified nucleotide
Adenine
N
O
O
-O
O-
O-
O
N
CH2
O
C
N
CH
C
N
OH
Phosphate groups
Figure 8.8
C
HC
O
O
O
NH2
H
H
H
OH
Powerpoint Templates
Ribose
OH
Page 12
• Energy is released when terminal phosphate bond is
broken
• Becomes ADP (diphosphate) and an inorganic phosphate
(Pi)
• Many endergonic
P
P
P
rxns are fueled by
Adenosine triphosphate (ATP)
phosphorylation from
HO
ATP.
2
P
i
+
Figure 8.9 Inorganic phosphate
P
P
Energy
Adenosine diphosphate (ADP)
Powerpoint Templates
Page 13
ATP – ADP Cycle
• Can’t store ATP
– Too reactive
– Transfers Pi easily
– Short term energy
Powerpoint Templates
Page 14
Activation energy
• Breaking down large molecules requires an
initial input of energy
– activation energy
– large biomolecules are stable
– must absorb energy to break bonds
cellulose
Powerpoint
TemplatesCO2 + H2O + heat
energy
Page 15
Reducing Activation energy
• Catalysts
– reducing the amount of energy to
start a reaction = activation energy
uncatalyzed reaction
catalyzed reaction
NEW activation energy
reactant
product
Powerpoint Templates
Page 16
Enzymes Decrease Activation
Energy
Powerpoint Templates
Page 17
• Biological catalysts
– Proteins
Enzymes
• Can be denatured
– Facilitate chemical reactions
• increase rate of reaction (catalyst)
• reduce activation energy
• doesn’t change free energy (G) released or required
– required for most biological reactions
– reusable
– highly specific
• thousands of different enzymes in cells
– End in “ase”
• Sucrase, Lactase, Lipase,
Polymerase
Powerpoint
Templates
Page 18
Enzymes vocabulary
substrate
• reactant which binds to enzyme
• enzyme-substrate complex: temporary association
product
• end result of reaction
active site
• enzyme’s catalytic site; substrate fits into active site
active site
substrate
enzyme
Powerpoint Templates
products
Page 19
Enzyme Catalyzed Reactions
Course of
reaction
without
enzyme
EA
without
enzyme
Free energy
EA with
enzyme
is lower
Reactants
∆G is unaffected
by enzyme
Course of
reaction
with enzyme
Products
Progress of the reaction
Figure 8.15
Powerpoint Templates
Page 20
Lock and Key vs. Induced Fit
• Lock and Key
– Substrates fit in active site perfectly
– H bonds hold substrate in active site
• Induced Fit
– Enzyme active site changes shape to fit snug around
active site
Powerpoint Templates
Page 21
Factors affecting enzyme
function
• Enzyme concentration
– as  enzyme =  reaction rate
• more enzymes = more frequently collide with substrate
– reaction rate levels off
reaction rate
• substrate becomes limiting factor
• not all enzyme molecules can find substrate
Powerpoint Templates
enzyme concentration
Page 22
Factors affecting enzyme
function
• Substrate concentration
– as  substrate =  reaction rate
• more substrate = more frequently collide with enzyme
– reaction rate levels off
reaction rate
• all enzymes have active site engaged
• enzyme is saturated
• maximum rate of reaction
Powerpoint Templates
substrate concentration
Page 23
•
Factors affecting enzyme
function
Temperature
– Optimum T°
• greatest number of molecular collisions
– Heat: increase beyond optimum T°
• increased energy level of molecules disrupts bonds in enzyme &
between enzyme & substrate
• denaturation = lose 3D shape (3° structure)
– Cold: decrease T°
• molecules move slower
• decrease collisions between enzyme & substrate
Powerpoint Templates
Page 24
Enzymes and temperature
• Different enzymes function in different
organisms in different environments
reaction rate
human enzyme
hot spring
bacteria enzyme
37°C
Powerpoint Templates
temperature
70°C
Page
25
(158°F)
Factors affecting enzyme
function
• pH
– changes in pH
• disrupts bonds, disrupts 3D shape
– disrupts attractions between charged amino acids
– affect 2° & 3° structure
– denatures protein
– optimal pH?
• most human enzymes = pH 6-8
– depends on localized conditions
– pepsin (stomach) = pH 2-3
– trypsin (small intestines) = pH 8
Powerpoint Templates
2611
0 1 2 3 4 5 6 7 Page
8 9 10
Factors affecting enzyme
function
• Salt concentration
– changes in salinity
• disrupts bonds, disrupts 3D shape
– disrupts attractions between charged amino acids
– affect 2° & 3° structure
– denatures protein
– enzymes intolerant of extreme salinity
• Dead Sea is called dead for a reason!
Powerpoint Templates
Page 27
Enzyme HELPERS
• Cofactors
– Non-proteins, ions
– Mg, K, Ca, Zn, Fe, Cu
– Ex: Fe in hemoglobin
• Coenzymes
– Non-Protein, Organic molecules
– Ex: Vitamins
Powerpoint Templates
Page 28
Enzyme INHIBITORS
• Competitive Inhibitors
– Compete for active sites
– Combat by increasing
substrate
– Ex: Penicillin
• Prevents bacterial cell
enzyme from making cell
walls
• Bacterial cell bursts
A substrate can
bind normally to the
active site of an
enzyme.
Substrate
Active site
Enzyme
(a) Normal binding
A competitive
inhibitor mimics the
substrate, competing
for the active site.
Figure 8.19
Powerpoint Templates
Competitive
inhibitor
(b) Competitive inhibition
Page 29
Enzyme INHIBITORS
• Non-Competitive Inhibitor
– Does not bond to active site, but somewhere else
– Causes enzyme to change shape
– Structure-Function Relationship
A noncompetitive
inhibitor binds to the
enzyme away from
the active site, altering
the conformation of
the enzyme so that its
active site no longer
functions.
Noncompetitive inhibitor
Figure 8.19
Powerpoint Templates
(c) Noncompetitive inhibition
Page 30
Regulation of Enzymes
• Allosteric Regulation
– Enzyme’s function at one site is affected by the binding
of a regulatory molecule at another site
– Causes a shape change
 Inhibitors
• keeps enzyme in inactive form
 Activators
• keeps enzyme in active form
Powerpoint Templates
Page 31
Allosteric enyzme
with four subunits
Allosteric activater
stabilizes active from
Active site
(one of four)
Regulatory
site (one
of four)
Activator
Active form
Stabilized active form
Allosteric activater
stabilizes active form
NonInactive form
functional
active
site
Figure 8.20
Inhibitor
Stabilized inactive
form
(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors
dissociate when at low concentrations. The enzyme can then oscillate again.
Powerpoint Templates
Page 32
Metabolic Pathways
• Begins with a specific molecule and ends with a
product
• Each step is catalyzed by a specific enzyme
Enzyme 1
A
Reaction 1
Starting
molecule
Enzyme 2
Enzyme 3
D
C
B
Reaction 2
Reaction 3
Product
Powerpoint Templates
Page 33
Feedback Inhibition
• The end product of a metabolic pathway shuts down the
pathway
• AKA Negative Feedback
Powerpoint Templates
Page 34
Initial substrate
(threonine)
Example
Active site
available
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Active site of
enzyme 1 no
longer binds
threonine;
pathway is
switched off
Enzyme 2
Intermediate B
Enzyme 3
Intermediate C
Isoleucine
binds to
allosteric
site
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine)
Figure 8.21
Powerpoint Templates
Page 35