Download Enzymes

Energy, Enzymes,
and Metabolism
Fig. 5-UN1
Amino
group
Carboxyl
group
Primary Structure
• There are four levels of protein structure:
primary, secondary, tertiary, and quaternary.
• The peptide backbone consists of repeating
units of atoms: N—C—C—N—C—C.
• Primary Structure is
determined by the
specific amino acids
that are coded for by
the DNA sequence
coding its synthesis.
Secondary Structure
• A protein’s secondary structure consists
of regular, repeated patterns in different
regions in the polypeptide chain.
• This shape is influenced primarily by
hydrogen bonds arising from the amino
acid sequence (the primary structure).
• The two common secondary structures are
the a helix and the b pleated sheet.
• β Structure
• Pleated
• Peptide regions
are parallel to one
another
•
•
•
•
α Structure
Helical
Right handed structure
R group always points
away from the peptide
backbone
Tertiary Structure
• Tertiary structure is the threedimensional shape of the completed
polypeptide.
• The primary determinant of the tertiary
structure is the interaction between R
groups and the location of disulfide
bridges
Quaternary Structure
Results from
binding and
interactions
between
more than
one
polypeptide
structure
Other factors influencing structure
– The nature and location of secondary
structures
– Hydrophobic side-chain aggregation and van
der Waals forces, which help stabilize them
– The ionic interactions between the positive
and negative charges deep in the protein,
away from water
Effects of the environment in
Proteins
• Changes in temperature, pH, salt
concentrations, and oxidation or reduction
conditions can change the shape of proteins.
• Chaperonins- proteins that keep other
proteins from inappropriately interacting with
one another.
• This loss of a protein’s normal threedimensional structure is called denaturation.
A biological catalyst is any substance that
increases the rate of a reaction
Catalyst are not themselves
used up in the reaction
Substrate
(sucrose)
Enzyme (sucrase)
OH
Glucose
HO
Fructose
H2O
• Some chemical reactions are slow
because there is a barrier between the
reactants and products
• Others require activation energy:
– Activation energy (Ea) is energy needed to put
molecules in a transition state with a higher
energy rate
– Heat is typically used in exergonic reactions
to increase kinetic energy of molecules and
initiate the reaction
• Do these problems exist in biological
systems?
Overcoming Problems
• Heat is not a logical solution to increasing
energy in reactions in biological systems –
• Enzymes:
– Bind to reactant substrates at ACTIVE SITE
– At active site  catalysis occurs
– Very specific due to shape and structure of
active site
• Certain substrates
• Certain reactions
• Certain environmental conditions
Enzyme specificity
Induced fit:
enzyme shape
is caused by
the substrate
binding
Remainder of
molecule provides
framework of the
protein so the
active site in the
correct position.
How an enzyme works
• Enzyme is bound to substrate by:
– Hydrogen bonding
– Ionic bonding
– Covalent bonding
• These forces hold substrate to enzyme producing
an enzyme-substrate complex (ES)
• The enzyme-substrate complex generates the
product and free enzyme
• Enzymes lower the activation energy of the reaction
but do not change the ΔG of the reaction
• Do not change the equilibrium of the reaction
Lowered Activation Energy
Enzyme Jobs
• At active sites,
enzymes and
substrates break old
bonds and form new
bonds
• To catalyze a reaction,
enzymes will:
– Orient the substrate
– Cause substrate to be in
“distress”
– Add positive or negative
charges to the substrate
Orienting a substrate
• In solution- substrate molecules collide randomly
• This produces low probability that substrate will be at
the correct angle for collision
• Enzyme orients the substrates so that reaction is more
likely to occur
Inducing strain/ distress
• The enzyme will cause the structure of
the substrate to change
• 1. Carbohydrate substrate enters the
active site in a strong flattened ring
shape ( like an “O”)
• 2. Enzyme active site changes the
shape to be straight on one end
(like a “D”)
• 3. This produces a strain on the bonds
of the ring making it more reactive with
water
Producing Charge
• R groups of the enzymes’ amino acid chains can
make a substrate more chemically active
• There are 3 types of interaction:
– ACID- BASE CATALYSIS:
• Covalent bonds in substrate may be destabilized when H ion
transfer occurs between the active site of the enzyme and
the substrate
– COVALENT CATALYSIS:
• R groups interact and temporarily bond with the substrate
– METAL ION CATALYSIS:
• Metal ion electrons are gained or lost without detaching from
protein
Energy and Energy Conversions
• Remember:
– Energy is the capacity to do work
– Energy is neither created or lost
– Cells must acquire energy from its
environment
– Energy exists in two forms
• Kinetic
• Potential
Kinetic & Potential Energy
• Kinetic Energy– Energy of motion
– Does work that alters the state
or motion of matter
• Potential Energy– Stored energy
– Energy of state or position
Laws of Thermodynamics
• 1st law of thermodynamics• AKA – Principle of Conservation of
Energy
– Energy put in will be equal to the
energy put out.
– Energy is conserved
– Even though cells are living systems
they must obey these rules.
– Energy is neither created nor
destroyed.
– Energy can be transferred and
transformed
Laws of Thermodynamics
• 2nd Law of thermodynamics– Every energy transfer or
transformation increases the
entropy of the universe
– Entropy is defined as the
measure of disorder or
randomness
– Randomness is constantly
increasing in the universe
Laws of Thermodynamics
Free Energy
• Portion of a system’s energy
that can perform work when
temperature is uniform
• “Free” for doing work- still
costs universe energy
Bottom Line:
• The QUANTITY of energy in the
universe is constant.
• The QUALITY of energy is not
constant.
• In any system:
– Total energy = usable energy +
unusable energy
– In a reaction, increase in entropy
causes products to be more random
than the reactants
Enthalpy (H)
• In any system:
– Total energy = usable energy +
unusable energy
H = G + TS
H = enthalpy
G = free energy
T = absolute temperature
S = entropy
Energy Transfer
• Change in systems is
measured in calories/joules
• ΔG = ΔH - T ΔS
• ΔG is positive= free energy is
required
• Anabolic reactions
• ΔG is negative = free energy is
released
• Catabolic reactions
Metabolism
• Defined as all of an organisms combined
chemical reactions
• Two types exist:
– Anabolic reactions• Link simple molecules to make more
complex ones
• Characterized as energy storage reactions
• Free energy is required
– Catabolic reactions
• Break down complex molecules into
smaller ones
• Characterized as energy releasing
reactions
• Free energy is released
Reaction Relationships
• There is a direct relationship between
the energy taken in and the energy
produced.
• Reactions have a tendency to run to
completion because of this relationship.
• Transfer of energy from catabolism to
anabolism = energy coupling
• Forward and backward reactions are at
the same rate:
Equilibrium
Exergonic and Endergonic Reactions
• Spontaneous reactions
Cellular Respiration
– Go more than halfway
without energy input
– EXERGONIC
REACTION
– neg. ΔG = release energy
AB
Exergonic
• Non-spontaneous reactions
Photosynthesis
– Need activation energy for
reaction to proceed
– ENDERGONIC
– REACTION
– pos. ΔG = consumes energy
B  A Endergonic
Endergonic and Exergonic reactions
Hydrolysis of Proteins
Synthesis of Proteins
Endergonic Reactions
• If the surroundings do not
supply heat, an
endothermic transformation
leads to a decrease in the
temperature of the system.
• If the surroundings do
supply heat, an
endothermic transformation
leads to an increase in the
temperature of the system.
Exergonic Reactions
• Combustion
Reactions
complex
sequence of
exothermic
chemical
reactions
between a fuel
and an oxidant
accompanied by
the production of
heat or both heat
and light
in
the form of
either a glow
or flames.
• Neutralization Reactions
Water forming reaction in which
an acid and a base or alkali
(soluble base) react and produce a
salt and water solution (H2O)
Coupled Reactions
• ATP hydrolysis releases
energy
ATP + water 
ADP + Pion + free energy
• ATP synthesis
consumes energy
ADP + Pion + free energy 
ATP + water
ATP
Interesting Facts
• ATP molecules undergo
10,000 cycles of synthesis and
hydrolysis everyday
• Cells require more than one
million molecules of ATP per
second for biochemical
activities.
Catabolic reaction
Anabolic reaction
Coupled reactions
ADP
+ Pion
Energy in
Energy out
ATP
Accumulation of free energy in cells