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Energy
An Introduction to Metabolism
Metabolism
catabolism - breakdown anabolism - synthesize
Metabolic Pathway
Series of enzymatically catalyzed reactions examples
Cellular respiration Photosynthesis
http://www.biomedical-engineering-online.com/content/figures/1475-925X-3-15-1-l.jpg
Energy
Capacity to do work, to move matter against opposing force
Kinetic Energy (KE) energy of motion
Potential Energy (PE) energy of location or structure
Energy Transformations
KE --------------------> PE sunlight glucose
PE ----------------------> KE glucose breathing
Thermodynamics
The study of energy transformations Unit of energy = Kcal = 1000 calories
Calorie Heat required to raise the temperature of 1
g of water 1 °C
Laws of Thermodynamics
Laws that govern energy changes
First Law of Thermodynamics Second Law of Thermodynamics
First Law of Thermodynamics Law of Conservation of Energy
Energy cannot be created or destroyed, only transferred and transformed quantity is constant, not quality
System collection of matter under study
Closed - system is isolated from its surroundings Open - energy can be transferred between the system and
surroundings
If energy is constant (1st law), why can’t organisms recycle their energy?
Every energy transformation or transfer,
some energy becomes unusable (unavailable to do work)
Second Law of Thermodynamics Entropy (S) increases in the
universe ordered forms of energy are partly converted to
heat
Energy transformations are not 100% efficient it is estimated that in 100 billion years all energy
will be converted to heat
Free Energy
energy available to do work ΔG = ΔH - TΔS
Δ means "change in"G = ecosystemH = change in total energy in the systemT = temperature (°K)→ °C + 273S = entropy
It informs us if a process can occur spontaneously free energy is required for spontaneous change
Types of Chemical Reactions
Endergonic reactions
Exergonic reactions
G = free energy G = G final state - G starting state
G < 0 releases energy Exergonic reaction spontaneous
G > 0 consumes energy Endergonic reaction nonspontaneous
G = 0 reaction at equilibrium
Exergonic
reactants products ΔG<O
example: cellular respiration
C6H12O6 + 6O2 6CO2 + 6H2O
ΔG = -686 Kcal/mole
Exergonic
Releases energy (36-38 ATP)
Endergonic
reactants products ΔG>O
Example: Photosynthesis
ΔG = +686 Kcal/mole
Endergonic
consumes energy (sun light)
6CO2 + 12H2O C6H12O6 + 6O2 + 6H20
Class Activity glutamic acid + ammonia
glutamine ΔG = +3.4 Kcal
Is this exergonic or endergonic? Does it release or consume energy? Which has greater free energy?
(reactants or products) How many ATP are needed?
GLU NH3
glutamic acid ammonia
+ =
glutamine
Without ATP
answers
glutamic acid + ammonia glutamine ΔG = +3.4 Kcal
Is this exergonic or endergonic? Endergonic, the ΔG is positive Does it release or consume energy? Consumes Which has greater free energy? Products
(reactants or products) How many ATP are needed? About half (one ATP requires 7.3 Kcal)
Cellular Work
Mechanical work movement of cell/organelle
Transport work active transport
Chemical work synthesis of polymers
ATP
Adenosine Tri Phosphate
Adenosine Adenine Ribose
3 phosphate
ATP Hydrolysis
In lab conditions (standard conditions) ΔG = -7.3 kcal/mole
exergonic
ATP + H2O ADP + Pi
ATP Synthesis
In lab conditions:
ADP + Pi ATP + H2O
G= +7.3 kcal/mole
endergonic
Activation Energy (EA)
Energy required to break existing bonds before forming new bonds
The difference between free energy of the products and the free energy of the reactants is the ΔG.
reactants absorb E toreach the state allowingbond breakage
new bonds form releasing
energy
A
B
A
B
Activation Energy (EA) cont.... Some require a low EA
Thermal energy provided by room temperature is sufficient to reach the transition state
Most require high EA Gasoline + oxygen, water evaporation Heat would speed reactions, but it would also
denature proteins and kill cells
Enzymes speed reactions by lowering EA
The transition state can then be reached even at moderate temperatures
Catalyst
Chemical agent that accelerates a reaction by reducing the amount of activation energy required
They don’t change the ΔG
Enzymes
Class of proteins serving as catalysts
specific suffix -ase
Catechol oxidase Sucrase ATP synthase Carbonic anhydrase
Enzymes (cont.)
CO2 + H2O H2CO3
without enzyme: 200 = 2 x 102 per hour
with enzyme: 2,000,000,000 = 2 x 109 per hr(carbonic anhydrase)
Enzymes are Substrate Specific Substrate
Active site of enzyme
Induced fit
enzyme-substratecomplex
Enzymes
A single enzyme molecule can catalyze thousands or more reactions a second
Enzymes are unaffected by the reaction
and are reusable
Most metabolic enzymes can catalyze a reaction in both the forward and reverse direction
Some Factors that Affect Enzyme Activity
temperature pH specificity cofactor necessity ionic concentration substrate concentration
1. Temperature As T° increases, activity increases
BUT at some point thermal agitation begins to
disrupt the weak bonds that stabilize the protein’s active conformation and the protein denatures
each enzyme has an optimal temperature
2. pH
pH also influences shape each enzyme has an optimal pH Most enzymes fall between pH 6 - 8
3. Specificity
How discriminating the enzyme is in catalyzing different potential substrates
4. Cofactor Necessity
Some enzymes require a cofactor (nonprotein portion) they bind to the enzyme permanently or reversibly
Inorganic (cofactor)→ minerals
Organic cofactors (coenzymes) → vitamins, NAD, FAD
The way in which cofactors assist catalysis are diverse
5. Ionic Concentration
Ions interfere with the enzymes ionic bonds
Can disrupt the tertiary level
6. Substrate Concentration Substrate concentration is directly
proportional to the rate until saturation of enzyme is reached
ACTIVITY
You are designing an experiment with an enzyme (amylase) that breaks down starch and is present in your small intestine.
What temperature will be the best? What pH will be the best? What substrate is the best? What other factors should you consider?
answers
You are designing an experiment with an enzyme (amylase) that breaks down starch and is present in your small intestine.
Temperature: 37°C pH: 8 Substrate: Starch Other factors to consider: cofactors
Effectors
Chemicals that regulate enzyme activity Inhibitors Activators
Inhibitors
Turn enzymes "off" end product competitive inhibitor
binds to active site reversible or permanent
noncompetitive inhibitor binds to allosteric site reversible
Applications
Pesticides are toxic to insects; Nerve gas toxic to humans inhibit key enzymes in the nervous system
DDT, malathion and parathion inhibit acetylcholinesterase Nerve cells cannot transmit signals, death occurs
Cyanide inhibits enzyme from making ATP
Many antibiotics inhibit enzymes in bacteria Penicillin inhibits an enzyme used in making cell walls
Cancer drugs inhibit enzymes that promote cell division
Allosteric Enzymes
Enzymes that exist in active or inactive form
There are 3 forms of regulation Allosteric activator Allosteric inhibitor Cooperativity
Active form
Allosteric Activator
Binds to allosteric site stabilize the conformation that has a
functional active site Increases enzyme activity
Allosteric Inhibitor (noncompetitive)
Binds to allosteric site stabilize the conformation that lacks an
active site. Reduces enzyme activity
Cooperativity
enzyme w/multiple subunits
Binding of one substrate to active site causes all subunits to assume their active conformation
A B C
Which of these (A, B, C) has a non-competitive inhibitor?
What is "X"?
What is “Z"?
What is “Y”?
ACTIVITY
X
Y
Z
answers
C Substrate Competitive inhibitor Enzyme
ACTIVITY
What type of enzyme is this?What is represented by A?What is the effect of C on the enzyme in this case?Is B an example of stable or inactive?
AB
C
answers
Allosteric Inactive subunit Activates the enzyme Stable
Enzyme structure (some)
Types of enzymes Enzyme: cofactor independent
Holoenzyme: has a permanently bound cofactor
Enzyme + cofactor Apoenzyme: has a temporary
cofactor Enzyme portion
Cofactor
Inorganic cofactor - metal ion Zn, Fe, Mg, Cu
Organic cofactors, coenzymes vitamins or molecules derived from vitamins NAD+ , NADP + , FAD
Feedback Inhibition Mechanism The switching off of a pathway by its end
product
Negative feedback prevents a cell from wasting resources
Feedback Inhibition
Too much production of isoleucine causesthe inhibition of theenzyme
Activity catechol + O2 → benzoquinone + H2O
what is the substrate? what is the enzyme? what is the product? knowing you need to heat it for the reaction to
occur, does it consume energy? Is it endergonic or exergonic?
catechol oxidase
answers
Substrate: Catechol Enzyme: Catechol oxidase Product: Benzoquinone Consumes energy? Yes Type of reaction: Endergonic
ACTIVITY
lactose + H2O → glucose + galactose what do you expect the name of the enzyme
will be? it needs the presence of Ca+2 and/or Mg+2, what
is their function? If having this reaction in the lab, how would you
stop it, considering all factors seen before? If using negative feed back to stop it, what do
you need to add to the solution where the reaction is taking place?
answers
Lactase Cofactors Either:
Increase or decrease in temperature Lower or increase the pH Subtract the cofactors
Lactose
The End