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 = ecosystem
H = change in total energy in the system
T = temperature (°K)→ °C + 273
S = 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
Example: Photosynthesis
ΔG = +686 Kcal/mole
Endergonic
consumes energy (sun light)
6CO2 + 12H2O
C6H12O6 + 6O2 + 6H20
ΔG>O
Class Activity
Without ATP
GLU
+
glutamic acid

glutamic acid + ammonia

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?



=
NH3
ammonia
glutamine
glutamine
answers






glutamic acid + ammonia
ΔG = +3.4 Kcal
glutamine
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


Transport work


movement of cell/organelle
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

G= +7.3 kcal/mole

endergonic
ATP + H2O
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 to
reach the state allowing
bond breakage A
new bonds form releasing
energy 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-substrate
complex
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
Active form

There are 3 forms of regulation



Allosteric activator
Allosteric inhibitor
Cooperativity
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
ACTIVITY
A
X
B
C
Z
Y
Which of these (A, B, C) has a non-competitive inhibitor?
What is "X"?
What is “Z"?
What is “Y”?
answers




C
Substrate
Competitive inhibitor
Enzyme
ACTIVITY
C
A
B
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?
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 causes
the inhibition of the
enzyme
Activity

catechol + O2 → benzoquinone + H2O
catechol oxidase





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?
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