Energy

An Introduction to Metabolism

Metabolism

catabolism - breakdown anabolism - synthesize

Metabolic Pathway

Series of enzymatically catalyzed reactions examples

Cellular respiration Photosynthesis

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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