GENERAL CHEM: INTRO TO ENZYMES - STEMPREP 2013€¦ · –Enzymes and catalysts both affect the rate of a reaction. –Neither catalysts nor enzymes are consumed in the reactions

GENERAL CHEM: INTRO TO ENZYMES

LESSON 5

GRADE 8

JULY 1, 2013


• OBJECTIVES:

– Catalysts & their functions

– Catalyst & Enzyme chemistry kinetics

– Enzymes and their functions

– 6 Classes of enzymes

– Common enzymes


First, let’s do a

bit of a

review…

Chemical eqns & stoichiometry review

• Last week we learned about chemical equations. Who can tell me the definition of a chemical equation?

– “A chemical equation is the symbolic representation of a chemical reaction wherein the [reactants] are given on the left hand side and the [products] on the right hand side.

– The coefficients next to the symbols and formulas of [atomic] entities are the absolute values of the stoichiometric numbers.”*

𝑨 + 𝑩 → 𝑪 + 𝑫 (REACTANTS) (PRODUCTS)

1 2 1 2

• Based on this information, what would be the stoichiometric mole ratio of A to B?

𝟐 𝒎𝒐𝒍 𝑩

𝟏 𝒎𝒐𝒍 𝑨

• What is the stoichiometric mole ratio for Na to HCl in the chemical equation below?

𝟐 𝑚𝑜𝑙 𝑁𝑎

𝟐 𝑚𝑜𝑙 𝐻𝐶𝑙

2HCl + 2Na → 2NaCl + H2



• Reactants interact with each other (OR COLLIDE) to form products during the course of a chemical reaction.

– For example:

– In order for the formation of products to occur, reactants must come together (OR COLLIDE) in a certain conformation.

– In some reactions, the reactants cannot do this on their own or it takes a very long time for it to happen.

– Which leads us to our discussion of catalysts and enzymes.

2HCl + 2Na → 2NaCl + H2

INTRO TO CATALYSTS & ENZYMES

• Reactions are always happening.

– Chemicals are always combining or breaking down, but this is not always happening at the same speed.

– Catalysts allow a reaction to proceed at a much faster rate.


• What is a catalyst?

– Catalysts are SUBSTANCES which help bring reactants together to form products.

– They have the following characteristics:

1. Catalysts SPEED UP the RATE (denoted as rate constant ‘k’) of the reaction.

2. Catalysts LOWER the ACTIVATION ENERGY (Ea) of the reaction.

3. Catalysts are NOT CONSUMED during the reaction.

Some definitions to help this all make sense

1. Catalysts speed up the reaction rate:

–Reaction rate (k)

• The reaction rate (rate of reaction, k) or speed of reaction for a reactant or product in a particular reaction

• Or, how fast or slow a reaction takes place.

– If a reaction has a low reaction rate, that means the reactant molecules collide/combine at a slower speed (relative to a reaction with a high reaction rate).

– If a reaction has a high reaction rate, that means the reactant molecules collide/combine to form product molecules at a faster speed (relative to a reaction with a low reaction rate).


• Catalysts speed up the reaction rate (k):

– Low reaction rate:

https://www.youtube.com/watch?v=OBjddJJCm2s

– Vs. high reaction rate:

https://www.youtube.com/watch?v=6FRzmTY7wrk







• The collision theory states:

– Only collisions with enough energy react to form products.

– As more collisions in a system occur, there will be more combinations of molecules colliding into each other.

– The reaction will go faster and the rate of that reaction will be higher.

• For example, think about how slowly molecules move in syrup compared to baking soda volcano with vinegar added. Which liquid has the least amount of collisions occurring?

Collision theory & reaction rates


2. Catalysts LOWER the ACTIVATION ENERGY (Ea) of the reaction:

‒ Activation Energy (Ea) The critical amount of energy to make the reaction proceed is called the Activation Energy.

• Can be thought of as an energy barrier.

• This energy is required for every reaction

‒ Regardless of whether the energy of the final product is more than (endergonic) or less than (exergonic) the reactants.

‒ Catalysts (& enzymes) affect the Ea, not the THERMODYNAMICS of the system.


ACTIVATION ENERGY

REACTION


A + B

C + D

A very important aside

• What is an exergonic reaction?

• Exergonic reaction An exergonic reaction is a chemical reaction wherein the change in the Gibbs free energy (∆G) is negative, indicating a

spontaneous reaction.

– This is true for processes which take place under

constant pressure and temperature conditions.

–∆G < 0

ACTIVATION ENERGY (Ea) is required regardless of whether the energy of the final product is more (endergonic) or less than (exergonic) the reactants. Catalysts & enzymes affect Ea, not the thermodynamics.

∆G < 0 spontaneous


• Endergonic reaction the reaction absorbs energy in the form of work.

– The reaction is not spontaneous.

– During an endergonic process, energy is put into the system, if the reaction process occurs at constant

pressure and temperature, ∆G > 0.


∆G > 0

not spontaneous



A + B

C + D

Notice that the energy of the products and reactants did NOT CHANGE after the

catalyst was added.

Catalysts only influence the KINETICS (rate) of the reaction, not the THERMODYNAMICS

(energy of the products or reactants).

Endergonic/ Exergonic are NOT the same as EXOTHERMIC & ENDOTHERMIC

• The terms Exothermic/Endothermic

– tell us about the heat of the reaction: ∆H

• The terms Endergonic/Exergonic

– tell us about the free energy of the reaction: ∆G

NEITHER of these energies are affected by catalysts!!

End of aside. Back to catalysts

Catalysts only influence the KINETICS (rate) of the reaction, not the THERMODYNAMICS (energy of the products or reactants).

• Thermodynamics:

– ∆G, ∆S, & ∆H

– Tells us:

• whether a reaction can occur at all (spontaneously or otherwise)

• The stability of a reaction

• The energy of a reaction (usually HEAT energy)

• Kinetics

– Reaction rate (rate constant k)

• How FAST a reaction will occur

• The TIME it will take a reaction to occur

• The SPEED of a reaction; or RAPIDITY

3. Catalysts are NOT CONSUMED during the

reaction.

+

What are some possible catalysts for this reaction?: • A Spoon • A Straw


• What is a catalyst?

– Catalysts are SUBSTANCES which help bring reactants together to form products.

– They have the following characteristics:

1. Catalysts SPEED UP the RATE of the reaction.

2. Catalysts LOWER the ACTIVATION ENERGY (Ea) of the reaction.

3. Catalysts are NOT CONSUMED during the reaction.

10 minute break!!

• There are FOUR classes of macromolecules included in the building blocks of life:

1. CARBOHYDRATES (or carbs)

– Carbs are the most abundant macromolecule of the four.

– What’s an example of a biologically important carb?

• Glucose

MORE DEFINITIONS

2. NUCLEIC ACIDS ‒ This class has the largest

macromolecules. ‒ What’s an example of a nucleic

acid? • DNA • RNA

• FOUR classes of macromolecules cont’d:

MORE DEFINITIONS

3. FATS • Made up of fatty acids

• This class is the most diverse.

• This is what 1 lb of fat looks like

4. PROTEINS • Made up of amino acids

• This class is the most complex.

• What 1lb of muscle looks like

• What is a protein?

– Proteins are large biological molecules consisting of one or more chains of amino acids (organic compounds of which proteins are comprised).

• Proteins perform a vast array of functions within living organisms, including: – catalyzing metabolic reactions,

– replicating DNA,

– responding to stimuli,

– and transporting molecules from one location to another.

– What do proteins have to do with enzymes?

INTRO TO ENZYMES

• Enzymes are complex proteins that cause a specific chemical change in the body. – For example, they can help break

down the foods you eat so your body can use them.

• Enzymes are needed for all body functions. They are found in every organ and cell in the body, including in the: – Blood – Intestinal fluids – Mouth (saliva) – Stomach (gastric juice)

Enzyme = biocatalyst

Enzymes are NOT CHANGED by the chemical

reaction!!

INTRO TO ENZYMES

• Why do we say catalyst sometimes instead of enzyme and vice versa? What’s the big deal?

– Enzymes and catalysts both affect the rate of a reaction.

–Neither catalysts nor enzymes are consumed in the reactions they catalyze.

– The difference between catalysts and enzymes is that while

catalysts are inorganic compounds, enzymes are largely

organic in nature and are termed bio-catalysts.

– Even though all known enzymes are catalysts, all catalysts are not enzymes.


INTRO TO CATALYSTS & ENZYMES • What is an enzyme?

– Enzymes are proteins which help bring reactants together to form products.

– Just like catalysts, they have the following characteristics: 1. SPEED UP the RATE (denoted as rate constant ‘k’) of the

reaction.

2. LOWER the ACTIVATION ENERGY (Ea) of the reaction.

3. Are NOT CONSUMED during the reaction.

See Ea catalyst slides. The same applies to enzymes.

INTRO TO CATALYSTS & ENZYMES Catalyst Enzyme

Function: Catalysts are substances that

increase the rate of a chemical reaction but remain unchanged.

Enzymes are proteins that

increase rate of chemical reactions converting substrate

into product.

Molecular weight:

Low molecular weight compounds.

High molecular weight globular proteins.

Nature: Catalysts are simple inorganic

molecules. Enzymes are complex proteins.

Alternate terms: Inorganic catalyst. Organic catalyst or bio-catalyst.

C-C and C-H bonds:

absent present

Example: vanadium oxide amylase, lipase

Activation Energy:

Lowers it Lowers it

• Enzymes are complex, three-dimensional proteins that are biological catalysts (bio-catalysts).

– Nearly every chemical reaction that takes place involves an enzyme

– EVERY chemical reaction that takes place in the body INVOLVES an enzyme

– For example: • Glucose ↔ Glucose-6-Phosphate

(glycolysis) – Involves the enzyme hexokinase.

• Pyruvate ↔ acetyl coenzyme A (aerobic respiration) – Involves the enzymes of the

pyruvate dehydrogenase complex (PDH or PDHC).

MORE ABOUT ENZYMES

• Most enzymes are named for the reactants of the reactions they catalyze.

– For example, glucose is a 6 carbon sugar,

hence, the name HEXOkinase (hexo = 6).

• Most enzyme names also end with the suffix ‘ASE’

– Some biologically important enzymes are: • Catalase

• Pyruvate Dehydrogenase Complex (a complex of 3 enzymes)

• Pyruvate kinase

• Malate dehydrogenase

• Carbonic anhydrase

• DNA Helicase

ENZYMES NOMENCLATURE

• Enzymes are sensitive to: 1. TEMPERATURE:

– Proteins change shape as the temperature increases

• A protein’s activity is based on its shape or folding

• Because enzymes are made of proteins, can be denatured by excess heat

– Denatured unfolded; when enzymes are not folded properly, they are not functional

– As the temperature decreases, proteins don’t collide as much

• Remember the collision theory?

PROPERTIES OF ENZYMES

• Enzymes are sensitive to: 2. pH:

– The acidity or basicity of an environment can also change the shape of proteins

• Remember pH is a measure of the amount of acidity

• The level of acidity can cause the protein molecules to twist and/or unravel

– Denatured unfolded; when enzymes are not folded properly, they are not functional

• The level of basicity can change the charge on the protein molecules and render them unable to interact with their substrate

PROPERTIES OF ENZYMES cont’d:

• Enzymes are created in cells but can function inside OR outside of the cell.

• Every enzyme is SPECIFIC for a particular substrate.

• Enzymes are re-usable.


• How an enzyme works (4 steps):

1. The enzyme and its substrate are in the same vicinity.

• The substrate is the biological molecule on which the enzyme does work.

2. The enzyme binds its substrate at a specific area

called the active site.

• The active site is a specifically shaped area of

the enzyme which fits around (binds to) the substrate.


• How an enzyme works (4 steps cont’d): 3. The substrate undergoes catalysis.

• Catalysis changes the substrate. –Can either:

» break down the substrate

» or combine it with another molecule to make a completely new substance.

4. The enzyme releases its substrate. • This is very important and is possible b/c the

substrate interacts with the enzyme via NON-COVALENT reactions.


NON-COVALENT FORCES

• A non-covalent force is a type of chemical bond

which does not involve the sharing of electron pairs, but rather involves electromagnetic interactions.

• Relatively weak compared to covalent bonds

– van der Waals forces

– Charge-charge interactions

– Hydrogen bonds

– Hydrophobic effect

• How an enzyme works (4 steps cont’d): • Once the enzyme is free:

–The enzyme returns to its original configuration/shape

– It is ready to repeat the process.

–However, the substrates are no longer the same and are now termed the products.


• There are six to know:

1. Oxidoreductase – At what types of reactions does the name hint?

– Redox. This is an enzyme which catalyzes redox reactions.

2. Transferase – What does it sound like this enzyme does in a chemical

reaction?

– Transfers a chemical group from one compound to another • For example: a phosphotransferase

• What does it sound like it transfers?

• A phosphate group

ENZYMATIC MECHANISMS

•Hydrolases –Catalyze the hydrolysis of a chemical bond

–What does HYDROLYSIS sound like?

– The use of water to break a chemical bond


• Lyases – Breaks chemical bonds by means OTHER THAN

oxidation and hydrolysis.

• Isomerases – Causes compounds to structurally rearrange – Catalyzes the formation of isomers

• Ligases – Ligand = ligates – Catalyzes the binding or gluing together of chemical

compounds


SOME COMMON ENZYMES

• Alcohol dehydrogenase – Breaks down alcohol in the liver

• Amylase – Breaks down starch in the saliva

• ATP synthase – Makes ATP from ADP

• Catalase – Breaks down hydrogen peroxide

• Restriction enzymes – Cut DNA or RNA at specific

locations

• Reverse transcriptase – Used by retroviruses to make

DNA from RNA

• Urease – Breaks down urea

3. Enzymes are NOT CONSUMED during the

reaction.

What are some possible catalysts for this reaction?: • Stomach enzymes • Intestinal enzymes • Metabolic enzymes

Do you think catalysts were involved in the following reactions?

https://www.youtube.com/watch?v=HdMHel8z7lE

Documents

GENERAL CHEM: INTRO TO ENZYMES - STEMPREP 2013€¦ · –Enzymes and catalysts both affect the rate of a reaction. –Neither catalysts nor enzymes are consumed in the reactions