Chemical Reactions and Enzymes

Enzymes - Introduction

What happens to the food we eat?

It breaks down into….

Carbohydrates

Proteins

Lipids

Nucleic acids!

Let’s look at… Lactose

• What is lactose?–Lactose is a

sugar found in dairy products

• They lack an enzyme: LACTASE

• Vocab:• Sugars end in “-ose”• Enzymes end in “-ase”

• But…what is an enzyme?

What do people who are lactose-intolerant lack?

Why do we study chemical reactions in biology?

• Chemistry isn’t just what life is made of, chemistry is also what life does

• Everything that happens in an organism is based on chemical reactions (growth, response to environment, etc.)

Chemical Reaction

• A process that changes reactants into products (the end substance in a the reaction).

• Slow Reactions vs. Fast Reactions

• Chemical reactions breaking bonds in reactants and forming bonds in products

CATABOLIC PATHWAY (CATABOLISM)Release of energy by the breakdown of complex molecules to simpler compoundsEX: digestive enzymes break down food

ANABOLIC PATHWAY (ANABOLISM)consumes energy to build complicated molecules from simpler onesEX: linking amino acids to form proteins

http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/nanoscience/sci_media/images/chemical_reactions_involve_making_new_combinations/53823-2-eng-NZ/chemical_reactions_involve_making_new_combinations_full_size_landscape.jpg

THERMODYNAMICS = the study of energy transformations

• CLOSED system (EX: liquid in a thermos) = isolated from its surroundings

• OPEN system energy + matter can be transferred between the system and its surroundings

• Organisms are open systems

http://ag.ansc.purdue.edu/sheep/ansc442/Semprojs/2003/spiderlamb/eatsheep.gif

Endergonic vs. Exergonic reactions

exergonic endergonic- energy released- digestion

- energy invested- synthesis

-G

G = change in free energy = ability to do work

+G

Reactions can occur without the help of catalysts, but not at the

speed our body requires.

Energy Changes• Some reactions release energy and some

absorb energy

• Activation Energy: the energy required to start a reaction

Speeding up Reactions• Slow reactions or reactions with high activation energies

need a catalyst

• Catalyst = any substance that lowers the activation energy of a reaction to “speed it up”

• Enzymes are proteins which act like a catalyst to speed up reactions. (found in the body, plants, animals, food, etc.

Where are enzymes?

• Enzymes are found in all cells

• Mostly in the stomach and intestines

Enzymes - Introduction

Enzymes• Enzymes provide a site where reactants can be

brought together to react. • In an enzyme-catalyzed reaction, the reactants

are called substrates (the starting substance – found in the same place you would find the enzymes – binds to the enzyme and is than made into a product).

• Each enzyme has a specific shape and a specific portion called the

active site, where substrates

bind.

• The substrates must fit exactly into the active site. This is called the lock and key model.

• The active site changes shape slightly to hold the substrate – induced fit

• Once the reaction is complete, the enzyme releases the products of the reaction.

• Enzymes can join or break substrates into products.

Breaking 1 Substrate into 2 Products

Enzymes can break or join substrates into products.

Joining 2 Substrates into 1 Product

Roles of Enzymes:1) regulating chemical pathways2) making materials3) releasing energy4) transferring info

Each enzyme works best at a certain temperature and pH.

What keeps enzymes from doing their jobs?

Temperature can affect an enzyme by changing its shape

Changes in pH can also change an enzyme’s shape

When an enzyme changes its shape it can’t do its job.

We say it is denatured!

So, if changing the shape of the active site keeps the enzyme from working, what else might keep it from working?

COFACTORS = non-protein enzyme helpers

• EX: Zinc, iron, copper

COENZYMES = organic enzyme helpers

• Ex: vitamins

http://www.wissensdrang.com/media/wis9r.gif

http://www.elmhurst.edu/~chm/vchembook/595FADcoq.html

COMPETITIVE inhibitor REVERSIBLE; Mimics substrate and competes with substrate for active site on enzyme

ENZYMEANIMATION

Enzyme Inhibitors

Enzyme InhibitorsNONCOMPETITIVE inhibitors bind to another

part of an enzyme, causing the enzyme to change shape and making the active site less effective

ENZYMEANIMATION

Digestive enzymes names match the foods they help react

Lactase helps break down

lactose.

Each enzyme is specially designed to react a certain

molecule

Lactase is just one enzyme that breaks down lactose but there are many

different enzymes at work in your body.

What happens if we don’t have them?

• Example: Lactose – Lactase

• We can’t convert it fast enough

into glucose So it builds up..

• Since our body can’t get rid of it..

• We feel sick.

(nauseous, throwing up)

More enzymes that break things down in your body…

Sucrose = Glucose + Fructose

Sucrose is table sugar!

AMYLASE: breaks down starch in your mouth and stomach

LIPASE: breaks down fats

PEPSIN: breaks down proteins

Every reaction in your body is helped by an enzyme.

Enzymes are the “workers” of your body.

Enzymes

Factors affecting enzyme function

• Enzyme concentration – as enzyme = reaction rate

• more enzymes = more frequently collide with substrate

– reaction rate levels off• substrate becomes limiting factor• not all enzyme molecules can find substrate

enzyme concentration

reac

tio

n r

ate

Factors affecting enzyme function

substrate concentration

reac

tio

n r

ate

• Substrate concentration – as substrate = reaction rate

• more substrate = more frequently collide with enzyme

– reaction rate levels off• all enzymes have active site engaged• enzyme is saturated• maximum rate of reaction

TEMPERATURE & ENZYME ACTIVITYEach enzyme has an optimal temperature at which it

can function (Usually near body temp) Optimum T°

greatest number of molecular collisions human enzymes = 35°- 40°C

body temp = 37°C Heat: increase beyond optimum T°

denaturation = lose 3D shape (3° structure) Cold: decrease T°

molecules move slower

http://www.animated-gifs.eu/meteo-thermometers/001.htm

7

pH

pH

reac

tio

n r

ate

20 1 3 4 5 6 8 9 10

pepsin trypsin

What’shappening here?!

11 12 13 14

pepsin

trypsin