Enzymes Chapter 3 Enzymes - PowerPoint Presentation

Slide1

Enzymes

Chapter 3

Enzymes

Part 1

Chapter 3Slide2

Learning outcomes

You should be able to:

explain how enzymes workdescribe and explain the factors that affectenzyme activityuse Vmax

and Km to compare the affinity of different enzymes for their substratesSlide3

Enzymes

Enzymes are protein molecules that can be defined as biological catalysts.

A catalyst is a molecule that speeds up a chemical reaction but remains unchanged at the end of the reaction.All metabolic reactions in living things are catalyzed by enzymes. Therefore enzymes are essential to life.Most enzymes end in “ase” such as amylaseSlide4

Enzyme substrate complexSlide5

Lock & Key hypothesis modified to Induced fit model

Each enzyme will only act on one substrate molecule.

Enzymes can either catalyze the break down of a substrate into two molecules or catalyse the joining of two substrate molecules into one.When a reaction is complete the substrate product/s leave the active site.Enzyme remains unchanged.Enzyme activity can happen very fast.

Catalase can split hydrogen peroxide into water and oxygen at a rate of 10 million per second!!!Slide6

Enzymes reduce activation energy

Enzymes

 are like the fast-forward button on your DVR remote. They buzz about 24/7 and involve themselves in chemical reactions, yet they always have these two properties:They don't change the thermodynamic properties of the reaction.They aren't consumed or modified in the reaction.Enzymes make the reaction go faster, which allows biological reactions to occur on a timescale compatible with life.Slide7

Enzymes reduce activation energy cont.

We can study enzymes in the context of 

activation energy. Many biochemical reactions need a little input of energy to jump-start a thermodynamically favorable reaction. The activation energy is the amount of energy needed for the reaction to go forward and get over its activation barrier.Slide8

Activation energy

ATP (adenosine triphosphate), the cell's energy molecule, needs a little help to get over its activation barrier.

Otherwise, ATP might donate its terminal phosphate group prematurely, resulting in an untimely release of energy. That would be bad—very bad. The cell makes sure that a reaction occurs when and where it wants by controlling the availability and abundance of enzymes.Slide9

Enzymes lower activation energy

The need to reach the activation energy can be compared to when a roller coaster needs to be "pulled" up the track and to the top of the hill before it can go rolling down at exhilarating speeds.

Until the coaster makes it over the hump, it won't be able to proceed down the other sideEnzymes lower the activation energy of desired reactions and kick-start them to get those reactions rolling.Slide10

Activation EnergySlide11

Hitting a pitched baseball vs a baseball on a tee

Enzymes lower the activation energy of a reaction by binding one of the reactants, called a 

substrate, and holding it in a way that lowers the activation energy.Enzymes are present in small controlled amounts. It's estimated that a typical enzyme will catalyze the reaction of about a thousand substrate molecules every second!!!Slide12

Enzyme efficiency

How 

efficient an enzyme is at catalyzing a reaction is dependent on the reaction conditions and on how good the enzyme is at finding its substrate. Molecules in the cell are constantly in motion, wandering around the cell in a process called diffusion. In diffusion, molecules move from areas of higher concentration to lower concentration.Slide13

Enzyme efficiency cont.

You can imagine, though, that the chance that any enzyme will meet its substrate is dependent on how much substrate is in the cell.

In this case, the substrate is the limiting factor of the reaction rate, slowing and eventually preventing any further reactions from occurring in its absence. If there is little substrate, the enzyme is less likely to find the substrate and catalyze the reaction.Slide14

Enzyme efficiency cont.

Alternatively, if the substrate concentration increases and reaches a high amount, the reaction rate becomes dependent on the limiting characteristics of the enzyme.

An enzyme is considered to be working at its maximal rate under this condition, where the amount of substrate exceeds the enzyme capacity. In this way, the cell directly controls the rate of reaction by controlling the amount of enzyme available to the substrate.Slide15

Network of biochemical reactions

There are specific enzymes for each biological reaction. Most biological reactions are also connected, meaning that the product from one enzyme-catalyzed reaction (say, enzyme A) is often used as a reactant in another reaction catalyzed by a different enzyme (say, enzyme B).

The result is a complicated network of biochemical reactions.Slide16

Enzymes are fragile

Because enzymes are proteins, they can be a bit fragile.

Like all proteins, an enzyme is only as good as its structure. Things like temperature, pH, or salt content can take a properly folded enzyme and make it useless. This is called denaturation.Slide17

Enzymes are fragile cont.

Changes to pH can also wreak havoc on protein function.

For instance, enzymes in the stomach are uniquely suited to function at very low pH. Take those enzymes to another part of the body where the pH is neutral, and they’ll fall apart faster than a preteen at a Bieber concert. Likewise, a blood enzyme that’s accustom to the slightly basic pH of 7.4 isn’t going to make it in the pH 2 environment of the stomach.Slide18

Type of Enzyme

Enzyme Function

Nuclease

Cleaves the bond connecting two nucleic acids.

Protease

Catalyzes the disruption of the bonds that connect amino acids in a protein.

Polymerase

Catalyzes the production of biological polymers, such as RNA and DNA.

Kinase

Adds a phosphate to one biological molecule through a process called 

phosphorylation

 (very creative). Kinases are important signaling molecules.

ATPase

Catalyzes the conversion of ATP into ADP, which releases energy to drive cellular processes.

Phosphatase

Catalyzes the opposite reaction of a kinase by removing a phosphate groupSlide19

Brain snack

Ever wonder why apple slices turn brown? Apples brown because of a family of enzymes called PPO (polyphenol oxidase, if you must know). These enzymes catalyze a reaction between the oxygen in the air and the iron-containing compounds in apples. The result? Enzymatic browning.

Own a pair of stonewashed jeans? Think again! Jean manufacturers now use enzymes instead of stones to give jeans that stonewashed look by degrading the denim fabric. This method actually damages the jeans less than the stone method.Slide20

Heat it upSlide21

Course of a reactionSlide22

Course of a reaction cont.Slide23

V

MAXSlide24

Effect of temperature on enzyme activity