Chapter 5 – Metabolism: Energy & EnzymesEnergy

Energy is the capacity to do work

Kinetic energy – Energy of motion

Potential energy – Stored energy

What do you use for energy?

Where do you think the energy is stored these molecules?

The BONDS!

Every time a bond is broken or formed, energy is being released or consumed.

Chapter 5 – Metabolism: Energy & EnzymesLaws governing the conversion of energy from one form to another

1st Law of Thermodynamics – Law of Conservation of Energy – Energy cannot be created or destroyed, but can only be changed from one form to another.

Think about your own car

What molecule is being consumed or broken down & how is the energy changed from one form to another?

2nd Law of Thermodynamics – Energy cannot be changed from one form to another without a loss of usable energy – the loss is in the form of heat – and heat is the most random form of energy & quickly dissipates into the environment

How do you quantify this loss of energy?

ENTROPY – Is a measure of randomness or disorder.

So considering all of the chemical reactions that are occurring in your own body, why haven’t you dissipated into physical non-existence?

Because as you lose heat energy, it is being replaced by other forms of energy when you eat

Think about a corpse, will it eventually dissipate into nothing? WHY?

Chapter 5 – Metabolism: Energy & EnzymesMetabolic reactions & Energy Transformations

Basically, you’re a big water balloon with a bunch of chemical reactions occurring inside - Define Metabolism, Catabolism, & Anabolism

Whenever you look at a chemical reaction, you want to see what you start out with & what you end up with!

Reactants – What you start with

Products – What you end with

The following are examples of simple chemical reactions

Which one is catabolic? Which one is anabolic?

If energy is stored in chemical bonds, which reaction do you think consumes energy? Releases energy?

A + B C D E + FCompare both to:

Glucose + Glucose Maltose ATP ADP + Pi (Free Phosphate)

Chapter 5 – Metabolism: Energy & EnzymesHow do we quantify the energy that is released or needed during a chemical reaction?

Free energy – Amount of energy available to do work after a chemical reaction has occurred

So if the total energy in the bonds of ADP & Pi are less than the energy of the ATP molecule that they were derived from, where did the remaining energy go?

Exergonic reactions – reactions in which energy is released due to the fact that the products contain less energy than the reactants- they have a negative free energy value to indicate that the products have less energy than the reactants

Endergonic reactions – reactions in which energy is required due to the fact that the products contain more energy than the reactants – they have a positive free energy value to indicate that the products have more energy than the reactants

Anabolic reactions build larger molecules & are endergonic

Catabolic reactions breakdown large molecules & are exergonic

How or where do the endergonic reactions taking place in your cells obtain the energy to proceed?

Chapter 5 – Metabolism: Energy & Enzymes

Chapter 5 – Metabolism: Energy & EnzymesCoupled reactions & ATP

The energy released by an exergonic reaction will be used to drive an endergonic reaction

Chapter 5 – Metabolism: Energy & Enzymes

Chapter 5 – Metabolism: Energy & EnzymesWhat regulates the chemical reactions occurring in your cells?

How easy would it be for 2 glucose molecules to find each other in a cell & link together to start the production of a glycogen molecule, considering the quantity & diversity of molecules in a cell, as well as their inherent molecular motion?

How could you speed up the movement of molecules to increase their probability of reacting (“bumping into”) one another?

HEAT! But what would it do to your cells?

So, this input of heat is nothing more than energy.

The energy needed to start a chemical reaction is called the energy of activation

So how can cells maximize the reactions between molecules (or start reactions) without increasing the temperature within the cell?

ENZYMES – protein molecules which act as catalysts (speed up) for chemical reactions

How do they work?

Chapter 5 – Metabolism: Energy & EnzymesEnzymes

Enzymes have the ability to pluck specific molecules out of a crowd & join them with other reactants or break them down.

Chapter 6 – Metabolism: Energy & EnzymesSubstrate – the reactants in an enzymatic reaction

Active site –specific part of an enzyme where the substrate binds to

Chapter 5 – Metabolism: Energy & EnzymesAs you can see, the energy activation is a barrier that must be overcome to get a chemical reaction to go

Do all chemical reactions need to overcome an energy of activation barrier?

Chapter 5 – Metabolism: Energy & EnzymesThink about an anabolic reaction. Do you think that an anabolic reaction needs energy to get started & go to completion?

Do you expend energy when you take a stack of playing cards & construct a house with them?

Think about a catabolic reaction. Do you think that a catabolic reaction needs energy to get started & go to completion?

Does your house of cards spontaneously fall down or does it take a little input of energy to get the process started?

Does a match spontaneously combust? What do you have to do to light it?

Whether a chemical reaction is endergonic or exergonic an energy of activation barrier must be overcome!

Chapter 5 – Metabolism: Energy & EnzymesFactors affecting enzyme speed

What can increase or decrease the speed of a reaction?

Think about an assembly line! You are an assembler (enzyme), what could we do to you or your reactants (substrates) to increase or decrease the assembly of a product?

Substrate concentration – Increase the amount of substrate, increase the amount of product formed (speed of the reaction)

Enzyme concentration – Increase the amount of enzyme, increase the speed of the reaction

Temperature – Increases in temperature, increases molecular motion, which increases the speed of the reaction.

But what happens if we increase the temperature to much?

Denaturation (breakdown) of the enzyme – active site changes, substrate can’t bind –reaction slows & finally stops

pH – Hydrogen ion concentration can alter the interaction between R-groups that determine the tertiary structure of an enzyme – active sites change!

Chapter 5 – Metabolism: Energy & Enzymes

Chapter 5 – Metabolism: Energy & EnzymesEnzyme inhibition

What happens when a factory over produces a product?

Chemical reactions can be regulated by the products of the reaction or by chemicals not normally found in the body

How do these molecules inhibit chemical reactions?

Normal enzymatic scheme

+

Sub A

Enz Q

Sub A

Enz Q

Enz Q

Pro B

Chapter 5 – Metabolism: Energy & EnzymesCompetitive inhibition

Competing molecule binds to the active site of the enzyme

Sub A

+ Enz QInh Z

Enz Q

Inh Z

Chapter 5 – Metabolism: Energy & EnzymesAllosteric (non-competitive) inhibition

Inhibitor binds to an allosteric site away from the active site.

Binding to this site changes the structure of the active site

Substrate can no longer bind to the active site! Reaction stops!

Enz W

Inh X

+ Enz WInh X

Sub A

Chapter 5 – Metabolism: Energy & Enzymes

Chapter 5 – Metabolism: Energy & EnzymesPRACTICE QUESTIONS

1. What is the difference between potential and kinetic energy?

2. Define the 1st and 2nd Laws of Thermodynamics

3. What is entropy?

4. Define free energy, exergonic, & endergonic

5. What is meant by a “coupled reaction”?

6. What is a substrate?

7. What is the active site?

8. What is the energy of activation?

9. How can we speed up a chemical reaction/

10. What is the difference between competitive inhibition & allosteric inhibition?