Chapter 5 – Metabolism: Energy & Enzymes
Energy
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 & Enzymes
Laws 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 & Enzymes
Metabolic 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
A+B
C
D
E+F
ATP
ADP + Pi (Free Phosphate)
Compare both to:
Glucose + Glucose
Maltose
Which one is catabolic? Which one is anabolic?
If energy is stored in chemical bonds, which reaction do you think consumes
energy? Releases energy?
Chapter 5 – Metabolism: Energy & Enzymes
How 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 & Enzymes
Coupled 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 & Enzymes
What 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 & Enzymes
Enzymes
Enzymes have the ability to pluck specific molecules out of a crowd & join them with
other reactants or break them down.
Substrate – the
reactants in an
enzymatic
reaction
Active site –
specific part of
an enzyme where
the substrate
binds to
Chapter 6 – Metabolism: Energy & Enzymes
Chapter 5 – Metabolism: Energy & Enzymes
As 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 & Enzymes
Think 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 & Enzymes
Factors 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 & Enzymes
Enzyme 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
Pro B
Enz Q
Enz Q
Chapter 5 – Metabolism: Energy & Enzymes
Competitive inhibition
Competing molecule binds to the active site of the enzyme
Sub A
Inh Z
Enz Q
Inh Z
+
Enz Q
Chapter 5 – Metabolism: Energy & Enzymes
Allosteric (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!
Sub A
Enz W
Inh X
Inh X
+
Enz W
Chapter 5 – Metabolism: Energy & Enzymes
Chapter 5 – Metabolism: Energy & Enzymes
PRACTICE 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?