EnzymeIntroThermo_Price - WordPress.com

flinkexistenceΜηχανική

27 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

98 εμφανίσεις

It’s time for new material!

Section 2.4


Chemical reactions and
Enzymes

We need to understand
some details about
enzymes that are NOT

in you book…so pay
ATTENTION!

Enzymes


Enzymes are proteins that
act as
biological catalysts


They lower the
activation
energy
of a specific
chemical reaction


Lowering the activation
energy has a profound effect
on how rapidly the reaction
is completed

In order to understand
enzyme activity, we
need to also understand
the energy
transformations that
occur during a chemical
reaction

What do you know about…


Energy?



The first law of thermodynamics?



The second law of thermodynamics?



Endergonic & Exergonic Reactions?



Enzymes

Let’s Review….

What is energy?


Etymology
:
Gk
,
energia


the capacity to do work or to perform vigorous
activity. Energy may occur in the form of heat, light,
movement, sound, or radiation.


Human
energy is usually expressed as muscle
contractions and heat production, made possible by
the metabolism of food that originally acquired the
energy from sunlight.
Chemical

energy is that
released as a result of a chemical reaction, as in the
metabolism of food.

Energy is..


The capacity to perform work


Kinetic Energy
: actually doing work


Thermal (Heat) Energy
:
energy associated with
movement of molecules


Potential Energy
: capacity to perform
work


Chemical Energy
: a form of potential energy related to
the structural arrangement of atoms or molecules.
Chemical energy can be transformed into other types
of energy during a chemical reaction

Thermodynamics

Thermodynamics is the field of physics that deals with
energy transformation


from heat to other forms


1
st

law of Thermodynamics:
The principle of
conservation of energy


2
nd

law of Thermodynamics
: Energy
conversions
reduce the order of the universe (aka: increase disorder
[entropy]).

The First Law of
Thermodynamics

Energy is neither created nor destroyed
(but it can be transferred from one part
of the universe to another…)

The Second Law of
Thermodynamics

‘Energy spontaneously disperses from being localised to


being dispersed, provided it is not hindered from doing so’

Some real life examples of the
Second Law


A rock falls if you pick it up then let it go


A frying pan will cool down if you take it off the
stove


Ice cubes melt in a warm room


High pressure air escapes from a puncture until
pressure is equalised

So how does this apply to
chemical reactions?


During a chemical reaction, one set of chemicals is
transformed into another


Both mass and energy are conserved during a
chemical reaction (1
st

Law of Thermodynamics)


Chemical reactions always involve
energy transfer


Chemical reactions always involve changes in
chemical bonds


Chemical reactions are classified
as
exergonic

or
endergonic

(I)

Chemical reactions can be endergonic or exergonic

Chemical reactions are classified
as
exergonic

or
endergonic

(I)

Enzymes activity

Chemical Reactions

Endergonic

Requires
a net input of
energy
(from
elsewhere)
.

Energy is absorbed by
the chemical products

Will not occur
spontaneously

Chemical Reactions

Exergonic

A
reaction that
releases energy
.

Occurs spontaneously

Enzymes

Lower the activation energy of a reaction

Enzymes Lower Activation Energy

What is

the cellular energy source?

ATP


adenosine
triphosphate


Powers nearly all forms of cellular work


It is a
nucleotide




How does ATP work?


ATP works by energy coupling


Energy Coupling
is the use of an
exergonic

process
to drive an
endergonic

process


Bonds between phosphate groups are broken and
energy is released (
exergonic
)


Called
dephosphorylation


What are enzymes?


Enzymes are typically
proteins


Enzymes are
specific


Enzymes act as
catalysts
to
speed up the rate of
reaction of a biological
process


Enzymes are not used up by
the reaction they catalyse

Enzymes are essential to all
forms of life…

Enzymes: Vocabulary Check


Catalyst:

A substance that speeds up a
chemical reaction without itself being changed


Enzyme:
A biological catalyst that is usually a
protein


Substrate:
The
reactant(s
) upon which an
enzyme has its action


Product:

A substance that results from a
chemical reaction


Enzyme
-
Substrate
Interaction

Factors affecting Enzymes


Substrate

concentration


Enzyme
availability


pH


Temperature


Inhibitors

© 2007 Paul Billiet
ODWS

Factors which affect enzyme
activity 1: Temperature

From: GCSE Bitesize:26.08.12


http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/importancerev4.shtml


The effect of temperature

Temperature /
°
C

Enzyme
activity

0

10

20

30

40

50

Q10

Denaturation

© 2007 Paul Billiet
ODWS

The effect of temperature


For most enzymes the optimum temperature is
about 30
°
C


Many are a lot lower,

cold water fish will die at 30
°
C because their
enzymes denature


A few bacteria have enzymes that can withstand
very high temperatures up to 100
°
C


Most enzymes

are
fully denatured at 70
°
C

© 2007 Paul Billiet
ODWS

Factors which affect enzyme
activity 2: pH

From: GCSE Bitesize:26.08.12

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/enzymes/enzymes1.shtml

The effect of pH


Optimum pH values

Enzyme
activity

Trypsin

Pepsin

pH

1

3

5

7

9

11

© 2007 Paul Billiet
ODWS

The effect of pH



Extreme pH levels will produce
denaturation


The structure of the enzyme is changed


The active site is distorted and the substrate molecules
will no longer fit in it


At pH values slightly different from the enzyme’s
optimum value, small changes in the charges of the
enzyme and
its
substrate molecules will occur


This change in ionisation will affect the binding of the
substrate with the active
site due to shape change.

© 2007 Paul Billiet
ODWS

Factors which affect enzyme activity 3:
Substrate and enzyme concentration

From: http://www.skinnersbiology.co.uk/enzyme.htm

August 26
th

2012


Complete this sentence…

The _____________
(more/less) enzyme,
the faster the
product is made.

Substrate concentration:
Enzymic reactions


Faster reaction but it reaches a saturation point when all the
enzyme molecules are occupied.


If you alter the concentration of the
enzyme

then
V
max

will
change too.


Reaction
velocity

Substrate concentration

V
max

© 2007 Paul Billiet
ODWS

Enzyme action can be blocked
by:


1. Inhibition (many drugs work through enzyme
inhibition)


2. Denaturation
-


Enzyme Inhibition

What does ‘enzyme
denaturation
’ mean?

Denaturation

is a change in the shape of an enzyme
which prevents it from fulfilling its function.

Enzymes (and other proteins) can be denatured by
heat, pH changes, or certain chemicals

NB:
Denaturation

is not the same as ‘killing’


proteins and
enzymes are not living things, so can’t be killed!

What does ‘enzyme
denaturation
’ mean?