Enzymes Lower Activation Energy - WordPress.com

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27 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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It’s time for a new Topic!

Section 3.6 and
7.6:Enzymes


7.1: Metabolic
reactions consist
of chains and
cycles of
enzyme
-
catalysed

reactions


The SIGMA
-
Aldritch Imaginogram of metabolic
pathways


An animation outlining buiochemical pathways

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: 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


Enzymes are essential to all
forms of life…

3.6.1
Explain enzyme substrate
specificity

7.6.2:
Describe the ‘induced fit’
model

Enzyme substrate specificity


Substrate specificity


Induced fit versus Lock and key mechanism


Induced fit in a moment....



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

7.6.3:
Explain that enzymes lower
the activation energy of the
chemical reactions they
catalyse

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

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

Energy and enzymes animation

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

The energy stored in the
products is less than the
energy stored in the
reactants

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
)


This process is called
dephosphorylation


3.6.3:
Explain

the
effects

of
temperature
, pH and
substrate

concentration on enzyme
activity

The best way to understand temperature, pH and
substrate concentration effects is through paying with this
game....

and here's another....

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


For
many
but not all
enzymes
the optimum
temperature is about 30
°
C. In warm blooded
animals
,
most
enzymes are fully denatured at 70
°
C


Optimal temperature is organism
-
deoendent
.
Many enzymes function optimally at a lower
temperature. For example, cold
water fish
can die
at 30
°
C
since many of their
enzymes
denature.
Many plant enzymes also function optimally at
lower temperatures.


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

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


pH change must change the
structure of the
enzyme,
associated with changes in bond
angles between amino acid R
-
groups


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.

Factors which affect enzyme activity 3:
Substrate and enzyme concentration

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

August 26
th

2012


Substrate concentration:
Enzymic reactions

Reaction
velocity

Substrate concentration

V
max

3.6.4:
Define denaturation

Denaturation

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

watch denaturation happen....

NB: Do NOT describe denaturation as ‘killing’


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

7.6.4:
Explain the difference
between competitive and non
-
competitive inhibition, with
reference to at least one
example of each

Enzyme Inhibition

Allosteric inhibition


A quick animation of allosteric inhibition


ha fantastic tutorial on enzyme inhibition
-

chemical
warfare and snake venom inclusive....