Post on 06-Jul-2018
transcript
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
1/33
Chapter 15
Biocatalysis (Part 2)
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
2/33
Chapter review…
biocatalysisbiocatalysis
roperties and
mechanisms of
actions
roperties
of enzymes
Mechanism
of enzyme
action
Activation
energy
Models
Lock
and key
2 hypotheses
Induced
fit
Cofactors
Types &
f(x) of
cofactors
Inhibition
reversible irreversible
Competitive Non
competitive
Factors
affecting
enzymatic
reaction
Classification
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
3/33
LEARNING OUTCOMES
• Explain factors that affect the enzymatic
reaction.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
4/33
Factors affecting the rate of enzymereactions
Enzyme Concentration
Substrate Concentration
Temperature
pH
Cofactors
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
5/33
Rate of reaction is proportional to the enzymeconcentration (pH and temperature kept
constant)
The rate of reaction .... by increasing theenzyme concentration
Enzyme Concentration
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
6/33
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
7/33
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
8/33
[Enzyme]
• At low concentration of enzymedecreases , rate of reaction increases.
• As enzyme concentration increases,
more active sites available forsubstrate to bind.• Rate of reaction keeps increasing if the
substrate is in excess•
If amount of substrate is limited, rateof reaction reaches its max
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
9/33
Substrate Concentration
The rate of enzyme reaction …… with increasingsubstrate concentration
Any further increase in substrate concentration
- no significant change in rate of reaction.
At high substrate concentration, all the activesites are fully occupied by substrate molecules.
Any extra substrate molecules will have to wait
for the ES complex to release the product andbecome available again.
What is the rate of reaction now?
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
10/33
•• At low [substrate], the rate of enzyme reactionAt low [substrate], the rate of enzyme reaction
increase as [substrateincrease as [substrate]] ……....
•• There areThere are moremore enzyme molecules comparedenzyme molecules compared
substrates, not all active sites aresubstrates, not all active sites are occupied.occupied.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
11/33
Figure : Effect of
temperature on therate of enzyme
–controlled reaction.
TemperatureTemperature
Optimum temperature -temperature that promotesmax. rate of reaction
At low temp, rate ofreaction is very lowmolecules move slowly,decreasing chances of
substrate molecules tocollide with enzymemolecules at active sites.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
12/33
Figure : Effect of
temperature on the rate
of and enzyme –controlledreaction.
as temperature increases,the kinetic Energy ofenzyme & substrateincreases, molecules movefaster, more effective
collision occur betweensubstrate & active site ofenzyme
More ES complexesform.
Rate of reactionincreases
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
13/33
For every 100C rise in temperature, the
rate of reaction is doubled
until it reaches optimum temperature
at which the rate of reaction reaches itsmaximum
beyond the optimum temperature, therate of reaction decrease drastically
due to denaturation of enzyme
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
14/33
• High temperature causes the weak bonds such as ionic/
H/ van der Waals/ hydrophobic interaction to break.
• Change the conformation of active sites
• Substrates can no longer bind to the active sites of the
enzyme
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
15/33
Figure : Effect of temperature on the rate of and
enzyme –controlled reaction.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
16/33
pH
Every enzyme functions most effective/efficient over a NARROW pH range.
Optimum pH – max. rate of reaction
Changes in pH above/ below optimum pH change H+ concentration alter ionic charges of functional/ sidechain/ acidic & basic groups of amino acids in the enzyme
Ionic & Hydrogen bonds that hold specific 3D shape ofenzyme disrupted change conformation of active sites substrate cannot fit into active site to form ES Complex
different enzymes have different optimum pH values
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
17/33
• The rate of reaction decreases quickly
• If the changes in pH is too high or too low, active
sites are distorted causing enzyme to denature
• Rate of reaction decreases drastically
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
18/33
Optimum pH values for someenzymes
Enzyme Optimum pH
Pepsin 2.00
Sucrase 4.50
Enterokinase 5.50
Salivary Amylase 4.80
Catalase 7.60
Trypsin 8.00
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
19/33
COFACTORS
LEARNING OUTCOME:
Define the meaning of cofactors
Explain the types and functions ofthree cofactors: metal ions,coenzymes, and prosthetic groups.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
20/33
Chapter review…
biocatalysisbiocatalysis
roperties and
mechanisms of
actions
roperties
of enzymes
Mechanism
of enzyme
action
Activation
energy
Models
Lock
and key
2 hypotheses
Induced
fit
Cofactors
Types &
f(x) of
cofactors
Inhibition
reversible irreversible
Competitive Non-
competitive
Factors
affecting
enzymatic
reaction
Classification
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
21/33
Cofactors Non-protein substance (organic/inorganic
ions) essential for some enzymes tofunction efficiently.
may be bound tightly to the active site as permanent
residents.
loosely & reversibly along with the substrate.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
22/33
Three types of cofactors
Metal ions(activators)
Coenzymes
Prosthetic group
Cofactors
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
23/33
BASIC TERMS
• Apoenzyme – the enzyme alone• Holoenzyme – enzyme + cofactor
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
24/33
Metal ions
Inorganic substances, mostly trace elements(micronutrients) - required in very smallamounts
Bound tightly & temporarily to the enzyme/substrate & change its active site/ shape
Easier for substrate molecules to fit intoactive site/ assist in the formation ESC
Increase the rate of reaction May also bind the enzyme & substrate
together
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
25/33
Examples of metal ion/ mineral
cofactors
Salivary amylase requires the presence of(Cl-) ions before efficiently convert starch
maltose.
The enzyme thrombokinase, which convertsprothrombin into thrombin during bloodclotting, is activated by calcium (Ca2+) ions.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
26/33
Action of metal cofactors. In this cartoon an enzyme is unable
to become functionally formed unless a metal ion is available.
Once the metal is bound the active site forms and the enzyme
is ready to carry out its function.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
27/33
Coenzymes
organic non-protein molecule bind loosely & temporarily to the enzyme.
many coenzymes are derived from vitaminsespecially vitamin B.
Vitamin K is found in alfalfa,
fish livers, leafy/green
vegetables, egg yolks, andsoybean oil. It is a
coenzyme that helps in
blood clotting.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
28/33
NAD+ acts as a coenzyme todehydrogenases by acting as an
electron & hydrogen acceptor.
Glyceraldehyde-3-phosphate
1,3-diphosphoglycerate
dehydrogenase
NAD+NADH + H+
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
29/33
Coenzymes
Vitamin Vitamin CoenzymesCoenzymes
Niacin (Vit B3)Niacin (Vit B3) NADNAD++
Panthothenic acidPanthothenic acid
(Vit B5)(Vit B5)Coenzyme A (coA)Coenzyme A (coA)
Coenzymes, consists of small organic molecules, many of
which are derived from vitamins. Hence, vitamins are often
precursors to coenzymes.
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
30/33
Structure of FADnitrogens 1 & 5 carry hydrogen atoms in FADH2
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
31/33
Prosthetic groups
organic non-protein molecules
Binds tightly and permanently to theenzyme a part of the enzyme.
As carriers & transfer grps of atoms/electrons from 1 molecule to another
Example:Example: haemhaem.. a ring- shaped organic molecule with
iron at its center
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
32/33
8/17/2019 Chapter 15 Part 2 Factors and Cofactors
33/33
cofactorcofactor
Summary
3 types3 types
(metal ions)(metal ions)
ProstheticProsthetic
groupgroup
coenzymescoenzymes