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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures forCampbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey
Chapter 5 The Working Cell
Topic 2 Enzymology Essential
Lecture edited by Harttini N.
1. Explain how energy is transformed during life processes
2. Explain how a chemical reaction can either release energy or store energy
3. Describe ATP and explain why it is considered to be the energy currency of a cell
4. Define enzyme and explain how enzymes cause a chemical reaction to speed up
5. Discuss the specificity of enzymesCopyright © 2009 Pearson Education, Inc.
Learning outcome
ENERGY AND THE CELL
© 2012 Pearson Education, Inc.
5.11 Chemical reactions either release or store energy
___________________is a chemical reaction that release energy.
– These reactions release energy in covalent bonds of the reactants.
– Burning wood releases energy in glucose as heat and light.
– Cellular respiration releases energy slowly and uses some of the released energy to produce ATP.
© 2012 Pearson Education, Inc.
Reactants
EnergyProducts
Amount ofenergy
released
Pote
ntia
l ene
rgy
of m
olec
ules
Exergonic reaction, energy released
5.11 Chemical reactions either release or store energy
An ______________________ requires an input of energy and yields products rich in potential energy.
Endergonic reactions
– begin with reactant molecules that contain relatively little potential energy
– end with products that contain more chemical energy.
– Eg. photosynthesis that produced energy-rich sugar molecules from energy in sunlight.
© 2012 Pearson Education, Inc.
ReactantsEnergy
Products
Amount ofenergy
required
Pote
ntia
l ene
rgy
of m
olec
ules
Endergonic reaction, energy required
5.11 Chemical reactions either release or store energy
A living organism carries out thousands of endergonic and exergonic chemical reactions.
The total of an organism’s chemical reactions = ___________________.
A _________________a series of chemical reactions that either
– builds a complex molecule
– breaks down a complex molecule into simpler compounds.
© 2012 Pearson Education, Inc.
5.11 Chemical reactions either release or store energy
_______________ uses energy released from exergonic reactions to drive endergonic reactions
– usually using the energy stored in ATP molecules.
© 2012 Pearson Education, Inc.
______, adenosine triphosphate consists of
– nitrogenous base adenine
– five-carbon sugar ribose
– three phosphate groups
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
© 2012 Pearson Education, Inc.
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called _________________.
Most cellular work depends on ATP energizing molecules by phosphorylating them.
© 2012 Pearson Education, Inc.
ADP: Adenosine Diphosphate
P P P Energy
H2OHydrolysis
RiboseAdenine
P P P
Phosphategroup
ATP: Adenosine Triphosphate
Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to other molecule in phosphorylation
The structure and hydrolysis of ATP
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
3 main types of cellular work driven by ATP:
1. chemical
2. mechanical
3. transport
© 2012 Pearson Education, Inc.
ATP ATP ATP
ADP ADP ADPP P P
P
P
P
P PP
Chemical work Mechanical work Transport work
Reactants
Motorprotein
Solute
Membrane protein
Product
Molecule formed Protein filament moved Solute transported
How ATP powers cellular work
ATP is a renewable source of energy for the cell.
In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose,is used in an endergonic reaction to generate ATP.
Energy fromexergonicreactions
Energy forendergonicreactions
ATP
ADP P
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
© 2012 Pearson Education, Inc.
The ATP cycle
Gp. Disc.: ATP
ATP can be broken down or synthesized
Does AMP → ADP require or release energy? *Why?
Is ADP → ATP an exergonic or endergonic reaction? *Why?
Which can be represented by the graph:
• ADP → ATP?• OR
• ADP → AMP?
Which can be represented by the graph:• ADP → ATP?
OR• ADP → AMP?
E.g., Glycolysis
Is energy is used up or released when a phosphate group is removed from a molecule?
ADP → ATP: energy is used up or released?
Glycolysis (Later)
•Is energy is used up orreleased when ATP is broken down to ADP?
•Is energy is used up or released to transferphosphate to glucose?
HOW ENZYMES FUNCTION
© 2012 Pearson Education, Inc.
5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Although biological molecules possess much potential energy, it is not released spontaneously.
– An energy barrier must be overcome before a chemical reaction can begin.
– This energy is called ________________________.
© 2012 Pearson Education, Inc.
Activationenergy barrier
Reactant
Products
Without enzyme With enzyme
Reactant
Products
EnzymeActivationenergy barrierreduced byenzyme
Ener
gy
Ener
gy
The effect of an enzyme in lowering EA
5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Enzymes
– function as biological catalysts by lowering the EAneeded for a reaction to begin
– increase the rate of a reaction without being consumed by the reaction
– are usually proteins, although some RNA molecules can function as enzymes
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Animation: How Enzymes WorkRight click on animation / Click play
Reactants
Products
Ener
gy
Progress of the reaction
a
b
c
The graph illustrate the course of a reaction with and without an enzyme. 1. Which curve represents the enzyme-catalyzed reaction? 2. What energy changes are represented by the lines a, b and c?
5.14 A specific enzyme catalyzes each cellular reaction
An enzyme
– is very selective in the reaction it catalyzes
– has a shape that determines the enzyme’s specificity.
The specific reactant that an enzyme acts on is called the enzyme’s ____________.
A substrate fits into a region of the enzyme called the ______________.
Enzymes are specific because their active site fits only specific substrate molecules.
© 2012 Pearson Education, Inc.
1
Enzyme(sucrase)
Active site
Enzyme availablewith empty activesite
The catalytic cycle of an enzyme
1. Sucrase starts with an empty active site
2
1
Enzyme(sucrase)
Active site
Enzyme availablewith empty activesite
Substrate(sucrose)
Substrate bindsto enzyme withinduced fit
The catalytic cycle of an enzyme
2. Sucrose enters the active site. The active site changes shape slightly to embrace substrate more snugly (induced fit)
3
2
1
Enzyme(sucrase)
Active site
Enzyme availablewith empty activesite
Substrate(sucrose)
Substrate bindsto enzyme withinduced fit
Substrate isconverted toproducts
H2O
The catalytic cycle of an enzyme
3. The strained bonds react with water, and the substrate is converted to products
4
3
2
1
Products arereleased
Fructose
GlucoseEnzyme(sucrase)
Active site
Enzyme availablewith empty activesite
Substrate(sucrose)
Substrate bindsto enzyme withinduced fit
Substrate isconverted toproducts
H2O
4. The enzyme releases the products and emerges unchanged
5.14 A specific enzyme catalyzes each cellular reaction
For every enzyme, there are optimal conditions under which it is most effective.
Temperature affects molecular motion.
– An enzyme’s optimal temperature produces the highest rate of contact between reactants and enzyme’s active site.
– Most human enzymes work best at 35–40ºC.
Optimal pH for most enzymes is near neutrality.
© 2012 Pearson Education, Inc.
Increasing temperature causes molecules to ___________________ Weak bonds break first: H-bonds, hydrophobic interactions Stronger bond break later: ionic bonds
Structure and surface configurations (including active site) are altered
Enzyme losses its catalytic functions
Enzyme is said to be denatured
When the structure of the enzyme is fully destroyed, no catalysis takes place
Temperature
1. Every enzyme has an optimum temperature that usually reflects the environment where the enzyme is naturally found
2. Reaction rate is highest at the optimal temperature
Changes in pH changes the concentration of _______in the medium
As [H+] changes, charges on the R groups change
This causes the ____________between charged R groups to break as the charges are _____________________
The 3-dimensional structure is then destroyed
The enzyme loses all catalytic activities and is completely denatured.
pH
Rat
e of
reac
tion
pH109876543210
Every enzyme has an optimum pH that usually reflects the environment where the enzyme is naturally found
Optimum pH (trypsin)
Optimum pH (pepsin)
Maximum rate of reaction trypsin
pepsin
trypsin
Maximum rate of reaction pepsin
a.
b. c.
d.
e.
f.
You should now be able to
© 2012 Pearson Education, Inc.
1. Explain how energy is transformed during life processes
2. Explain how a chemical reaction can either release energy or store energy
3. Describe ATP and explain why it is considered to be the energy currency of a cell
4. Define enzyme and explain how enzymes cause a chemical reaction to speed up
5. Discuss the specificity of enzymes