microfilaments differ from microtubules in that microfilaments a) are larger than microtubules. b)...
TRANSCRIPT
Microfilaments differ from microtubules in that microfilaments
A) are larger than microtubules. B) are found only in plants whereas microtubules are
found in plants and animal cells. C) are mainly composed of actin whereas
microtubules are composed of tubulin. D) anchor organelles, whereas microtubules primarily
function to help cells change shape and move. E) form the inner core of cilia and flagella whereas
microtubules regulate metabolism.
Cellular Energetics: Thermodynamics, ATP, and Enzyme
catalysisCampbell Biology
Chapter 5
Energy and Thermodynamics
Energy is the capacity to do work
• There are many forms of energy:– Kinetic energy– Potential energy– Chemical energy– Electrical energy
All Living Things Require and Consume Energy
• We get our energy from food
• Ultimate source of energy for all life on earth is the sun
The First Law of Thermodynamics
• Energy cannot be created or destroyed
• The amount of energy in the universe is constant
• Energy can be interconverted from one form to another:– Potential energy– Kinetic energy– Radiant energy
Potential energy
• Energy is the ability to do work
• Potential Energy of position
• Gravitational potential energy
• Chemical potential energy
Kinetic energy
• Energy of motion• KE= 1/2mv2
• Temperature is a measure of molecular kinetic energy
The 1st Law of Thermodynamics: Energy can be interconverted from one
form to another
More energy interconversions
The 2nd Law of Thermodynamics : The Law of Entropy
• Interconversions of energy are never 100% efficient
• Entropy!• Entropy is a measure of
disorder (i.e. chaos, randomness)
• Each interconversion of energy involves loss of usable energy
Entropy in Action
Biochemical reactions are inefficient
The price of minimizing entropy is the constant expenditure of free energy
• Given a finite amount of energy, each energy interconversion will result in an ever-increasing amount of unusable energy (entropy)
Closed systems will deplete themselves of usable (free) energy
Recognizing Entropy in the world
Which system has more entropy?
A B
Can living systems reduce entropy?
Recognizing Enthalpy
Enthalpy = Energy in chemical bondsB
Which systems have more Enthalpy?
These?
Or these?
Biochemical reactions are spontaneous only if ∆G is negative
• Reactions which release energy are exergonic
• Reactions which require energy are endergonic
∆ G = ∆H - T∆S• Only exergonic processes
with a negative ∆G are spontaneous
• Spontaneous processes can be harnessed to perform work
C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l)
Will the Reaction happen?Well, is heat given off?Does entropy increase?
G = ∆H - T∆S∆H = enthalpy (heat in chemical bonds)
∆S= Degree of entropy (chaos) created by RxnT= Temperature at which Rxn occurs
If ΔG < 0, the reaction is spontaneous (it will happen)
Important: Spontanous ≠ fast
LE 5-2b
Heat
Glucose
Oxygen
Chemical reactions
ATP ATP
Energy for cellular work
Carbon dioxide
Water
Which of these diagrams depicts an endergonic reaction?
Energy released
Reactants
Products
Amount ofenergy
required
Po
ten
tial
en
erg
y o
f m
ole
cu
les
Po
ten
tial
en
erg
y o
f m
ole
cu
les
Reactants
Products
Amount ofenergy
releasedEnergy required
A B
LE 8-7a
G = 0
A closed hydroelectric system
G < 0
LE 8-7c
A multistep open hydroelectric system
G < 0G < 0
G < 0
In living things, a state of equilibrium most often means ___________.
A) Efficiency is optimizedB) The reaction is EndothermicC) Enthalpy is increasedD) Entropy is minimizedE) You are dead
ATP
A steer must eat over 100 pounds of grain to gain less than 10 pounds of
muscle tissue. This illustrates • A) the first law of thermodynamics. B) the second law of thermodynamics. C) that some energy is destroyed in every
energy conversion. D) that energy transformations are typically
100% efficient. E) None of the choices are correct.
Living cells manage to perform endergonic activities
• How is this possible?
ATP hydrolysis can be coupled to endergonic reactions to power cellular work
• A cell does three main kinds of work:– Mechanical– Transport– Chemical
• To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one
The Structure and Hydrolysis of ATP• ATP (adenosine triphosphate) is the cell’s energy shuttle• ATP provides energy for cellular functions• ATP is a nucleic acid monomer
ATP is the energy currency of all living things
Phosphate groups
Ribose
Adenine
ATP: Adenosine Triphosphate
LE 8-9
Adenosine triphosphate (ATP)
Energy
P P P
PPP i
Adenosine diphosphate (ADP)Inorganic phosphate
H2O
+ +
Phosphorylation can change the conformation of proteins
LE 8-10
Anabolic (building up) reactions are usually endergonic
Breakdown of ATP is exergonic
G = +3.4 kcal/mol
G = –7.3 kcal/mol
G = –3.9 kcal/mol
NH2
NH3Glu Glu
Glutamicacid
Coupled reactions: Overall G is negative;together, reactions are spontaneous
Ammonia Glutamine
ATP H2O ADP P i
+
+ +
How ATP Performs Work• ATP drives endergonic reactions by phosphorylation,
transferring a phosphate group to some other molecule, such as a reactant
• The recipient molecule is now phosphorylated
•Mechanical
•Transport
•Chemical
Three types of cellular work are powered by ATP
hydrolysis
The Regeneration of ATP• ATP is regenerated by addition of a phosphate group
to ADP• The energy to phosphorylate ADP comes from food• The chemical potential energy temporarily stored in
ATP drives most cellular work
LE 8-12
Pi
ADP
Energy for cellular work(endergonic, energy-consuming processes)
Energy from catabolism(exergonic, energy-yielding processes)
ATP
+
Enzymes
At which level of protein structure are interactions between R groups
most important?A) primaryB) secondaryC) tertiaryD) quaternaryE) the R groups are not related to the overall
structure of a protein
Sugar is an energy-rich molecule
• Breakdown of sugar is spontaneous
• C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l)
Wood and paper are made of cellulose
• Cellulose is a polymer of glucose
• Why doesn’t our jar of sugar burst into flame?
Exergonic reactions still require activation energy
• Spontaneous ≠ fast• Ea is dependent on
temperature• At high temperatures,
reactions happen faster
Jumping bean analogy• Molecules are like
jumping beans• Temperature ≈ height of
jump• Living things cannot wait
for a good jump• After a long time, where
will the beans be?• All of them?• Will they ever stop
jumping?
Living things can use enzymes to speed up reactions
• Enzymes speed up reactions by lowering energy of activation
• They are catalysts
Catalysts speed up reactions
• Platinum is used in catalytic converters
• 2CO + 02 2CO2
• Catalysts are not consumed in a reaction
• They cannot add energy to a reaction
Enzymes are protein catalysts
• Catalysts- things added to chemical reactions which speed up those reactions
• Catalysts are not consumed in a reaction
• Catalysts cannot add energy to a reaction
• -ase: The enzyme suffix
Catalase
Enzymes can dramatically lower the energy of activation for a reaction
Reaction Course
Energyreactants
products
E a
E a
no enzyme
with enzyme
12Note that the equilibrium of the reaction is unaffected
How enzymes work Structure aids
function An active site
naturally fits substrate
Enzyme specificity depends on shape
Substrate Binding and Reaction
Some important Enzymes
Cellulase
NitrogenaseATP synthase
Catalysis in the Enzyme’s Active Site• In an enzymatic reaction, the substrate binds to the
active site• The active site can lower an EA barrier by
– Orienting substrates correctly– Straining substrate bonds– Providing a favorable microenvironment– Covalently bonding to the substrate
LE 5-6
Enzyme availablewith empty activesite
Active site
Glucose
Fructose
Products arereleased
Enzyme(sucrase)
Substrate(sucrose)
H2O
Substrate isconverted toproducts
Substrate bindsto enzyme withinduced fit
Factors Affecting Enzyme Activity
1. Salts2. Temperature3. pH4. Inhibitors and Activators
Effects of Temperature and pH
• Each enzyme has an optimal temperature in which it can function
• Each enzyme has an optimal pH in which it can function
• Tertiary structure can be radically altered by changes in pH
LE 8-18
Optimal temperature fortypical human enzyme
Optimal temperature forenzyme of thermophilic (heat-tolerant bacteria)
Temperature (°C)
Optimal temperature for two enzymes
0 20 40 60 80 100
Rate
of r
eacti
on
Optimal pH for pepsin(stomach enzyme)
Optimal pHfor trypsin(intestinalenzyme)
pH
Optimal pH for two enzymes
0
Rate
of r
eacti
on
1 2 3 4 5 6 7 8 9 10
Enzyme Inhibition
• Competitive inhibitors bind to the active site of an enzyme, competing with the substrate
• Noncompetitive (allosteric) inhibitors bind to another part of an enzyme, causing the enzyme to change shape (allostery) and making the active site less effective
Many drugs are enzyme inhibitors
• Protease inhibitors fight HIV
Can enzymes catalyze endothermic reactions?
• If so, how?• If not, why not?
Inhibition of an enzyme is irreversible when
A) a competitive inhibitor is involved. B) a noncompetitive inhibitor is involved. C) the shape of the enzyme is changed. D) bonds form between inhibitor and enzyme. E) None of the choices are correct.