metabolism: energy and enzymes - welcome to biology! -...
Post on 09-Mar-2018
216 Views
Preview:
TRANSCRIPT
1
Chapter 6 Metabolism: Energy
and Enzymes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
6.1 Life and
the Flow of Energy
• Energy is the ability to do work or bring
about change
• Cells (and organisms) need a constant
supply of energy
• Life on Earth is dependent on solar
energy
– Photosynthesis provides nutrients
6.1 Life and
the Flow of Energy
• Forms of Energy
– Kinetic energy is the energy of motion
– Potential energy is stored energy
• Food is chemical energy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
heat
heat
heat
Mechanical energy
Solar
energy
Chemical
energy
6.1 Life and
the Flow of Energy
• Two Laws of Thermodynamics
1. Energy cannot be created or destroyed,
but it can be changed from one form to
another
• Law of conservation of energy
2. Energy cannot be changed from one form
to another without a loss of usable energy
• A leaf cell photosynthesizes
– Use solar energy to form carbohydrates
– Some energy is lost as heat
• Moose uses carbohydrates to power its
muscles
– Some energy is lost as heat
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
solar energy carbohydrate synthesis
sun
H2O
CO2
heat
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carbohydrate muscle contraction
heat
6.1 Life and
the Flow of Energy
• The second law of thermodynamics can
be stated another way
• Every energy transformation makes the
universe less organized and more
disordered
• Entropy refers to the relative amount of
disorganization
6.1 Life and
the Flow of Energy
• Every process that occurs in cells
always does so in a way that increases
the total entropy of the universe
• Cellular processes obviously require an
input of energy from an outside source
• Living things depend on a constant
supply of energy from the sun
C6H12O6
H2O
CO2
energy
a.
• more organized
• more potential energy
• less stable (less entropy)
Glucose
• less organized
• less potential energy
• more stable (more entropy)
Carbon dioxide and water
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
channel protein
energy
b.
• more organized • more potential energy • less stable (less entropy)
• less organized • less potential energy • more stable (more entropy)
H+
H+
H+ H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Unequal distribution
of hydrogen ions
Equal distribution
of hydrogen ions
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
C6H12O6
H2O
CO2
channel protein
energy
energy
a.
b.
• more organized • more potential energy • less stable (less entropy)
Glucose
• less organized • less potential energy • more stable (more entropy)
Carbon dioxide and water
• more organized • more potential energy • less stable (less entropy)
• less organized • less potential energy • more stable (more entropy)
H+
H+
H+ H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Unequal distribution
of hydrogen ions
Equal distribution
of hydrogen ions
6.2 Energy Transformations
and Metabolism
• Metabolism is the sum of all the chemical
reactions that occur in a cell
• Catabolism – breaking down molecules
• Anabolism – building molecules
6.2 Energy Transformations
and Metabolism
• Free energy (∆G) is the amount of energy
available.
– Exergonic reactions are ones where energy is
released (∆G is negative)
• Products have less free energy than reactants
– Endergonic reactions require an input of
energy (∆G is positive)
• Products have more free energy than reactants
6.2 Energy Transformations
and Metabolism
• Exergonic reactions
– Spontaneous
– Release energy
• Endergonic
– Require an input of energy to run
– Require ATP
6.2 Energy Transformations
and Metabolism
• ATP stands for adenosine triphosphate
– Energy currency for cells
– ATP is generated from ADP (adenosine diphosphate) + an inorganic phosphate molecule ( P )
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
adenosine triphosphate
P P
P
adenosine diphosphate phosphate +
+
+ P
P P P
Energy from
exergonic reactions
(e.g., cellular
respiration)
Energy for endergonic
reactions (e.g., protein
synthesis, nerve impulse
conduction, muscle
cont r action) ADP
ATP
6.2 Energy Transformations
and Metabolism
• ATP is a nucleotide composed of:
– Adenine (a nitrogen-containing base)
– Ribose (a 5-carbon sugar)
– Three phosphate groups
• Energy stored in these chemical bonds
6.2 Energy Transformations
and Metabolism
• Coupled Reactions
– The energy released by an exergonic
reaction is used to drive an endergonic
reaction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ATP
coupling
P
A + B C + D
ADP +
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b. Muscle contraction is endergonic
and cannot occur without an input
of energy.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P ADP + +
a. ATP breakdown is exergonic.
ATP energy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ADP + P
c. Muscle contraction
becomes exergonic
and can occur
when it is coupled to
ATP breakdown.
heat
ATP
muscle contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P
ADP + P
c. Muscle contraction
becomes exergonic
and can occur
when it is coupled to
ATP breakdown.
ADP + + heat
a. ATP breakdown is exergonic.
ATP energy
ATP
muscle contraction
b. Muscle contraction is endergonic
and cannot occur without an input
of energy.
6.2 Energy Transformations
and Metabolism
• ATP can be used for
– Chemical work
• Powers anabolism
– Transport work
• Supplies energy to pump substances across
plasma membrane
– Mechanical work
• Supplies energy to make muscles contract, cilia
and flagella beat
6.3 Enzymes
and Metabolic Pathways
• Metabolic pathways are a series of
linked reactions.
– These begin with a specific reactant and
produce an end product
6.3 Enzymes
and Metabolic Pathways
• Enzymes
– Proteins that function to speed a chemical
reaction
– Enzymes serve as catalysts
• Participates in chemical reaction, but is not
used up by the reaction
6.3 Enzymes
and Metabolic Pathways
• Energy of Activation (Ea)
– Energy that must be added to cause
molecules to react with one another
• Need a match to start wood burning
– Enzymes lower the energy of activation
• Do not change the end result of the reaction
• Increase the reaction rate
Fre
e E
ne
rgy
energy of
product
energy of
activation
(Ea)
energy of
activation
(Ea)
Progress of the Reaction
energy of
reactant
enzyme not present
enzyme present
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
6.3 Enzymes
and Metabolic Pathways
• How Enzymes Function
– Enzyme binds substrate to form a complex
E + S ES E + P enzyme substrate enzyme-substrate
complex enzyme product
• Substrate binds to active site on enzyme
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
products
enzyme
enzyme
Degradation
The substrate is broken
down to smaller products.
enzyme-substrate
complex
substrate
active site
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
product
enzyme
enzyme
Synthesis
The substrates are combined
to produce a larger product.
enzyme-substrate
complex
active site
substrates
6.3 Enzymes
and Metabolic Pathways
• Induced fit model
– Substrate and active site shapes don’t
match exactly
– Active site is induced to undergo a slight
change in shape to accommodate
substrate binding
– Change in shape facilitates reaction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
substrate active site
b.
6.3 Enzymes
and Metabolic Pathways
• Reaction requires specific enzyme
• Enzymes often named for their
substrate
– Lipid – lipase
– Urea – urease
– Maltose – maltase
– Lactose – lactase
6.3 Enzymes
and Metabolic Pathways
• Factors affecting enzymatic reaction rates
– Substrate Concentration
– Temperature and pH
– Enzyme Activation
– Enzyme Inhibition
– Enzyme Cofactors
6.3 Enzymes
and Metabolic Pathways
• Substrate Concentration
– Enzyme activity increases as substrate
concentration increases
• More collisions between substrate and enzyme
– Maximum rate is achieved when all active
sites of an enzyme are filled continuously
with substrate
6.3 Enzymes
and Metabolic Pathways
• Temperature
– Enzyme activity increases as temperature
rises
– Higher temperatures cause more effective
collisions between enzymes and
substrates
– Enzyme may denature at high
temperatures
• Loss of structure and function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rate
of
Reacti
on
(pro
du
ct
per
un
it o
f ti
me)
0 10 20 30 40 50 60
Temperature °C
a. Rate of reaction as a function of
temperature.
b. Body temperature of ectothermic
animals often limits rates of reactions.
c. Body temperature of endothermic animals
promotes rates of reactions.
b: © Brand X Pictures/PunchStock RF; c: © Digital Vision/PunchStock RF
6.3 Enzymes
and Metabolic Pathways
• pH
– Each enzyme has an optimal pH
– Enzyme structure is pH dependent
– Extremes of pH can denature an enzyme
by altering its structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pH
Ra
te o
f R
ea
cti
on
(pro
du
ct
pe
r u
nit
of
tim
e)
0 1 2 3 4 5 6 7 8 9 10 11 12
pepsin trypsin
• Enzyme Activation
– Cell regulates metabolism by regulating
which enzymes are active
– Genes producing enzymes can be turned
on or off to regulate enzyme concentration
– Enzyme can be modified by adding or
removing phosphates – changes shape
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P
kinase
P
inactive protein active protein
6.3 Enzymes
and Metabolic Pathways
• Enzyme Inhibition
– Occurs when enzyme cannot bind its
substrate
– Activity of almost every cell enzyme is
regulated by feedback inhibition
6.3 Enzymes
and Metabolic Pathways
• Enzyme Inhibition
– When product is abundant it binds to the
enzyme’s active site and blocks further
production
• When product is used up, it is removed from
the active site
• Enzyme begins to function again
6.3 Enzymes
and Metabolic Pathways
• Enzyme Inhibition
– In a more complex type of inhibition,
product binds to a site other than the active
site, which changes the shape of the active
site
– Poisons are often enzyme inhibitors
• Cyanide inhibits an essential enzyme
• Penicillin blocks the active site on a bacterial
enzyme
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
E2 E3 E4 E5
E1
first
reactant
A
site of enzyme
where end product F
can bind
end
product
F
a. Active pathway
A E B C D
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
E1
E1
end
product
F
altered site of
enzyme due to
binding of F
b. Inactive pathway
Reactant A cannot bind,
and no product results.
end
product
F
first
reactant
A
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
E2 E3 E4 E5
A E
E1
E1
E1
first
reactant
A
site of enzyme
where end product F
can bind
end
product
F
end
product
F
altered site of
enzyme due to
binding of F
a. Active pathway
b. Inactive pathway
Reactant A cannot bind,
and no product results.
end
product
F
first
reactant
A
B C D
6.3 Enzymes
and Metabolic Pathways
• Enzyme Cofactors
– Molecules which help enzyme function
– Copper and zinc are examples of inorganic
cofactors
– Organic non-protein cofactors are called
coenzymes
• Vitamins are often components of coenzymes
6.4 Oxidation-Reduction
and Metabolism
• Oxidation-Reduction or Redox
– Oxidation is the loss of electrons
– Reduction is the gain of electrons
– Ex: when oxygen combines with Mg
• Oxygen gains electrons – becomes reduced
• Mg loses electrons – becomes oxidized
6.4 Oxidation-Reduction
and Metabolism
• Oxidation-Reduction
– The term oxidation is used even when
oxygen is not involved
– Ex: Na+ + Cl- NaCl
• Sodium is oxidized
• Chlorine is reduced
6.4 Oxidation-Reduction
and Metabolism
• Oxidation-Reduction
– Also applies to covalent reactions involving
hydrogen atoms (e- + H+)
– Oxidation is the loss of hydrogen atoms
• Loss of electrons
– Reduction is the gain of hydrogen atoms
• Gain of electrons
6.4 Oxidation-Reduction
and Metabolism
• Photosynthesis
– Energy + 6CO2+6H2O C6H12O6 + 6O2
– Hydrogen atoms are transferred from water to
carbon dioxide and glucose is formed
– Energy is required and this comes in the form
of light energy from the sun
– Chloroplasts convert solar energy to ATP
which is then used along with hydrogen to
reduce carbon dioxide to glucose
6.4 Oxidation-Reduction
and Metabolism
• Cell Respiration
– C6H12O6 + 6O2 6CO2 + 6H2O + energy
– Glucose is oxidized (lost hydrogen atoms)
– Oxygen is reduced to form water (gained hydrogen atoms)
– Energy produced is used to form ATP
– The oxidation of glucose to form ATP is done in a series of small steps to increase efficiency
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
heat
heat
heat
mitochondrion chloroplast
O2
Photosynthesis Cellular respiration
CO2 + HO2
ATP for synthetic
reactions, active
transport, muscle
contraction,
nerve impulse
sun carbohydrate
(leaves): © Comstock/PunchStock RF; (runner): © PhotoDisc/Getty RF
6.4 Oxidation-Reduction
and Metabolism
• Human beings are involved in the
cycling of molecules between
chloroplasts and mitochondria
• Our food is derived from plants or we
eat animals that have eaten plants
• Food nutrients and oxygen enter our
mitochondria to produce ATP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
O2 CO2
Nutrients
Cellular respiration
Eating
O2 CO2
Breathing
ATP
Getty Images/SW Productions RF
6.4 Oxidation-Reduction
and Metabolism
• Your diet is not all glucose
• Our food consists of carbohydrates, fats, and proteins
• Broken down into simpler molecules in digestion
• Can enter cellular respiration at various steps in the pathway to make ATP
• Excess glucose can be used to form fatty acids – Fatty acids and glycerol form lipids or fat
top related