Download energy, cellular respiration

Cool “Fires” Attract Mates and Meals
• Fireflies use light to
signal to potential mates
• attract males of other
species — as meals
• luciferin-luciferase
system
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Energy and cells
• What is energy? Why do we need it?
• How do chemical reactions use or produce
energy?
• How does ATP transfer energy?
• How do enzymes affect rates of chemical
reactions?
•Energy is the capacity to perform work
Chemical energy is due to the arrangement of
atoms in molecules
Rearrangement of atoms will either store or
release energy
chemical reaction = rearrangement of atoms
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Potential energy of molecules
– Endergonic reactions absorb energy and yield
products rich in potential energy
Products
Amount of
energy
INPUT
Reactants
Figure 5.3A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Potential energy of molecules
– Exergonic reactions release energy and yield
products that contain less potential energy than
their reactants
Reactants
Amount of
energy
OUTPUT
Products
Figure 5.3B
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Energy content of common
chemicals (foods)
Energy used in activities
ATP shuttles chemical energy within the cell
• In cellular respiration, some energy is stored in
ATP molecules
• ATP powers nearly all forms of cellular work
• ATP is key to energy coupling
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• This reaction supplies energy for cellular work:
Phosphate
groups
Adenine
Hydrolysis
Energy
Ribose
Adenosine triphosphate
Adenosine diphosphate
(ADP)
Figure 5.4A
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How is ATP’s chemical energy used to
do work in a cell?
How do enzymes work?
• For a chemical reaction to begin, reactants must
absorb some energy
– energy of activation (EA) = energy barrier
Enzymes lower energy barriers
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Enzyme
• enzymes can decrease the energy barrier
EA
barrier
Reactants
1
Products
Figure 5.5A
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2
• enzyme is unchanged
and can repeat the
Glucose
process
Enzyme
(sucrase)
Fructose
4
Active
site
Substrate
(sucrose)
1
Enzyme available
with empty active
site
Products are
released
3
A specific
enzyme
catalyzes
each cellular
reaction
Substrate is
converted to
products
Figure 5.6
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2
Substrate
binds to
enzyme with
induced fit
The cellular environment affects enzyme activity
• Enzyme activity is influenced by
– temperature
– salt concentration
– pH
• Reaction rate is affected by amount of substrate
• Allosteric regulation by other factors
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•Some enzymes require nonprotein cofactors
Ex. zinc, iron
coenzymes = cofactors that are organic molecules
Ex. vitamins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
A. Cellular respiration
1. Glycolysis
1. Kreb cycle
1. Electron transport chain
B. Fermentation
• Cellular respiration breaks down glucose
molecules and banks their energy in ATP
– uses O2 and releases CO2 and H2O
Glucose
Oxygen
gas
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Carbon
dioxide
Water
Energy
Redox reactions are linked oxidations and reductions
• Glucose gives up energy as it is oxidized
oxidation = loss of H
Oxygen is reduced (gains H)
Loss of hydrogen atoms
Energy
Glucose
Gain of hydrogen atoms
Figure 6.4
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• An overview of cellular respiration
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Pyruvic
acid
Cytoplasmic
fluid
Figure 6.8
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KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
Glycolysis harvests chemical energy by oxidizing
glucose to pyruvic acid
Glucose
Figure 6.9A
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Pyruvic
acid
Pyruvic acid is chemically groomed for the Kreb
cycle
• Each pyruvic acid molecule is broken down to
form CO2 and a two-carbon acetyl group, which
enters the Kreb cycle
Pyruvic
acid
Acetyl CoA
(acetyl coenzyme A)
CO2
Figure 6.10
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The Krebs cycle completes the oxidation of organic
fuel
Acetyl CoA
• enzymes strip
away electrons
and H+ from
each acetyl
group,
generating
many NADH
and FADH2
molecules
KREBS
CYCLE
Figure 6.11A
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2
CO2
Steps in the Electron Transport System
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Figure 3.28
• Electron Transport System and
chemiosmosis in the mitochondrion
Protein
complex
Intermembrane
space
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
Figure 6.12
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ATP SYNTHASE
cell
outer
membrane
inner
membrane
mitochondrion
glycolysis
inner
membrane
outer
membrane
electron
transport
chain
Krebs
cycle
H+
eO2
outer
compartment
H2O
inner compartment
Certain poisons interrupt critical events in cellular
respiration
Rotenone
Cyanide,
carbon monoxide
ELECTRON TRANSPORT CHAIN
Figure 6.13
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Oligomycin
ATP SYNTHASE
• An overview of cellular respiration
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Pyruvic
acid
Cytoplasmic
fluid
Figure 6.8
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
Fermentation is an anaerobic alternative to aerobic
respiration
• Without oxygen, cells can use glycolysis alone
to produce small amounts of ATP
– But a cell must replenish NAD+
Glucose
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Pyruvic
acid
• In alcoholic fermentation, pyruvic acid is
converted to CO2 and ethanol
– This recycles NAD+ to keep glycolysis working
FERMENTATION
GLYCOLYSIS
released
2 Pyruvic
Glucose
acid
2
Ethanol
Figure 6.15C
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• In lactic acid fermentation, pyruvic acid is
converted to lactic acid
– NAD+ is recycled
• Produces cheese and yogurt
GLYCOLYSIS
2 Pyruvic
Glucose
Figure 6.15B
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acid
2 Lactic
acid
Cells use many kinds of organic molecules as fuel
for cellular respiration
• Polysaccharides
glucose for glycolysis
• Proteins
• Fats
monosaccharides
amino acids
acetyl-Co A
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Krebs cycle
Krebs cycle
• Pathways of molecular breakdown
Food, such as
peanuts
Polysaccharides
Fats
Proteins
Sugars
Glycerol Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvic
acid
Acetyl
CoA
GLYCOLYSIS
Figure 6.16
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KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Food molecules provide raw materials for
biosynthesis
• cells need raw materials for growth and repair
– Some directly from food
– Others made from intermediates in glycolysis
and the Krebs cycle
• Biosynthesis uses ATP (endergonic)
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• Biosynthesis of macromolecules from
intermediates in cellular respiration
ATP needed to
drive biosynthesis
KREBS
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvic
acid
G3P
Glucose
Amino
groups
Amino acids
Fatty acids Glycerol
Sugars
Proteins
Fats
Polysaccharides
Cells, tissues, organisms
Figure 6.17
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings