capturing and releasing energy
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Capturing and Releasing Energy. Chapter 5. 5.1 Impacts/Issues Green Energy. We and most other organisms sustain ourselves by extracting energy stored in the organic products of photosynthesis Photosynthesis - PowerPoint PPT PresentationTRANSCRIPT
Capturing and Releasing Energy
Chapter 5
5.1 Impacts/IssuesGreen Energy
We and most other organisms sustain ourselves by extracting energy stored in the organic products of photosynthesis
Photosynthesis• Metabolic pathway by which photoautotrophs
capture light energy and use it to make sugars from CO2 and water
Biofuels
Green Energy
Autotroph• Organism that makes its own food using carbon
from inorganic sources, such as CO2, and energy from the environment
Heterotroph• Organism that obtains energy and carbon from
organic compounds assembled by other organisms
Green Energy
Current biofuel research focuses on ways to break down abundant cellulose in fast growing weeds and agricultural wastes
Solar power
5.2 Capturing Rainbows
Energy radiating from the sun travels through space in waves and is organized in packets called photons
The spectrum of radiant energy from the sun includes visible light
Capturing Rainbows
Humans perceive different wavelengths of visible light as different colors
The shorter the wavelength, the greater the energy
Wavelength• Distance between the crests of two successive
waves of light
Capturing Rainbows
Photosynthetic species use pigments to harvest light energy for photosynthesis
Pigment• An organic molecule that can absorb light at
specific wavelengths
Chlorophyll a• Main photosynthetic pigment in plants
Wavelength and theElectromagnetic Spectrum
Some Photosynthetic Pigments
5.3 Storing Energy in Carbohydrates
Photosynthesis converts the energy of light into the energy of chemical bonds, which can power reactions of life and be stored for later use
Photosynthesis takes place in two stages• Light-dependent reactions• Light-independent reactions
The First Stage of Photosynthesis
Light-dependent reactions (“photo”)• Convert light energy to chemical energy of ATP
and NADPH, releasing oxygen• Occur at the thylakoid membrane in plant
chloroplasts
Photosystem• Cluster of pigments and proteins that converts
light energy to chemical energy in photosynthesis
Chloroplasts and the Thylakoid Membrane
Chloroplast• Organelle of photosynthesis in plants and some
protists
Thylakoid membrane• Chloroplast’s highly folded inner membrane system• Forms a continuous compartment in the stroma
The Second Stage of Photosynthesis
Light-independent reactions (“synthesis”)• ATP and NADPH drive synthesis of glucose and
other carbohydrates from water and CO2
• Occurs in the stroma
Stroma• Semifluid matrix between the thylakoid
membrane and the two outer membranes of a chloroplast
Fig. 5-3, p. 83
A Many photosynthetic cells in a leaf B Many chloroplasts in a photosynthetic
cell
C Many thylakoids in a chloroplast
A Leaf: Sites of Photosynthesis
Sites of photosynthesis
“green spots” arechloroplast
Summary: Photosynthesis
6CO2 + 6H2O → (light energy) → C6 H12O6 + 6O2
A Chloroplast
Fig. 5-4, p. 84Stepped Art
glucose
light water
light-dependent reactions
carbon dioxide, water
light- independent
reactions
NADPH, ATP
oxygen
NADP+, ADP
Chemical bookkeeping
5.4 The Light-Dependent Reactions
Chlorophylls and other pigments in the thylakoid membrane absorb light energy and pass it to photosystems, which then release electrons
Energized electrons leave photosystems and enter electron transfer chains in the membrane; hydrogen ion gradients drive ATP formation
Oxygen is released; electrons end up in NADPH
Light-Dependent Reactions
Steps in Light-Dependent Reactions
1. Light energy ejects electrons from a photosystem
2. Photosystem pulls replacement electrons from water, releasing O2
3. Electrons enter an electron transfer chain (ETC) in the thylakoid membrane
4. Electron energy is used to form a hydrogen-ion gradient across the thylakoid membrane
Steps in Light-Dependent Reactions
5. Another photosystem receives electrons from the ETC
6. Electrons move through a second ETC; NADPH is formed
7. Hydrogen ions flow across the thylakoid membrane through ATP synthase and power ATP formation in the stroma
Electron Transfer Phosphorylation
Electron transfer phosphorylation• Metabolic pathway in which electron flow through
electron transfer chains sets up a hydrogen ion gradient that drives ATP formation
Fig. 5-5, p. 85
to light-independent reactionslight energy light energy
41 5 7
2
thylakoid compartmentthylakoid membrane
The Light-Dependent Reactions of Photosynthesis
stroma3 6
Light-Dependent Reactions
5.5 The Light-Independent Reactions
Driven by the energy of ATP and electrons from NADPH, light-independent reactions use carbon and oxygen from CO2 to build sugars
Carbon Fixation
In the stroma of chloroplasts, the enzyme rubisco fixes carbon from CO2 in the Calvin–Benson cycle
Carbon fixation• Process by which carbon from an inorganic
source such as CO2 becomes incorporated into an organic molecule
Calvin-Benson Cycle
Calvin-Benson cycle• Light-independent reactions of photosynthesis• Cyclic pathway that forms glucose from CO2 • Uses energy from ATP and electrons from
NADPH
Rubisco• Enzyme that fixes carbon from CO2 to RuBP in
the Calvin-Benson cycle
Fig. 5-6, p. 86
chloroplast
CO2, H2Ostroma
PGA RuBPATP Calvin–
Benson CycleNADPH ATP
sugars
Light-Independent Reactions
Calvin-Benson cycle
Carbon-Fixing Adaptations
Several adaptations, such as a waterproof cuticle, allow plants to live where water is scarce
Stomata• Gaps that open between guard cells on plant
surfaces; allow gas exchange through the cuticle
C3 plants• Use only the Calvin-Benson cycle to fix carbon• Conserve water by closing stomata on dry days
Photorespiration
When stomata are closed, oxygen builds up and interferes with sugar production
Photorespiration• Reaction in which rubisco attaches O2 instead of
CO2 to RuBP
Fig. 5-7d, p. 87
5.6 Photosynthesis and Aerobic Respiration: A Global Connection
Earth’s atmosphere was permanently altered by the evolution of photosynthesis
Oxygen and the Atmosphere
Photoautotroph• Photosynthetic autotroph
Anaerobic• Occurring in the absence of oxygen
Aerobic• Involving or occurring in the presence of oxygen
Extracting Energy From Carbohydrates
Eukaryotic cells typically convert chemical energy of carbohydrates to chemical energy of ATP by oxygen-requiring aerobic respiration
Aerobic respiration• Aerobic pathway that breaks down carbohydrates
to produce ATP• Pathway finishes in mitochondria
Photosynthesis and Aerobic Respiration
An Overview of Aerobic Respiration
Aerobic respiration is divided into three steps1. Glycolysis2. Acetyl CoA formation and the Krebs cycle3. Electron transfer phosphorylation
In the first two stages, coenzymes pick up electrons
In the third stage, electron energy drives ATP synthesis
Aerobic Respiration Begins
Glycolysis• Reactions in which glucose or another sugar is
broken down into 2 pyruvates, netting 2 ATP
Pyruvate• Three-carbon product of glycolysis
Aerobic Respiration Continues
Krebs cycle• Cyclic pathway that, along with acetyl CoA
formation, breaks down pyruvate to CO2, netting 2 ATP and many reduced coenzymes
Acetyl CoA Formation and the Krebs Cycle
Fig. 5-10a, p. 90
Mitochondrion
outer membrane (next to cytoplasm)
inner membrane
inner mitochondrial compartment
outer mitochondrial compartment (in between the two membranes)
A An inner membrane divides a mitochondrion’s interior into an inner compartment and an outer compartment. The second and third stages of aerobic respiration take place at the inner mitochondrial membrane.
Fig. 5-10b, p. 90
Second Stage of Aerobic Respiration
2 pyruvate
outer membrane (next to cytoplasm)
inner membrane
6 CO 22 acetyl–CoA2 ATP
Breakdown of 2 pyruvate to 6 CO2 yields 2 ATP. Also, 10 coenzymes (8 NAD+, 2 FAD) combine with electrons and hydrogen ions, which they carry to the third and final stage of aerobic respiration.
Krebs Cycle
8 NADH
2 FADH2
B The second stage starts after membrane proteins transport pyruvate from the cytoplasm to the inner compartment. Six carbon atoms enter these reactions (in two molecules of pyruvate), and six leave (in six CO2). Two ATP form and ten coenzymes accept electrons and hydrogen ions.
The Krebs Cycle - details
Fig. 5-11, p. 91
Third Stage of Aerobic Respiration: Electron Transfer Phosphorylation
4
2
3 5
1
Stepped Art
Electron Transfer Phosphorylation
Summary: Aerobic Respiration
C6H12O6 (glucose) + 6O2 (oxygen) + 36 ADP →
6CO2 (carbon dioxide) + 6H2O (water) + 36 ATP
ATP C The third and final stage, electron transfer phosphorylation, occurs inside mitochondria. 10 NADH and 2 FADH2 donate electrons and hydrogen ions to electron transfer chains. Electron flow through the chains sets up hydrogen ion gradients that drive ATP formation. Oxygen accepts electrons at the end of the chains.
ATPATP
Electron Transfer Phosphorylation
H2Ooxygen32 ATP
Fig. 5-9, p. 89
glucose Aerobic RespirationCytoplasm
2 ATP ATP Glycolysis 4 ATP (2 net)
ATP A The first stage, glycolysis, occurs in the cell’s cytoplasm. Enzymes convert a glucose molecule to 2 pyruvate for a net yield of 2 ATP. 2 NAD + combine with electrons and hydrogen ions during the reactions, so 2 NADH also form.2 NADH 2 pyruvate
Mitochondrion
Krebs Cycle
6 CO2
B The second stage occurs in mitochondria. The 2 pyruvate are converted to a molecule that enters the Krebs cycle. CO2 forms and leaves the cell. 2 ATP, 8 NADH, and 2 FADH2 form during the reactions.
2 ATP ATP
8 NADH, 2 FADH2
Stepped Art
Summary: Aerobic Respiration
Overview of aerobic respiration
Where pathways start and finish
Third-stage reactions
Mitochondrial chemiosmosis
5.7 Fermentation
Fermentation• Anaerobic pathway that harvests energy from
carbohydrates • Alcoholic fermentation and lactate fermentation
In fermentation, ATP is formed by glycolysis only• Net yield of 2 ATP per glucose molecule• Coenzyme NAD+ is regenerated, which allows
glycolysis to continue• Fermentation pathways finish in the cytoplasm
Alcoholic Fermentation
Alcoholic fermentation• Anaerobic pathway that converts pyruvate to
ethanol and produces ATP• Examples: baking, wine production
Fig. 5-12b, p. 92
NADH NAD+
+
pyruvate ethanolacetaldehydecarbon dioxide
pyruvate lactate
NADH NAD+
Fermentation pathways
Lactate Fermentation
Lactate fermentation• Anaerobic pathway that converts pyruvate to
lactate and produces ATP• Examples: cheese, pickles
5.8 Alternative Energy Sources in the Body
Carbohydrates Fats Proteins
Energy from Carbohydrates
Glucose is absorbed from the intestines into the blood and broken down by glycolysis
Blood glucose levels are regulated by the pancreatic enzymes insulin and glucagon
Excess glucose intake stimulates storage as glycogen and fatty acids
Energy from Fats
The body stores most fats as triglycerides
When blood glucose falls, enzymes break triglycerides into glycerol and fatty acids• Glycerol enters glycolysis• Fatty acids enter the Krebs cycle as acetyl-CoA
Fatty acids yield more energy (ATP) than carbs
Energy from Proteins
Proteins enter the bloodstream as amino acids
Amino acids can be used for energy by removing the amino group (as ammonia) and converting the carbon backbone to acetyl-CoA, pyruvate, or an intermediate of the Krebs cycle
Food
Complex Carbohydrates
glucose, other simple sugars
Glycolysis
NADH pyruvate
Krebs Cycle
NADH, FADH2
Electron Transfer Phosphorylation
Fig. 5-14, p. 95
Fats
fatty acids glycerol
acetyl–CoA intermediate of glycolysis
Proteins
amino acids
acetyl–CoA
intermediate of Krebs cycle
Stepped Art
Alternative Energy Sources in the Body
5.9 Impacts/Issues Revisited
Human activities are disrupting the global cycling of carbon dioxide; we are adding more CO2 to the atmosphere than photoautotrophs are removing from it
The resulting imbalance fuels global warming
Fossil Fuel Emissions
Biofuels of the Future
Digging Into Data:Energy Efficiency of Biofuel Production