Post on 08-Feb-2023
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Announcements
• Problem Set #1 answers will be posted on website tomorrow. • Problem Set #2 will also be posted on website tomorrow and form the basis for discussion sections next week. • On Tuesday, we will watch “Life Story”. We will start it at the end of today’s class since it is longer than 80 minutes. Exam will feature questions related to film. • First midterm is Tuesday, January 28th. Scantron. Bring ID and #2 Pencils.
Chapter 4: Energy
From the sun to you in two easy steps
Lecture 4 Outline
I. Energy A. Potential vs. Kinetic B. ATP
II. Photosynthesis
A. Chloroplasts B. Light and Pigments C. “Photo” Reactions D. “Synthesis” Reactions E. Variations
III. Respiration
A. Glycolysis B. Citric Acid Cycle C. Oxidative Phosphorylation D. Various Inputs to System
Energy flows from the sun and through all life
on earth.
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
Organic molecules + O2
ATP
powers most cellular work Heat energy
Energy flow and chemical recycling in ecosystems
Chemical Energy Energy Conversions q Only ~1% of the energy released by the sun that
earth receives is captured and converted by plants. • Converted into chemical bond energy
q What happens to the other 99%?
Insert new fig 4-5
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How do cells directly fuel their chemical reactions?
q None of the light energy from the sun can be used directly to fuel cellular work.
q First, it must be captured in the bonds of a molecule called adenosine triphosphate (ATP).
Structure of ATP
Insert new fig 4-7
ATP molecules are like free-floating rechargeable batteries in all living cells.
Recycling in the Cell ADP + Phosphate group + Energy = ATP
Insert new fig 4-8
4.5 Where does plant matter come from? Photosynthesis: the big picture.
From a seed to a tree: Where does the mass come from?
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PHOTOSYNTHESIS • Combination of two distinct processes:
PHOTO = harvesting of light energy --> Light Reactions
SYNTHESIS = Using E to build sugar --> Calvin Cycle • “Respiration in Reverse”:
6CO2 + 6H2O + Light E -----> C6H12O6 + 6O2
Photosynthesis: The Big Picture
q Three inputs
q Two products Insert new Figure 4-‐11
Photosynthesis takes place in the chloroplasts.
Organelles Found in Plant Cells
Insert new Figure 4-‐12
A Closer Look at Chloroplasts
Insert new Figure 4-‐13
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4.7 Light energy travels in waves: Plant pigments absorb specific wavelengths.
Light Energy q A type of kinetic energy
q Made up of little energy packets called photons
Electromagnetic Spectrum
q Range of energy that is organized into waves of different lengths
q The shorter the wavelength, the higher the energy
Insert new Figure 4-‐14
Insert new Figure 4-‐15a
Excitation of isolated chlorophyll by light
Excited state
Ene
rgy
of e
lect
ion
e–
Heat
Photon (fluorescence)
Chlorophyll molecule
Ground state Photon
(a) Excitation of isolated chlorophyll molecule (b) Fluorescence
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The Passing of Electrons in Their Excited State
q Chief way energy moves through cells q Molecules that gain electrons always carry
greater energy than before receiving them.
• Can view this as passing of potential energy from molecule to molecule
4.9 Photosynthesis in detail: The energy of sunlight is captured as chemical energy.
FOLLOW THE ELECTRONS!
Insert new Figure 4-‐17
The “Photo” Part q Sunlight q ATP q A high-energy electron carrier
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An Electron Transport Chain Connects the two photosystems Product #1 of the “Photo”
Portion of Photosynthesis:
ATP
The Second Photosystem q Follow the electrons Product #2 of the “Photo”
Portion of Photosynthesis:
NADPH
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“SYNTHESIS”
4.10 Photosynthesis in detail: The captured energy of sunlight is used to make
food.
The Calvin Cycle
q Series of chemical reactions
q Occurs in stroma
q Enzymes are reCYCLEd.
The Processes in the Calvin Cycle Occur in Three Steps:
The battle against world hunger can use plants adapted to water
scarcity.
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Photosynthetic Adaptations to harsh environments
• On dry, hot days, plants must close stomata to conserve H2O. O2 from the light reactions then builds up inside the chloroplast. When [O2] gets high enough, it binds to the Rubisco enzyme (normally fixes CO2 into Calvin Cycle). This results in a 2C compound produced from the Calvin Cycle which is broken down to CO2 and H2O and is termed PHOTORESPIRATION. This generates no E and is very wasteful to the plant. Adaptations have evolved in tropical and desert plants to avoid photorespiration. Key to both are use of enzymes other than Rubisco to fix C from CO2.
Stomata Pores for gas exchange
How to get CO2 when stomata are shut?
C4 and CAM photosynthesis compared
Organic acids release CO2 to Calvin cycle
Spatial separation of steps. In C4 plants, carbon fixation and the Calvin cycle occur in different types of cells.
(a) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times.
(b)
Pineapple Sugarcane
Bundle- sheath cell
Mesophyll Cell
Organic acid
CALVIN CYCLE
Sugar
CO2 CO2
Organic acid
CALVIN CYCLE
Sugar
C4 CAM
CO2 incorporated into four-carbon organic acids (carbon fixation)
Night
Day
1
2 Organic acids release CO2 to Calvin cycle
CO2
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All Three Photosynthetic Pathways
http://indianapublicmedia.org/amomentofscience/solarpowered-sea-slugs/
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis in chloroplasts
Cellular respiration
in mitochondria
Organic molecules + O2
ATP
powers most cellular work
Heat energy
Energy flow and chemical recycling in ecosystems The production of ATP by food breakdown • The oxidation of organic molecules releases energy. Exergonic; ΔG<0 • Organic molecules contain a great deal of energy, but unlike gasoline combustion, E must be extracted slowly such that the process releases usable E for the cell. RESPIRATION • Highly efficient catabolic pathway where enzymes and O2 extract the E from organic molecules like glucose. • Yields ATP, the energy currency of the cell.
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CELLULAR RESPIRATION • Respiration occurs in 3 different stages, using over 20 steps to efficiently harvest E present in chemical bonds. 1) Glycolysis: Splits Glucose into two pyruvate molecules Occurs in cytosol; does NOT require O2 2) Citric Acid Cycle (Krebs Cycle): Completes breakdown of glucose. Occurs in Mitochondrial matrix. 3) Oxidative Phosphorylation: Generates the vast majority of ATP. Occurs in Mitochondrial inner membrane. Driven by e- transport chain --> O2 ultimate acceptor of the e- derived from breakdown of glucose. Chemiosmosis couples ETC to ATP production.
Cellular Respiration
The big picture
INPUTS
OUTPUTS
A Human Example
q Eat food q Digest it q Absorb nutrient molecules into bloodstream q Deliver nutrient molecules to the cells
q At this point, our cells can begin to extract some of the energy • Stored in the bonds of the food molecules
The first step of cellular respiration: Glycolysis is the universal energy-releasing pathway.
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The second step of cellular respiration: The Krebs cycle extracts energy from sugar.
The Preparatory Phase to the Krebs Cycle
Energy Payoff of Krebs Cycle
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The third step in cellular respiration:
ATP is built in the electron transport chain.
Mitochondria
q Two key features of mitochondria are essential to their ability to harness energy from molecules:
• Feature 1: mitochondrial “bag-within-a-bag” structure
• Feature 2: electron carriers organized within the inner “bag”
The “Bag-within-a-Bag” Follow the Electrons, as We Did in Photosynthesis
2) This proton concentration gradient represents a significant source of potential energy!
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Proton Gradients and Potential Energy
The force of the flow of H+ ions fuels the attachment of free-floating phosphate
groups to ADP to produce ATP.
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q Oxygen deficiency limits the breakdown of fuel because the electron transport chain requires oxygen as the final acceptor of the electrons generated during glycolysis and the Krebs cycle.
Eating a complete diet: Cells can run on protein and fat as well as on glucose.