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Announcements Chapter 4: Energy

• 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.

From the sun to you in two easy steps

Lecture 4 Outline

I. Energy A. Potential vs. Kinetic B. ATP

II. Energy flows from the sun and through all life A. on earth. B. Light and Pigments C. “Photo” Reactions D. “Synthesis” Reactions E. Variations

III. Respiration A. B. C. Oxidative D. Various Inputs to System

1 Energy flow and chemical recycling in ecosystems

Light energy

ECOSYSTEM

Photosynthesis in chloroplasts Organic CO2 + H2O + O2 Cellular respiration in mitochondria

ATP powers most cellular work

Heat energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 energy q What happens to the other 99%?

Insert new fig 4-5

2 How do cells directly fuel their Structure of ATP chemical reactions? ATP molecules are like free-floating rechargeable batteries in all living cells. 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 called Insert new fig 4-7 (ATP).

4.5 Where does plant matter come Recycling in the Cell from? Photosynthesis: the big picture. ADP + group + Energy = ATP

From a seed to a tree: Where does the mass Insert new fig 4-9

Insert new fig 4-8 come from?

3 PHOTOSYNTHESIS

Photosynthesis: The Big Picture • Combination of two distinct processes:

q Three inputs PHOTO = harvesting of light energy --> Light Reactions

SYNTHESIS = Using E to build sugar --> Calvin Cycle q Two products Insert new Figure 4-11 • “Respiration in Reverse”:

6CO2 + 6H2O + Light E -----> C6H12O6 + 6O2

Photosynthesis takes place in the A Closer Look at Chloroplasts chloroplasts. Organelles Found in Plant Cells

Insert new Figure 4-13

Insert new Figure 4-12

4 4.7 Light energy travels in waves: Plant pigments absorb specific Electromagnetic Spectrum wavelengths. q Range of energy that is organized into Light Energy waves of different lengths q A type of kinetic energy Insert new Figure 4-14 q The shorter the q Made up of little energy packets called photons wavelength, the higher the energy

Excitation of isolated chlorophyll by light

Excited – e state

Heat

Insert new Figure 4-15a Energy of election election of Energy

Photon (fluorescence) Ground Photon Chlorophyll state molecule

(a) Excitation of isolated chlorophyll molecule (b) Fluorescence

5 Fluorescent Fish

Insert new Figure 4-16a Insert new Figure 4-16b

6 The Passing of Electrons in Their Excited State 4.9 Photosynthesis in detail: The energy of sunlight is q Chief way energy moves through cells captured as chemical energy. q Molecules that gain electrons always carry FOLLOW THE ELECTRONS! greater energy than before receiving them. • Can view this as passing of potential energy from molecule to molecule

The “Photo” Part q Sunlight q ATP q A high-energy electron carrier

Insert new Figure 4-17

7 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

8 The Calvin Cycle

q Series of chemical “SYNTHESIS” reactions q Occurs in

4.10 Photosynthesis in q are detail: The captured energy reCYCLEd. of sunlight is used to make food.

The battle against world hunger can The Processes in the Calvin Cycle use plants adapted to Occur in Three Steps: scarcity.

9 Photosynthetic Adaptations to harsh environments Stomata • On dry, hot days, plants must close stomata to conserve Pores for gas exchange H2O. O2 from the light reactions then builds up inside the . When [O2] gets high enough, it binds to the Rubisco (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 .

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. How to get CO2 when stomata are shut?

C4 and CAM photosynthesis compared

Sugarcane Pineapple

C4 CAM CO CO Mesophyll Cell 2 2 Night Organic acid 1 CO2 incorporated Organic acid into four- Bundle- organic acids sheath cell () Day CO2 (a) Spatial separation of (b) Temporal separation of steps. In C plants, 4 CALVIN 2 Organic acids CALVIN steps. In CAM plants, carbon fixation and the CYCLE CYCLE carbon fixation and the release CO2 to Calvin cycle occur in Calvin cycle Calvin cycle occur in the different same cells Sugar types of cells. Sugar at different times.

10 All Three Photosynthetic Pathways

http://indianapublicmedia.org/amomentofscience/solarpowered-sea-slugs/

Energy flow and chemical recycling in ecosystems The production of ATP by food breakdown

• The oxidation of organic molecules releases energy. Light energy Exergonic; ΔG<0 ECOSYSTEM • Organic molecules contain a great deal of energy, but

Photosynthesis unlike gasoline combustion, E must be extracted slowly in chloroplasts Organic such that the process releases usable E for the cell. CO + H O + O 2 2 Cellular molecules 2 respiration in mitochondria RESPIRATION

• Highly efficient catabolic pathway where enzymes and O2

ATP extract the E from organic molecules like . powers most cellular work • Yields ATP, the energy currency of the cell. Heat energy

11 INPUTS 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 Cellular Occurs in ; does NOT require O2 Respiration 2) Citric Acid Cycle (Krebs Cycle): Completes breakdown of glucose. Occurs in Mitochondrial matrix. The big picture 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 OUTPUTS couples ETC to ATP production.

A Human Example The first step of cellular respiration: Glycolysis is the universal energy-releasing pathway. 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

12 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

13 Mitochondria

q Two key features of mitochondria are The third step essential to their ability to harness energy in cellular respiration: from molecules:

ATP is built in the electron • Feature 1: mitochondrial “bag-within-a-bag” transport chain. 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!

14 Proton Gradients and Potential Energy

The force of the flow of H+ fuels the attachment of free-floating phosphate groups to ADP to produce ATP.

15 q 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.

16 Energy and :

Reading:

Chapter 4

Do PS #2

Answers to PS#2 posted next Friday

Movie tonight and Tuesday

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