Cell Energy

Adapted from A. Anguiano & J. Zhen

All organisms need energy to live.

Autotrophs Organisms that make their own food.They use sunlight to produce food.

Example: Plants

Autotrophs

Heterotrophs Organisms that get energy from the food they eat.

Examples: animals

Heterotrophs

Photosynthesis …. Process by which plants

convert water and carbon dioxide to high-energy carbohydrates (glucose).

Plants = “autotrophs” (make their own food)

Carbohydrates are: Glucose, starch and cellulose

What are examples of carbohydrates?

Glucose is used to store energy (ATP)

1 Glucose gives 36 ATP

36 ATP

6CO2 + 6H2O C6H12O6 + 6O2

PRODUCTSPRODUCTSREACTANTSREACTANTS

Reactants: are what goes into a chemical reaction

Products: Are what is produced at the end of the chemical reaction.

Photosynthesis Equation

light

Photosynthesis Equation

6CO2 + 6H2O C6H12O6 + 6O2

Carbon Dioxide

Water

Glucose

Oxygen

light

Light

6 CO2

6 H2O

6 O2

C6H12O6

Where Photosynthesis

happens

Chloroplast Site of photosynthesis Contains chlorophyll, a

pigment that absorbs energy from sunlight

Structure of a chloroplast:

1) Double membrane2) Thylakoid: contain chlorophyll; where light rxn takes place3) Granum: stacks of thylakoids4) Photosystems: light-collecting units of the chloroplast (a

cluster of chlorophyll in the thylakoid)5) Stroma: space outside the thlakoid membrane

3

4

1

2

5

Plants plant cells Chloroplast Chlorophyll a

Chlorophyll is a pigment* found in the Chloroplast.

This is what gives it the green color.

*A pigment is a molecule that absorbs light.

The sun shines white light.

White light is made up of a rainbow of colors.

SUN

Each drop of water acts like a prism.

Why do plants look green? Plants look green because

they contain chlorophyll αα which reflects green light.

Photosynthesis

Plant Pigments

Main pigment = chlorophyll a (absorbs blue/red light reflects green/yellow)

Photosynthesis

Photosynthesis

Plant Pigments

Accessory pigments = chlorophyll b (absorbs

blue/red light reflects green/yellow

carotene(absorbs blue/green light reflects yellow/orange)

Photosynthesis is divided into 2 parts:

1. Light Dependent reactions

2. Dark reaction (Calvin Cycle) (Light InIndependent ~ no Light is needed)

Light Dependent Reactions

Light Independent Reactions

Two Reactions Occurs in 2 stages:

1) Light reaction (requires sunlight)

2) Dark reaction (does not require sunlight; also called the Calvin Cycle)

1. Light Dependent Reactions- Requires sunlight; occurs in

thylakoids

Sunlight

Electron excited

Chlorophyll ATP, NADPH

1) Chlorophyll in each thylakoid absorbs energy (in the form of photons) from sunlight

2) The energy is transferred to electrons and they leave the chlorophyll

3) Water (H2O) gets split. Electrons from water replace the electrons that chlorophyll lost and Oxygen (O2) is released as a waste product

4) Thylakoid uses the energy to make two products to be used in Dark rxn later:

- ATP (Adenosine Triphosphate) = energy-carrying molecule- NADPH = a temporary energy storage molecule

Reactant

Product

Energy carrying molecules

NADPH: molecule that carries electrons

NADPH holds 2 electrons

NADP+ is ready to accept 2 electrons & H+

Photosynthesis

Chemical Energy and ATP

Storing Energy ADP has two phosphate groups instead of three. A cell can store small amounts of energy by adding a

phosphate group to ADP.

ADPATP

Energy

Energy

Partiallycharged battery

Fullycharged battery

+

Adenosine Diphosphate (ADP) + Phosphate

Adenosine Triphosphate (ATP)

Chemical Energy and ATP

Releasing Energy Energy stored in ATP is released by breaking the

chemical bond between the second and third phosphates.

P

ADP

2 Phosphate groups

Light-Dependent Reactions

Photosystem II

Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level.

Photosystem II

These high-energy electrons are passed on to the electron transport chain.

Electroncarriers

High-energy electron

Photosystem II

2H2O

Enzymes on the thylakoid membrane break water molecules into:

Electroncarriers

High-energy electron

Photosystem II

2H2O

hydrogen ions oxygen atoms energized electrons

+ O2

Electroncarriers

High-energy electron

Photosystem II

2H2O

+ O2

The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain.

High-energy electron

Photosystem II

2H2O

As plants remove electrons from water, oxygen is left behind and is released into the air.

+ O2

High-energy electron

Photosystem II

2H2O

The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane.

+ O2

High-energy electron

Photosystem II

2H2O

Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space.

+ O2

Photosystem II

2H2O

High-energy electrons move through the electron transport chain from photosystem II to photosystem I.

+ O2

Photosystem I

2H2O

Pigments in photosystem I use energy from light to re-energize the electrons.

+ O2

Photosystem I

2H2O

NADP+ then picks up these high-energy electrons, along with H+ ions, and becomes NADPH.

+ O2

2 NADP+

2 NADPH2

2H2O

As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane.

+ O2

2 NADP+

2 NADPH2

2H2O

Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged.

+ O2

2 NADP+

2 NADPH2

2H2O

The difference in charges across the membrane provides the energy to make ATP

+ O2

2 NADP+

2 NADPH2

2H2O

H+ ions cannot cross the membrane directly.

+ O2

ATP synthase

2 NADP+

2 NADPH2

2H2O

The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it

+ O2

ATP synthase

2 NADP+

2 NADPH2

2H2O

As H+ ions pass through ATP synthase, the protein rotates.

+ O2

ATP synthase

2 NADP+

2 NADPH2

2H2O

As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP.

+ O2

2 NADP+

2 NADPH2

ATP synthase

ADP

2H2O

Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well.

+ O2

ATP synthase

ADP2 NADP+

2 NADPH2

2. Dark Reactions (Calvin Cycle)- Does not require

sunlight; occurs in stroma (CO2 enters)

Light Dark

NADPH Used to form glucose

ATP stored or used elsewhere

1) ATP & NADPH from Light rxn are used to take carbon atoms from CO2 to make glucose

2) It takes 6 turns of Calvin cycle to fix CO2 (1 carbon) into C6H12O6 (6 carbons)

ReactantProduct

Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules.

CO2 Enters the Cycle

The result is twelve 3-carbon molecules, which are then converted into higher-energy forms.

The energy for this conversion comes from ATP and high-energy electrons from NADPH.

12 NADPH

12

12 ADP

12 NADP+

Energy Input

Two of twelve 3-carbon molecules are removed from the cycle.

Energy Input

12 NADPH

12

12 ADP

12 NADP+

The molecules are used to produce sugars, lipids, amino acids and other compounds.

12 NADPH

12

12 ADP

12 NADP+

6-Carbon sugar produced

Sugars and other compounds

The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle.

12 NADPH

12

12 ADP

12 NADP+

5-Carbon MoleculesRegenerated

Sugars and other compounds

6

6 ADP