Unit V- Cellular Energetics

ATP and Photosynthesis

The Need for Energy

• Adenosine Triphosphate (ATP)
• Energy storing molecule made in the mitochondria.
• ATP consists of 3 phosphate groups, ribose, and adenine.

The Need for Energy

• Adenosine Triphosphate (ATP)

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• Energy is stored in the bonds between phosphates.

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• Most energy = ATP �3 phosphates = �3 phosphate bonds��
• Less energy = ADP�2 phosphates = �2 phosphate bonds��
• Least energy = AMP�1 phosphate = �1 phosphate bond

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The Need for Energy

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• Some enzymes release the phosphate molecules.
• breaking the bonds = releasing energy!�
• Some enzymes add phosphate molecules.
• Forming the bonds = storing energy!

The Need for Energy

• Whenever energy is needed
• ATP → ADP + P �(bond was broken…�energy was released)�
• Whenever energy is stored
• ADP + P → ATP or � AMP + P → ADP�(bond was formed…�energy was stored)�
• ATP stores the energy �gained by the breakdown �of glucose as chemical �energy rather than as heat.

The Need for Energy

• Chemical Energy�
• Stored in bonds of compounds.�
• Stored energy in glucose is released in small amounts through a series of steps.�
• ATP is made from this release of energy.

The Need for Energy

How are these folded membranes beneficial?

This is the membrane of the mitochondria…showing the enzyme ATP synthase creating ATP from ADP, P, and a proton

This animation shows mitochondria creating enough energy in a NADH molecule to form ATP

MORE folds equals MORE surface area which equals MORE ATP production!!!

Check for Understanding

• What is the name given to organisms that cannot make their own food?�
• How can an organism get food if it can’t make it?�
• What is the name given to organisms that make their own food?�
• Give an example of an organism that makes its own food.�
• How does an organism make food (process)?

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• Rank the following molecules from the LEAST ENERGY to the MOST ENERGY: ADP, ATP, AMP

Heterotroph

Consume it

Autotroph

Plants, Bacteria, and Algae

Photosynthesis

3

2

1

Photosynthesis

Photosynthesis:

• The process of using the Sun’s energy to make simple sugars.

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• “photo” meaning “light”

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• “syntithenai” meaning �“to put together/build”.

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• Photosynthesis puts together sugar molecules by combining water, carbon dioxide, and energy from light.

Photosynthesis

Happens in Two Stages

• Light-Dependent Reaction
• Converts light energy into chemical energy.�
• Calvin Cycle (Light-Independent Reaction)
• Produces simple sugars.�
• Both processes happen in the chloroplast of a cell.

EQUATION FOR PHOTOSYNTHESIS

6CO₂ +

6H₂O +

ENERGY from Light

C₆H₁₂O₆ +

6O₂

CARBON DIOXIDE

WATER

GLUCOSE

OXYGEN

REACTANTS

PRODUCTS

Photosynthesis

Photosynthesis

Photosynthesis

• Chloroplasts

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• Stacked membrane sacs called thylakoids.�
• Thylakoid membranes contain pigments. �
• Pigments absorb certain wavelengths of light.

Photosynthesis

• Most common pigment is chlorophyll.

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• Chlorophyll absorbs all wavelengths of visible light except green.

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• Reflects green, which is what your eyes see.

Photosynthesis

• What color is being reflected by the apple?

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• What colors are absorbed by the apple?

Photosynthesis

• Chlorophyll is so abundant that other pigments in the leaves are not visible.

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• This is why most plants appear green.

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• Why do the leaves of some plants change color in the fall?

Photosynthesis

• Plants stop making chlorophyll when the temperature drops.

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• Then other pigments become visible.

Photosynthesis- Stage 1

Light Dependent Reactions

• First stage in photosynthesis.

- Requires light = light dependent

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• Energy in the light is transferred to electrons in chlorophyll.

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• Electrons are then passed to protein molecules in the thylakoid membrane of the chloroplast.

Photosynthesis- Stage 1

• Electrons are passed from protein to protein in the electron transport chain.

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• At each step in the chain electrons lose energy.

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• Finally combine with electron carrier called NADP⁺ to form NADPH and ATP.

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• This energy is stored for later use in light-independent reactions (Calvin Cycle)

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Light Dependent Reactions cont’d

NADPH is an energy storing molecule, but DOES NOT contain as much energy as ATP.

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Photosynthesis- Stage 1

• Electrons are lost from chlorophyll when light is absorbed and must be replaced.

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- Photolysis = splitting of water

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• Forms oxygen, hydrogen ions, and electrons.
• Supplies chlorophyll with the needed electrons.
• Releases oxygen we breathe into the air.
• Hydrogen ions provide energy for making ATP.

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• Chemiosmosis = the movement of hydrogen ions to form ATP.

Light Dependent Reactions cont’d

Photosynthesis- Stage 2

• Second Phase of Photosynthesis and DOES NOT require light.

- No light needed = light independent

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• Also called the Calvin Cycle or Dark Reactions.

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• Uses carbon dioxide to form sugars.

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• Takes place in the stroma of the chloroplast.

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Light Independent Reactions

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Photosynthesis

• Light Independent Reactions �(Calvin Cycle)
• Called a cycle because it begins and ends with same chemical = RuBP

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• Begins with RuBP (a 5-carbon molecule) and adds CO₂ (carbon dioxide) to it to form a sugar
• Called “carbon fixation” because carbon is “fixed” into a 6 carbon sugar

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• Sugar breaks down in series of reactions and is converted to two 3-carbon sugar called PGAL
• Uses ATP and NADPH from light dependent reaction
• PGAL can be made into sugars or RuBP to start the cycle again

Photosynthesis- Stage 2

�

Light Independent Reactions cont’d

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Photosynthesis- Overview

Light Dependent

Happens in:�

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Starts with:����End products:

Light Independent

Happens in:�

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Starts with:�

��End product:

CO₂