Chemical Energy and ATP Chapter 4.1

Chemical Energy The energy used by cells is carried by ATP. You eat food because the bonds that hold those molecules together are broken and give you energy. ATP (Adenosine triphosphate) Molecule that transfers energy from the break down of food particles to usable energy. Cellular respiration and Photosynthesis are common ways for cells to generate this energy. (most known organisms use one of these methods) Later sections detail both of these processes.

ATP This 3rd phosphate group is very unstable and can break off easily. When it is broken off we can see energy become available. After ATP releases the phosphate, then it will be come ADP. This molecule is reusable, so it can be “recharged” by adding another phosphate back into place.

ATP – ADP Cycle

Food This means organisms break down carbon-based molecules for making ATP (mainly carbohydrates) The food we eat is very important. This is usually in the form of carbohydrates like starches and simple sugars. Lipids that are broken down provide much more ATP. (Body’s second choice in energy molecule) Proteins can be broken down as well. (Last resort)

Lipids (fats) are worth about 9 calories per mg Proteins (meats) are worth about 4 calories per mg Carbohydrates (sugars and starches) are worth about 4 calories per mg Preferred

Non-light Sources Most organisms rely on photosynthesis, but some don’t need sunlight. Chemosynthesis Process that doesn’t use light energy, but finds chemical energy to use. Still uses ATP, just creates it from a different source.

Geothermal Vents (AKA Black Smoker Vents) Hydrogen Sulfide Notice the living organisms (tube worms) despite cold, dark conditions

Intro to Photosynthesis Chapter 4.2

Photosynthesis Plants capture solar energy to make sugars. Photosynthesis takes place in plant cell organelles called chloroplasts. These chloroplasts contain chlorophyll. Chlorophyll is the light absorbing molecule. Chloroplasts have 3 parts: Thylakoid , Grana, Stroma

Chemical formula for photosynthesis 6 CO2 + 6 H2O Makes C6H12O6 + 6 O2 Light Energy

Defining photosynthesis Photosynthesis – process that captures energy from the sun to make sugars that store chemical energy. Chloroplasts contain a molecule called chlorophyll that absorbs the energy from the sun. (two types: chlorophyll a and b) This absorbs a lot of red and blue light, but not much green. This green light bounces off the plant and is seen. (This is why plants are generally green) Thylakoids are small coin-shaped membrane compartments that stack to form grana in chloroplasts. This is where the chlorophyll is contained. Stroma is contained in the extra space in the chloroplast

Chloroplast

Light Reflected light Chloroplast Absorbed Granum light Transmitted Fig. 10-7 Light Reflected light Chloroplast Figure 10.7 Why leaves are green: interaction of light with chloroplasts Absorbed light Granum Transmitted light

Two Stages Light-dependent Reactions Light-independent Reactions Light is absorbed. Energy moved into thylakoid. Water broken down, oxygen released. Energy that was carried to thylakoid is moved to ATP. Light-independent Reactions Carbon Dioxide is added. Energy from step 2 used. Simple sugar is formed.

Interior of Chloroplast Light Dependent Light Independent

Why photosynthesis is important Almost all life on our planet is dependent on the sun. Even if an organism doesn’t use photosynthesis itself, it requires eating the sugars made through photosynthesis of other organisms. The next section describes photosynthesis in much more details, highlighting the processes of light dependent and light independent reactions Factors that might affect the rate of photosynthesis? Amount of water Amount of sunlight Type of light CO2 levels

Photosynthesis in Detail Chapter 4.3

First Stage This stage captures and transfers energy This is the Light-Dependent Reactions Broken into two parts Photosystem I Photosystem II This works in a strange order. II occurs before I does (This is tricky to remember)

Photosystem II Energy Absorbed from Sunlight Water Molecules Split Chlorophyll and other light absorbing molecules take in energy from the sun and transfer it electrons (these electrons then enter the electron-transport chain) Water Molecules Split Enzymes break down water molecules. Oxygen is released as waste. Leftover electrons are used to refill the used up chlorophyll Hydrogen Ions Transported Electrons move from protein to protein. Moves H+ ions into the thylakoid AGAINST concentration gradient (uses energy). Then these electrons are moved to photosystem I

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Photosystem I Energy is absorbed from sunlight Chlorophyll absorbs sunlight and electrons are energized and leave the molecules NADPH is produced when electrons are added to NADP+ This is like another version of ATP  ADP. NADP+ is the low energy version and NADPH is the high energy version Hydrogen Ions diffuse through protein channel. Ions carry a charge on them. Since they are flowing against gradient they are building up a charge in the chemiosmotic gradient. ADP is changed into ATP when hydrogen ions flow through ATP synthase. This is a complex enzyme that makes ATP from ions passing through protein.

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Second Stage This stage uses energy from the first stage to make sugars. This is called Light-Independent Reactions. (called this because it doesn’t require sunlight to occur. This could be the process plants experience at night) Also called the Calvin Cycle.

Calvin Cycle Carbon dioxide added Three-carbon molecules are formed Added to 5-carbon molecules, makes 6-carbon molecules Three-carbon molecules are formed ATP from light dependent is used to split 6-carbon molecules and form 3- carbon molecules Three-carbon molecules exit When two leave they bond to make larger new 6-carbon molecules Three-carbon molecules recycled Turned into 5-carbon molecules and reused to start Calvin cycle again

Interior of Chloroplast Light Dependent Light Independent