Review: Energy CurrencyWe already know: The energy currency for the cell is a molecule called…

Adenosine Triphosphate (ATP)

A = Adenosine ATP = A ~ P ~ P ~ P P = Phosphate ADP = A ~ P ~ P ~ = chemical bond AMP = A ~ P The breaking of a bond (~) in ATP releases energy

A~P~P~P → A~P~P + P + ENERGY

The making of a bond (~) in ATP“bottles up” energy for later userequires energy input

A~P~P + P + ENERGY → A~P~P~P

Energy and LifeAll living things have a need for energyenergy

(this is a characteristic of life!)

Scientists classify living organisms into two groups based on how they get their food…

Autotrophs : organisms (like plants) that produce their own food from the energy in sunlight

Are there any other autotrophs besides plants?Are there any other autotrophs besides plants?

Heterotrophs : organisms that cannot make their own food and must consume in order to obtain energy

A Story of EnergyOn a sunny plain in Africa, a herd of zebras peacefully eat the grass. But watch out! – the unsuspecting grazers are about to be harshly interrupted. A group of lions is stalking the herd, creeping ever closer, and nearly ready to pounce. Suddenly, the lions strike forward, killing one of the zebras and devouring its carcass.

Answer the following questions in your notebook:• How many different types of living things

(organisms) are featured in this story?• Which (if any) are heterotrophs? … autotrophs?• Where is the energy of this system coming from?• Without producers, what would happen to consumers?

Energy Cycling• Photosynthesis, Respiration, the formation

of ATP, and the breakdown of ATP form a fundamental biological cycle

• Photosynthesis – Stores energy from sunlight in glucose molecules

• Respiration – Releases the energy from glucose molecules and generates ATP

• ATP breakdown – Powers cell activities

• Biochemical Pathway: A series of chemical reactions, in which the product of one reaction is the reactant in the next reaction

Example: Photosynthesis

Intro to: PhotosynthesisPhotosynthesis – the cellular process by which solar energy is stored in chemical bonds

• Overall, the reaction is as follows: Reactants Products

6 CO2 + 6 H2O + (light) energy → C6H12O6 + 6 O2

Photosynthesis is a complicated, 2-step processLight Reactions• Light is captured• Oxygen is released• ATP is formed Dark Reactions• Carbon dioxide is combined with

hydrogen in order to form glucose

ChloroplastsStructure• Double membrane• Interior is organized into

flattened sacs (thylakoids)• A stack of thylakoids is

called a granum (plural → grana)• Lumen : interior space of a thylakoid• Stroma : protein-rich solution found

between the thylakoid membrane and the outer membrane of the chloroplast

• Light reactions occur on the thylakoid membranes• Dark reactions occur in the stroma

The Nature of LightThe Nature of Light

• Light from the sun appears white, but it is actually composed of a variety of colors

Violet Indigo Blue Green Yellow Orange Red

• Light is made of particles of energy that move in waves (“dual nature”)

→ Each color has a different amount of energy

→ Each color has a different wavelength

When striking something, colors may be: - Absorbed (we no longer see it) - Reflected (we see it) - Transmitted (it passes through)

The Biology of Autumn Colors

• Pigment – a colored chemical compound that absorbs light

• The main photosynthetic pigment found on the membranes of the chloroplasts is called CHLOROPHYLL (Two types: “a” and “b”)

• Responsible for the green appearance of plants

• In the fall, photosynthesis slows down, as does chlorophyll production

• This reveals other pigments(Example: caroteniods, which appear orange/yellow/brown)

Question: What color(s) do chlorophyll a and b each absorb and reflect?

Plant Pigment Separation by ChromatographyPlant Pigment Separation by Chromatography

Light (Dependent) Reactions

Question: Why do they call it this?

Three Steps of the Light Reactions:

- Electron Transport Chain

- Restoring Photosystem II

- Chemiosmosis

I. Electron Transport Chain

• Photosystem: a cluster of pigment molecules• A light photon “excites” an electron in Photosystem II• This electron travels from molecule to molecule along

the transport chain, losing energy along the way• The energy “lost” by the electron is used to

pump protons (H+) into the thylakoid lumen• Similarly, light “excites” an electron in Photosystem I,

which is passed along another transport chain• At end of this chain: e- + H+ + NADP+ → NADPH

II. Restoring Photosystem II

• The answer is……. WATER !!!!!

• A thylakoid enzyme splits water molecules as follows:

2H20 → 4H+ + 4e- + O2

• This creates: ELECTRONS for the transport chain, as well as OXYGEN

• We know that the electron departing from Photosystem I is replaced by the electron finishing Photosystem II’s transport chain

• BUT…how are the electrons leaving Photosystem II replaced?

III. Chemiosmosis• Chemiosmosis synthesizes ATP• Remember : the high concentration

of protons built up inside the thylakoids as a result of the transport chain

• The protons diffuse (which direction?) through a carrier enzyme called… ATP synthase

• The protons passing through this enzyme cause it to synthesize ATP from ADP + P

The 2 Main Products of the Light Reactions:•NADPH•ATP(Both will be needed in the dark reactions)

Photosynthesis: The Big Picture

Remember → this is called a biochemical pathway