AP Biology - Photosynthesis

Two parts of photosynthesis

Light independent (Calvin Cycle) and the light dependent

Products of the light-dependent reaction

ATP and NADPH

Products of the light-independent reaction

G3P (to make glucose)

General formula of photosynthesis

CO2 + H2O → O2 + C6H12O6

Summative Reaction

A formula that summarizes thousands of reactions; the majority of their products are used as reactants in later reactions, cancelling each other out.

Goal of photosynthesis

To make ATP and glucose

Plants’ storage of energy

Plants cannot store ATP, but they can store glucose

ATP is for immediate usage, while glucose is for when it cannot make ATP

Where is energy stored in ATP?

In the bond of the 2nd and 3rd phosphate

Antenna molecules (AKA pigments)

Molecules that make up the antenna complex

Antenna complex

an array of proteins and pigments that captures light for photosynthesis

Chlorophyll A

the primary pigment, found in all photosynthetic organisms (best absorbs red and blue light)

accessory pigment

any pigment that is not Chlorophyll A, in order to absorb other colors of light

Reaction center

a complex made of a primary electron acceptor and Chlorophyll A

Primary Electron Acceptor (PEA)

a specialized molecule sharing the reaction center with the Chlorophyll A molecule

P680 (Chlorophyll A)

The Chlorophyll A found in the reaction center; absorbs light best at the wavelength of 680 nm

Redox Reaction

a reaction when two molecules exchange an electron

LEO the lion goes GER

LEO: Loses Electron = Oxidation

GER: Gives Electron = Reduced

Facilitated diffusion

when a substance goes from high concentration to low concentration through a channel protein (does not require energy)

Active Transport

When a substance goes from low concentration to high concentration (requires energy and transport proteins)

Concentration gradient

high and low concentrations separated by a membrane

What is the 2nd Reaction Center made of?

Primary Electron Acceptor and P700

Phosphorylation

the process of adding a phosphate to something

photophosphorylation

the process of making ATP from ADP using light energy

What is photosystem II made of?

an electron transport chain

Thylakoid

the flat disc-like structure in the chloroplast that acts as the site for the light-dependent reaction

thylakoid membrane

the PSI, PSII, and antenna complex reside in this

Granum (Grana)

a stack of thylakoids

Stroma

the liquid portion of the chloroplast that is the site for the light-independent reaction

ATP Synthase

a channel protein and enzyme needed for the synthesis of ATP

Synthesis of ATP

ADP + inorganic phosphate → ATP

inorganic phosphate

a phosphate that is free-floating or one that’s attached to a molecule without a carbon backbone

Chemiosmosis

The process of moving ions across a biological border; begins with the active transport of H⁺ and ends with the formation of ATP

In chemiosmosis, how many H⁺ must pass through ATP Synthase before it is activated?

three

What happens to the electron before it enters PSI?

It is re-energized when entering the 2nd reaction center

Product of Photosystem I

NADPH from NADP+

Production of NADPH

NADP⁺ + H⁺ → NADPH

Noncyclic photophosphorylation

the normal pathway of photosynthesis, where the electron starts at the first reaction center, ends up at NADPH, and never retraces its steps

cytochrome complex

the portion of PSII’s ETC that does chemiosmosis and makes ATP

What is the cytochrome complex made of?

membrane proteins

Plastoquinone

the first membrane protein in the cytochrome complex

Plastocyanin

the last membrane protein in the cytochrome complex

Ferredoxin

the gatekeeper molecule of PSI’s ETC

How does ferredoxin work?

it can allow electrons to continue down PSI’s ETC (noncyclic) or send them back to the cytochrome complex in PSII (cyclic)

Why do plants do cyclic photophosphorylation?

If there’s a shortage of ATP, the electron will retrace its steps (NO NADPH IS MADE; ATP ONLY)

How much ATP and NADPH is needed for the Calvin Cycle?

2 ATP and 1 NADPH