Chloroplasts

3 Differences between mitochondria and chloroplasts

-Chloroplasts do not have stuff in the inner membrane like mitochondria

-Thylakoid membranes have chlorophyll

-Stroma instead of matrix

Chlorophyll a = main pigment

Peaks at purple/violet and red

Wider spectrum than chlorophyll b

Chlorophyll b

Peaks at blue and yellow

Slightly narrower than chlorophyll a spectrum

chlorophyll c

found in algae and bacteria

what are the 2 main stages of photosynthesis?

1: light reactions (create energy as ATP & NADPH)

2: carbon fixation / calvin cycle (energy can't leave chloroplast...must be used)

photosynthesis stage 2: carbon fixation / calvin cycle

-light independent

-calvin cycle

-ATP and NADPH can't leave chloroplast so the energy must be converted into organic molecules

-creates organic molecules for the plant to use

Antenna complex & Reaction center

-Antenna complex embedded in thylakoid membrane

-Reaction center is a chlorophyll dimer (it holds electrons at a lower energy by utilizing proteins that lower their energy)

-Light excites electron → Excited electron jumps from antenna to antenna until it hits the reaction center.

-After reaction center the electron is transferred to an electron carrier and then to the ETC / photosystems

Photosystem I: NOT independent

-Electron transferred from antenna complex

-Receives electrons from PS2

Photosystem II: semi-independent

-Necessary for photosystem I to run.

-ATP created on stroma side.

-H2O splitting

-provides electrons to PS1

Water splitting complex

-Occurs in photosystem II

-4 rounds of energy transfer must occur before water splitting enzyme can release 4H+ and 1 O2 from 2 water molecules

ATP and NADPH production in Chloroplasts

-Photosystems II and I boost electrons to a higher energy level which is necessary to produce atp and nadph

-ATP and NADPH cannot leave the chloroplast → must be used in stage 2 of photosynthesis (carbon fixation)

-RuBisCo: transforms inorganic carbon into an organic molecule

Calvin Cycle (carbon fixation)

1: Rubisco uses CO2

2: sugar formation

3: 1 molecule of Glyceraldehyde leaves the cycle

relationship between photosynthesis and cellular respiration

Products of photosynthesis are used in cellular respiration to make usable energy --> Without cellular respiration, the energy from photosynthesis cannot be used

Cyanobacteria vs. Chloroplasts

Cyanobacteria are photosynthetic prokaryotes; chloroplasts share many features including thylakoid membranes and pigment systems.

Chlorophyll Types

Includes chlorophyll a (main pigment) and b (accessory pigment) in plants

Carotenoids

-Accessory pigments that extend the range of light absorption.

-protects from light damage by quenching singlet oxygen.

-alpha & beta forms

Phycobilins

-Water-soluble pigments found in cyanobacteria and red algae that absorb light in wavelengths chlorophyll doesn't.

-phycocyanin & phycoerythrin

Phycoerythrin

A red or pink pigment that absorbs blue and green light efficiently.

Phycocyanin

A blue pigment that absorbs orange and red light, complementing chlorophyll's absorption.

Light Reactions

-Light absorption --> electron transferred to reaction center --> electron transport through PSII cytochrome b6f --> electron carried to PSI reaction center --> ferrodoxin NADP+ reductase produces NADPH while ATP synthase produces ATP

-Occur in thylakoid membranes.

How do PSII and PSI help produce ATP and NADPH?

PSII & PSI boost electrons to the energy level needed for ATP and NADPH production

Carbon Fixation / calvin cycle

-Occurs in stroma

-The ATP and NADPH generated are used to convert inorganic CO₂ into sugars.

Antenna Complex

A group of pigments that collect light energy and funnel it to the reaction center.

Reaction Center

A specialized chlorophyll pair that donates a high-energy electron to the electron transport chain.

Photosystem II (PSII)

The first complex in the light reactions; uses light energy to split water and generate ATP.

-electrons from reaction center --> mobile carrier brings them --> enter cytochrome b6f --> pumps H+ across membrane --> H+ gradient powers ATP synthase.

Photosystem I (PSI)

The second complex; boosts electrons to a higher energy level to reduce NADP⁺ into NADPH.

-electrons PSII go to reaction center --> ferro mobile carrier--> ferro NADP+ reductase --> creates NADPH from NADP+

-gets electrons for reaction center from PSII

How are electrons replenished in the reaction centers?

-water splitting (PSII)

-ETC (PSI)

Water-Splitting Complex

Found in PSII; provides replacement electrons by oxidizing water, releasing O₂ as a byproduct.

Electron Flow Between Photosystems

Electrons move from PSII to PSI via mobile carriers, forming a linear electron transport chain.

Mobile Carriers

Include plastoquinone, cytochrome b6f, and plastocyanin — shuttle electrons between components of the transport chain.

ATP Production

Driven by proton gradient created by electron transport; ATP synthase in the thylakoid membrane synthesizes ATP.

NADPH Production

Generated by Photosystem I when high-energy electrons reduce NADP⁺ to NADPH.

ATP & NADPH Use

Remain inside the chloroplast and fuel the Calvin cycle in the stroma.

Calvin Cycle

A series of enzymatic reactions that fix atmospheric CO₂ into 3-carbon sugars using ATP and NADPH.

Rubisco

-used during calvin cycle / carbon fixation

-the enzyme that catalyzes the fixation of CO₂ into organic molecules.

-pyrenoids are in chloroplasts of algae & use rubisco

Pyrenoid

A chloroplast subcompartment that concentrates Rubisco and enhances the efficiency of carbon fixation.

Glyceraldehyde-3-Phosphate (G3P)

A 3-carbon sugar produced by the Calvin cycle; can be used to synthesize glucose or other organic molecules.

metabolite production in photosynthetic cells

sugars from photosynthesis exit the chloroplast --> sugars in cytosol --> sugars release metabolites --> sugars enter the mitochondria for citric acid cycle (like pyruvate)

Organic Molecule Storage

-Photosynthetic cells convert G3P into starch for storage for later use.

-lipids can be stored as fat droplets in the cytosol