Chloroplasts or something

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photosynthesis purpose

convert low-energy CO₂ + H₂O into high-energy glucose using sunlight energy

photoautotrophs

organisms that capture sunlight to produce glucose; basis of all biomass

chlorophyll pigments

chlorophyll a, chlorophyll b, carotenoids; absorb light except green

porphyrin ring + Mg²⁺

captures photons and stabilizes excited electrons

why plants are green

chlorophyll absorbs all colors except green, which is reflected

thylakoid membrane

location of photosystems, ETC, proton gradient, ATP synthase

grana

stacks of thylakoids packed with photosystems

stroma

chloroplast equivalent of mitochondrial matrix; site of Calvin cycle, sugar synthesis

light reactions purpose

capture sunlight, strip electrons from water, generate proton gradient, make ATP + NADPH

photosystem II function

absorbs light first, strips electrons from water, produces O₂, sends electrons to PQ

photolysis

splitting of water at PSII reaction center to replace lost electrons

PQ → PQH₂

electron carrier that picks up 2 electrons + 2 H⁺ from stroma

cytochrome b6f

receives electrons from PQH₂, pumps H⁺ into thylakoid lumen, transfers electrons to plastocyanin (PC)

source of lumen protons

water splitting, PQH₂ depositing H⁺, cytochrome b6f pumping H⁺

plastocyanin (PC)

transfers electrons from cytochrome b6f to photosystem I

photosystem I function

re-excites electrons using sunlight; transfers electrons to ferredoxin

ferredoxin (Fd)

transfers electrons to FNR

FNR

enzyme that reduces NADP⁺ → NADPH

NADPH

high-energy electron carrier used in Calvin cycle

purpose of proton gradient

stores electrochemical energy that drives ATP synthase

why lumen gets high H⁺

small lumen volume + constant proton pumping

electrochemical gradient

80% electrical (charge difference), 20% chemical (H⁺ concentration)

thylakoid membrane = charged battery

protons stick to membrane like a magnet due to negative charge in stroma

ATP synthase

molecular turbine powered by H⁺ flow from lumen → stroma

chemiosmosis

using proton gradient to power ATP synthase (professor emphasized exam question)

why ATP synthase is ion channel in reverse

instead of pumping ions using ATP, it uses ion flow to generate ATP

ATP export

ATP made in chloroplast stays in stroma; cannot leave chloroplast (professor emphasized)

chloroplast vs mitochondria membranes

thylakoid membrane is functionally analogous to mitochondrial inner membrane

why chloroplasts need mitochondria

chloroplast ATP never leaves; mitochondria provide ATP to cytosol

cyclic photosynthesis

electrons cycle around PSI only; makes ATP but no NADPH; used in high light

linear (Z-scheme) photosynthesis

electrons flow PSII → PQ → cyt b6f → PC → PSI → Fd → NADPH

Calvin cycle purpose

fix CO₂ into sugars using ATP + NADPH

rubisco

most abundant enzyme on Earth; fixes CO₂ to RuBP

Calvin cycle step 1

CO₂ + RuBP → 3-PGA (via rubisco)

Calvin cycle step 2

3-PGA + ATP → 1,3-bisphosphoglycerate

Calvin cycle step 3

1,3-bisphosphoglycerate + NADPH → G3P

fate of G3P

one exits cycle to become sugar; five are recycled to regenerate RuBP

Calvin cycle regeneration

uses ATP to convert 5 G3P → 3 RuBP

where starch is made

in the stroma from G3P

where sucrose is made

in the cytosol from exported G3P

chloroplast genome

circular DNA, larger than mitochondrial DNA (prof highlighted), encodes ~5–10% chloroplast proteins

chloroplast protein import

most proteins synthesized in cytosol, imported post-translationally

plastids types

chloroplasts, chromoplasts, amyloplasts, etioplasts; interconvertible (prof emphasized fall leaf colors)

photophosphorylation

ATP production in chloroplasts using light-powered proton gradient

peroxisomes function

fatty acid oxidation, detoxify H₂O₂ using catalase (prof emphasized ROS)

peroxisome biogenesis

can divide from preexisting ones or form de novo from ER (difference from mitochondria/chloroplasts)

very long chain fatty acid oxidation

occurs in peroxisomes but produces no ATP (prof emphasized)

locations summary

PSII/PSI/ETC/ATP synthase = thylakoid membrane; Calvin cycle = stroma

exam question: analogous membranes

thylakoid membrane is analogous to mitochondrial inner membrane (NOT chloroplast inner envelope)

exam question: universal ETC usage

all life forms use electron transport chains + ATP synthase (prof stressed multiple times)

exam question: why plants still need mitochondria

chloroplast ATP cannot leave the organelle

exam question: order of photosystems

PSII occurs before PSI (discovered in reverse order)

exam question: electron source vs acceptor

source = water; final acceptor = NADP⁺

exam question: proton sources

water splitting, PQH₂, cytochrome b6f pumping

exam question: what increases lumen acidity

continuous H⁺ pumping and tiny lumen volume