Biology Chapter 18 Summary

Chapter 18

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Takusagawa’s Note©

Chapter 18: Photosynthesis
1. CHLOROPLASTS - Photosynthesis is carried out at chloroplasts. Structure of chloroplast

Outer membrane Stroma lamellae Inner membrane Thylakoid

Chloroplast

Granum Dark reaction Stroma Light reaction

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Composition of innermembrane and granum membrane are unusual. - Phospholipid (negatively charged) ~10% - Neutral lipid (galactose) ~80%

Photosynthesis occurs in two distinct phases: 1. Light reactions --- Generates NADPH & ATP by using light energy at thylakoid membrane (prokaryotes: inner membrane). 2. Dark reactions --- Synthesize carbohydrates from CO2 + H2O by using NADPH & ATP at stroma.

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Chapter 18 2. -

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Takusagawa’s Note©

LIGHT REACTION Initially believed: CO2 + H2O ⎯light → CH2O + O2 ⎯ van Niel showed: CO2 + 2H2S ⎯light → CH2O + 2S + H2O ⎯ In general: CO2 + 2H2A ⎯light → CH2O + 2A + H2O ⎯

This suggested that photosynthesis is two step reactions: 1. Light energy oxidizes H2A (light reaction): 2H2A ⎯light → 2A + 4[H] ⎯ 2. The reducing agent [H] reduces CO2 (dark reaction): 4[H] + CO2 ⎯→ CH2O + H2O

A. Absorption of light - The principal photoreceptor is chlorophyll (Chl) derived from protoporphyrin IX. - Major differences between chlorophyll and hemes are: - Chl has an extra ring (V) (cyclopentanone). - Ring IV of Chl is more reduced. -
At there, glycolate is converted to glycine (Gly) by receiving NH3. The Gly is transported into a mitochondrion. At there, two Gly are condensed into serine (Ser) and CO2. The Ser is re-transported into a peroxisome. At there, the Ser is deaminated and becomes glycerate. The glycerate is phosphorylated by ATP in cytosol, and becomes 3PG. The 3PG is re-transported into chloroplast, and enters the Calvin