genbio

Photosynthesis

the conversion of light energy to chemical energy in the form of sugar and other organic molecule

Photosynthetic organisms

include plants and some protists, archaeans, and bacteria

Primary producers

organisms that convert sunlight into chemical energy

Consumers

live by eating plants or other animals

Decomposers

bacteria, fungi, and other organisms that obtain chemical energy by breaking down organic matter from producers and consumer

Light-dependent reaction

• light energy is converted into chemical energy

• involve two main processes:

  1. Light absorption

  2. Synthesis of NADPH and ATP

Light-independent reaction

electrons in NADPH are used as a source of energy to convert inorganic CO₂ to an organic form

CO2 fixation

a reduction reaction in which electrons and protons (H⁺) are added to CO₂

Oxidation reaction

loss of electrons, loss of hydrogen

CO2 + H+ + e- > (CH2O)n

co2 fixation equation

2 H2O > 4 H+ + 4 e - + O2

oxidation reaction equation

Oxygen

generated from the splitting of water and released into the environment

C6 H12 O6

glucose equation

Photons

particle of light

Theodor Englemann

• used a glass prism to break light into a spectrum of colors across algae and aerobic bacteria

• constructed an action spectrum

Blue, violet, red

colors where bacteria grew best

Action spectrum

for wavelengths of light showing which colors most affect photosynthesis

Chlorophyll

• green pigments that absorb blue and red light

• reflect/transmit green light

Carotenoids

yellow-orange accessory pigments that help absorb additional light

Pigment color

produced by transmitted or reflected light

Absorption spectrum

the amount of light of different wavelengths absorbed by a pigment

Action spectrum

the effectiveness of light of each wavelength in driving photosynthesis

Photosystems

• sites at which light energy is converted into chemical energy

• embedded in thylakoid membranes and stromal lamellae

Photosystem 1 P700

reaction center contains chlorophyll a molecules that absorb light at 700 nm

Photosystem 2 P680

reaction center contains chlorophyll a molecules that absorb light at 680 nm

Photosystem 2

uses light to excite electrons and split water (H₂O → O₂ + H⁺ + e⁻)

Plastoquinone PQ

transfers electrons to cytochrome complex

Cytochrome complex

energized by electrons; pumps protons (H⁺) from stroma to lumen, creating a proton gradient

Plastocyanin PC

electron carrier that moves electrons to Photosystem I

Photosystem 1

re-excites electrons using light energy

Ferredoxin Fd

electron carrier transferring electrons to NADP⁺ reductase

NADP+ reductase

enzyme that transfers electrons from Fd to NADP⁺, reducing it to NADPH

ATP synthase

uses the energy stored in the proton (H⁺) gradient to produce ATP

1 H2O > 1 NADPH + 1 ATP + (1/2 O2)

energy yield equation

for each pair of electrons, 1 NADPH and 1 ATP are produced

for each pair of electrons (2 e⁻) from water splitting, how many NADPH and ATP are produced?

Carbon fixation

• CO₂ is added to ribulose 1,5-bisphosphate (RuBP).

• The six-carbon molecule splits into two 3-phosphoglycerate (3PGA).

• Enzyme: RuBP carboxylase/oxygenase (Rubisco).

• Plants that fix carbon this way are C₃ plants.

Reduction

• ATP and NADPH convert 3PGA → G3P (Glyceraldehyde-3-phosphate).

• After three turns, one G3P exits the cycle.

• Five G3P are used to regenerate RuBP.

Regeneration

G3P → ribulose 5-phosphate → RuBP (using ATP).

one net G3P

3 turns of calvin cycle =

one six-carbon carbohydrate or glucose

6 turns of calvin cycle =

one molecule of glucose

two G3P’s =

form starch

glucose chains

G3Ps

can also be used in lipid and protein synthesis

2 ATP + 2 NADPH

reduction uses

1 ATP

regeneration uses

CO2 + 2 NADPH + 3 ATP > (CH2O) + 2 NADP+ + 3 ADP + 3 Pi

calvin cycle equation

Thylakoid

site of light-dependent reactions

Stroma

site of light-independent reactions

Water

electron donator in photosynthesis

ATP

energy molecule used during reduction and regeneration in Calvin Cycle

G3P

product of Calvin Cycle, building block of sugars

NADPH

molecule that carries electrons and hydrogen; used in reduction

3PGA

first stable product of CO₂ fixation

RuBP

five-carbon sugar that reacts with CO₂

Rubisco

enzyme that captures CO₂ from the atmosphere