Part 2 Flashcards
Electron Carriers
The high-energy electrons produced by chlorophyll are highly reactive and require a special “carrier.”
An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule.
NADPH can carry the high-energy electrons that were produced by light absorption in chlorophyll to chemical reactions elsewhere in the cell.
Photoautotrophs Absorb Light Energy
Uses photosynthesis to convert CO2 and water into sugars
Then enzymes
– convert sugars into amino acids and other organic molecules
Chemoautotrophs
oxidize inorganic molecules (sulfur, iron)
bacteria – living in extreme places-extremophiles, like no light, ex. in hydrothermal vents
-uses the energy from oxidation to convert CO2 dissolved in ocean water into sugar
The oxidation of H2S :
H2S + 2O2—->SO42- + 2H+ -releases energy
These chemoautotrophs
-provide food for other vent dwellers, ex. Tubeworms
a symbiotic relationship
Energy released
from oxidation of hydrogen sulfide
is used to convert CO2 (dissolved in water) + H20 to sugar
-rearranges the atoms - increases potential energy
Oxidation
a type of Redox reaction – an oxidation reaction paired with a reduction reaction
Oxidize = lose an electron
Reduce = gain an electron
Light-Dependent Reactions
Light-dependent reactions require the direct involvement of light and light-absorbing pigments.
Light-Independent Reactions
Light-independent reactions use ATP and NADPH molecules produced in the light-dependent reactions to produce high-energy sugars from carbon dioxide
Thylakoid membranes
Light Dependent reactions occur here
Photosystems are made up of clusters of chlorophyll molecules
Photosystems are embedded in the thylakoid membranes
The two photosystems are:
Photosystem I
Photosystem II
Photosystem I
Discovered First, but occurs second
Active in the final stage of the Light Dependent Reaction
Almost completely chlorophyll a
Photosystem II
Discovered Second, but occurs first
Active in the beginning stage Of the Light Dependent Reaction
Contains about equal amounts of chlorophyll a and chlorophyll b
Photosynthesis Begins
Photosystem II absorbs light energy
Electrons in chlorophyll are energized and passed down an Electron Transport Chain of molecules
Energy transfers with high energy e- to next chlorophyll molecule over and over in Photosystem I until e- reaches a
“Reaction Center”
Reaction Center= one final chlorophyll + a primary electron acceptor molecule, NADP+
(Gets Reduced!)
Lost electrons in chlorophyll are replaced from enzymes splitting water into 2H+, free electrons, and Oxygen
H+ pumped across thylakoid membrane
2H20 -> 4H+ + 4e- + O2
Light Dependent Reactions
Light energy is converted to chemical energy:
Splits water to produce Oxygen – released into the air,and H+ ions
Converts ADP into ATP
Also forms the energy carrier NADPH from NADP+
Energy Carriers
Nicotinamide Adenine Dinucleotide Phosphate (NADP+)
NADP+ picks Up 2 high-energy electrons and one H+ from the Light Reaction to form NADPH…Gains e-…Reduced
Traps energy!
NADPH carries energy to be passed on the Calvin Cycle to reduce CO2
PSII (Photosystem II)
traps light energy, splits water into H+ ions and oxygen (released as O2), and produces ATP(via enzyme ATP Synthase)
PSI (Photosystem I)
produces NAPDH, by attaching an H+ to NADP+ and stores 2 high energy e-
Phosphorylation
Enzyme in thylakoid membrane called ATP Synthase
As H+ ions pumped through thylakoid membrane,H+ builds up on one side of membrane. This increases potential energy!
H+ can then diffuse out through an enzyme, ATP Synthase. The kinetic energy is used by the enzyme to phosphorylate (add P) to ADP
Forming ATP
Light Independent Reaction
The Calvin Cycle
ATP & NADPH from light reactions used as energy to power the Calvin Cycle (not stable enough molecules to store energy for the cell)
Atmospheric C02 is used to make sugars like glucose and fructose
-sugars are more stable molecules to store energy
Six-carbon Sugars made – carbon and oxygen from CO2, hydrogen from water
Occurs in the stroma
Does not require light
Two 3-carbon sugars are initially made “G3P”, also known as PGAL: glyceraldehyde 3-phosphate
Plants combine two G3P molecules to make glucose
Factors Affecting the Rate of Photosynthesis
Amount of available CO2
Temperature
Amount of available light energy
Concentration of O2
