Ch. 8 Photosynthesis Flashcards
photosynthesis
biochemical process for building carbohydrates from sunlight and carbon dioxide; carbohydrates are then used to make ATP
what has more energy stored in bonds? CO2 or Carbs?
carbs!
photosynthesis requires an input of energy. where does this energy come from?
sunlight!
reduction reaction
when a molecule acquires electrons and gains energy
oxidation reaction
when a molecule loses electrons and releases energy
what happens to CO2 during photosynthesis?
CO2 molecules are reduced to form higher-energy carbohydrate molecules
where do the electrons that reduce CO2 come from? what is the ultimate electron donor?
they other electrons come from the oxidation of other molecules
ultimate electron donor is water!
what does the oxidation of water ultimately produce as by products?
electrons, protons, O2
what is the formula for photosynthesis?
CO2 + H2O = C6 H12 06 + O2
what is the photosynthetic electron transport chain? (PETC)
series of redox reactions in photosynthesis
- absorption of light by photosystems
- movement of electrons to drive the production of ATP and NADPH
- ATP and NADPH are energy sources for the calvin cycle which produces carbohydrates using CO2
photosystems
protein-pigment complexes
absorb light and set the PETC in motion
how much carbon does photosynthesis remove from the atmosphere per year?
100 billion metric tons
what organisms mainly carry out marine photosynthesis?
phytoplankton (single celled eukaryotes)
cyanobacteria (photosynthetic bacteria)
photic zone
marine surface layer about 100m deep where photosynthesis occurs
prior to photosynthetic evolution, what were the limitations of simple photosynthetic organisms?
- they only had one photosystem, this could not capture enough electrons to oxidize water and reduce electrons to CO2
- they didn’t produce O2 as a by product because they didn’t use water
- were limited to environments where HS2 electron donors were present
who were the first organisms who were able to pull electrons from water?
cyanobacteria
-they incorporated 2 photosystems into a single PETC
where did all of the oxygen in the earth’s atmosphere come from?
it came from photosynthesis by organisms containing two photosystems!
horizontal gene transfer
the transfer of genetic material between organisms that are NOT parents and offspring
how did bacteria obtain photosynthetic capabilities?
horizontal gene transfer
endosymbiosis of cyanobacteria —> chloroplasts
thylakoid membrane
third highly folded membrane which fills much of the center of the chloroplast
-location of the PETC
grana
groups of flattened thylakoid membrane sacs
lumen
fluid filled interior compartment of thylakoid membrane
stroma
surrounding region of thylakoid membrane
where is the outer membrane of the chloroplast double membrane thought to have come from?
from the plasma membrane of the eukaryotic cell which surrounded the ancestral cyanobacterium as it was being engulfed
where is the inner membrane of the chloroplast double membrane thought to have come from?
form the plasma membrane of the ancestral free-living cyanobacterium
what does the thylakoid membrane correspond to in ancestral cyanobacterium? what does the stroma correspond to?
thylakoid membrane - internal photosynthetic membrane found in cyanobacteria
stroma - cytoplasm of the ancestral cyanobacterium
how many chloroplasts can one photosynthetic cell have?
100! (it also has mitochondria)
how many chemical reactions does the Calvin Cycle consist of? what are the 3 main parts?
15 total reactions
- carboxylation
- reduction
- regeneration
define carboxylation as it pertains to the Calvin cycle
CO2 absorbed from the air is added to 5 carbon sugar called RuBP
-this is catalyzed by the enzyme rubisco (acts as a carboxylase)
define reduction as it pertains to the Calvin Cycle
energy and electrons are are transferred to the molecules formed from carboxylation
define regeneration as it pertains to the Calvin Cycle
regeneration of the 5-carbon molecule needed for carboxylation
what is the most abundant protein on the earth?
rubisco (ribulose biphosphate carboxylase oxygenase)
- most important enzyme to the Calvin Cycle
- this enzyme is particularly slow, so much of it is produced
what is 3-PGA?
3-phosphoglycerate (2 of them)
- first stable products of the Calvin Cycle after carboxylation
- 3 carbon molecules
what is NADPH? what is its function?
“nicotinamide adenine dinucleotide phosphate”
- reducing agent used in the Calvin Cycle
- NADPH transfers the energy and electrons that allow carbs so be synthesized from O2
how is NADPH produced? where does it exist? when can it be catalyzed?
- produced by the electron transport chain
- free living in the stroma
- energy/electrons are only transferred from NADPH under the catalysis of specific enzymes (lots of control!)
what are the 2 steps to reducing 3-PGA?
- ATP is used to phosphorylate 3-PGA
2. NADPH transfers two high energy electrons to the phosphorylated compound
how many molecules of 3-PGA are formed each time rubisco catalyses the incorporation of one CO2?
two molecules of 3-PGA per one O2
triose phosphates
- the “true” products of the Calvin Cycle
- (GAP + DHAP)
- 3 carbon carbohydrate molecules exported from the chloroplast
- later sugars are assembled from these
for every 6 triose phosphate molecules that are produced, how many can be withdrawn from the Calvin Cycle?
for every 6 produced, 1 can be withdrawn
what does ATP provide energy for? what does NADPH provide energy for?
ATP - energy to regenerate RuBP
NADPH - energy to make bonds in carb molecules
what happens to excess carbs produced by the calvin cycle?
stored as starch (starch is not soluble, does not upset osmotic balance)
how is ATP produced?
PETC functions as a proton pump
- accumulates protons in the thylakoid lumen
- proton accumulation drives synthesis of ATP
how is NADPH produced?
produced by linear flow of electrons through the PETC from water –> NADP+
what is the key function of a photosystem? where is it located?
to convert absorbed light energy into the movement of electrons
-located in the thylakoid membrane
define visible light
the portion of the electromagnetic spectrum that is visible to our eyes
-includes range of wavelengths used in photosynthesis
what are the exact wavelengths of visible light?
400nm to 700nm
define pigments, why do they look colored?
molecules that absorb some wavelengths of visible light
-look colored because they reflect the lights that they do NOT absorb
define chlorophyll
- major photosynthetic pigment
- appears green because it is poor at absorbing green wavelengths
- consists of a head (magnesium) and a tail (hydrocarbon)
define accessory pigments
- orange yellow carotenoids (mainly)
- absorb light that is poorly absorbed by chlorophyll
- allow cell to absorb broader range of wavelengths
define reaction center
- specially configured pair of chlorophyll molecules
- where light energy is converted into electron transport
what is the “Z scheme”?
- configuration of the PETC
- electrons jump back and forth in a Z pattern
- every other step along the PETC is associated with a small decrease in the energy of electrons
define Photosystem 2
provides electrons to the beginning of the electron transport chain (comes first) pulls electrons from water
(oxidizes water)
define photosystem 1
(comes after photosystem 2)
-energizes electrons with a second input of light energy so they have enough energy to reduce NADP+
