Section 4: Photosynthesis Flashcards
What is the overall equation for photosynthesis?
6CO2 + 6H2O –> C6H12O6 + 6O2 (+6H2O)
Photosynthesis begins with light absorbing ____ in plant cells
They are able to absorb energy from _______
Pigments
light
What are the pigments involved in photosynthesis that absorb energy from light?
Chlorophyll a, b, and carotenoids (red orange, yellow)
In photosynthesis, light energy is incorporated into _____
Electrons
Excited electrons in photosynthesis re-emit absorbed energy, which is then reabsorbed by neighboring electrons of a nearby _____ molecule
Pigment
The photosynthesis process ends when energy is absorbed by one of two special ___________ molecules
What are these two molecules?
Chlorophyll a molecules
P680 and P700
This chlorophyll a molecule forms pigment cluster (PSI)
P700
This chlorophyll a molecule forms pigment cluster (PSII)
P680
This type of pigement capture wavelengths that chlorophyll a does not, and passes it on to chlorophyll a where the direct light reaction occurs
Antenna pigment
What are the antenna pigments?
Chlorophyll b, carotenoids, phycobilins (red algae pigment)
Chlorophyll a has a ______ ring, which is alternating double and single bonds, the double bonds are critical for light rxns
What is it complexed with?
Poryphin ring
Mg atom
What is the equation for photophosphorylation? AKA the light dependent reaction in photosynthesis
ADP + Pi + light => ATP
In this part of photophosphorylation, electrons are trapped by P680 in PSII are energized by light
Photosystem II
In photophosphorylation, two excited electrons are passed to a primary electron ______, primary because it is the first in a chain of them
Acceptor
The electron transport chain in photophosphorylation consists of ________ which contains proteins and a cofactor
Plastoquinone complex (PSII)
What is an example of a protein that plastoquinone complex (PSII) in photophosphorylation contains?
What cofactor does it contain?
Cytochrome
Fe2+
What is the electron transport chain analagous to in cellular respiration?
Oxidative Phosphorylation
In photophosphorylation, this phase moves 2 electrons down the primary acceptor chain
Does this cause the loss or gain of energy?
Phosphorylation
Loss of energy
How much energy does it cost to phosphorylate in photophosphorylation?
~1.5 ATP
In this part of photophosphorylation, the electron transport terminates with PSI (P700)
The electrons are again energized by ____ and passed on to another primary electron acceptor
From THIS point forward things can become cyclic or noncyclic
Photosystem I
sunlight
If noncyclic photophosphorylation, after photosystem I, 2 electrons pass down a short ETC with proteins like ferrodoxin to combine and create…..
NADPH (coenzyme)
NADP+ + H+ + 2e- => NADPH
In noncyclic photophosphorylation, after the formation of NADPH, the loss of electrons from the ____ initially is replaced with….
What does it form
PSII
H2O
2e-, 2H+ and 1/2O2
Where does noncyclic photophosphorylation take place in plants?
Thylakoid Membranes
How many photosystems in each thylakoid?
A few hundred
Where does cyclic photophosphorylation take place?
Stroma Lamellae (piece connecting the thylakoids)
Where does photolysis occur?
Thlaykoid lumen (passes e- to the membrane for noncyclic photophos)
Where does the calvin cycle take place?
Stroma
Where does chemiosmosis take place
Thylakoid Membrane
All of the aforementioned processes (photolysis, chemiosmosis, calvin cycle, photosystems, etc) take place inside of the
Chloroplast
What absorbs light in photosynthesis?
Thlyakoid membranes, NOT chloroplast membranes
This type of photophosphorylation replenishes ATP when the calvin cycle consumes it
When excited, 2 electrons from _____ join with protein carrier in the first ETC and generate how many ATP as they pass through?
They are then recycled into _____ and can take either the cyclic or noncyclic path
Cyclic photophosphorylation
PSI
1 ATP
PSI
The Calvin cycle fixes ______
It repeats this ____ times
It is used to produce
This is _____ photosynthesis
CO2
6 times (6CO2)
C6H12O6 (glucose)
C3 photosynthesis (dark reaction)
In this step of cyclic photophosphorylation, 6CO2 + 6RuBP => 12PGA
What catalyzes the reaction? It’s the most common protein in the world!
Why is the calvin cycle called C3 photosynthesis?
Carboxylation
RuBisCo
PGA is 3C
After carboxylation, this step occurs with the reaction 12PGA => 12G3P
What 2 things do this conversion?
What are the by-products and where do they go?
Reduction
12ATP+12NADPH convert it
NADP+ and ADP
They go into noncyclic photophosphorylation
After reduction, in this step 6 ATP convert to 10G3P to 6RuBP, which allows the cycle to repeat
Regeneration
After regeneration, what happens to the 2 remaining G3P?
They are used to build glucose
6CO2 + 18ATP + 12NADPH + H+ => 18ADP + 18Pi + 12NADP+ + 1glucose (2G3P)
Can the “dark reaction” aka calcin cycle occur without light?
No. It is dependent upon high energy molecules produced from the light rxn (ATP and NADPH)
The energy stored in glucose during photosynthesis is in the form of chemical bonds, but the energy initially comes from
Light
Plants DO/DO NOT have mitochondria that make ATP
What is the important difference to remember, then?
They do have mitochondria that make ATP
ATP from photosynthesis comes from the chloroplast, not mitochondria
Where does the glucose that is made during photosynthesis go to be used as energy?
Mitochondria
Is photosynthesis ATP used for general cell fxn?
No. ?
This organelle is where light dependent and light independent reactions occur
Chloroplast
Does the chloroplast have a double membrane like the mitochondria and nucleus?
Yes
What are the three components of the double membrane in the chloroplast?
Outer membrane (phospholipid bilayer/plasma membrane)
Intermembrane space
Inner Membrane (phospholipid bilayer/plasma membrane)
This is the fluid material that fills inside the inner membrane of the chloroplast
What occurs here?
Stroma
The Calvin Cycle (fixing Co2=>G3P)
These are suspended within stroma (stacks), and are individual membrane layers
What is an entire stack of them called?
Thylakoids
Granum
What does the membrane of thylakoids contain?
Are thylakoids a phospholipid bilayer?
PSI and PSII, cytochromes, and other e- carriers.
Yes.
This is the interior of the thylakoid
What accumulates here?
Thylakoid Lumen
H+
Gradient uses ________ to move the accumulated H+ from thylakoid lumen to _______
H+ moves in to out to generate _______ via the synthase
How is this different than oxidative phosphorylation?
ATP synthase
Stroma
ATP
H+ builds up outside and is shuttled INTO the mitochondria to generate ATP via synthase
In chloroplasts, this is the term for using H+ gradient to generate ATP
Chemiosmosis
What accumulates inside of thylakoids during chemiosmosis?
Where are they released when H2O is split by PSII?
It is also carriend into lumen from stroma by ____ between PSIII and PSI
H+ ions
Lumen
cytochrome
What type of gradient is created during chemiosmosis?
A pH and electrical gradient
What is the pH of the gradient during chemiosmosis?
pH 5
What generates ATP during chemiosmosis?
ATP synthase
phosphorylate ADP + Pi => ATP. (3H+ is required for 1ATP
The Calvin cycle produce _________ using NADPH and CO2 and ATP
At the end of the ETC following PSI, 2 electrons produce
2 G3P
NADPH
This is the fixation of oxygen by rubisco (can also fix CO2) => produces no ATP or sugar
Photorespiration
Is photorespiration efficient?
No,rubisco will fix both CO2 and oxygen at the same time if both are present. Probably arose because early earth
atmosphere didn’t have much O2 so it didn’t matter. Peroxisomes breakdown the products of this process
This type of photosynthesis occurs when CO2 enters a leaf, it is absorbed by mesophyll cells instead of being fixed by rubisco into PGA
CO2 combines with PEP to form ____ by PEP carboxylase in the mesophyll
C4 Photosynthesis
OAA
Why is it called C4 synthesis?
OAA has 4C
What does OAA become in C4 photosynthesis?
Where is it transported to via plasmodesmata?
Malate
Bundle Sheath Cell
What is malate converted to in C4 photosynthesis?
Pyruvate + CO2
When malate is converted to pyruvate and CO2 in C4 photosynthesis, where does each go?
CO2 is used in Calvin cycle
pyruvate is moved back to the mesophyll
The overall purpose of C4 photosynthesis is to move CO2 from the mesophyll to the
Bundle Sheath Cell
This is the structure of C4 photosynthesis
This is the process of C4 photosynthesis
Kranz anatomy
Hatch-Slack pathway
Where is C4 photosynthesis found?
It requires 1 additional _____ which becomes ____
Hot, dry climates (faster fixation speed and more efficient)
ATP, AMP
C3 typically occurs in ____ cells
C4 typically occurs in _____ cells
mesophyll cells
Bundle Sheath cells
This is another thing that evolved from C3, it is almost identical to C4. It comprises CRASSULEACEAN ACID METABOLISM
CAM photosynthesis
In CAM photosynthesis, PEP carboxylase fixes CO2 + PEP to
This product is converted to
OAA
Malic Acid
Where is malic acid shuttled to in CAM photosynthesis?
Vacuole of cell
In CAM photosynthesis, at night, stomato are ______ which is the opposite of normal
What is active?
So what accumulates in the vacuole?
Open
PEP carboxylase
Malic Acid
In CAM photosynthesis, during the day, stomata are ____ (opposite of normal)
Where is malic acid?
What is it converted to?
What does this release?
Closed
Out of the vacuole
Back to OAA (requires 1 ATP)
CO2 and PEP
Where does the CO2 go that is produced during CAM photosynthesis?
Calvin cycle with rubisco
The advantage of CAM photosynthesis is that it can…
Proceed during day while stomata are closed (reduces H2O loss)
As leaves age, chlorophyll breaks down to extract valuable components like Mg2+, ______are visible.
carotenoids
The calvin cycle occurs in the ___ of chloroplast
Stroma
The splitting of H2O provides ___ for noncyclic photophosphorylation
Where is it incorporated?
2e-
NADPH and calvin cycle
Is the calvin cycle dependent upon light?
No, but ATP and NADPH are produced from a light dependent reaction
