Photosynthesis Dark reaction

1. PSI uses which energy to excite electrons and pass them to NADP+ to produce NADPH

light

plastoquinone

2. PSII uses light energy to excite electrons which are passed to what

3. Plastoquinone takes the electrons to Cytb6f, which passes them to plastocyanin
- how many protons are pumped into the lumen by Ctyb6f

4

Plastocyanin donates the electrons to what to reset it

PSI

PSII pulls electrons from water to reset itself, producing O2
- how many protons are removed from H2O into the lumen

4

chloroplast

Protein Gradient

1. what ATP synthase allows the protons in the lumen to re-enter the stroma

stroma

Protein Gradient

2. Rotational energy from this proton flow is used to produce ATP where

Protein Gradient

2. Rotational energy from this proton flow is used to produce ATP in the stroma
- how many ATP per turn of ATP synthase

3

PS I needs 2 electrons to make 1 NADPH, so it must absorb 2 photons
PS II must replace those 2 PS I electrons, so it must also absorb 2 photons
Therefore making 1 NADPH requires how many photons

4

Those 2 PS II electrons must be replaced
Splitting 1 H2O yields 2 electrons and how many O2

½

Splitting 1 H2O yields 2 electrons and ½ O2
But making 1 molecular O2 requires splitting how many H2O (so things are doubled)

2

photons

movement of electrons and protons during photosynthesis light reactions in chloroplast
energy source?

movement of electrons and protons during photosynthesis light reactions in chloroplast
2H2O + 8 photons + 2NADP+ + ~3ADP+ + ~3Pi → O2 + ~3ATP + 2NADPH

whats geting oxidzed?

H2O

movement of electrons and protons during photosynthesis light reactions in chloroplast
2H2O + 8 photons + 2NADP+ + ~3ADP+ + ~3Pi → O2 + ~3ATP + 2NADPH

whats geting reduced?

NADP+

bacterial

The chloroplast and the mitochondria are derived
from internalized what cells

which reactions occur in the stroma of the chloroplast

Dark

Dark reactions’ occur in the stroma of the chloroplast and use
ATP and NADPH from the light reactions to reduce a fully-oxidized
carbon in CO2 into a more reduced what sugar

hexose

calvin

Photosynthesis: dark reactions called the what cycle after the scientist who investigated them

The Calvin cycle has how many stages

3

The Calvin cycle has three stages:
1. Fixation of CO2 (C1) with ribulose 1,5-bisphosphate (C5) to
form how many molecules of 3-phosphoglycerate (2 @ C3)

2

The Calvin cycle has three stages:
2. The what of 3-phosphoglycerate to form hexose phosphate

reduction

regeneration

The Calvin cycle has three stages:
3. The what of ribulose 1,5-bisphosphate

The Calvin Cycle Uses the Products of the what Reactions

Light

Takes how many Turns of the Calvin Cycle to make one Hexose

6

CO2

Calvin Cycle Stage 1
one what condenses with a five-carbon acceptor, ribulose 1,5-bisphosphate,
to form an unstable six carbon compound

3-phosphoglycerate

Calvin Cycle Stage 1
one CO2 condenses with a five-carbon acceptor, ribulose 1,5-bisphosphate,
to form an unstable six carbon compound that breaks down into two molecules of three-carbon
what

plants in which the three-carbon compound
3-phosphoglycerate is created as the first intermediate in
photosynthesis
- trees, wheat, oats, rice, beans, peas, and spinach

C3 plants

The enzyme that catalyzes which step in the Calvin cycle
is ribulose 1,5-bisphosphate carboxylase/oxygenase
(rubisco)

1st

Fixation of CO2 into 3-Phosphoglycerate by Rubisco

acts as a what – attaches a CO2 group to ribulose
1,5-bisphosphate

carboxylase

Fixation of CO2 into 3-Phosphoglycerate by Rubisco
we will see later it also has an oxygenase activity which is
a productive or non-productive side reaction in C3 plants

non-productive

enzyme

rubisco can be up to 50% of the protein in chloroplasts, because of this, it is likely
the most abundant what on the planet

rate-limiting

The fixation of CO2 by rubisco is the what step in hexose synthesis and pretty
much in the world’s biochemistry

CO2 fixation is the process of turning what carbon (from CO2) into what
compounds that allow much of life on earth

inorganic, organic

carbohydrates

Photosynthetic organisms turning light into what is the ultimate source
of most useful carbon compounds on the planet

Structure of Rubisco
how many large subunits each with active site
how many small subunits of unknown function

8,8

Mg2+

Rubisco Active Site

Rubisco requires what for its catalytic activity

Rubisco Active Site

Rubisco requires Mg2+ for its catalytic activity
a carbamoylated what side chain binds the Mg2+

Lys

Rubisco Requires how many Enzymes to Perform Catalysis

2

rubisco activase

Rubisco Requires a Second Enzyme to Perform Catalysis
another enzyme, what, uses the
energy of ATP hydrolysis to activate rubisco
by removing the substrate, then the reaction
can proceed

rubisco is a very what enzyme, with a turnover number of 3 sec-1 at 25°C

inefficient

Calvin Cycle Stage 2
how many 3-phosphoglycerates (3-PG) are reduced to
two triose phosphates (GAP and DHAP)

2

Calvin Cycle Stage 2
In the first step 3-PG is phosphorylated
In the second step it is what to GAP

reduced

1,3-bisphosphoglycerate

Calvin Cycle Stage 2
3-phosphoglycerate kinase catalyzes the
transfer of a phosphoryl group from ATP to
3-phosphoglycerate, yielding
what

NADPH

Calvin Cycle Stage 2

glyceraldehyde 3-phosphate dehydrogenase
(GAPDH) catalyzes a reduction between
what and 1,3-bisphosphoglycerate,
producing glyceraldehyde 3-phosphate (GAP)
and NADP+

Calvin Cycle Stage 2

what phosphate isomerase interconverts
glyceraldehyde 3-phosphate (GAP) and
dihydroxyacetone phosphate (DHAP)

triose

Calvin Cycle Stage 2

requires how many of 3 ATP and hoow many NADPH made in
light reactions

2, 2

glycolysis

Calvin Cycle Stage 2 & 3 compared to what

same compounds and enzymes as in what
but going in the opposite direction

isozymes

These are specific versions of
these enzymes in the chloroplast
for use in the Calvin cycle

There are other versions of the
enzymes in the cytoplasm for use
in glycolysis

monophosphates

Calvin Cycle Stage 3a:
making hexose what

aldolase

Calvin Cycle Stage 3a: making hexoses
what condenses triose phosphates
GAP and DHAP into fructose 1,6-
bisphosphate, a hexose phosphate

Calvin Cycle Stage 3a: making hexoses

fructose 1,6-bisphosphatase cleaves a
phosphate from fructose 1,6-bisphosphate
to make fructose 6-phosphate
- this reaction is strongly what and
essentially what

exergonic, irreversible

carbohydrate

Calvin Cycle Stage 3a: making hexoses

This pool of hexose phosphates is used to
make starch, sucrose and cellulose and
other what needed by the cell

Calvin Cycle Stage 3b:
Regeneration of Ribulose 1,5-Bisphosphate
stromal enzymes rearrange the carbon skeletons to generate what phosphate intermediates

pentose

ribulose 5- phosphate

Calvin Cycle Stage 3b:
Regeneration of Ribulose 1,5-Bisphosphate
stromal enzymes rearrange the carbon skeletons to generate pentose phosphate intermediates these are converted to what which is phosphorylated to ribulose 1,5-bisphosphate to complete
the Calvin cycle

Synthesis of One Usable Triose Phosphate
Requires Three CO2, Six NADPH and Nine ATP
fixation of 3 CO2 in how many turns of the cycle yields 6 triose phosphates

3

Synthesis of One Usable Triose Phosphate
Requires Three CO2, Six NADPH and Nine ATP

how many are used to regenerate
the compound needed
at the start of the cycle

5

Synthesis of One Usable Triose Phosphate
Requires Three CO2, Six NADPH and Nine ATP

5 are used to regenerate
the compound needed
at the start of the cycle
only 1 is available for
which processes

anabolic

Net reaction for Calvin cycle
The balanced equation for the net reaction of the Calvin cycle is
6 CO2 + 18 ATP + 12 NADPH + 12 H2O à C6H12O6 + 18 ADP + 18 Pi + 12 NADP+ + 6 H+
Each glucose made by the Calvin cycle requires six turns of the
cycle incorporating how many CO2 and using how many ATP and how many NADPH

6, 18, 12

Starch and Sucrose Are the Major Carbohydrate Stores in what

Plants

The fixed carbons from photosynthesis have two principal fates:
1. What, which is synthesized and stored in the chloroplast

Starch

Starch and Sucrose Are the Major
Carbohydrate Stores in Plants
The fixed carbons from photosynthesis have two principal fates:
1. Starch, which is synthesized and stored in the chloroplast

what is an unbranched chain of glucose
connected by (α1→4) linkages

amylose

Starch and Sucrose Are the Major
Carbohydrate Stores in Plants
The fixed carbons from photosynthesis have two principal fates:
1. Starch, which is synthesized and stored in the chloroplast
what is a branched polymer of glucoses
connected by (α1→4) and (α1→6) linkages

amylopectin

ADP-Glucose Is the Substrate for Starch Synthesis in the chloroplast
starch = a high molecular weight polymer of D-glucose
condensation of glucose 1-phosphate with ATP yields what-glucose,
a ‘sugar nucleotide’ (an activated sugar carrier)

ADP

starch synthase

transfers glucose residues from ADP-glucose to
the end of a preexisting starch molecule

Starch and Sucrose Are the Major
Carbohydrate Stores in Plants
The fixed carbons from photosynthesis have two principal fates:
2. what , which is synthesized in the cytoplasm from 3-
phosphoglycerate. whatis the transport form of carbohydrates
in many plants (energy for other cells in the plant)

Sucrose

sucrose is synthesized in how many steps from the sugar nucleotide
UDP-glucose and fructose 6-phosphate from the Calvin cycle

2

Most plants transport what through their
vascular tissue for use throughout the plant

sucrose

some plants use what as their
long-term carbohydrate storage form,
storing it in their roots like sugar beets, or in
their stalks like sugar cane

sucrose

cellulose

Some Homopolysaccharides Serve
Structural Roles:
what = linear, unbranched homopolymer consisting of 10,000 to 15,000
D-glucose units

cellulose = linear, unbranched homopolymer consisting of 10,000 to 15,000
D-glucose units
- linked by (what1→4) glycosidic bonds which gives a linear structure

beta

wall

cellulose = linear, unbranched homopolymer consisting of 10,000 to 15,000
D-glucose units
- tough, fibrous, water-insoluble, component of plant cell what

polysaccharide

cellulose = linear, unbranched homopolymer consisting of 10,000 to 15,000
D-glucose units
- most abundant what on the planet

plasma membrane

cellulose is synthesized from
intracellular precursors but
deposited and assembled
outside the what

cellulose

UDP-Glucose is also used for what synthesis

synthase

cellulose what catalyzes the
assembly of cellulose chains

O2

Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) also Catalyzes a Wasteful Oxygenase Reaction
2) The binding site for CO2 in rubisco can also bind what

phosphoglycolate

Iff rubisco reacts O2 instead of CO2 it generates 3-phosphoglycerate and a
compound called what

f rubisco reacts O2 instead of CO2 it generates 3-phosphoglycerate and a
compound called phosphoglycolate
- instead of C5 + C1 à 2 @ C3
- it performs C5 + O2 à C3 + C2
à no carbons are fixed in the what reaction

oxygenase

Ribulose 1,5-bisphosphate carboxylase/oxygenase
(rubisco) also Catalyzes a Wasteful Oxygenase Reaction
how many of rubisco catalytic events occurs with O2 instead of CO2

1/4

CO2

Rubisco Also Catalyzes a Wasteful Oxygenase Reaction

Phosphoglycolate is metabolized to yield a molecule of what

photorespiration

If rubisco reacts with O2 instead of CO2 it generates 3-phosphoglycerate and a compound called phosphoglycolate
Phosphoglycolate is metabolized to yield a molecule of CO2

Because this reaction uses oxygen and produces carbon
dioxide it is called what– basically the opposite of
what rubisco should be doing

what= energy from light is used to split water,
O2 is made and CO2 is fixed to make carbohydrates

photosynthesis

what = carbohydrates are oxidized,
O2 is used and CO2 is produced

mitochondrial respiration

what= a costly side reaction of photosynthesis,
O2 is used and CO2 is produced

photorespiration

Rubisco Also Catalyzes a Wasteful Oxygenase Reaction
The rubisco oxygenase activity what with temperature, so
as the planet warms up, plants will fix carbon less well

increases

The C4 Pathway of Tropical Plants Accelerates
Photosynthesis by Concentrating Carbon Dioxide
Because the oxygenase activity of rubisco is worse at higher
temperatures, plants that evolved in warmer climates such as the
tropics reduce photorespiration by what the concentration of CO2 in
photosynthetic cells

increasing

Because the oxygenase activity of rubisco is worse at higher
temperatures, plants that evolved in warmer climates such as the
tropics reduce photorespiration by concentrating CO2 in
photosynthetic cells
This pathway is called the what pathway because the first step in CO2
incorporation in these plants involves a four-carbon intermediate not
a three-carbon intermediate, and plants using this pathway are called
what plants.

C4

oxaloacetate

Diagram of the C4 Pathway

CO2 is brought into one type of cell and
reacts with phosphoenolpyruvate to form
what , a four-carbon molecule (C4)
that is subsequently converted to malate

Diagram of the C4 Pathway

Malate moves into the cells where the
Calvin cycle occurs and is what
to pyruvate and CO2. Pyruvate is shuttled
back out of these cells, but the CO2
accumulates in these cells where rubisco is
active

decarboxylated

Diagram of the C4 Pathway

A what substrate concentration (CO2 )
means the enzyme will bind it it more often
and there is less photorespiration
(remember what Km is)

higher

ATP

Diagram of the C4 Pathway
what is needed, so there is an energy cost
to being a C4 plant

which plants need five ATP molecules to assimilate one molecule of CO2

C4

which plants need only three ATP molecules

C3

crassulacean acid metabolism (CAM)

The use of the C4 pathway to trap CO2 at night for later use is called
what (desert plants)