ch 8 carbon reactions

what is produced by calvin cycle?

- ADP

- Pi

- NADP+

- sugar

where do carbon reactions occur?

stroma

what is the only rxn that can capture CO2 from atmosphere and fix it?

calvin

do all CO2 molecules that are fixed become sugar?

no

net Calvin cycle reaction

3CO2 + 5H2O + 6NADPH + 9ATP -> G6P + 6HADP+ + 3H+ + 9ADP + 8Pi

3 phases of calvin cycle

- carboxylation

- regeneration

- reduction

which phase has the carbon input?

carboxylation

which phase consumes ATP?

reduction

which phase makes ATP?

regeneration

starting material for carboxylation in plant

ribulose 1,5-bisphosphate

what is produced by the reduction reaction?

glyceraldehyde-3-phosphate

what is required to make sugar?

RuBP

how many carbons does RuBP have?

5

how many reactions occur in the reduction phase?

2

what do the 2 rxns of the reduction phase require per CO2?

- 2 ATP

- 2 NADPH

what is the most extensive phase in the calvin cycle?

regeneration

Rubisco

The most abundant protein on earth that performs Carbon Fixation in the Calvin Cycle

what does rubisco do to RuBP?

carboxylates or oxygeneates it

is carboxylation of RuBP controlled?

yes so it is not always occuring

what is the amount of enzyme regulated by?

transcription or translation

how many subunits does rubisco have?

8 small and 8 large

what are large subunits coded by?

chloroplast genome

what are small subunit coded by?

nuclear genome

what is the activity of rubisco regulated by?

posttranslational modifications

types of posttranslational modifications

- covalent

- noncovalent

what is the most common covalent postranslational modification?

phosphorylation/dephosphorylation

noncovalent modification examples

- binding of regulators

- change of ionic environment

what is an regulator of final activity of rubisco?

reversible formation of rubisco supramolecular complex

is the dark rxn totally independent of light?

no, because light affects the regulation of enzymes in dark rxn

what are the stages of the calvin cycle?

- carboxylation where rubisco adds atmosphereic CO2 onto a 5C acceptor molecule

- reduction where triphosphate molecules are formed using photogenically generated ATP and NADPH

- regeneration where triose phosphate molecules are reassembled back into 5C CO2 acceptor molecules

light influences the activty and expression of key enzimes in the calvin cycle in which of the following ways?

- photoreceptors influence on expression of enzymes

- the ferredoxin-thioredoxin system

- formaiton of supramolecular complexes of chloroplast enzymes

- ion movement

to assimilate 3 molecuels of CO2, how many molecules of NADPH and ATP are required?

6 NADPH, 9 ATP

3 multiple choice options

what is substrate for rubisco?

RuBP

what does rubisco do?

oxygenate/carboxylate RuBP

if rubisco carboxylates RuBP, what is produced?

2 3-phosphoglycerates

if rubisco oxygenates RuBP, what is produced?

- 1 2-phosphoglycate

- 1 3-phosphoglycerate

when does oxygensze function occur?

- in warm, dry climates

- when [O2] is higher than [CO2]

characteristics of when oxygenase occurs?

- CO2 less soluble than O2

- low carboxlylation capacity of rubisco

- closed stomata

what is 2-phosphoglycolate used for?

photorespiration

photorespiration

A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide.

what types of plants make 3PG?

C3

C3 plant

A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.

why is rubisco functioning as an oxygenase bad?

it takes in O2 and releases CO2 which is wasteful as photosynthesis is still going on

glycolate pathway

Complex ATP-consuming process for the recovery of C2 fragments from photorespiration

what three organelles are involved in glycolate pathway?

- chloroplast

- peroxisome

- mitochondrion

pathway of photorespiration

`1. RuBP [5C]+ O2--> phosphoglycolate [2C]+ 3-phosphoglycerate (3PG) [3C]

2. phosphoglycolate hydrolyzed to glycolate

3. glycolate diffuses into peroxisomes and converted to glycine

3. glycine diffuses to mitochondria: 2 glycine--> serine+ CO2

4. Serine diffuses to peroxisomes and converted to glycerate

5. glycerinate moves to chloroplast and is phosphorylated to 3PG that enters Calvin cycle

6. 2phosphoglycolate [4C] +O2--> 3PG [3C] + CO2

is ATP produced or consumed by glycolate pathway?

consumed

why is glycolate wasteful?

- O2 consumed

-CO2 released

- ATP consumed

what are the products of the oxygenase activity of rubisco on RuBP?

1 molecule each of 3-PG and 2-phosphoglycolate

3 multiple choice options

conversion of 2-phosphoglycolate during photorespiration

2-phosphoglycolate -> glycolate -> glycine -> serine -> glycerate -> 3PG

inorganic carbon concentrating mechanisms

C4 and CAM

Kranz anatomy

Refers to the structure of C-4 leaves and differs from C-3 leaves. In C-4 leaves, the bundle sheath cells lie under the mesophyll cells, tightly wrapping the vein deep within the leaf, where CO2 is sequestered

where is the bundle sheath cells in kranz anatomy?

surround vascular tissue under mesophyll

where are the mesophyll cells in kranz anatomy?

outside of the bundle sheath cells

what happens in mesophyll cells in kranz anatomy?

C3 + CO2 -> C4

what happens in bundle sheath cells in kranz anatomy?

- C4 -> CO2 + C3

- CO2 is assimilated and rubisco can be used in calvin cycle to do carboxylation

is [CO2] higher in bundle sheath cells or outside plant in C4 plants?

inside bundle sheath, thereby making calvin cycle possible using rubisco

single cell C4 plants

C4 diffused to interior of cell and C3 diffuses to outside so that CO2 can be assmilated

are single cell C4 plants common?

no

what happens in mesophyll cells for C4 (more in-depth)?

- CO2 e3nters via stomata and 4C compound formed (oxaloacetate)

- PEP carboxylase does not promote photorespiration and PEP (3C) -> OA (4C)

what happens in bundle sheath cells for C4 (more in depth)?

4C compound transferred that releases a steady supply of CO2

in hot, dry climates, what do C4 plants do?

reduce photorespiration and water loss

PEP carboxylase

- does not have oxygenase activity

- has higher affinity to HCO3-

- allows C4 plants to reduce stomatal aperture and conserve water

what is treu about C4 photosynthesis?

- kranz anatomy is specific to C4 photosynthesis

- photorespiration is minimized in comparison with C3 photosynthesis

- four carbon acids are the first stable intermediates of photosynthesis

- carboxylation and decarboxylation occur simultaneously

how does carboxylation and decarboxylation occur simultaneously?

In the same cycle; PEP is carboxylated to OA and then malate is decarboxylated to pyruvate

the activity of key enzimes in teh calvin cycle are regulatated by light. the activitiy of key enzymes in the C4 fixation cycle that precedes the Calvin cycle are not regulated by light.

false

1 multiple choice option

when do CAM plants open the stomata?

at night

Crassulacean Acid Metabolism

plant that does not have bundle sheath cells so it does C4 and C3 at different times to fix CO2

when do CAM plants do C4?

at night so that they can take in as much CO2 as possible and process it through C4 cycle to store for C3

when do CAM plants do C3?

during day and use the stored carbon from the night to make sucrose

CAM plant dark rxn pathway

CO2 -> bicarbonate in cytosol -> oxaloacetate -> malate -> malic acid in vacuole

CAM plant light rxn pathway

malic acid -> malate in cytosol -> pyruvate in mitochondria -> trios phosphate -> start OR pyruvate -> Calvin cycle -> starch

the timing of stomatal opening and closing in CAM plants is special in what ways?

CAM plants capture atmosphereic CO2 through open stomata at night and scavenge respiratory CO2 behind closed stomata during day

2 multiple choice options

comparisons of C4 and CAM photosynthesis

- C3 compounds (PEP) are used to capture atmospheric carbon dioxide (in form of bicarbonate)

- in both systems, CO2 is comibned with PEP and reduced to C4 acid

- both systems reduce photorespiration compared to C3 plants

the assimilation fo CO2 in the leaves results in sucrose in the cytosol and starch in the chloroplast

true

sucrose is made during the day and transported to source tissues

false

source tissues

producer of sugar

sink tssues

receptor of sugar

what happens to sugar at night?

no direct production of sucrose occurs so starch is broken down to make it

what happens to sugars during day?

made directly photosynthesis