Photosynthesis

Question 1

Why is carbon fixation important?

Answer 1

Carbon fixation by plants it the major source of sugars and carbon for biomass generation for animals

Question 2

Plants BLANK CO2 to trioses

Answer 2

Reduce

Question 3

Products from triode phosphates

Answer 3

Glucose
Sucrose
Carbon skeletons

Question 4

Enzyme for co2 fixation

Answer 4

Rubisco

Question 5

Ribulose 1,5 phosphate structure reminder

Answer 5

M with three Os in middle
Two phosphate groups: 1 per end

Question 6

3 phosphoglycerate structure reminder

Answer 6

3 carbon aldose
1 PO4 on other end of carboxyl group

Question 7

Rubisco rxn

Answer 7

1co2 + 1,5bisphosphate —> 2 3-phosphoglycerate

Question 8

Reaction for rubisco requires

Answer 8

Mg2+
CO2
Ribulose 1,5 bisphosphate
Histidine side chain
Carbomylated lys side chain
Other lys side chain

In active site

Question 9

How many active sites does rubisco have?

Answer 9

8 total

Question 10

Lays side chain that is carbamoylated

Answer 10

201

Question 11

Lys side chain that originates final product for rubisco

Answer 11

175

Question 12

When does enediolate intermediate attack co2 during rubisco enzyme reaction

Answer 12

2nd carbon after double c bond produced via lys 201 de protonating carbon 3

CO2 accepts because polarized by Mg2+

Question 13

Calvin cycle general

Answer 13

Takes fixed co2 in Form of 3PGA
Produces GAP = for either starch in chloroplast
Or sucrose in cytosol

3CO2 fixed to make 6 3PGA + 9ATP + 6NADPH —> GAP (glyceraldhyde 3 phosphate) + 1ADP + 8ATP

5/6 GAPs are regenerated into Ribulose 1,5bisphosphate
8/9 ATPs regenerated

Question 14

CO2 fixation steps

Answer 14

1. Rubisco’s carbocylase activity
2. Reduction
3. Regeneration of Ribulose 1,5 bisphosphate from triose phosphates

Question 15

Is the regeneration of Ribulose 1-5 bisphosphate reversible?

Answer 15

No
3 exergonic reactions make it basically irreversible
Transaldose
Transketose
Kinase

Question 16

Ribulose 5phosphate kinase does what

Answer 16

1 ATP consumed to produce Ribulose 15 bisphosphate from
Ribulose 5 phosphate

Question 17

General overall formula for regernwrion of 1,5 bisphosphate from trioses

Answer 17

5 triose —> 3 Ribulose 5 phosphate

Where 3 trioses = GAP, 2 trioses = DHAP

Ribulose 5 phosphate needs ATP and Ribulose 5 phosphate kinase to convert to 15 bisphosphate

Question 18

GAP vs DHAP trioses

Answer 18

GAP = aldose
DHAP = ketose

Question 19

How does co2 move through cell membranes?

Answer 19

Diffusion

No phosphorylated molecules can pass freeely

Question 20

What type of triose can the pi triose phosphate anti porter transport to cytosol?

Answer 20

DHAP
Ketose

Question 21

How does transport of DHAP have indirect effect of replenishing NADH in cytosol?

Answer 21

…..

Question 22

Regulation of Calvin cycle via light

Answer 22

Light entering cell means that stroma
Mg2+ up
Ph up to 8
Activation of rubisco is improved by both factors

So is fructose 16 bisphosphate

Question 23

Fructose 16 bisphosphatase

Answer 23

1st step to regeneration 2 trioses
Transaldose
Regulated via light with mg and pH

Question 24

How does DHAP transport to cytosol indirectly replenish both NADHP and ATP in cytosol?

Answer 24

GAP —> 13 bisphosphoglycerate produces NADPH

13 bisphosphoglycerate —> 3-phosphoglycerate produces ATP

3 phosphoglycerate can be returned to stroma via pi transport in exchange for pi from stroma

Question 25

Regulation via light - enzymes

Answer 25

Ribulose 5 phosphatase kinase Fructose 16 bisphosphatase Sedoheptulose - 7 bisphosphatase Glyceraldehyde 3 phosphate dehydrogenase

Question 26

Exergonic enzymes for regeneration of Ribulose 15 bisphosphate

Answer 26

Fructose 16 bisphosphatase Sedoheptulose 17 bisphosphatase Ribulose 5phosphate kinase

Question 27

Is glucose 6 phosphatase inactivated or activated by reduction of disulfide bonds?

Answer 27

Inactive! In light 1st step of PPP ox is blocked Ox pathway needed in dark to produce more NADPH when photosynthesis isn’t doing it

Question 28

Is regeneration of 15BisP inactivated or activated by light?

Answer 28

Activated! Active form of enzymes is reduced disulfide bonds Light = replenishing Calvin cycle = co2 fixation

Question 29

Enzymes for glycolate pathway

Answer 29

Salvaging 2 phosphoglycolate Glycine decarboxylase complex Serine hydroxymethyl transferase

Question 30

C4 pathway rubisco equivalent enzyme Accepts what form of carbon?

Answer 30

PEP carboxylase Accepts HCO3 (aq)

Question 31

In c4 plants, how are the c4 and c3 pathways separated?

Answer 31

Cell type C4= mesophyll cells C3 = bundle sheath cells

Question 32

When C4 pathway PEP carboxylase fixes HCO3, what molecule is accepting the hco3? What is first product?

Answer 32

Phosphoenolpyruvate Oxaloacetate

Question 33

Malate importance

Answer 33

CO2 Carrier Oxaloacetate in mesophyll cells reduced to malate Malate is transferred to bundle sheath cells Malate reduces NADP with help of malic enzyme Pyruvate + co2 for Calvin cycle produced = artificially high concentration of co2 in bundle sheath cells

Question 34

Fructose 6 phosphate structure reminder

Answer 34

6 carbons Ketose Product in non ox PPP Can be converted to 15bisphosphase for Calvin cycle