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Biochem > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Why is carbon fixation important?

A

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

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2
Q

Plants BLANK CO2 to trioses

A

Reduce

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3
Q

Products from triode phosphates

A

Glucose
Sucrose
Carbon skeletons

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4
Q

Enzyme for co2 fixation

A

Rubisco

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5
Q

Ribulose 1,5 phosphate structure reminder

A

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

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6
Q

3 phosphoglycerate structure reminder

A

3 carbon aldose
1 PO4 on other end of carboxyl group

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7
Q

Rubisco rxn

A

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

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8
Q

Reaction for rubisco requires

A

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

In active site

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9
Q

How many active sites does rubisco have?

A

8 total

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10
Q

Lays side chain that is carbamoylated

A

201

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11
Q

Lys side chain that originates final product for rubisco

A

175

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12
Q

When does enediolate intermediate attack co2 during rubisco enzyme reaction

A

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

CO2 accepts because polarized by Mg2+

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13
Q

Calvin cycle general

A

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

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14
Q

CO2 fixation steps

A
  1. Rubisco’s carbocylase activity
  2. Reduction
  3. Regeneration of Ribulose 1,5 bisphosphate from triose phosphates
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15
Q

Is the regeneration of Ribulose 1-5 bisphosphate reversible?

A

No
3 exergonic reactions make it basically irreversible
Transaldose
Transketose
Kinase

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16
Q

Ribulose 5phosphate kinase does what

A

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

17
Q

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

A

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

18
Q

GAP vs DHAP trioses

A

GAP = aldose
DHAP = ketose

19
Q

How does co2 move through cell membranes?

A

Diffusion

No phosphorylated molecules can pass freeely

20
Q

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

A

DHAP
Ketose

21
Q

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

A

…..

22
Q

Regulation of Calvin cycle via light

A

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

23
Q

Fructose 16 bisphosphatase

A

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

24
Q

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

A

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

25
Q

Regulation via light - enzymes

A

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

26
Q

Exergonic enzymes for regeneration of Ribulose 15 bisphosphate

A

Fructose 16 bisphosphatase
Sedoheptulose 17 bisphosphatase
Ribulose 5phosphate kinase

27
Q

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

A

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

28
Q

Is regeneration of 15BisP inactivated or activated by light?

A

Activated!

Active form of enzymes is reduced disulfide bonds

Light = replenishing Calvin cycle = co2 fixation

29
Q

Enzymes for glycolate pathway

A

Salvaging 2 phosphoglycolate

Glycine decarboxylase complex

Serine hydroxymethyl transferase

30
Q

C4 pathway rubisco equivalent enzyme
Accepts what form of carbon?

A

PEP carboxylase
Accepts HCO3 (aq)

31
Q

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

A

Cell type

C4= mesophyll cells
C3 = bundle sheath cells

32
Q

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

A

Phosphoenolpyruvate
Oxaloacetate

33
Q

Malate importance

A

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

34
Q

Fructose 6 phosphate structure reminder

A

6 carbons
Ketose

Product in non ox PPP

Can be converted to 15bisphosphase for Calvin cycle

Biochem (23 decks)

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