phototrophic energy metabolism

site of photosynthesis in eukaryotes

double membrane organelle - chloroplast

3 compartments of chloroplast

stroma, thylakoid membrane, thylakoid lumen

The main pigment used to gather light energy during photosynthesis

chlorophyll

- attached to proteins in thylakoid membrane as part of antenna complexes

photosynthetic electron transfer process

electrons excited in PS2 then replaced with electrons from water

transproted through carriers - results in H+ pumping

re-energized by PS1 which transfers them via carriers to ferridoxin or NADPH

what is the key for ATP production in photosynthesis

H+ gradient

what is the process of ATP synthesis in photosynthesis

photophosphorylation

what is the H+ pmf in mitochondria

0.22 V

what is the pH difference in chloroplast

~2 between stroma and lumen (gives 0.12 V)

what is the membrane potential difference in chloroplast

0.03V

difference between mitochondria ATP synthesis and Chloroplast

chloroplast need more H+ transfer to make ATP

- require ~4 H+ transferred to synthesize 1 ATP

ATP synthase complex in chloroplast

CF0CF1

chloroplast subunit composition

14 copies of gear protein

3 ATP made per revolution

to synthesize 2 ATP what happens

8 H+ are pumped per O2 released

- means tHAT ATP and NADPH are made at about an equimolar ratio

if Q cycle is active, may produce one more ATP

cyclic photophosphorylation

The generation of ATP by cyclic electron flow.

needs to occur wen cell needs more ATP than NADPH

process of cyclic photophosphorylation

electron from P700 is transferred through the normal e- carriers within the system

but ferredoxin doesn't pass e- to NADP+ --> instead to cytochrome B6/f complex where H+ are pumped to lumen (at least 3 H+ pumped per 2 e-)

then cytochrome b6/f complex passes e- to plastocyanin

this e- regenerates the P700 chlorophyll

how is direction of e- transfer from ferredoxin regulated

by ATP/ADP ratio in cell

what are cabohydrates used for

export to other cells, longer term storage

- things that ATP and NADPH cannot do

calvin cycle

Co2 + H2O --> [CH2O]n

light independent reaction

when does the calivn cycle occur

when energy needs to by stored as carbohydrates (convert ATP and NADPH into reduced C)

where does the calvin cycle occur

in the stroma of the chloroplast

where ATP and NADPH are

basic steps of calvin cycle

a 5C sugar is carboxylated to give 2 - 3C sugars

then converted to reduced form

most used to rebuild 5C sugar

some made available for anabolic reactions

enzyme that catalyzes the calvin cycle

how big?

where found?

how abundant?

ribulose 1,5- biphosphate carboxylase/oxygenase (rubisco)

large enzyme (560,000 daltons)

found in chloroplast stroma

most abundant protein on planet

overall calvin cycle reaction energetics

takes 3 CO2 --> 1 glyceraldehyde-3-phophate

requires 6NADPH and 9 ATP and 5 H2O

3 ribulose-1,5-bisphosphate is regenerated

what is CO2 fixed to in the calvin cycle

G-3-P (dark reactions)

how are key enzymes regulated in photosynthesis

levels of specific photosynthesis metabolites

what happens as light reaction proceed (regulators)

reduced ferredoxin - NADPH and ATP levels build up

pH of stroma increases (more H+ onto lumen)

Mg2+ increases in stroma (counterion)

what is the redox state of the cell sensed through

what does that do?

thioredoxin

- captures e- and H+ from ferredoxin

uses to reduce key calvin cycle enzymes when reducing power available

what does rubisco do

carboxylation

catalyzes another reaction : use of O2 to split R-1,5-bP into 2-PG and phosphoglycolate

- reaction diverts resources from the calvin cycle

how do a cell recover lost carbon from phosphoglycolate

glycolate pathway

minimize rubisco use of O2 - Hatch-slack cycle

crassulacean acid metabolism

glycolate pathway

involves transfer of glycolate from chloroplast to peroxisome

in peroxisome, glycolate is converted to glycine by oxygenation and transamination

then passed to mitochondria

2 glycines are converted to serine (with loos of CO2 = production of NADH

serine is converted to glycerate back in peroxisome

transferred back to chloroplast to enter Calvin cycle as 3-phophoglycerate

2 phophoglycerates are converted to 3-PG and CO2 using 2 ATP and 2 ferredoxin (1 NADPH)

What is the hatch slack cycle?

It involves the localization of Calvin cycle reactions to internal cells.

How is CO2 captured in the hatch slack cycle?

CO2 is captured in organic molecules in external cells.

What is the process of capturing CO2 in the hatch slack cycle?

Capture involves carboxylation of PEP to form oxaloacetate.

What enzyme catalyzes the formation of oxaloacetate in the hatch slack cycle?

PEP carboxylase in the cell cytosol.

Is PEP carboxylase affected by O2?

No, it can efficiently use CO2 at low concentrations.

What happens to oxaloacetate in the hatch slack cycle?

It is transferred to chloroplasts and converted to malate.

What does malate carry in the hatch slack cycle?

Malate carries reducing energy.

Where is malate transferred after being formed from oxaloacetate?

It is transferred to bundle sheath cells.

What is produced in bundle sheath cells from malate?

CO2 and NADPH for the Calvin cycle.

What happens to decarboxylated pyruvate in the hatch slack cycle?

It is transferred to mesophyll cells for ATP-dependent conversion to PEP.

How many ATP are used per CO2 fixed in the hatch slack cycle?

5 ATP per CO2 fixed, compared to 3 for C3 plants.

What compensates for the increased ATP usage in the hatch slack cycle?

Increased Rubisco efficiency compensates.

What is crassulacean acid metabolism (CAM) primarily found in?

Desert plants where H2O loss is critical

How does CAM separate the Calvin cycle?

In time, not space

How does CAM capture CO2 during the night?

As malate in the dark

Where is malate stored in CAM plants?

In vacuoles

What happens to malate when light is available in CAM plants?

It is decarboxylated for Calvin cycle reactions

What advantage does CAM provide to plants in arid climates?

It allows CO2 to be provided to the Calvin cycle without opening the stomata, reducing water loss

How is the CO2 cycling regulated in CAM plants?

Closely regulated to ensure CO2 isn't futilely cycled

primary product of photosynthesis

glyceraldehyde-3-phosphate

what can glyceraldehyde-3-P be interconverted to ? by what?

interconverted to DHAP by isomerase