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calvin cycle/photosynthetic carbon reduction cycle

The cyclic pathway in plants
that fixes carbon dioxide and produces triose
phosphates

plastid

In plants, a self-replicating organelle bound by double membrane and contains a small genome that encodes some of their proteins;
may differentiate into a chloroplast

chloroplasts

Chlorophyll-containing photosynthetic
organelles in some eukaryotic cells; sites of CO2 assimilation; enzymes for this process in stroma; green leaves are reach in these

amyloplast

colorless plastids (lack chlorophyll and other pigments found in chloroplasts); no internal membrane analogous to photosynthetic membranes (thylakoids) of chloroplasts; in plant tissue rich in starch, are packed w/ starch granules; dominate in nonphotosynthetic tissues that store starch in large quantities

carbon fixation rxn/co2 fixation

The reaction,
catalyzed by rubisco during photosynthesls or
by other carboxylases, in which atmospheric
CO2 is initially incorporated (fixed) into a three-C
organic compound, the triose phosphate 3 phosoglycerate; condensation of CO2 w/ five-carbon acceptor, ribulose 1,5 bisphosphate to form 2 molecules 3-phoshoplycerate

pentose phosphate pathway

A pathway
present in most organisms that serves to
interconvert hexoses and pentoses and is a
source of reducing equivalents (NADPH) and
pentoses for biosynthetic processes; it beglns
with glucose 6-phosphate and includes 6-
phosphogluconate as an intermediate. Also
called the phosphogluconate pathway and the
hexose monophosphate pathway

reductive pentose phosphate cycle

photosynthetic assimliation of CO2, essentially same set of rxns as nonoxidative phase of pentose phosphatte pathwway operating in other direction, going from hexose phosphate to pentose phosphates; uses same enzymes and several more enzymes that make reductive cycle irreversible; all 13 enzymes are in chloroplast stroma

c3 plants

3 phosphoglycerate as first intermediate

ribulose 1,5 bisphosphate carboxylase/oxygenase (rubisco)

enzyme that catalyzes incorporation of C02 into organic form (3-phosphoglycerate)

rubisco activase

overcomes inhibitions of carbamoylation by binding tightly active site and locking the enzyme "closed" conformation by promoting ATP-dependent release of ribulose 1,5 bisphosphate, exposing Lys amino group to nonenzymatic carbamolyation by CO2, followed by Mg2+ binding, activating the rubisco.

aldolase

enzyme used in stage 3 of Carbon assimilation; in step one, first catalyzes the reversible condensation of glyceraldehyde 3-phosphate w/ dihydroxyacetone phosphate, giving fructure 1,6-biphosphate; acts again in step 4 combining erythrose 4-phosphate w/ dihydroxyacetone phosphate to form 7-carbon sedoheptulose 1,7-bisphosphate

transketolase

enzyme used in stage 3 of Carbon assimilation; has TPP as prosthetic group and requires Mg2+. step 3, catalyzes the reversible transfer of 2-C ketol group from a ketose phosphate donor, fru-6-phosphate, to an aldose phosphate acceptor, gly-3-phos, forming pentose xylulose 5-phosphate and tetrose erythrose 4-phos.; in step 6, converts sedoheptulose 7-phos and gly-3-phos to two pentose phosphate.

carbon-assimilation rxns

Reaction sequences in which atmospheric CO2 is
converted into organic compounds

thioredoxin

with illumination, electrons flow from PSI to ferredoxin which passes electrons to a small, soluble, disulfide-containing protein called this

ferredoxin-thioredoxin reductase

catalyzes thioredoxin

photorespiration/oxidative photosynthetic carbon cycle (c2 cycle)

Oxygen consumption occurnng in illuminated temperate-zone plants, largely due to oxidation of
phosphoglycolate; consume O2 and produces CO2, and like photosynthesis, driven by light. costly side rxn of photosynthesis.

2-phosphoglycolate

formed when rubisco catalyzes the condensation of O2 w/ ribulose 1,5-bisphosphate, and as a result forms 3-phosphoglycerate and this

glycolate pathway

converts two molecules of 2-phosphoglycolate to a molecule of serine and a molecule of CO2

c4 plants

x

phosphoenolpyruvate carboxylase

when first intermediate into which 14 CO2 is fixed is oxaloacetate, a four-carbon compound, this occurs in cytosol and is catalyzed by this; for c4 plants

malic enzyme

in c4 plants, in bundle sheath cells, malate is oxidized and decarboxyate to yield pyruvate and CO2 by the action of this enzyme

pyruvate phosphate dikinase

The pyruvate formed by decarboxylation of malate
in bundle-sheath cells is transferred back to the mesophyll cells, where it is converted to PEP by an unusual enzymatic rxn catalyzed by this enzyme

CAM plants

see pg. 790

nucleotide sugars

c

ADP-glucose

c

starch synthase

cc

sucrose 6-phosphate synthase

c

fructose 2,6 biphosphate

c

ADP-glucose pyrophosphorylase

s

cellulose synthase

d

peptidoglycan

A major component of bacterial
cell walls; generally consists of parallel
heteropolysaccharides crosslinked by short
peptides

metabolite pools

s

co2 assimilation

green plants contain chloroplasts unique enzymatic machinery that catalyze conversion of CO2 to simple (reduced) organic compounds

proplastids

converted from chloroplasts that lose internal membranes and chlorophyll and are interconvertible w/ amyloplasts

ribulose 1,5 bisphosphate

five-carbon acceptor that condenses w/ CO2 to form 2 molecules 3-phosphoglycerate

3-phosphoglycerate

forms from condensation of CO2 w/ ribulose 1,5 bisphosphate; dominant w/ 14C in carboxyl carbon atom, early intermediate in photosynthetic

3-phosphoglycerate kinase

in first step of stage 2 of C assimiliation, this catalyzes the transfer of phosphoryl group from ATP to 3-phosphoglycerate, giving 1,3-biphosphoglycerate

glyceraldehyde 3-phosphate dehydrogenase

enzyme in stage 2 of C assimilation in which NADPH donates electrons in a reduction catalyzed by this chloroplast-specific isozyme, giving glyceraldehyde 3-phosphate and Pi

sedoheptulose 1,7 bisphosphate

step 4 of stage 3 of C-assimilation, combining erythrose 4-phosphate w/ dihydroxyacetone phosphate to form 7-carbon sedoheptulose 1,7-bisphosphate

ribulose 5-phosphate

pentose phosphates formed in the transketolase
reactions-ribose 5-phosphate and xylulose bphosphate-are converted to this

mitochondrial respiration

oxidation of substrates to CO2 and conversion of O2 to H2O

glycine decarboxylase complex

oxidizes glycine to CO2 and NH3, w/ concomitant reduction of NAD+ to NADH and transfer of remaining carbon from glycine to cofactor tetrahydrofoqlate

c4 plants

temporary fixation of CO2 into a four carbon compound, step prior to CO2 ix fixed into a three carbon product, 3-phosphoglycerate

c4 metabolism/c4 pathway

c4 plants assimilation process

c3 plants

first step rxn of CO2 w/ ribulose 1,5 biphosphate to form 3-phosphoglycerate are called this types of plants

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