FINAL EXAM: CARBS Flashcards
1
Q
plants are versatile
A
they can:
use energy of sunlight to support biosynthesis
build organic compounds from CO2
move intermediates between cellular compartments
adapt to changing environments
2
Q
assimilation of CO2 by plants
A
animal cells: use 3C intermediates (pyruvate, lactate) for synthesis — must eat it
plant cells: make 3C intermediates for further synthesis
using Co2 to make intermediates = carbon assimilation aka carbon fixation
3
Q
3C intermediates for plants
A
make glyceraldehyde-3P (GA3P)
made from CO2, H2O, ATP, and NADPH from photosynthesis
4
Q
plastids
A
organelles in plants and algae
enclosed by a double membrane
own small genome
can specialize
5
Q
chloroplasts
A
photosynthesis
6
Q
amyloplasts
A
starch storage
7
Q
chromoplasts
A
pigment storage
8
Q
elaioplats
A
lipid storage
9
Q
carbon assimilation
A
occurs in the stroma of chloroplasts via Calvin cycle
once called dark reaction but runs under light
10
Q
what does carbon assimilation require
A
ribulose 1,5-bisphosphate which is constantly regenerated using ATP energy and NADPH
11
Q
carbon assimilation produces
A
3-phosphoglycerate, then glyceraldehyde-3P (GA3P) in quillibrium with DHAP
triose phosphates
12
Q
CO2 is reduced in carbon assimilation
A
with oxidation of NADPH that was generated in the light reactions of photosynthesis
13
Q
three stages of calvin cycle
A
- carbon assimilation
- 3-phosphoglycerate reduction
- regeneration
14
Q
carbon assimilation stage
A
3 ribulose 1,5-bisophosphate + 3CO2
6 3-phosphoglycerate
rubisco catalyzes
(6c divided in half)
15
Q
3-phosphoglycerate reduction stage
A
6 3-phosphoglycerates converted to 6 triose phosphates (reduction to DHAP and GA3P) using NADPH and ATP from photophosphorylation
5 triose phosphates go to regenerate ribulose 1,5-bisphosphate; 1 utilized for other pathways
16
Q
3-phosphoglycerate reduction is catalyzed by
A
phosphoglycerate kinase and glyceraldehyde 3P dehydrogenase
17
Q
regeneration stage
A
5 triose phosphates made to 3 ribulose 1,5-bisphosphate
18
Q
overall calvin cycle reaction
A
3CO2 + 6NADPH + 5H2O + 9ATP
glyceraldehyde-3P + 6NADP+ + 2H+ + 9ADP + 8Pi
19
Q
where can the glyceraldehyde 3P go from calvin cycle?
A
energy production via glycolysis, starch, or sugar synthesis
20
Q
rubisco
A
catalyzes carbon assimilation
large Mg2+ containing enzyme
carboxylase and oxygenase functionality
21
Q
carboxylase functionality in rubisco
A
adds Co2 to ribulose 1,5-bisphosphate
makes new CC bond
cleaves 6C intermediate into 2 3phosphoglycerates
22
Q
oxygenase functionality in rubisco
A
less useful in plants
reacts with O2 instead of CO2 in an inefficient side reaction
23
Q
rubisco reaction
A
ribulose 1,5-bisphosphate + H2O + CO2
2 molecules of 3phosphoglycerate
24
Q
rubisco exits in two major forms: form 1
A
plants, algae, cyanobacteria
8 large catalytic subunits (encoded by plastid genome) + 8 small subunits (encoded by nucleus
25
rubisco exists in two major forms: form II
photosynthetic bacteria only
2 catalytic subunits, resemble large plant subunits
26
rubisco quality
inefficient
low turnover of 3/sec
50% of plant enzymes are rubisco
27
catalytic role of Mg2+ in rubisco’s carboxylase activity
Mg2+ is held by negatively charged side chains of Glu, Asp, and carbamoylated Lys
brings together the reactants in a correct orientation, stabilizes the negative charge that forms upon the nucleophilic attach of enediolate to CO2
28
carbamoylated Lys
negative CO2 binds to N on side chain of lysine
29
rubisco is activated via covalent modification
highly regulated
inactive until Lys-201 is carbamoylated by CO2 (CO2 binds to R group nitrogen; allows binding of Mg2+ to the enzyme which is critical for catalytic activity)
rubisco activase
30
rubisco activase
ribulose 1,5-bisP bound in active site blocks Lys-201 from being carbamoylated
rubisco activase changes rubisco conformation - causes ribulose-1,5-bisP to leave and exposes Lys-201
reaction requires ATP
triggered by light in some species
31
rubisco can be inhibited by a nocturnal inhibitor
2-carboxyarabinitol 1-phosphate inhibits carbamoylated rubisco
32
2-carboxyarabinitol 1P
inhibits carbamoylated rubisco;
transition state analog of beta-keto acid intermediate
synthesized in the dark in some plants
* binds to rubisco, doesn’t work in inappropriate times**
33
stage 2: 3-phosphoglycerate reduced to glyceraldehyde 3P reaction
6 3PG + 6ATP + 6NADPH + 6H+
=
6 GA3P + 6ADP + 6NADP+ + 6Pi
34
3PG reduced to GA3P
requires NADPH and ATP from photosynthesis
similar to gluconeogensis but uses NADPH
enzymes: 3phosphoglycerate kinase; glyceraldehyde 3phosphate dehydrogenase
driven forward by high conc. of NADPH and ATP in chloroplast stroma
35
enzymes for stage 2 calvin cycle
3PG kinase
| GA3P dehydrogenase
36
phosphoglycerate kinase
3PG + ATP
| = 1,3bisphosphoglycerate
37
glyceraldehyde-3P dehydrogenase
1,3-bisphosphoglycerate + NADPH
=
glyceraldehyde-3P
redox
38
fates of glyceraldehyde-3P
5 of 6 recycled to make ribulose 1,5-bisphosphate
remaining:
converted to starch in chloroplast for storage
converted to sucrose in cytosol for export
broken down in glycolysis in cytosol for energy
39
stage 3: regeneration of ribulose 1,5-bisphosphate reaction
3 GA3P + 2DHAP + 3ATP
=
3 ribulose 1,5,bisphosphate + 2Pi + 3ADP
5 three carbon sugars converted to 3 five carbon sugars
40
stoichiometry and energy cost of CO2 assimilation
fixation of 3 CO2 molecules yields one GA3P
9 ATP and 6 NADPH are consumed
light reactions of photosynthesis produce ATP and NADPH at about this same ratio (3/2)
41
fates of Pi from ATP hydrolysis in stages 2 and 3
8 of 9 Pi: available to combine with ADP to regenerate ATP
9th Pi: incorporated into GA3P and could be moved to cytosol
- requires that Pi be transferred from cytosol back into chloroplast
- uses special Pi-triosephosphate antiporter
42
Pi-triose phosphate antiporter
needed for sucrose synthesis
sucrose made in cytosol (unlike starch in chloroplast stroma)
- used for transport to distant plant tisuses
inner membrane is impermeable to phosphorylated compounds
antiporter exchanges GA3P or DHAP for one Pi
- sends triose phosphates into cytosol for sucrose synthesis
- sends Pi back into the chloroplast
43
carbon assimilation is more effective when its light
photosynthesis of one molecule of GA3P (plus recycled ones) requires 24 photons of light
- H+ go from stroma to thylakoid lumen
- creates alkaline conditions in stroma
Mg2+ transport from thylakoid lumen to stroma
enzymes of assimilation more active in alkaline, high Mg2+ conditions of stroma during photophosphorylation
44
plants oxidize water to ____ and reduce ____ to make _________
oxidize water to O2 and reduce CO2 to make carbohydrates
45
plants carry out cellular respiration
O2 reduced to water
| Substrates oxidized to CO2
46
wasteful side reaction
catalyzed by rubisco
in chloroplasts
consumes O2 and yields CO2
photorespiration reaction is enhanced by light and is costly; does not yield energy
47
oxygenase activity of rubisco
O2 competes with CO2 for active site
1/3 or 4 turnovers = O2 binds
worse in hot, dry climates where plants close their stomata to limit water loss
ribulose 1,5-bisphosphate bound by O2 and split to form 3PG and 2PG
48
oxygenase activity: ribulose 1,5-bisphosphate bound by O2 and split
into 2PG and 3PG
2PG is metabolically useless
salvaging its carbons requires energy and reactions in several organelles
2 2PG are converted to serine + CO2
serine eventually salvaged to 3PG
49
glycolate pathway
```
2PG to glycolate, goes out of chloroplast to peroxisome
converted to glyoxylate
then glycine
goes to mitochondria
2 Glycine releases CO2 and NH3
becomes serine
serine goes to peroxisome
becomes hydroxypyruvate
then glycerate
goes to chloroplast
then 3PG
```
50
most plants cannot avoid oxygen binding to rubisco
atmosphere is mostly O2
pure water has more O2
Km for oxygen is much higher
some plants, C4 and CAM have a bypass mechanism to avoid this side reaction
51
C4 vs C3 plants
most crops: C3 — first step in calvin cycle is CO2 fixation to make 3C product, 3PG
C4: earlier step before rubisco — bypass assimilation step by fixing CO2 to make a 4C compound (oxaloacetate from PEP)
- hotter climates
52
C4 plants
physically separate CO2 capture from rubisco reaction
53
C4 plants physically separate CO2 capcture from the rubisco reaction
CO2 and PEP are used to make oxaloacetate (4C) using PEP carboxylase in mesopyll cells of leaf
oxaloacetate is converted to malate or aspartate
malate or aspartate pass into bundle-sheath cells and release CO2 during conversion to another molecule (malate to pyruvate or aspartate ot PEP)
54
in bundle sheath cells
[CO2]>>>>[O2] and here is where rubisco is located
O2 can not replace CO2 in this system
C4
55
why do C4 plants often outperform C3 plants in heat and drought?
C4 pathway has higher energy cost (2ATP) but as temperature increases (and affinity of rubisco for CO2 decreases), gain in efficiency outweighs energy cost
C4 plants sometimes do better in heat and drought than C3 plants do
56
CAM plants separate CO2 trapping and carbon assimilation in TIME
another pathway to avoid rubisco reaction with oxygen
found in plants that grow at high temps, dry conditions; minimize loss of water vapor
57
how do CAM plants separate CO2 trapping and carbon assimilation?
time
58
how do Cr plants separate CO2 capture from rubisco reaction?
physically
59
CAM plants open stomata only at night to allow entry of gases
at night: air is cooler, more moist; stomata open
- CO2 absorbed at night is fixed to PEP to make oxaloacetate(4C) via PEP carboxylase
- oxaloacetate is reduced to malate and stored in vacuoles
daytime: stomata close
- malate converted to pyruvate by NADP-linked malic enzyme
- CO2 released from malate and used by rubisco
- since stomata are closed, [O2] is low; rubisco only binds CO2
60
excess triose phosphates are converted to
starch and sucrose
61
starch in plants
made in chloroplasts for short-term storage
or made in amyloplasts of nonphotosynthetic tubers, seeds, roots for long term storage
- sucrose goes from cells capable of photosynthesis to these other parts of plant to provide monomers
starch provides bulk of energy storage for most plants
62
sucrose in plants
made in cytosol for transport
63
first thing made from triose phosphates to convert to starch/sucrose
glucose-1P
64
glucose-1P made from triose phosphates to make starch/ sucrose
ALDOLASE: combines DHAP and GA3P to make fructose-1,6-bisP
FRUCTOSE-1,6-BISPHOSPHATASE: removes phosphate to make fructose-6P
PHOSPHOHEXOSE ISOMERASE: converts fructose-6P to glucose-6P
PHOSPHOGLUCOMUTASE: converts glucose-6P to glucose-1P
65
aldolase
combines DHAP and GA3P to make fructose-1,6bisP
66
fructose-1,6-bisophosphatase
removes phosphate to make fructose-6P
67
phosphohexose isomerase
converts fructose-6P to glucose-6P
68
phosphoglucomutase
converts glucose-6P to glucose-1P
69
starch synthesis
ADP glucose = monomers
similar to glycogen synthesis
70
ADP-glucose
reaction of glucose-1P with ATP
requires further breakdown of PPi
ADP-glucose pyrophosphoyrlase
71
ADP-glucose pyrophosphorylase
makes ADP-glucose from glucose-1P with ATP
72
amylose
straight chain polysaccharide
alpha1-4 bonds
catalyzed by starch synthase
73
amylopectin
branched chain polysacc
alpha1-4 bonds by starch synthase
alpha1-6 branches by branching enzyme
74
UDP-glucose
sucrose or cellulose synthesis
UDP-glucose pyrophosphorylase
75
ADP-glucose
starch synthesis
ADP-glucose pyrophosphorylase
76
starch synthesis is regulated at
ADP-glucose pyrophosphorylase
77
activator of ADP-glucose pyrophosphorylase
3PG
produced during photosynthesis — precursor
78
inhibitor of ADP-glucose pyrophosphorylase
Pi
Pi accumulates when condensation of ADP and Pi slows
so low ATP
(wants to use sugars in glycolysis to make ATP instead of storing them as starch)
79
sucrose synthesis substrates
fructose-6P and UDP-glucose
80
synthesis of fructose-6P and UDP-glucose
ALDOLASE: combines DHAP + GA3P to make fructose-1,6-bisP
FRUCTOSE-1,6-BISPHOSPHATASE: dephosphorylates fructose-1,6-bisP to form fructose-6P
PHOSPHOHEXOSE ISOMERASE/PHOSPHOGLUCOMUTASE: some fructose6P converted to glucose 6P and then to glucose 1P
UDP-GLUCOSE PYROPHOSPHORYLASE: glucose-1P and UTP to make UDP-glucose
81
sucrose synthesis reaction 1
substrates: UDP glucose + fructose-6P
sucrose-6P made with alpha1-beta2 bond between glucose and fructose-6P
sucrose-6P synthase
82
sucrose 6P synthase
makes sucrose-6P with alpha1-beta2 bonds between glucose and fructose-6P
83
sucrose synthesis reaction 2
sucrose-6P dephosphorylated to make sucrose by sucrose-6Phosphatase
84
sucrose-6phosphatase
dephosphorylates sucrose-6P
85
sucrose synthesis needs to be synthesized in cytosol
triose phosphate precursors must be exported from chloroplasts using Pi-triose phosphate antiporter
86
Regulation of sucrose synthesis
occurs at interconverstion of F1,6BisP to F6P
FBPase1
PP-PFK1
87
forward enzyme of sucrose synthesis
fructose-1,6-bisphosphatase (FBPase-1)
88
reverse enzyme of sucrose synthesis
PPi-dependent phosphofructokinase-1 (PP-PFK-1)
similar to glycolytic enzyme except using pyrophosphate instead of ATP as phosphate donor
89
regulation of sucrose synthesis: dark
no photosynthesis, no triose phosphoates, no sucrose synthesis — but breakdown needed
```
FBPase1 inhibited (don’t make it)
PP-PFK-1 active (break down hexoes for energy)
```
90
regulation of sucrose synthesis: in light
triose phosphates made, so sucrose synthesized
```
FBPase1 active (make sucrose_
PP-PFK1 inhibited (don’t break down hexoses)
```
91
regulation of sucrose synthesis: sucrose-6P synthase regulation
activated by: glucose 6P (precursor to substrate)
inhibited by: Pi (not being transported into chloroplasts)
92
plants in the light
triose phosphates made in chloroplasts; made into starch or sent to cytosol with Pi transported back in
cytosol: hexoses and then sucrose are synthesized; sucrose transported to non-photosynthetic cells
nonphotosynthetic cells: sucrose broken down to hexoses to make starch or to be oxidized using glycolysis/CAC (ATP from oxpho in mito)
mostly no need for long term storage because sun comes back
93
plants in the dark
no triose phosphates made
starch broken down into glucose which can be used for energy by glycolysis/CAC
ATP by oxpho in mito
94
synthesis of cellulose for cell walls
glucose monomers with beta1-4 linkages
allows H bonds within chain and between chains to make strong microfibrils
synthesized from intracellular precursors but fiber grows outside of plasma membrane
95
monomer for cellulose synthesis
UDP-glucose
96
UDP-glucose generated by
sucrose synthase
UDP-glucose pyrophosphorylase
97
generating UDP-glucose: sucrose synthase
breaks down sucrose
sucrose + UDP = UDP-glucose + fructose
may be in complex with cellulose synthase
different enzyme than sucrose-6P synthase
98
generating UDP-glucose: UDP-glucose pyrophosphorylase
synthesize UDP-glucose
glucose-1P + UTP = UDP-glucose + PPi
99
cellulose synthase
makes chains of cellulose
involves primer
- synthase complexes and forms rosettes within the plasma membrane
- multiple chains of cellulose synthesized at each rosette; forms microfibrils that extend outside the membrane
- 18 chains/microfibril
- cellulose can have different lengths up to 15k glucose monomers
100
plants convert lipids to carbs
plants store lipids and proteins in seeds for germination, growth
LIPASES: remove fatty acids from glycerol
- glycerol modified to enter gluconeogenesis
- FA broken down by beta-oxidation to acetyl-CoA
glyoxylate cycle, CAC, and gluconeogenesis: convert acetyl-CoA from fatty acids into hexoses
- fructose and glucose can be used to synthesize sucrose to move energy to other cells in the germinating plant
101
glycerol from stored triacylglycerols in seeds to glucose
glycerol goes to DHAP and then to GA3P to enter gluconeogensis
must have both to make fructose-1,6-bisP bc pathways for both starch and sucrose
102
glyoxylate cycle
plants, some invertebrates, some microorganisms
- in glyoxysomes of plants
uses: 2 acetyl-CoA in a cycle similar to CAC
103
glyoxylate cycle: 2acetyl-COA
utilizes acetyl-CoA from FA catabolism
produces succinate which goes into CAC
uses some of CAC reactions but different isozymes
bypasses the decarboxylation steps with 2 enzymes
104
2 enzymes that bypass the decarboxylation steps in glyoxylate cycle
isocitrate lyase
malate synthase
105
isocitrate lyase
cleaves isocitrate to succinate and glyoxylate
106
malate synthase
makes malate from glyoxylate and acetyl-CoA (2nd)
107
glycoxylate cycle
```
1st acetyl-CoA + oxaloacetate|| citrate synthase
=
aconitase
=
isocitrate || isocitrate lyase
=
succinate (goes to CAC) and glyoxylate
=
glycoxylate + 2nd acetyl-CoA || malate synthase
=
malate + NAD+ || malate dehydrogenase
=
oxaloacetate + NADH
```
108
process in glyoxysome
FA beta oxidation
makes acetyl-CoA
```
acetyl coA + oxaloacetate
citrate
isocitrate = succinate and glyoxylate
glyoxylate + acetyl-CoA
malate
oxaloacetate
```
```
succinate into CAC
fumarate
malate
goes to cytosol
converted to oxaloacetate
PEP —> gluconeogenesis
hexose —> sucrose
```
