Final Flashcards
describe primary metabolism
growth and development and reproduction
describe secondary metabolism
the production of all compounds not necessary for growth development and reproduction
-also helps plants cope with stress and survive niches
where do secondary metabolites come from
primary metabolism
Describe an alkaloid
pharmacologically active, N-containing basic compounds
What are the 5 main classes of alkaloids
- Monoterpenoid Indole alkaloids (MIAs)
- Isoquinoline Alkaloids
- Tropane Alkaloids
- Pyrollizidine Alkaloids (PAs)
- Purine Alkaloids
What is the key intermediate in MIA biosyn and how is it formed
Strictosidine formed from tryptamine condensed with secologanin (Pictet-Spengler condensation, catalyzed by STR)
what is the precursor to all isoquinoline alkaloids
norcoclaurine
what is the key intermediate in TA synthesis
N-methylputrescine
what are all purine alkaloids produced from
xanthosine
How can you make a caffeine free coffee plant
disrupt caffeine synthase which causes theobromine to accumulate
what is unique about the enzymes produced in alkaloid-producing plants
their substrate specificity (acquired through mutation of existing genes)
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what’s a major factor in the evolution of the alkaloid biosynthesis pathway
gene duplication followed by mutation (neofunctionalization)
what are 5 key reaction that account for much of the diversity of alkaloids
- decarboxylation
- oxidation
- methylation
- acetylation
- glycosylation
what are glucosinolates
S and N containing plant secondary metabolites
Where are glucosinolates found
in the order brassicales
-brassica crops (cabbage, arabidopsis
what are glucosinolates derived from?
from different a.a.
what are the 3 types of glucosinolates
- aliphatic
- aromatic
- indolic
describe the first step of glucosinolate synthesis
Elongation
aliphatic and aromatic a.a. are elongated by inserting methylene groups into their side chains
describe the second step of glucosinolate synthesis
Core Structure Assembly
the a.a. moeity is metabolically reconfigured to give the core structure of glucosinolates
describe the third step of glucosinolate synthesis
Secondary Modifications
the initially formed glucosinolates are modified by various secondary transformations
How many C are gained in each round of chain elongation of glucosinolate synthesis
net gain of one C
After plant damage how does the process of glucosinolate degradation begin
with myrosinase-catalyzed hydrolysis of the thioglucoside linkage
What do epithiospecifier proteins (ESP) do
dictate the nature of the degradative product in glucosinolate degradation
describe the glucosinolate-myrosinase relationship
chemical herbivory defense system
-they are physically separated but after tissue damage are brought together then myrosine can activate glucosimulates
where is myrosinase localized
in idioblasts
what is an idioblast
a cell that differs in form from other in the same tissue
what does glucosinolate sulfatase do
desulfates glucosinolates which then cannot be hydrolyzed by myrosinase and therefore the toxic products are not longer synthesized
what are all isoprenoids synthesized from
IPP and its isomer DMAPP
what are the two pathways for IPP/DMAPP synthesis in plants
- MVA pathway
- MEP pathway
Where does the MVA pathway occur
The cytosol
What is the central intermediate in the MVA pathway
HMG-CoA
what inhibits HMGR and how does it inhibit it
mevinolin by competitive inhibition
What does IPP isomerase do
catalyzes the isomerization of IPP to DMAPP
where does the MEP pathway occur
in the plastids
how does the MEP pathway begin
formation of DXP from pyruvate and G3P
name an inhibitor of DXP
fosmidomycin (an antibiotic that is an analog of DXP
in the MEP pathway is IPP or DMAPP formation favoured
IPP over DMAPP (6:1)
How can someone figure out what pathway IPP was from
isotopically label glucose because glucose gets converted into precursors for both pathways then the C from the glucose will be labelled at different parts in the IPP from either pathway
what is GPP made of
1 IPP and 1 DMAPP
What is FPP made of
2 IPP and 1 DMAPP
what is GGPP made of
3 IPP and 1 DMAPP
Give an example of alkaloids in ecology
Ithomiine butterflys feed on plants that produce alkaloids which protects the butterfly
Give an example of alkaloids in ag
lupin seeds accumulate toxic alkaloids that threaten livestock - cause crooked calf disease
Give an example of alkaloids in plant defense
coffee plants produce alkaloids that inhibit competition and also kills tobacco hornworm
Give an example of alkaloids in medicine
Madagascar periwinkle contains vinblastine
what are the degradation products of the myrosinase system
Isothiocyanates, nitriles, epithionitriles, oxazolidine-2-thiones
how does the host plant avoid toxicity from the myrosinase system
myrosinase is in idioblasts so they aren’t in contact with glucosinolates
how have some organisms evolved to disarm the mustard oil bomb
cabbage moth contains glucosinolate sulfates which disulfates glucosinolates making it inaccessible to myrosinases
what are the steps in the MVA pathway
acetyl Coa > acetoacetyl CoA > HMG CoA > MVA
what are the steps in the MEP pathway
G3P + pyruvate > DXP > MEP
what reaction does HMGR catalyze
HMG-CoA > MVA
how is HMGR regulated
regulated by feedback, transcription, translation, phosphorylation and degradation
where is HMGR located
in the ER but has a cytosol exposed C-terminal catalytic domain
what are the key intermediates in the MEP pathway and are these used for other reactions in secondary metabolism
DXP, MEP, CDP-ME, CDP-MEP, MEcPP, HMB-PP
COME BACK TO THIS
How can stable isotope labelling be used to distinguish the MVA/MEP pathways
if you isotopically label glc at C1 you can track it as it goes through the pathway. glc gets converted into precursors for both pathways but the C from the glc will be labelled at dif. parts in IPP from either pathway
when and where does IPP/DMAPP get introduced into other pathways
MIA synthesis- used to form GPP which is the start of the pathway that produces strictosidine
what catalyzes the isomerization of IPP to DMAPP
IPP isomerase
what are the 2 types of prenyltransferases and how do they differ
- trans-prenyltransferase (TPTs)
-add IPP in the trans configuration - cis- prenyltransferase (CPTs)
-add IPP in the cis configuration
what do terpene synthases do
enzymes that rearrange the linear prenyl diphosphates
where are many terpenes synthesized
trichomes
what are the 3 different classes of monoterpenes
- acyclic
- monocyclic
- bicyclic
give examples of the different classes of monoterpenes
acyclic - citral
monocyclic - menthol
bicyclic - eucalyptol
why can the sesquiterpene synthases generate a much larger array of products
sesquiterpene carbocation intermediate has an additional 5C atoms with which to interact
-therefore a greater # of cyclization is possible
what is the pathway to the precursor of GA
GGPP > ent-CPP > ent-kaurene
what is the importance of triterpenoid squalene and what isoprenoids are derived from it
squalene is the precursor for cholesterol and sitosterol
how are diterpenes derived differently than monoterpenes and sesquiterpenes
GGPP is protonated at the C14-15 double bond and protonation results in the formation of a stable intermediate
how do sterols affect membrane fluidity
interaction of sterols with acyl chains restricts their motion and reduces membrane permeability
what does a double bond do to a sterol
when a sterol has a double bond it has a reduced ordering effect
-if has no DB then more efficient
what pathway are sterols derived from
MVA
-FPP is precursor and synthesized in the cytosol
what enzyme catalyzes the first step in the synthesis of carotenoids from GGPP
phytoene synthase
what physiological role do carotenoids play
colours flowers, fruits and seeds
what is the significance of introgression lines and how can they be used for gene discovery
they use genetic material from a wild relative to create new varieties with exotic traits
-important for identifying genes that control complex traits
what are the 2 classes of carotenoids
- carotenes
- xanthophylls
what are the different classes of lipids and where do they come from
- fatty acids -synthesized from chloroplasts
- glycerolipids
-synthesized from a fatty acid esterified to glycerol
what does sn-1 sn-2 sn-3 indicate
the placement of the glycerol moiety
what are lipids precursors for
waxes, suberin, pigments, hormones
why is the C chain of a lipid almost always an even # of C
fatty acid biosyn results form the concatenation of 2 C units
what would happen if biomembranes only contained saturated fatty acids
hydrophobic tails would give a semi-crystalline gel that would interfere with mobility
what are the 5 types of glycerolipids
- tricylglycerol (TAGs)
- phospholipids
- galactolipids
- sulfolipids
- sphingolipids
why are TAGs referred to as neutral lipids
non polar and can accumulate in high amounts without disrupting osmotic potential
where are all fatty acids made
in the chloroplast
what is the initial C precursor in fatty acid biosyn and how is it made
acetyl -CoA
- pyruvate dehydrogenase (PDC) converts pyruvate into acetyl-CoA
how is acetyl CoA activated
ACCase activates acetyl -CoA via carboxylation to malonyl CoA
what is the central cofactor in the assembly of fatty acids
acyl-carrier protein (ACP
How do the subunits of ACCase function
BC- activates CO2
BCCP- binds the biotin
alpha-CT/ beta-CT - transfer CO2 from biotin to acetyl-CoA
What are the 3 KAS isoenzymes and what do they do
KASI, KASII, KASIII
they transfer acetyl groups onto the growing acetyl chains
what is the role of malonyl-ACP
joins with acetyl-CoA to from acetoacetyl-ACP
what are the kinds of reactions that need to happen to elongate the acyl-ACP
reduction, dehydration, reduction, condensation
how is fatty acid chain elongation terminated
hydrolysis of the acyl moiety from ACP end the cycle and is catalyzed by acyl-ACP thioesterase
what are the 2 types of thioesterases
Fat A and Fat B thioesterases
how are double bonds introduced into the chain (enzyme?)
catalyzed by acyl-ACP desaturase
what does the elongase system do
the extension of fatty acids beyond C18 to produce very long chain fatty acid
what lipids are made by the DAG and CDP-DAG branches of the prokaryote lipid synthesis pathway
DAG- sulfolipids, MGD, DGD, SQD
CDP-DAG- PG
what lipids are made by the DAG and CDP-DAG branches of the eukaryote lipid synthesis pathway
DAG- PE and PC
CDG-DAG- PG, PI, PS, CL , PE
where are the pro and euk lipid synthesis pathways
pro= plastid
euk= ER
what is a cellulose microfibril and how is it made
assemblies of beta 1,4-linked glucose units
-microfibrils are laid down in a parallel array and have inter and intra chain bonds
how many chains is each microfibril composed of
30-36 chains
how do cellulose synthases (CesA) work
makes long chains of glc
what is the cellulose synthases association with sucrose synthase and why is it important
sucrose synthase contribute substrate directly into the catalytic site of the enzyme
where is CesA found and what does it react with
occurs on the outer face of the PM
-reacts with dextrin primer
how are microfibrils locked in place
-hemicellulose (cross-linking glycans)
– interlock the cellulose scaffold by H-bonding to cellulose microfibrils
-galacturonans
what does expansion do in the cell wall
breakage of H-bonds between microfibrils (clip off cross-linking glycans) which allows cell wall to expand
how do specific cell wall proteins contribute toward cell expansion
expansin- breaks H-bonds between microfibrils
extensins- heavily glycosylated proteins that allow the cell wall to expand and contract
where does the shikimate pathway take place within the cell and what are the 2 precursors
connects central C metabolism to the aromatic a.a network and takes place in the plastid
1. erythrose-4-phosphate
2. PEP
what is the enzyme that transfers sugars onto biomlcs
glycosal transferase
how does round up work. mech of action and enzyme target
glyphosate binds to EPSP synthase and competitively inhibits PEP in the shikimate pathway
what enzyme converts phenylalanine to trans-cinnamic acid and why is this enzyme important
PAL
-first step in benzenoid biosyn
what distinguishes the oxidative and non-oxidative pathway for benzoic acid biosyn
oxidative - benzyl-CoA
non oxi - benzaldehyde
what are the 2 ways to make volatile and simple benzenoids
oxidative and non oxidative pathway
what are the 3 monolignols
- coniferyl alcohol (g unit)
- p-coumaryl alcohol (H unit)
- sinapyl alcohol (S unit)
how does the contribution to lignin composition differ between species
gymnosperm lignin= lots of G little H
angiosperm = mix of G and S
monocot grasses= mix of G S and H
how are flavanoids synthesizes
formed from p-courmaroyl and malonyl CoA which condense to form chalcone the precursor for many classes of flavanoids
what are 2 functions of flavanoids
- protect from harmful UV radiations from reaching plant tissue
- floral colour
what does the shikimate pathway lead to
chorismate which makes Trp, Phe, Tyr (aaa) which makes plant phenolics (benzenoids, flavanoids
what is the role of benzenoids
class of plant VOCs that are sythesized to attract pollinators and derived exclusively from Phe
give 2 examples of how plants have evolved to be more efficient
- combined on one polypeptide
- product of firt enzymatic activity is the substrate of the second (shikimate) - riboswitch
-thiamine can regulate its own biosynthesis
why do we need thiamine
pyruvate dehydrogenase requires thiamine as a cofactor
what is the role of vit E
as antioxidant to scavenge lipid peroxyl radicals
give an example of what 2 vitamins are used for
vitamin E = antioxidant
folate = revert anemia
what are the active forms of riboflavin
excited singlet state and excited triplet state
-can move between them by intersystem crossing
what are the prenylated acylphloroglucinole class of compounds
make the bitter flavour of beer
precursors: leu, val, ile
enzymes: isovalenyl-CoA, Isobutyryl-CoA, 2-methylbutyryl-CoA
how does MBT formation work
formation requires isohumulones and riboflavin
-light absorption by riboflavin causes the mlc to become excited to the triplet state
how could you engineer beer to avoid MBT formation
develop yeast strains that can metabolize precursors to MBT or are less susceptible to MBT formation
