second midterm reup Flashcards
What is facilitated diffusion?
involves movement of specific molecules
needs specific channels or carrier proteins
needs no ATP
In a system with charged species, what happens at equilibrium?
Influx = efflux, and the electric field will balance out the concentration gradient
What is the primary active transport system?
H pumping ATPase - pumps protons out of the cell to generate pH and electric gradietns
How to determine passive or active transport from voltage current plots?
Efflux is positive Y axis, influx is negative y axis
- if influx is greater than efflux, and the potential points towards influx, it is passive transport
- if it is different than the one it points to its active transport
Stomatal opening is highly correlated to what?
photosynthetically active radiation
Guard cell osmotic adjustment is mediated by what?
K+ and malate 2- or Cl-
or sucrose and / or starch
When guard cells are open / closed, what molecules are flowing in/out?
Open
- H+ out
- K+ in
- H2O in
Closed
- Cl- out (triggered by ABA)
- K+ out
- H2O out
How does energy transfer occur during photosynthesis?
Physical phenomenon
- no chemical changes
- done by resonance energy transfer - energy is transferred from pigment to pigment by resonance until it reaches the reaction center pigment
How does a photosystem harvest light?
Light harvesting complex are pigments bonded to proteins
- special pair of chlorophyll a that acts as an electron acceptor
Plants and green algae have what kinds of light harvesting complexes?
membrane embedded
Where are both of the photosytems?
In thylakoid membranes
What electron carriers move electrons from PSII to cytochromeB6 and to PSI
Plastoquinone - PSII - Cyt
Plastocyanin - Cyt - PSI
What does the oxygen evolving complex do?
- Each excitation of P680 is followed by withdrawal of an electron from Mn, when Mn4+ is reached the complex oxidizes 2H2O and releases O2`
Explain electron transfer in PSII
Light converts reaction center P680 to excited form
- electron leaves P680* forming P680+
- the electron is transferred to Pheophytin forming Pheo-
- Pheo - passes the elctron to Qa to form Qa-
- Qa_ passes electron to Qb to produce Qb-
What does cytochrome B6f do?
transfers electrons and protons
- first PQH2 delivers two protons to lumen, one electron to PC
- next PQ absorbs two electrons and two protons to regenerate and cycle again
How does electron transfer happen in PSI?
PSI is surrounded by LCHI complexes
ferrodoxin transfers electrons via ferrodoxinNADPreductase (FNR)
Resultsd in 2NADPH that go to ATP synthase
In the photosystem reactions - what is the electron donor and final electron acceptor
Z scheme and linear electron transport taking electrons from water and transferring them to NADP+
The light dependent reactions occur in the
thylakoid membranes
What is photophosphorylation?
Phosphorylation to make ATP during photosynthesis
- energy from photons
- electrons from H2O
- protons accumulate into the thylakoid of the chloroplasts
- protons move out of the thylakoid space during AATP synthesios
Where is the electron transport cyclic?
PSI
- electrons can be moved from ferrodoxin back to PQ onstead of going into NADP+
- used to control ATP levelsd
Overview of three pathways of electron transport
Linear
- electrons transferred from H2O to NADPH
- involves PSII, Cyc, PSI
- makes NADPH and ATP
Cyclic
- electrons cycle with no net production of NADPH
- involves Cyc and PSI
- Product only ATP (from proton gradient at CYC)
Water water cycle
- electrons transferred from H2O to H2O
- involves PSII, Cyc, PSI
- product is ATP
the binding change mechanism of ATP synthase accounts for what?
ATP synthesis in response to proton flow
What size is ATP synthase?
400kD
What can excess excitation energy lead to?
photooxidative damage - ROS
How does cyclic electron transport work for photoprotection?
cyclic electron flow back to PQ and Cyc lead to a generation of pH gradient accross thylakoid (protons)-
- qE energy dependent quenching is activated
How is Rubisco assembly different for large and small subunits?
Large rbcL is encoded by a single gene in the chloroplast genome
small subunit rbcS is encoded by a single gene in the nuclear genome
Chaperone molecules are required for enezyme assembly
How is Rubisco reversibly inhibited?
Inactive when a sugar phosphate inhibitor is bound to enzyme
- rubisco activase will remove it and activate enzyme
Rubisco mediated carboxylation of RuBP yeilds what?
2 molecules of 3 phosphoglycerate
What does Rubisco mediated oxygenation of RuPB yeild?
1 3 phosphoglycerate and 1 2-phosphoglycolate
Where is RuBP regenerated in the calcin cycle?
At he final step
What does CO2 fixation require ?
3 ATP 2 NADPH
How do O2 and CO2 differ in solubility?
SOlubility of CO2 decreases faster than O2 at high temperatures (30C)
- the portion of O2 in cytosol and stroma is higher relative to CO2 at high temp
How does increases O2 affect photosynthesos
Decreases rate
While the carboxylation reaction of Rubisco yeilds two 3PGA that go to calvin cycle for energy, what happens in the oxygenase reaction?
2 PG will be recycled to 3PGA CO2 and NH3
Photorespiration is a multi organelle processes across what three organelles?
chloroplast, peroxisome, mitochondrion
What is the peroxisome?
- single celled organelle with no inner membrane
- no DNA or ribosomes
- urate oxidase crystalline core in dense matrix
- tehtered to chloroplast
What is the main purpose of the photorespiratory cycle?
Takes the 2PG product from the oxygeanse reaction of Rubisco and uses it to reform intermediates
- site of ROS
What are the two byproducts of photorespiration?
CO2 and NH3
converts glycine to serine
What is the glycine decarboxylase complex?
glycine cleavage system in mitochondira during photorespiration
- once CO2 and NH3 are released the central C of glycine is transferred to THF
- serine hydroxymethyltransferase transfers C to another glycine to form serine
When does photorespiration occur?
- C3 plants close stomata to prevent excess water loss in heat
- causes low CO2 concentration
- increased atm temp and leaf temp decrease Rubiscoaffinity to CO2
- Rubisco combines with O2 instead of CO2 to form 3-PGA and 2PG
The oxgenase and carboxylase reactions occur when in rubisco
if O2 or CO2 binds
What is the significance of photorespiration (5)
- only found in C3 plants not C4
- prevents total depletion of CO2 in chlorplasts
- glycolate detoxification - glycolate oxidase
- protects from photoinhibition
- ammonium assimilation
Why is photorespiration a wasteful process?
- no ATP
- 25% carbon is lost as CO2
- reduces efficiency of photosynthetic carbon assimilation
(would be 50% more efficient without)
What is different about C4 plants compared to C3 plants
they have carbon concentrating mechanisms, and accumulate CO2 in the vicinity of Rubisco producing a high CO2/O2 ratio
What were the selection pressures on C4 photosynthesis evolution?
They lived in hot and dry conditions leading to stomatal closure and CO2 limitation causing an increase in photorespiration which is inefficient
How do C3 plants differ in terms of structure from C4 plants (4)
C3
- photosynthesis in mesophyll cells
- absensce of Kranz anatomy
- no chloroplasts in bundle sheath cells
- relatively thinner bundle sheath cell layers than C4
C4
- photosynthesis occurs in mesophyll and bundle sheath cells
- Kranz anatomy
- chloroplasts are in bundle sheath cells
- Thicker bundle sheath cell layers
What is Kranz anatomy in C4 plants
Bundle sheath cells form a ring around the vascular tissue and mesophyll cells form a ring around bundle sheath cells
What are dimorphic chloroplasts in C4 plants?
Mesophyll cells have chloroplasts with grana and bundle sheath cells have chloroplasts without grana
Advantages of C4 photosynthesis under hot and dry weather CA / PEPC
- stomata closed preventing water evaporation and CO2 uptake so concentration of CO2 is low
- HCO3 (bicarb) is generated from CO2 by carbonic anhydrase (CA)
- phosphoenolpyruvate carboxylase (PEPC) fixes HCO3- recycling it
Which type of photosynthesis is better under which conditions?
In cool temp C3 is better because C4 requires more ATP for the additional carboxylation steps but in hot and or sunny weather C4 carbon fixation is not carbon limited and does not become fully saturated even in full sunlight
What are the two CO2 fixation reactions in C4 photosynthesis?
First CO2 fixation in mesophyll cells using PEPC
Second CO2 fixation in bundle sheath cell using RuBP and Rubisco
What are the products of the PEPC reaction in C4 photosynthesis?
PEP turns to oxaloacetate via PEPC which goes to malate and aspartate
How does PEPC usage differ in CAM plants from C4?
PEPC fixes HCO3- at night
- stomata open at night for CO2 uptake
- HCO3- is fixed bby PEPC
- CO2 is stored as C4 carbon acids in vacuole
- Stomata close during the day
-CO2 released by decarb process in daytime
-rubisco fixes CO2 during the day
What is the main difference between C4 and CAM plants to avoid photorespiration?
C4 - carboxylases spatially separated
CAM - carboxylases temporally seperated
Which type of plant has the highest water use efficiency?
CAM
what is a negative effect of increased CO2 levels?
causes a decrease in protein and nutrient content but an increase in carbs
What is a test for plant reponses to CO2 fertilization?
Free air CO2 enrichment (FACE)
When does starch accumulate and when is it degraded?
accumulates in the day degraded at night
What are the two forms of starch?
amylose - linear chains
amylopectin - branched chains
Which starch branching enzyme has higher affinity for amylose?
starch branching enzyme 1, will act repeatedly to form highly branched amylopectin
enzyme 2 will go straight to highly branched
3 key enzymes for hydrolytic starch degradation?
A-amylase - targeting endo a1-4 glycosidic bonds
Beta amylase - targets exo a1-4 glycosidic bonds
limit dextrinase - targets branch points at a 1-6
2 Key enzymes for sucrose biosynthesis?
sucrose 6 phosphate synthase and sucrose 6 phosphate phosphatase
Where is sucrose and starch synthesized and from what product of the calvin cycle
both from triose phosphate (G3P)
sucrose in cytosol
starch in chloroplast
What is different between sucrose synthase and sucrose invertase?
synthase is reversible for sucrose synthesis and degradation but inveratase is irriversible and only for degradation
(UDP glucose v glucose)
explain the four steps for generation of UDP glucose for cell wall biosynthesis during sucrose degredation?
- sucrose synthase generates UDP glucose - UDP glucose is the substrate for cellulose synthase
- cellulose synthase of an enzyme rosetter synthesizes a long cellulose chain outside t he plasma membrane
- microtubules direct movement of cellulose synthase complexes (rosettes) along PM
- parallel cellulose chains crystalize to form cellulose microfibril
What is the difference between starch and cellulose?
starch is 1 4 linkage of a glucose in the same orientation - storage polysaccharide
cellulose is 1 4 linkage of b glucose monomers every glucose is upsidown
- structural polysaccharide
comparison of photosynthesis and respiration in organelle, reactants, products, energy and role
Organelle - chloroplast v mitochondria
Reactants - CO2 and H2O v sugars and H2O
Products - Sugars and O2 vs CO2 and H2O
Energy - sotred vs released
Role - carbon fixation vs oxidation of photoassimilates
4 steps of respiration
glycolysis, oxidative pentose phosphate pathway, krebs cycle, oxidative phosphorylation
What is glycolysis in plants?
conversion of glucose into 2 pyruvate
- forms 4 atp but uses 2 so net 2
- gives 2 NADH
What is the oxidative pentose phosphate pathway?
chemical reactions in cytoplasm and plastid
- release of CO2 and production of 2 NADPH
- makes ribulose 5 phosphate for Rubisco to woek on
- major supplier of NADPH in non photosynthetic plastids like roots
where does citric acid cycle occur?
mitochondrion matrix
2 stages of citric acid cycle?
Stage 1 - carbon condensation (C2 and C4 – C6)
Stage 2 - Oxaloacetate regeneration from succinyl coa
What are the total yeilds of the citric acid cycle?
Uses 2 pyruvate to get
6 CO2
2 ATP
8 NADH
2 FADH2
What is the goal of oxidative phosphorylation?
the final step in energy production during metabolism
- uses the elctron energy from NADH and FADH2 to produce ATP
Which complex in oxidative phosphorylation does not contribute to proton pumping?
Complex II
- oxidation of succinate synthesized in citric acid cycle instead
Which ion plays a central role in electron transport processes?
Fe - heme rings
Comparison of chemiosmosis in mitochondria and chloroplast - e- donors and acceptors
Mito
- NADH and FADH2 are e- donors
- O2 is acceptor
Chloro
- Light converts H2O to be an e- donor
- NADP+ is an e- acceptor
List 3 plant micronutrients
B, Cl, Mn, Fe, Ni, Cu, Zn, Mo
Are micronutrients usually mobile or immobile?
Immobile
What form is iron usually found as in plants?
FeIII - largely oxidized and insoluble
What is chelation?
Formation of bonds between two or more binding sites within a ligand with a single central atom
To maintain Fe in a way that it can be used (soluble) what happens?
Citrate binds to Fe to make it soluble
What are the two different strategies for iron uptake in plants?
Strategy 1 - chelate Fe III with citrate - use FRO2 to turn it into Fe II which is soluble - transport into the cell using iron regulated transporter 1
Strategy 2 - in monocots - Fe III binds to phytosiderophore which is exported out of the cell using TOM1 - Fe(III)-PS moves into the cell using YS/YSL - instead of changing the form of the iron the entire complex is transported into the cell
Micronutrients usually have a narrow _____ ______
optimal concentration
How do you calculate if a K+ flux system is in dynamic equilibrium?
DeltaE = RT/zIF x ln(a^o/a^c)
Will give in mV
zI = 1
R = 8.32
K = 273+C (298)
F = 96,500
