Midterm 1 extra Flashcards
Provide the ‘carbon’ reactions occurring in the chloroplast that require the products of the light reactions?
-CO2 fixation by the CBB cycle
-the photorespiratory cycle
-end product synthesis
-N/S assimilation
-synthesis of many parts of the cell (wall, lipid, protein, chl)
What information can be calculated or derived from data showing the relationship between the net C fixation rate of a leaf and irradiance?
In a C3 leaf there are 14-25 photons/ C fixed
-also after an irradiance of ~2000 CO2 assimilation levels off
Provide 6 reasons why organisms on earth are C-based. Your answers should indicate the significance of each factor.
- has 4 valence e-s, sig: can form covalent bonds with other elements (O,H,N,P,S)
- small in size, sig: bond readily and strongly with other C atoms + accessible to enzymes
- stable but also reactive, sig: the e- ionization energy shows this, good for bonding
- abundant on earth + can be gas or in solution, sig: easy to access by many organisms
- can exist in different oxidation states, sig: increases the possible metabolic reactions
- long C polymers can exist (compared to crystalline C structures, sig: allows the formation of starch, DNA, proteins, and lipids
What is the C oxidation series and its relationship to photosynthetic C metabolism?
The oxidation state of C goes from a more oxidized to a more reduced state as e-s are added.
-This is the same as what happens in photosynthesis
Explain autotrophy in terms of the use of oxidized, inorganic precursors to synthesize reduced intermediary compounds, building blocks, macromolecules, assemblies, and organelles.
-starts with the basic oxidized building blocks (CO2, H2O, NO3-, SO42-).
-then macromolecules are made that are polymers of C, (nucleic acids, proteins, lipids)
-C polymers are assembled into various structures (cell wall, light harvesting complexes, membranes) that allow organelles to be formed.
From what inorganic, oxidized compounds and reactions are the C, H & O in green plants primarily obtained?
C + O derived from CO2 (via RuBisCo)
H derived from H2O (via splitting of water)
Provide the general equation for CO2 fixation in photoautotrophs.
CO2 + 2 H2O = CH2O + H2O + O2
Unlike animal cells, plant cells show an elemental composition for C, H, and O close to 1:2:1, respectively. Explain.
Plants have a C:H:O ratio close to 1:2:1 owing to the cellulose in the cell wall, which is where much of the dry weight in a plant is found
Cellulose = C6H10O5
What is the C3 cycle and what is a C3 plant?
A C3 cycle refers to the Calvin cycle,
A C3 plant primarily uses this Calvin cycle for carbon fixation with the stable compound produced is a three-carbon molecule (3-PGA)
What is the 1st end product of photosynthesis?
triose- P (3C)
What are the two principle end products of photosynthesis and their function in the plant?
starch
sucrose
What are the three main components of photosynthetic C metabolism in plants?
- the C3 cycle
- Rubisco
- end products being starch and sucrose
What are general characteristics of Rubisco?
- most abundant enzyme on earth
- is both a carboxylase and oxygenase
- four forms exist (forms I-IV)
Why do plants require such high concentrations of Rubisco in photosynthetic tissues?
because it is inefficient and the plant compensates by making a lot
What is the subunit structure of the 2 major forms of Rubisco that have been identified?
Form II - large subunit dimer
Form I - hexadecamer of 8 large subunits and 8 small subunits (found in green plants)
Which form of Rubisco is found in land plants and how many active sites is there in this Rubisco protein?
Form I
-2 active sites
What are the 3 phases in the CBB cycle and their function?
- Carboxylation (3-PGA formation)
- Reduction (formation of Triose-P)
- Regeneration (formation of RuBP the CO2 acceptor)
Provide the general chemical reaction for the CBB cycle starting with 3 CO2.
3 CO2 + 9ATP + 6NADPH = triose-p + 8Pi + 9ADP + 6NADP+
What enzymes and reactions in the CBB cycle are unique to the cycle?
3 enzymes- Rubisco, S-1,7-BP, phosphoribulokinase
4 reactions in the cycle are unique to it.
What is the fate of the 6 triose-P that are produced for every 3 CO2 fixed in the CBB cycle?
-one triose-P is removed from the cycle for end product synthesis
-remaining 5 triose-P are cycled back to 3 RuBP to maintain the pool size of RuBP
what is the function of the regeneration phase of the Calvin cycle?
Five of the triose-P recycle back to regenerate 3 RuBP
Why was 14CO2 used in the experiments by Calvin and co-workers?
could follow its movement into substrates
Explain the experiment designed by Calvin and co-workers to determine the first product of CO2 fixation in the green alga Chlorella.
Studied the green alga Chlorella, this through time course labeling studies with 14CO2 and identifying labeled metabolites on paper chromatography in the order and amounts that appeared.
What are 2 major reasons/considerations for why the Calvin cycle and photosynthesis needs to be regulated by light?
- coordinates the light reactions and photosynthetic C metabolism
- inhibits or activates the CBB cycle and respiratory metabolism
What are the 5 major types of light regulation that occur in photosynthetic C metabolism in response to light?
