Lecture 2/5/13 Flashcards
What was Darwin’s dilema? What was his hypothesis?
When talking about the Cambrian explosion, he said that that a lot of animal evolution has occurred but you just couldn’t see it. Even through there was no fossil, there was still some time elapsed.
What are the two lines of evidence for the evolution of oxygenic photosynthesis?
The electron flow
Reaction centers
Based on electron flow? What are bacteria are the PS related to?
PS2 is related to green non-sulfur and purple
PS1 to green sulfur and helios
What bacteria do the PS resemble?
Reaction centers of purple bac look like PS2
(Purple and green non-sulfur bac have quinone as their e acceptor and quinone at its core)
Reaction centers of green S bacteria look like PS1
(Heliobac and green sulfur have iron sulfur at its core)
Why aren’t phylogenic methods helpful for understanding which PS came first?
Because cyanobacteria is closely related to purple AND green sulfur bac
What is the trade off that Rubisco has to make?
It can either be fast or selective but not both. It is non-specific when it’s fast. But to be specific would have to be slow.
What needs to happen for Rubisco to be more selective?
In order for Rubisco to become more selective, the intermediate (between RUBP and 3-phosphoglycerate) must be bound more tightly to the active site. By binding it more tightly, it makes it harder for it to cleave, thus slowing down.
What is the cause of being fast/slow for rubisco?
Faster rubiscos are less selective; pickier rubiscos are slower.
What should an organism do to prevent rubisco from acting as an oxygenase?
Increase the concentration of CO2 through Carbon-concentrating mechanisms.
How does C4 minimize photorespiration?
By SPATIALLY separating where carbon gets fixed and where it’s acquired.
What fixes carbon is C4? What is the product? Why?
PEP carboxylase
It fixes CO2 to Malate (four carbon cmpd) because easier to transport instead of relying on diffusion.
Where does the CO2 go in C4 photosynthesis?
CO2 goes to the chloroplast and the C3 compound is exported to close the cycle.
What specialized anatomy goes the C4 pathway require? Why are they important?
Mesophyll cells - lack rubisco; contain PEPcase
bundle sheath cells: contain decarboxylases to increase rubiso efficiency
veins: including water and photosynthate transport cells (xylem and phloem)
Where does C4 tend to evolve?
Strong selection pressure with low CO2, high tempt, and aridity
How does C4 deal with photorespiration? What are the things it does?
C4 Ps separates the assimilation, carboxylation, and reduction reactions in space.
What are two of the main differences between C4 and CAM plants? Which one is more costly?
C4 requires specialized anatomy and has spatial separation
CAM is inducible in a lot of plants and has temporal separation.
C4 pathway costs more energy
What causes CAM photosynthesis in some plants?
CAM photosynthesis is a response to a variety of environmental stimuli primarily water loss. CAM plants can switch back to the C3 pathway if things get better.
Why is C4 a somewhat disadvantage?
It requires a lot of energy
How does CAM pathway work?
CAM Ps separates assimilation and carboxylation in time. CAM plants open their stomata to take up CO2 at night, when cooler and wet. Store the CO2 in values and fix the carbon during the day.
How do we identify plants with a CCM? Or tell which CCM the plant used?
Use carbon isotopes
How do carbon isotopes work?
Enzymatic preferences result in isotope ratio variation.
The amount of 13C/12C helps us see what type of metabolic pathways it might be.
How can we differ between C3, C4, and CAM in carbon isotopes?
Rubisco prefers 12C to 13C when taking CO2. So would result in a more neg ratio
PEPCase fixes all CO2 that approaches bundle sheath cells. Little discrimination so lower neg number
What are the values of carbon isotope that helps ID the diff pathways?
- 22% for C3
- 19% for CAM
- 12% for C4
Why are carbon isotopes important?
In principle, we can use the isotopic composition of organic carbon to fingerprint the metabolic pathway used to fix that carbon.
What are some examples of non-traditional fossils?
- look at similar biochem of PS
- using stable isotope analysis to ID biochem pathways
- biomarkers
- mapping fossilized bac to reconstruct the trophic structure of the ocean
What are crown groups and stem groups?
Crow groups include the last common ancestor of everything living in a group.
Stem groups are lineages that diverges before the last common ancestor of everything living.
