Lecture 2/5/13

Question 1

What was Darwin’s dilema? What was his hypothesis?

Answer 1

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.

Question 2

What are the two lines of evidence for the evolution of oxygenic photosynthesis?

Answer 2

The electron flow

Reaction centers

Question 3

Based on electron flow? What are bacteria are the PS related to?

Answer 3

PS2 is related to green non-sulfur and purple

PS1 to green sulfur and helios

Question 4

What bacteria do the PS resemble?

Answer 4

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)

Question 5

Why aren’t phylogenic methods helpful for understanding which PS came first?

Answer 5

Because cyanobacteria is closely related to purple AND green sulfur bac

Question 6

What is the trade off that Rubisco has to make?

Answer 6

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.

Question 7

What needs to happen for Rubisco to be more selective?

Answer 7

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.

Question 8

What is the cause of being fast/slow for rubisco?

Answer 8

Faster rubiscos are less selective; pickier rubiscos are slower.

Question 9

What should an organism do to prevent rubisco from acting as an oxygenase?

Answer 9

Increase the concentration of CO2 through Carbon-concentrating mechanisms.

Question 10

How does C4 minimize photorespiration?

Answer 10

By SPATIALLY separating where carbon gets fixed and where it’s acquired.

Question 11

What fixes carbon is C4? What is the product? Why?

Answer 11

PEP carboxylase

It fixes CO2 to Malate (four carbon cmpd) because easier to transport instead of relying on diffusion.

Question 12

Where does the CO2 go in C4 photosynthesis?

Answer 12

CO2 goes to the chloroplast and the C3 compound is exported to close the cycle.

Question 13

What specialized anatomy goes the C4 pathway require? Why are they important?

Answer 13

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)

Question 14

Where does C4 tend to evolve?

Answer 14

Strong selection pressure with low CO2, high tempt, and aridity

Question 15

How does C4 deal with photorespiration? What are the things it does?

Answer 15

C4 Ps separates the assimilation, carboxylation, and reduction reactions in space.

Question 16

What are two of the main differences between C4 and CAM plants? Which one is more costly?

Answer 16

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

Question 17

What causes CAM photosynthesis in some plants?

Answer 17

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.

Question 18

Why is C4 a somewhat disadvantage?

Answer 18

It requires a lot of energy

Question 19

How does CAM pathway work?

Answer 19

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.

Question 20

How do we identify plants with a CCM? Or tell which CCM the plant used?

Answer 20

Use carbon isotopes

Question 21

How do carbon isotopes work?

Answer 21

Enzymatic preferences result in isotope ratio variation.

The amount of 13C/12C helps us see what type of metabolic pathways it might be.

Question 22

How can we differ between C3, C4, and CAM in carbon isotopes?

Answer 22

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

Question 23

What are the values of carbon isotope that helps ID the diff pathways?

Answer 23

• 22% for C3
• 19% for CAM
• 12% for C4

Question 24

Why are carbon isotopes important?

Answer 24

In principle, we can use the isotopic composition of organic carbon to fingerprint the metabolic pathway used to fix that carbon.

Question 25

What are some examples of non-traditional fossils?

Answer 25

• 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

Question 26

What are crown groups and stem groups?

Answer 26

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.