Undergraduate level notes. 1 – Limitations of RuBisCO Slow enzyme: catalytic turnover of ca.3 molecules s -1. 3.8 billion years old – evolved before atmosphere.

Slides:



Advertisements
Similar presentations
Photosynthesis & Cellular Respiration
Advertisements

Physiological ecology of C4 vs C3
Undergraduate Level Notes. Compensation Point Can also do this as a drawdown graph. An important physiological parameter in comparing C3 and C4 photosynthesis.
Topics: 1.Regulation of the Calvin Cycle 2.Photorespiration 3.CO2 concentrating mechanisms 4.Sucrose and starch synthesis.
Plant Biology Fall 2006 BISC Plant Physiology Lab Spring 2009 Notices: The photosynthesis labs are running again this week Reading material (Taiz.
 Allow for the entry of CO 2 and exit of water vapor (transpiration).  On sunny, hot, dry days, guard cells close to preserve water, but this poses.
Chapter 8 - Photosynthesis 6CO 2 + 6H 2 O + light  C 6 H 12 O 6 + 6O 2 The capture and conversion of solar energy to chemical bond energy.
Photorespiration.
Photorespiration When weather is hot and dry, guard cells decrease the size of stomata, also decreasing the concentration of carbon dioxide. Oxygen (O2)
Photosynthesis: the light- independent reactions Biol 3470 Plant Physiol Biotech 5.5 to 5.12 Lecture 9 Thurs. Feb. 2, 2006 From Rost et al., “Plant Biology”,
Photosynthesis: Energy from the Sun. Identifying Photosynthetic Reactants and Products  Reactants needed for photosynthesis:  H 2 O, & CO 2,  Products.
Photosynthesis. Types of Nutrition Heterotrophic – organisms break down complex organic molecules into simple soluble ones. Animals, fungi, some bacteria.
Photosynthesis part II – carbon fixation
I. Photorespiration II. CO 2 concentrating mechanisms - variation on the “C3” photosynthetic metabolism.
Rubisco (Triose-phosphate) CALVIN CYCLE: NET REACTION 6CO H NADPH + 18ATP  Fructose-6-phosphate + 12 NADP + + 6H ADP 17 P.
Fig. 8.2 The Calvin Cycle (reductive pentose phosphate cycle) 3 Stages Carboxylation Reduction Regeneration A 3 carbon molecule An outline of C3 photosynthesis.
Undergraduate level notes. Biochemical Mechanisms in Plants Variations on C3 photosynthesis in which the drawing down of CO 2 is not directly performed.
Alternative Methods of Carbon Fixation Photorespiration & C 3 Plants Photorespiration & C 3 Plants C 4 Photosynthesis & Plants C 4 Photosynthesis & Plants.
PHOTORESPIRATION This process interferes with successful performance of the Calvin Cycle by preventing CO 2 from fixing and removing the RuBP.
Plant Adaptations: C3 and C4 plants
Carbon enters the cycle in the form of CO 2 and leaves in the form of sugar (C 6 H 12 O 6 ) ATP and NADPH are consumed.
Figure 8.1 The light and carbon reactions of photosynthesis in chloroplasts of land plants.
The Dark Reaction - - light-independent - - energy stored in ATP and NADPH (from light reaction) is used to reduce CO 2 to sugar.
Photosynthesis Photosynthesis in Overview Process by which plants and other autotrophs store the energy of sunlight into sugars. Requires sunlight, water,
Photosynthesis As a Metabolic Process. What is it? Process where green plants (and certain photosynthetic bacteria) absorb sunlight and convert it to.
Calvin Cycle Calvin cycle cannot be called “dark reaction” because it is still light- dependent.
Photosynthesis Photosynthesis. I. How do living things get the energy they need to live? Photosynthesis: The process by which plants (autotrophs) and.
Photosynthesis, Environment & Adaptation C3 vs. C4 vs. CAM Photosynthesis.
Alternative Mechanisms of Carbon Fixation (5.4). RuBisCO RuBisCO is the most abundant protein on Earth catalyzes the first reaction of the Calvin cycle.
Variations in Photosynthesis Lecture 9 Fall 2008.
Biosynthesis of carbohydrate polymers Starch in plants, glycogen in vertebrates These polymerization reactions utilize sugar nucleotides as activated substrates.
Carbon Fixation (dark reactions)
The carbon reactions (Dark Reactions)
C4 Photosynthesis AP Biology Unit 4 Review: C3 Photosynthesis During “regular” photosynthesis, CO 2 is trapped into a 3-carbon compound by Rubisco 
NOTES: CH 10, part 3 – Calvin Cycle (10.3) & Alternative Mechanisms of C-Fixation (10.4)
The Calvin Cycle Photosynthesis. Calvin Cycle Calvin Cycle Overview Calvin cycle is a cyclical process which: 1.Fixes carbon (make C-C bonds) 2.Utilizes.
Photosynthesis. Overall equation Structure of a Chloroplast.
Fig Light Reactions: Photosystem II Electron transport chain Photosystem I Electron transport chain CO 2 NADP + ADP P i + RuBP 3-Phosphoglycerate.
Photosynthesis in plants: C3 and C4
Chapter 10: Photosynthesis
Chapter 10. Photosynthesis: Variations on the Theme
Rate of Photosynthesis in Response to Differing Percentages of Atmospheric Oxygen.
8. Photosynthesis: “Dark Reactions” (continued)
Variations of Photosynthesis
Photosynthesis Green plants converts CO2 to organic compound.
8. Photosynthesis: “Dark Reactions”
ADAPTIONS TO TEMPERATURE AND DROUGHT
Photosynthesis Part 2 Calvin Cycle Adaptations Factors Affecting Rate.
Cellular Energy Photosynthesis.
Light Reaction Review:
Two Stages of Photosynthesis
Photosynthesis: Life from Light and Air
Two Stages of Photosynthesis
Alternative Methods of Carbon Fixation
Photosynthesis: Variations on the Theme
Alternatives in carbon fixation Page
Photosynthesis: Life from Light and Air
Volume 23, Issue 14, Pages R594-R599 (July 2013)
Assignment for next Friday, October 13th
Photosynthesis.
C2 C3 C4 & CAM Variations on the theme of photosynthesis.
Cyclic Electron Flow Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH Cyclic electron flow generates surplus ATP, satisfying.
Photosynthesis: Variations on the Theme
Photosynthesis: Variations on the Theme
Do Now.
Photosystem I Light strikes P700 Electron released
Photosynthesis: Carbon Reactions
Photosynthesis & Cell Respiration
Alternative Methods of Carbon Fixation
Why Do Plants and Algae have Carbon Concentrating Mechanisms (CCMs)?
Presentation transcript:

Undergraduate level notes

1 – Limitations of RuBisCO Slow enzyme: catalytic turnover of ca.3 molecules s billion years old – evolved before atmosphere was oxygenated, therefore non-specific for CO 2. Oxygenase activity competes with carboxylase activity (increasingly at high temperature); generates 1 molecule 3- phosphoglycerate (3-PGA) (  CBB cycle) and 1 molecule of 2- phosphoglycolate (2-PG). Photorespiration is process by which 2-PG converted to 3-PGA (see next)

2 – Photorespiration 2-PG  2 molecules glycolate in chloroplast glycolate  glyoxylate in peroxisome, accompanied by production of H 2 O 2 (dissociates to O 2 + 2H 2 O, by catalase) glyoxylate  glycine (by incorporation of 2 glutamate and release of 2 2-oxoglutarate) 2 mol glycine  1 mol serine in mitochondria by glycine decarboxylase, releasing NH 4 + which returns to chloroplast, NH glutamate  glutamine (glutamine synthase). (cont.  )

Photorespiration (continued) Serine converted ultimately to glycerate (via hydroxypyruvate) in peroxisome. glycerate  3-PGA in chloroplast. Overall process consumes 2 molecules ATP (glutamine synthase step and glycerate  3-PGA step) and 2 reducing equivalents, per O 2. (Taiz and Zeiger, 2010, fig. 8.8 and table 8.2 for full details)

3 – Unavailability of CO 2 Atmospheric CO 2 : O 2 = 0.04% : 21% Soluble CO 2 concentration = ca.10μM (at ambient temperature and pressure) ≈ Km of RuBisCO for CO2. Therefore RuBisCO can only ever operate at about half V max.

4 – CO 2 in an aquatic environment Diffuses 10,000 times slower than in air. Slow to equilibrate between water and air, resulting in CO 2 depleted waters. Equilibrates with HCO 3 -, on a pH dependent basis – the pH of seawater (7.2) results in relatively low CO 2 availability.

Summary – Why do Plants and Algae need photosynthetic turbochargers? RuBisCO is old, slow and non-specific. Photorespiration (to retrieve the carbon lost through RuBisCO’s oxygenase activity) is wasteful. CO 2 is in low availability both in the atmosphere and in water. CCMs go some way towards overcoming these limitations