Biochemistry
This presentation is the property of its rightful owner.
Sponsored Links
1 / 40

Biochemistry PowerPoint PPT Presentation


  • 67 Views
  • Uploaded on
  • Presentation posted in: General

Biochemistry. Lecture 15. Photosynthesis. Chemiosmotic Gradient. Endosymbiotic Theory. Photosynthesis. Assimilation of CO 2 by Plants. CO 2 Assimilation Occurs in Plastids. Organelles found in plants and algae Enclosed by a double membrane Have their own small genome

Download Presentation

Biochemistry

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Biochemistry

Biochemistry

Lecture 15


Photosynthesis

Photosynthesis


Chemiosmotic gradient

Chemiosmotic Gradient


Endosymbiotic theory

Endosymbiotic Theory


Photosynthesis1

Photosynthesis


Biochemistry

Assimilation of CO2 by Plants


Co 2 assimilation occurs in plastids

CO2 Assimilation Occurs in Plastids

Organelles found in plants and algae

Enclosed by a double membrane

Have their own small genome

The inner membrane is impermeable to ions such as H+, and to polar and charged molecules


Origin and differentiation of plastids

Origin and Differentiation of Plastids

Plastids were acquired during evolution by early eukaryotes via endosymbiosis of photosynthetic cyanobacteria

Plastids reproduce asexually via binary fission

The undifferentiated protoplastids in plants can differentiate into several types, each with a distinct function

Chloroplasts for photosynthesis

Amyloplasts for starch storage

Chromoplasts for pigment storage

Elaioplasts for lipid storage

Proteinoplasts for protein storage


Photosynthesis2

Photosynthesis


Biochemistry

Review: Light Reactions Generate ATP and NADPH


Biochemistry

The Calvin Cycle


Rubisco ribulose 1 5 bisphosphate carboxylase oxygenase

Rubisco (ribulose 1,5 bisphosphate carboxylase / oxygenase )


Biochemistry

The Calvin Cycle


Rubisco is activated via covalent modification of the active site lysine

Rubisco is Activated via Covalent Modification of the Active Site Lysine


Fates of g3p

Fates of G3P


Remaking r1 5bp

Remaking R1,5BP


Photorespiration

Photorespiration

So far, we saw that plants oxidize water to O2 and reduce CO2 to carbohydrates during the photosynthesis

Plants also have mitochondria where usual respiration with consumption of O2 occurs in the dark

In addition, a wasteful side reaction catalyzed by Rubisco occurs in mitochondria

This reaction consumes oxygen and is called photorespiration; unlike mitochondrial respiration, this process does not yield energy


Oxygenase activity of rubisco

Oxygenase Activity of Rubisco

The reactive nucleophile in the Rubisco reaction is the electron-rich enediol form of ribulose 1,5-bisphosphate

The active site meant for CO2also accommodates O2

Mg++ also stabilizes the hydroperoxy anion that forms by electron transfer from the enediol to oxygen


Salvage of 2 phosphoglycerate

Salvage of 2-Phosphoglycerate

Complex ATP-consuming process for the recovery of C2 fragments from the photorespiration

Requires oxidation of glycolate with molecular oxygen in peroxisomes, and formation of H2O2

Involves a loss of a carbon as CO2 by mitochondrial decarboxylation of glycine


Rubisco in c 3 plants cannot avoid oxygen

Rubisco in C3 Plants Cannot Avoid Oxygen

Plants that assimilate dissolved CO2 in themesophyll of the leaf into three-carbon 3-phosphoglycerate are called the C3 plants

Our atmosphere contains about 21% of oxygen and 0.038% of carbon dioxide

The dissolved concentrations in pure water are about 260 M O2 and 11 M CO2(at the equilibrium and room temperature)

The Km of Rubisco for oxygen is about 350 M


Separation of co 2 capture and the rubisco reaction in c 4 plants

Separation of CO2 capture and the Rubisco Reaction in C4 Plants

Many tropical plants avoid wasteful photorespiration by a physical separation of CO2 capture and Rubisco activity

CO2 is captured into oxaloacetate (C4) in mesophyll cells

CO2 is transported to bundle-sheath cells where Rubisco is located

The local concentration of CO2 in bundle-sheath cells is much higher than the concentration of O2


  • Login