Photosynthesis and Calvin Cycle: Key Concepts for Biology

Photo

Convert solar energy to chemical energy (ATP)

Synthesis

Building organic molecules (glucose) from inorganic nutrients (CO2 + H20)

What is the formula for photosynthesis?

CO2 + H2O --> C6H12O6 + O2

Photo in photoautotroph's

Convert solar energy to chemical energy (ATP)

Autotroph in photoautotroph's

building organic molecules from inorganic nutrients (CO2 + H2O)

Marine Phytoplankton

algae, diatoms, photosynthetic bacteria, photosynthetic protists

What do marine phytoplankton do?

maintain our oxygen rich atmosphere as we know it

What is at the thylakoid membrane?

ETC

What is at the thylakoid space?

H+ gradient

What is at the stroma?

Calvin cycle

Visible light

a narrow range of electromagnetic radiation that we can detect

Why do molecules appear white?

because most molecules reflect all wavelengths of visible light

Pigments

molecules that absorb some wavelengths of light and reflect others so they appear the color of the wavelengths they reflect

Green plants use two pigments in photosynthesis called?

chlorophyll alpha (Ca) and chlorophyll beta (Cb)

What colors do Ca and Cb most effectively absorb?

red and blue light and reflect green light

What are carotenoids?

a class of pigment not used in photosynthesis

What is the function of carotenoids?

maybe absorb extra light to prevent sun damage reflecting yellow, orange, and red

Where are photosystems located?

They are embedded in the thylakoid membrane

What is the Light Harvesting Complex?

Where the chlorophylls are, can be Ca and/or Cb

What happens at the LHC?

light strikes a chlorophyll and an e- jumps to a higher shell and immediately falls back

How is energy passed through the LHC?

Energy is passed laterally from one chloroplast to the next, until it reaches the special pair in the Reaction Center Complex

What does the Reaction Center Complex have?

It has a special pair of chlorophyll alphas bound together

When the e- at the special pair jumps, what is it picked up by?

It is picked up by the primary e- acceptor

Which photosystem has a special pair of P680?

photosystem 2

What happens first in photosystem 2?

P680s e- goes down an ETC

After P680s e- goes down an ETC, what happens?

H+ are shuttled from the stroma into the thylakoid space.

From there, what is established in the thylakoid space?

A H+ gradient

What allows H+ in the thylakoid space to diffuse back into the stroma

ATP Synthase

What does having H+ in the thylakoid space to diffuse back into the stroma generate?

it generates ATP in the stroma, Photophosphorylation

How does P680 replace the lost e-?

by taking e- from H2O

When H2O breaks down, what do the oxygens that recombine form?

O2 gas

Which photosystem has a special pair of P700?

Photosystem 1

P700s e- are sent to e- carrier NADP+ to form what?

NADPH in the stroma, these e- are used in the Calvin cycle

P700 replaces lost e- by?

taking P680's e- from the ETC, takes e- from the ETC to replace lost e-

The calvin cycle uses more ATP than e-, so what occurs?

an imbalance is created, too much NADPH and too little ATP

What corrects the imbalance?

cyclical flow of e-, NADPH gives its e- back to the ETC to regenerate extra ATP

What is the "synthesis" part?

The calvin cycle

What is the first step in the calvin cycle?

carbon fixation

What happens in carbon fixation

converts CO2 gas to a solid by attaching it to another molecule as a carboxyl

In carbon fixation, it does this by attaching it to ribulose bis phosphate as a carboxyl with the help of enzyme rubisco, creating what?

an unstable 6 carbon molecule that splits into 2 PGAs

After carbon fixation converts CO2 gas to a solid by attaching it to another molecule as a carboxyl, what happens

you start with 3 ribulose bisphosphates, the enzyme rubisco then fixes 1 CO2 to each of the 3 RuBPs. This results in 6-C compound that is so unstable that it immediately breaks into two

When the unstable 6-C compound breaks into two it ends?

with 6 PGAs

What is the second step of the calvin cycle?

Reduction

What happens in reduction?

ATP transfers Phosphate to the PGAs which destablilizes PGA

After destabilizing the PGA, what happens

PGA accepts e- from NADPH and PGA expels extra Phosphate

At the end of reduction, what is left?

6 Glyceraldehyde-3 Phosphates ( 6 G3Ps)

What is the third step of the calvin cycle?

release

What happens in release?

one G3P molecule is released to other metabolic pathways

What is the fourth step of the calvin cycle?

regeneration

What happens in regeneration?

The remaining 5 G3Ps are turned back into 3 RuBPs

What is a stomata?

sites of gas exchange on the leaf, CO2 into the stomata, O2 and H2O out

The stomata can be...

opened and closed

In hot, dry weather the plant does what?

the plant closes the stomata to prevent water loss and photorespiration

When the stomata are closed, what happens

it prevents gas exchange from occuring in the leaf, CO2 levels fall and O2 levels rise, bad since photorespiration may occur

What is photorespiration?

Bad because Rubisco fixes O2 to RuBP instead of CO2, which causes RuBP to be broken down/lost

What mechanisms are there to prevent photorespiration?

C4 plants and CAM plants

What are C4 plants?

grasses like corn, wheat, oats, etc

What do C4 plants do?

has a second enzyme PEPco, which has no affinity for O2 (won't bind)

What are CAM plants?

succulents

What do CAM plants do?

only open stomata at night. CO2 is stored as an acid until day