L26: Calvin Cycle

Question 1

The stroma is like the ___ of the ____

Answer 1

• Matrix, Mitochondria

Question 2

Where does photosynthesis occur in bacteria?

Answer 2

• Do not have chloroplasts

- Have photosynthetic internal membranes

Question 3

What are the light dependant reactions?

Answer 3

• Chloroplast needs to make lots of energy (ATP) and high energy intermediates (NADPH)
• Water is oxidized to produce O2 (donates electrons to an ETC)

Question 4

How do light dependant reactions occur?

Answer 4

• Via an ETC called photophosphorylation

Question 5

Why do light dependant reactions occur?

Answer 5

• For the next set of reactions in the Calvin cycle

Question 6

Where do light dependant reactions occur?

Answer 6

• in the thylakoid membranes

Question 7

What is going on with NADPH?

Answer 7

• Similar to NADH but with an extra phosphate group
• NADH = catabolic reactions, NADPH = anabolic reactions
• Another high energy intermediate that is synthesized in photophos and then used in anabolic reactions

Question 8

The Calvin Cycle is an __ __

Answer 8

• Anabolic reaction

Question 9

Photophos in a nutshell

Answer 9

• cell uses the chloroplast to convert light energy into high energy intermediates such as ATP and NADPH
• this is accomplished by photophos - an ETC
• there are 2 photosystems and are often referred to as the Z-scheme

Question 10

Why is it called a z-scheme?

Answer 10

• photosystems II and I work together in the thylakoid membrane
• hits of light provide energy
• energy is used to pump protons across the membrane

Question 11

What are the inputs and outputs of photophos?

Answer 11

• Inputs: Photons, water, NADP+, ADP

- Outputs: ATP, NADH, O2

Question 12

Where is ATP synthesized?

Answer 12

• Stroma

Question 13

Where is the ETC?

Answer 13

• Thylakoid membranes

Question 14

Is NADPH a TEA?

Answer 14

• NO! NADP+ is an internal molecule and not from the environment.

Question 15

What is step 1 of photophos?

Answer 15

Electrons are supplied by H2O

Question 16

What is step 2 of photophos?

Answer 16

Light energy is required for PS2 to “strip” the electrons from the water

Question 17

What is step 3 of photophos?

Answer 17

Electrons move along the ETC to provide energy to pump protons (H+) into the lumen

Question 18

What is step 4 of photophos?

Answer 18

an electrochemical gradient is created in the thylakoid lumen

Question 19

What is step 5 of photophos?

Answer 19

more light energy input at PSI. this energizes the electrons to drive the reduction of NADP+

Question 20

What is step 6 of photophos?

Answer 20

NADPH is synthesized in the stroma and will be used in the Calvin cycle

Question 21

What is step 7 of photophos?

Answer 21

ATP is synthesized in the stroma via chemiosmosis. H+ moves through the ATP synthase

Question 22

In the light-dependent reactions of photosynthesis, light energy is used to oxidize __ to ___

Answer 22

H2O to O2

Question 23

The electrons derived from H2O are used to reduce __ to ___ in the dependent reactions

Answer 23

NADP+ to NADPH

Question 24

Photophos summary

Answer 24

• called the Z scheme
• 2 photosystems work together to synthesize ATP and NADPH
• light energy captured in the photosystems excites electrons to drive them through an ETC
• the ETC creates a proton (H+) gradient for the synthesis of ATP
• a second photosystem and ETC drives electrons to end up on high energy intermediate NADPH

Question 25

What is oxygenic photophos?

Answer 25

- electrons from water reduce the PSII photosystem and release O2 - oxygen is a product of the reaction and released

Question 26

Does photophos have a TEA?

Answer 26

- NO!!! - NADP+, the electron acceptor, is a molecule found inside the cell, and is thus not by definition the TEA! - it's just an electron acceptor

Question 27

Photosynthesis overview

Answer 27

LIGHT DEPENDENT REACTIONS: - water is oxidized to O2 - NADP is reduced to form NADPH - ATP is synthesized via proton gradient driven by chemiosmosis LIGHT INDEPENDENT REACTIONS: - ATP and NADP are used - CO2 is reduced to form carbohydrates

Question 28

Where is the H+ gradient created?

Answer 28

Thylakoid lumen

Question 29

Chloroplast and mitochondria equivalents.

Answer 29

- thylakoid lumen = intermembrane space | - stroma = matrix

Question 30

What is the evidence that mitochondria and chloroplasts evolved from ancient prokaryotes?

Answer 30

- both have double membranes - both have their own circular DNA (genomes) - both grow and multiply by binary fission - independently of the eukaryotic cell! - both have their own ribosomes, synthesizes proteins, etc

Question 31

Where does the Calvin Cycle Occur?

Answer 31

Stroma

Question 32

Photolithoautotrophs use __ as a carbon source and fix them into ___ ___

Answer 32

CO2, Organic molecules

Question 33

When something is fixed, it means that...

Answer 33

- it is being converted from a gaseous state to a solid or liquid state - oxidized form → more reduced form

Question 34

Oxidized carbon vs reduced carbon

Answer 34

OXIDIZED: CO2 - only C-O bonds - More strongly bonded REDUCED: Cellular biomolecules - i.e. glucose, proteins, etc. - C-H bonds - less strongly bonded

Question 35

What are the 3 steps of the Calvin Cycle?

Answer 35

- Carbon Fixation - Reduction - Regeneration

Question 36

What is the first step of the Calvin Cycle?

Answer 36

CARBON FIXATION: - each CO2 reacts with RuBP, producing two G3P molecules - the enzyme that catalyzes this reaction is called rubisco - the attachment of CO2 to an organic compound is called carbon fixation

Question 37

What is the second step of the Calvin Cycle?

Answer 37

REDUCTION: the two 3-phosphoglycerate molecules are phosphorylated by ATP and reduced by NADPH to produce glyceraldehyde 3-phosphate (G3P or called GAP)

Question 38

What is the third step of the Calvin Cycle?

Answer 38

REGENERATION: | - the remaining G3P/GAP is used in ATP dependent reactions that regenerate RuBP

Question 39

How is the GAP/G3P (reduced carbon) related to CR?

Answer 39

- notice that after the "glucose splitting" (step 5 of glycolysis) the substrate produced is G3P - the G3P from the Calvin cycle can enter glycolysis here

Question 40

What is the fate of GAP/G3P?

Answer 40

leaves the chloroplast and can be used in CR or used to build other macromolecules

Question 41

what are the inputs and outputs of the Calvin cycle?

Answer 41

- Inputs: RuBP, CO2, NADPH, ATP | - Outputs: GAP, ADP, Pi, NADP+

Question 42

Calvin Cylce Summary

Answer 42

- CO2 is oxidized - NADPH donates electrons for reducing C - GAP/G3P is reduced carbon - Used to build all other C-containing organic cellular molecules