BCH Exam 3 - Light reactions and the calvin cycle

Light reactions

Form ATP and NADH from photons

Dark reaction/calvin cycle

Use ATP and NADH from light reactions to turn CO2 into carbs

Where are sugars synthesized?

In the stroma

Where do the light reactions take place?

Thylakoid membranes

Chlorophyll

A pigment that acts as a photoreceptor and is made up of a tetrapyrole with a phytol, a long 20 carbon chain alcohol

How do light harvesting complexes work?

They funnel light/photons using antenna complexes to the reaction center, increasing photosynthetic efficiency

Why should you not eat green potatoes?

They produce chlorophyll and solanine, which inhibits acetylcholinesterase which controls nerve firing

How does photosystem I work?

Electrons from P700 reaction center flow to ferredoxin, which then gives its electrons to NADP+ with the help of ferredoxin-NADP+ reductase, resulting in production of NADPH

How does photosystem II work?

P680 transfers electrons from water to PSI using an ETC

PSI and PSII reaction center names

PSI - P700

PSII -P680

Cytochrome b6f

Generates a proton gradient and provides electrons to PI by pumping protons into the lumen from stroma, connecting PII to PI

Where does cytochrome b6f pump protons?

Into lumen from stroma

What is responsible for the extraction of electrons from water and the generation of oxygen in the light reactions?

P680 of photosystem II

How is ATP synthesized in photosynthesis?

Flow of electrons from water to NADP+ makes a proton gradient that drives the synthesis of ATP

Where are carbohydrates synthesized in photosynthesis?

In the stroma

Which herbicides inhibit photosystem II? Which herbicide inhibits photosystem I?

PSII - Diuron and atrazine, PSI -Paraquat

Stage 1 of Calvin Cycle

Fixation of CO2 by ribulose 1,5-bisphosphate to form 2 molecules of 3-phosphoglycerate+

Stage 2 of the calvin cycle

Reduction of 3-[phosphoglycerate to hexose sugar

Calvin cycle stage 3

Regeneration of ribulose 1,5-bisphosphate (molecule that fixes carbon dioxide)

Which molecule fixes carbon dioxide?

ribulose 1,5-bisphosphate

What step of the calvin cycle is this? Label each molecule (endiolate intermediate/3-phosphoglycerate/ribulose 1,5-bisphosphate/unstable intermediate)

Stage 1 (Ribulose 1,5- bisphosphate to 3-phosphoglycerate step)

1. 1,5 Ribulose bisphosphate

2. Endiolate intermediate

3. Unstable intermediate

4. 3-phosphoglycerate

What molecules is needed to complete the reaction?

H2O

Which stage and specific steps of the Calvin cycle uses ATP and NADH from the light reactions?

Stage 2

3 phosphoglycerate to 1,3 bisphosphoglycerate uses 2 ATP

1,3-bisphosphoglycerate to G3P uses 2 NADPH

What is the conversion of 3-phosphoglycerate to hexose in the calvin cycle most similar to?

Gluconeogenesis

What 3 sugars make up the hexose monophosphate pool?

Glucose 1-phosphate, glucose 6-phosphate, and fructose 6-phosphate

How is ribulose 1,5-bisphosphate regenerated?

Fructose 6-phosphate, 2 G3P, 3ATP, and dihydroxyacetone phosphate are all used to make 3 ribulose 1,5-bisphosphate

How many ATP and NADPH’s are needed to incorporate a CO2 to a hexose?

3ATP and 2NADPH

What are the two major carbohydrate stores in plants and what are they used for?

Starch - branched long term storage of glucose

Sucrose - transport form of carbohydrates, such as sap which is 65% sucrose as well as some glucose and fructose

How is the calvin cycle regulated?

Thioredoxin and reduced ferredoxin and NADPH from photosystem II regulates many enzymes throughout the calvin cycle

How does ferredoxin-thioredoxin reductase affect calvin cycle enzymes?

Activates some enzymes by reducing disulfide bonds

What is the fate of G3P in the calvin cycle?

One leaves the cycle to be used to make glucose, 5 go into regenerating ribulose bisphosphate