Lecture 30: Glucose Anabolism (Photosynthesis)

Question 1

Photosyntesis overview

What does photosyntesis primarily happen in, general?

Answer 1

Plants
and some bacteria and protists

Question 2

Photosyntesis overview

What are the two stages to photosynthesis?

Answer 2

Light Reaction
* light dependant
* converts solar energy to chemical
* produces ATP and NADPH
Dark Reaction - Calvin Cycle
* light independant
* Uses ATP and NADPH from light reaction to make glucose

Question 3

Photosyntesis overview

What does photosynthesis require to produce glucose?

Answer 3

Light energy, H2O, and CO2

Question 4

Photosyntesis overview

What is the general equation for photosynthesis?

Answer 4

6 CO2 + 6 H2O + Energy
–>
C6H12O6 + 6 O2

Question 5

Photosyntesis overview

What is the light energy used for?

Answer 5

powering ATP synthesis (using a proton gradient) and formation of NADPH (biosynthetic reducing power, similar to NADH)

Question 6

Photosyntesis overview

What are organisms that use CO2 and H2O to form glucose called?

Answer 6

autotrophs

Question 7

Photosyntesis overview

What are organisms that use chemical fuels to form glucose called?

Answer 7

heterotrophs

Question 8

Photosyntesis overview

Where does photosynthesis take place, more specific?

Answer 8

Chloroplasts

Question 9

Photosyntesis overview

What are the parts of a chloroplast?

Answer 9

• Double membrane
• Inner membrane surrounds the space called the Stroma
• Within the stroma are membranous sacs called thylakoid

Question 10

Photosyntesis overview

Where are light reactions located?

Answer 10

In the Thylakoid

Question 11

Photosyntesis overview

Where are dark reactions located?

Answer 11

In the Stroma

Question 12

Chloroplasts Pigments

What are the pigments in chloroplast?

Answer 12

Chlorophyll a: pricipal photoreceptor in chloroplasts of green plants
Chlorophyll b: accessory pigment
Carotenoids: accessory pigment

Question 13

Chloroplasts Pigments

What wavelengths of light do the different pigments absorb?

Answer 13

Chlorophyll: Blue (420nm) and red (660nm)
Carotenoids: blue and green (not yellow or red)

Question 14

Chloroplasts Pigments

What does this light absorption do?

Answer 14

Induces electron transfer
(electron in the pigment molecule jumps to a higher energy state and transfers to a nearby molecule that has a lower one)

Question 15

Photosystems

How many photosystems (PS) are there in green plants?

Answer 15

2:
PS I and PS II

Question 16

Photosystems

What does PS I do?

Answer 16

generates NADPH

Question 17

Photosystems

What is the reaction center for PS I called and what does it respond to?

Answer 17

P700, wavelegnths less than 700nm

Question 18

Photosystems

What does PS II do?

Answer 18

replenishes the elctrons in PS I while generating a proton gradient to synthesize ATP

Question 19

Photosystems

Where are the missing electrons in PS II replaced from?

Answer 19

photolysis of water

Question 20

Photosystems

What is the reaction center to PS II called and what does it absorb?

Answer 20

P680, wavelengths 680nm and under

Question 21

Light Reactions

What are the two possible routes for electron flow in light reactions?

Answer 21

Cyclic Electron Flow (cyclic photophosphorylation)
noncyclic electron flow ( noncyclic photophosphorylation)

Question 22

Light Reactions

What does the cyclic electron flow use and generate?

Answer 22

PS I and ETC
ATP

Question 23

Light Reactions

What does the noncyclic electron flow use and generate?

Answer 23

PS II and PS I then the ETC

O2 (from splitting H2O), ATP and NADPH

Question 24

Chemiosmosis

What does chemiosmosis do in photosynthesis?

Answer 24

The elctron transport chains are arranged with photosystems to bring H through the thylakoid membranes into the middle space. When they try to flow back out, they are forced to move through theATP synthase to make ATP

Question 25

# Chemiosmosis What is photophosphorylation?

Answer 25

the use of light energy from photosynthesis to untimately provide the energy to convert ADP to ATP

Question 26

# Dark Reactions What types of carbon fixations do dark reactions have?

Answer 26

C3 fixation (Calvin Cycle) C4 Fixation

Question 27

# Dark Reactions What is C3 fixation?

Answer 27

CO2 is fixed to form a 3-carbon unit (rice, wheat, soybeans, trees)

Question 28

# Dark Reactions What is C4 fixation?

Answer 28

CO2 is fixed to form a 4-carbon unit (crabgrass, sugarcane, and corn) common in warmed areas

Question 29

# Dark Reactions What is the Calvin Cycle?

Answer 29

A biochemical pathway that allows for carbon fixation

Question 30

# Dark Reactions What does the Calvin Cycle use to synthesize hexose?

Answer 30

CO2 and H2O

Question 31

# Dark Reactions How long and how much energy does it take for the Calvin Cycle to produce Glucose?

Answer 31

6 turns 18 ATP 12NADPH

Question 32

# Dark Reactions What is the general net equation for the Calvin Cycle?

Answer 32

6 CO2 + 18 ATP + 12 NADPH + 12 H2O --> C6H12O6 + 18 ADP + 18 Pi + 12 NADP + 6 H

Question 33

# Dark Reactions Q from Lecture: How many molecules of NADPH and how many molecules of ATP are consumed in incorporating a single CO2 molecule into Hexose?

Answer 33

3 ATP and 2 NADPH

Question 34

# Calvin Cycle What are the 3 stages of the Calvin Cycle?

Answer 34

Stage 1 Stage 2 Stage 3

Question 35

# Calvin Cycle Stage 1:

Answer 35

Fixation of CO2 by ribulose 1,5-biphosphate to form 2 molecules of 3-phosphoglycerate Catalyzed by ribulose 1,5-biphosphate carbxylase/oxygenase (rubisco) | Rate limited step

Question 36

# Calvin Cycle What is rubisco? | general, not specific

Answer 36

the most abundant enzyme in the biosphere, key enam

Question 37

# Calvin Cycle Stage 2:

Answer 37

reduction of 3-phosphoglycerate to form hexose monophosphates (fructose-6-phosphate to glucose-6-phosphate to **glucose-1-phosphate**) uses 2 ATP and 2 NADPH | very similar to gluconeogenic pathway

Question 38

# Calvin Cycle Stage 3:

Answer 38

regeneration of ribulose 1,5-biphosphate using transketolase and aldolase Transketolase converts and 6C and 3C into a 4C and 5C Alsolase combines the 4C and 3C to form a 7C sugar The 7C reacts with a 3C to form two additional 5C sugars | C meaning carbon

Question 39

# Calvin Cycle What is the general equation for stage 3?

Answer 39

Fructose-6-phosphate + 2 glyceraldehyde-3-phosphate + dihydroxyacetone phosphate + 3 ATP --> 3 ribulose-1,5-biphosphate + 3 ADP | track the carbons