CH 10: Light Energy, ETC Photosyn, Calvin Cycle

Define Electromagnetic radiation

Light energy which travels in wavelength rhythms

the wavelength’s peaks are called crests

and their droops are called troughs

the wavelength spans between crests

Electromagnetic spectrum

the range of different wavelength and electromagnetic radiation

the size: shorter contains more energy, longer wavelengths = less energy

Why is electromagnetic spectrum important for

its important because within the spectrum there is

narrow band of light wavelength’s which are visible to us

visible light powers photosynthesis (350-750nm

and the amount of energy is connected to the length of a wavelength

Photon’s energy

light particles which hold pockets of energy (amount related to the ;enth of wavelength

Photosynthetic Pigments as light receptors

pigments such as chropyll which absorp light energy

different pigments will take in different amount of light energy

What happens to Wavelengths that are not absorbed?

the light wavelengths are reflected *bounce back or transmitted moves through thylakoid (doesnt contribute much to energy)

(depending on the pigment)

Why do we see chlroplasts as green

because we are seeing chrophyll green pigment reflected by unabsourbed light (bounced back)

the other pigments contribute more to photosynthesis than green

Absorption spectrum

graph that plots absorption versus wavelength

Absorption Spectrum: chlorphyll A B

chlorophyll A chlorophyll B absorb light with slower/longer wavelengths.

their crests peak at blue/violet area and drop around yellow/green where they reflect light

they are more absorped in shorter wavelengths (orange red)

Absoroption spectrum: carotenoids

carotenoids have an orange pigment

absorped in blue/violet region (longer wavelength) most reflect red, orange, yellow (faster/shorter wavelengths)

Action spectrum

a graph plotting the rate of photosynthesis vs wavelength

(wavelength of the plant vs how much oxygen produced)

Action spectrum

plants produce more oxygen (more photosynthesis occurs) at violet blue and red wavelengths

which correlates with the absorption spectrum

Correlation between light absoprtion spectrum and acton spectrum

the correlation shows there would not be photosynthesis without light absoprtion

when theres photosynrhsis theres light being absorped

Define pigments

molecules which have colour, and absorp light energy

What are the 2 main types of pigment in photosynthesis and explain their uses

Chlorophyll is the main pigment used in photosynthesis (it is green)

Caretenoid is another pigment used (it is orange-red) called an acessory pigment

they are good for letting a wider range of light be absorped

and they stop the Photosynthetic ETC from getting damaged by ultra violet light

What is meant by Excitation of Chlorophyll

when the chlrorophyll esp type A absorpes light tis electrons jump to further electron shells, increasing energy of the atom,

making it unstable. So it returns and loses energy releasing,emitting it as light or heat

What can happen to Chlorophyll when excited in biological system

1. Florescence: energy is emitted as light

2. Heat: energy is emitted as heat

3. Resonance: the electron excites the neighboring electrons of other chlorophylls

4. Redox reactions: the electron is donated to a electron acceptor

Define Floresence

electron in chlrorophyll energy is emitted as light

Define Resosnance

3. the electron excites the neighboring electrons of other chlorophylls

aka energy transfer:

(electrons are not jumping molecules just sending energy to other chlrorophyll’s electrons)

Explain redox reaction when electrons excited

the electron transfers to an electron acceptor

(jumping from chloropyl molecule to acceptor to ETC)

Photosystems

A large protein complex in the thykaloid membrane

consists of different pigments all working together

200-300 chlorophyll molecul es and accessory pigment molecules

its core is called the reaction center complex

has antenna chlorophyll

Reaction center complex

the center of the photosystem/ the site where electrons are moved to electron acceptors

it hold special excitable chlorophyll molecules and a special pair of chlorophyll which can transfer high energy electrons to primary electron acceptor

uses light energy to do so (solar power)

note it is the first step of light reactions

this pair of chlorophyll will get oxidized (lose)

and the acceptor will get reduced (gain)

Chlorophyll antenna

chlorophylls which stays around reaction center to absorb light and funnel electrons (energy) into reaction center so they can be transfered to acceptors

What are the 2 Photosystems

Photosystem II (PS II)

Photosystem II (PS II)

this photosystem goes 1st

best at absorbing wavelengths of 680 nm

because its reaction center has a pair of chlorophyls called P680 which gets electron

to electron acceptor called Pheophylitin that moves it to a ETC where it powers proton motive force and thus makes ATP energy

Photosystem I (PSI)

this photosystem goes 2nd

its best at absorbing wavelengths of 700nm

its chlorophyll pair in the reaction center is called

P700

electrons of 2 photons go to reacton center after P700 transfers 2e- it to acceptor: Ferradoxin

energy makes NADP + H = NADPH

and it gets transfered to NADPH

which then bring it to ETC, then proton motive force, then ATP

photosystem names comes from when they were discovered not order energy flows in

so order of their function is the opposite of their name

Differentiate between the oxidized and reduced forms of photosystems chlorophyll pairs and Electron transport carriers

P680 is the reduced form (gained electron - so less +)

P680+ is the oxidized form (lost electrons so more +)

P700 is the reduced form (gained electron - so less +)

P700+ is the oxidized form (lost electrons so more +)

NADP+ is oxidized

NADPH is reduced because gain electrons (since NADP+ + H+) = its less +

What are the 2 routes electrons can flow in (during light reactions)

Linear electron flow

Cyclic electron flow

Linear electron flow

the main light reaction pathway it uses both Photosystem 1 and 2

it produces NADPH and ATP using light energy

Cyclic Electron Flow

Light reaction pathway that only uses Photosystem I

it only produces ATP

this leads to too much ATP

Why is Clyclic electron flow useful for Calvin Cycle

this pathway is good for Calvin cycle since it

needs more ATP (becuase it makes up for underproduction of ATP and overproduction of NADPH in calvin cycle)

Pathway order in LINEAR Electron Flow

1. photon hits antenna chlorophyll’s pigment

electrons pass their energy across chlrorphyll molecules using resonance

until electrons are passed to special pair of chloroplasts P680 in reaction center

2. P680 oxidizes: P680+ then transfered to primary electron acceptor

   Primary electron acceptor (is reduced)

3. for P680 to continue it needs electron back

so Photolysis: H2O is spilt, P680+ gets 2 e-

= {P680 again)

4. takes electrons to ETC

5. Photophosphorylation: (proton motive force) by electrons produces ATP

then electrons go to

6. Photosystem 1:

   as electrons go to PSI, light will hit PSI, and all this energy exicites PSI, electrons move through resonance to…

   P700+ (chlorophyll pair)

   P700+ give up electrons oxidizing to P700

   electrons from primary acceptor in PSII go to reduce P700 back to P700+

P700+ moves more electrons to Electron acceptor of PSI

7. Excited electrons go to ETC (no ATP it makes an enzyme: NADP Redutase)

   which puts electrons to NADPH), some electrons used to reduce NADP + Pi = NADPH

for reducton needs 2 e-, also this process removes H+ from stroma

8. NADPH made

   NADPH and ATP used for Calvin Cycle

Explain Photophosphorylation

occurs in the thylakoid membranes during photosynthesis. In this process, light energy is used to drive electrons through the photosynthetic electron transport chain (ETC).

• The thylakoid lumen becomes more acidic (higher concentration of H⁺ ions), while the stroma becomes more basic (lower concentration of H⁺ ions) due to the movement of protons.

• Electrons are excited by light in Photosystem II (PSII) and move down the ETC, passing through various complexes (plastoquinone, cytochrome b6f complex, and plastocyanin) before reaching Photosystem I (PSI).

• The energy released by electrons as they move down the ETC is used to pump protons (H⁺) into the thylakoid lumen, creating a proton gradient.

• ATP synthase uses the proton gradient to drive the synthesis of ATP from ADP and inorganic phosphate (Pi) as protons flow back into the stroma.

This process is similar to oxidative phosphorylation in cellular respiration, where a proton gradient drives the production of ATP.

ETC structure in Photosynthesis

electrons along ETC power proton pumps H+ ions out into Thykaloid space, making a electrochemical gradient

which powers ATP synthesis

Photolysis: How is H2O spilt into 2 electrons: 2 H+ and ½ O2. what happens to parts

H2O is broken down into

two H+ + two e- + ½ O2

because

1 H = proton + e-

now O wants to fill valence shell and double bond with another O (thus ½ O2)

this allows…

the electrons replace the ones lost in special chloroplast pair (P680)

the H+ becomes used in the electrochemical gradient (thylakoid space)

the ½ of O2 pairs with another half and create an O (free)

Pathway order of Cyclic Electron Flow

Photosystem 1

Electron acceptor

ETC

ATP prooduced

Goes back to photosystem 1

Compare and Contrast Structure Chemiosmosis in Chloroplasts and Mitochondria

Chloroplasts:

Thylakoid space - Acidic H+

Stroma - Basic

electrons come from H2O spilt (going through chlorophyll)

Mitochondria:

Intermembrane space, (in Cristae) - Acidic

Mitochondrial Matrix - Basic

electrons come from glucose

Linear Electron Flow (Math)

Photosystem II

4 Photons

4 e- go to P680 to electron aceptor

P680+ need 4 e-

(2 H20 = 4 H+, 4 e-, O2)

now with 4 e- → P680

then rest (ETC, proton motive pump → H+ in thykaloid space → H+ in ATP synapse = ATP

Photosystem I

4 Photons

4 e- to P700 to electron aceptor

transfer becomes P700+

reducing back with 4 e- from PS!!

4 e- then used to make 2 NADPH (2 NADP+ + H+)

2 NADPH and ATP used to make sugar in calvin cycle next

O2 made released

3 processes that contribute to H+ proton gradient (explain)

1) H2O spilt during Photosystem II (H+ left is given to gradient)

2) Cytochrome of ETC using electron energy to move H+ across membrane (from stroma to thykaloid space) (creates a gradient that brings in more H+)

3) When H+ is removed from Stroma to make NADPH since it reduces H+, enabling gradient

Where are ATP and NADPH produced

In the stroma (not thykaloid space) (sticking out)

this is where the Calvin cycle is facing

Cyclic flow of electrons

Calvin Cycle Briefly define

process which converts CO2 into glucose (from smaller molecules) using ATP energy and NADPH from Light energy reaction. (anabolic)

CO2 enters the cycle leaves as G3P

this Anabolic cycle does not stop in its production of and needs _ to slow it down

Calvin Cycle’s 3 Phases

1. Fixation (CO2 → organic molecule)

2. Reduction (G3PA → G3P)

3. Regeneration (remake intimal molecule Ribulose Biphosphate)

Lay out steps of the Calvin Cycle (MATH)

5 carbon molecules 3× , 3 CO2 6x

= 15 + 18

3PGA 6x: combines electrons of ATP, NADPH to produce 3GP 6x

1 of 3GP leaves to make glucose

3 ATPs used in the calvin cycle

• 6 ATPs from Light Energy Processing

• 3 ATP

6 NADPH used in calvin cycle

Lay out steps of the Calvin Cycle

1. Ribulose Bisphosphate is combined with 3 carbons from CO2

2. this makes it unstable until it is broken down into 3 Phosphoglycerates 6x (3PGA) 6x

3. ATP (from light energy process) is used to break it into 3PGA into Glyceraldehyde phosphate (G3P) 6x

   aka 3 carbons to 1 phosphate x 6

4. lose 1 G3P to make glucose and now G3P is 5x left

5. G3P 5x loses 3 Pi groups

and are added back using 3 ATP

6. now 3 RuB again cycle continues

Fixation (in depth)

1. The enzyme: ribulose catalyzes a reaction that combines Ribulose Biphosphate (5 carbon sugar) and CO2

2. Produces an unstable intermidate with 6 C and 2 Pi groups which is quickly broken down into a 3 C molecule (3-PGA)

3 RuBp + 3 CO2 → 6 3PGA

needs 3 Carbons to produce 1 G3P to make sugar

Reduction (in depth)

1. 6 3GPA is broken into 6 G3P using 2 processes

ATP is used to phosphorelate 3GPA (add phosphate groups)

NADPH moves 2 high energy e- to phosphorylated compound

6 3GPA + 6 ATP + 6 NADPH = 6 3GP

1 3GP is taken out and used to make sugar

(hald glucose) leaving 5 3GP

Regeneration (In depth)

Is 12 of 15 steps in the Calvin Cycle

5 3GP going in comes out as 3 RuBP

5 3GP + 3 ATP = 3 RuBP

For Net Synthesis of G3P 1 how many CO2 must be fixed

3

How many CO2 molecules must be fizzed to make a glucose molecule?

if 3 CO2 = ½ glucose

6 CO2 = 1 glucose

Why do we not see changein phosphate groups after ATP is used during Reduction phase? no need

Rubisco

ATP relation to Pi (removed vs added)