CELL BIOLOGY - CLUTCH CH. 12 - PHOTOSYNTHESISlightcat-files.s3.amazonaws.com/packets/admin_cell...5. A light photon enters into the light harvesting center of photosystem I and hits

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CELL BIOLOGY - CLUTCH

CH. 12 - PHOTOSYNTHESIS

CONCEPT: OVERVIEW OF PHOTOSYNTHESIS

● Photosynthesis is the process of converting ____________________ energy into ATP and sugars □ The light dependent reactions create ATP and NADPH

- Undergoes photophosphorylation – uses an electron transport chain to drive ATP synthesis

- Similar to oxidative phosphorylation (but the final electron donation is not given to O2)

- Light energy is absorbed by the photosynthetic pigment chlorophyll which is used to drive ATP synthesis

- Photoreduction is the process through which the final electron is donated to NADP+ creating NADPH

□ The light independent (carbon fixation) reactions use ATP and NADPH to create _______________ from CO2

- Product is a 3 carbon sugar, which is the transformed into larger sugars

- To create glucose uses: 18 ATP, 12 NADPH and converts 12 H2O to O2

EXAMPLE: An overview of photosynthesis



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PRACTICE:

1. Which of the following is not a part of photosynthesis? a. Light dependent reactions b. Photoreduction c. Light independent reactions d. Photocycle

2. The 3-carbon sugar created during photosynthesis is generated in which of the following processes? a. Light independent reaction b. Photophosphorylation c. Photoreduction d. Light dependent reaction



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CONCEPT: CHLOROPLAST

● The chloroplast has a distinctive structure and has it’s own circular genome □ It is surrounded by two ___________________________________

- Outer membrane and inner membrane

- Like the mitochondria, it also contains an intermembrane space

□ The stroma is the internal space of the chloroplast

□ The stroma is filled with thylakoids which are flat discs that are the sites of photosynthesis

- Grana are stacks of thylakoids

- Thylakoids can be connected together forming a single large compartment

EXAMPLE: Model of chloroplast structure

● A chloroplast is one member of the plastid family of plant ____________________ □ All plastids develop from pro-plastids which are undifferentiated organelles present in rapidly dividing cells

□ There are many types of plastids other than the chloroplast

- Chromoplasts: Lack chlorophyll but contain carotenoids (a light absorbing plant pigment)

- Amlyoplasts: Store starch



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EXAMPLE: Types of plastids

PRACTICE:

1. Match the following term with it’s definition a. Stroma _________________ b. Thylakoids ________________ c. Grana ________________

i. Stacks of thylakoids ii. Internal space of the chloroplast iii. Flat discs that are the sites of photosynthesis



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2. Which of the following plastids lacks chlorophyll but contains carotenoids? a. Chloroplast b. Chromoplast c. Amlyoplast



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CONCEPT: LIGHT DEPENDENT REACTIONS

Photosystem Structure

● Photosystems are two protein ___________________________ where the light-dependent reactions take place □ Photosystems are embedded in the thylakoid membrane

□ The light harvesting center (antenna complex) absorbs the light energy and turns it into electrical energy

- Photoexcitation is when light energy excites an electron

□ The reaction center accepts the electrical energy and transfers it to chemical energy

□ The photosynthetic pigment chlorophyll accepts light energy in the chloroplast

- Contains a light-absorbing ring (porphyrin ring) with easily __________________________ electrons

- Once electrons are excited they want to release the energy – can be converted to different energy forms

□ Electrons travel between photosystems and other protein complex through electron carriers

EXAMPLE: Overview of a photosystem

Light

PrimaryAcceptor

e-

LightHarvestingComplex

ReactionCenter

Chlorophyll



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Light Dependent Reaction Steps

1. A light photon enters into the light harvesting center of photosystem II and hits a chlorophyll molecule 2. An electron in the chlorophyll pigment is excited, and that energy bounces around between many chlorophylls

- Called resonance energy transfer when energy transfers between pigment molecules 3. Eventually this energy is transferred to a special pair of electrons (P680) and one electron is transferred to

plastoquinoine (becomes reduced to plastoquinol) - The donated electron is replaced by splitting two H2O (phoyolysis) molecules to form O2 - Primary electron acceptor is the molecule that accepts electrons from the reaction center

EXAMPLE: First three light dependent steps in Photosystem II

4. Plastoquinol transfers the electrons to an electron transport system - Cytochrom B6F complex uses the energy from the electron to pump H+ into thylakoid space - The electron is transferred to the electron carrier plastocyanin

EXAMPLE: Step 4 of light-dependent reactions shows electrons flow down the electron transport system

Light

PrimaryAcceptor

e-

H20

e-e-

O2 + 2H+

1

2

3

Light

PrimaryAcceptor

e-

H20

e-e-

O2 + 2H+

1

2

3CytochromeComplex

Pq

Pc

4



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5. A light photon enters into the light harvesting center of photosystem I and hits a chlorophyll molecule 6. An electron in the chlorophyll pigment is excited, and that energy bounces around between many chlorophylls 7. This energy is transferred to a special pair of electrons (P700) and one electron is transferred to ferrodoxin

- The donated electron is replaced by the electron from photosystem II

EXAMPLE: Steps 5-7 of the light-dependent reactions involving photosystem I

8. Ferrodoxin carries the electron to NADP+ reductase to form NADPH in the stoma (used in the light independent reaction)

EXAMPLE: NADP+ reductase forming NADPH in stroma

9. The H+ gradient is funneled through ATP synthase to form ATP

Light

PrimaryAcceptor

e-

5

7

CytochromeComplex

Pc

4

Fd

6

e-

NADP+

reductase

Fd8

NADPH+H+



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EXAMPLE: Overview of photosynthesis

Cyclic Light Dependent Reactions (Cyclic Photophosphorylation)

● In cyclic light dependent reactions the process _______________________ ATP but not NADPH □ Photosystem II works the same as in the linear pathways

□ Photosystem I works in reverse and transports an electron to the electron transport center

- Creates more ATP instead of NADPH

EXAMPLE: Cyclic light dependent reactions

Ph

ATP

PrimaryAcceptor

e-CytochromeComplex

Pc

Fd

e-

Light

PhotosystemI



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PRACTICE: 1. Which part of the photosystem is responsible for accepting a light photon?

a. Chlorophyll b. Reaction Center c. Primary Acceptor d. Cytochrome

2. Oxygen is formed by a reaction occurring where? a. Photosystem I b. Photosystem II c. Cytochrome B6F complex d. NADP+ reductase



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3. Where in the chloroplast is NADPH synthesized? a. Thylakoid membrane b. Grana c. Thylaoid lumen d. Stroma

4. Cyclic photophosphorylation is different than photosynthesis in what way? a. Photosystem II reverses and generates CO2 b. Photosystem I reverses and transports and electron to the electron transport center c. The entire process generates more NADPH than ATP d. Photolysis doesn’t occur



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CONCEPT: LIGHT INDEPENDENT REACTIONS (CALVIN CYCLE)

Carbon Fixation (Calvin Cycle)

● Carbon fixation uses ATP and NADPH to fix carbon from CO2 in order to create sugar in C3 plants (majority of plants) □ CO2 is attached to ribulose 1,5 bisphosphate (5 carbon sugar)

- Creates two 3-phosphoglycerates (two three carbon sugars) (Step 1)

- Reduced to form glyceraldehyde 3-phosphate (Step 2)

- Releases O2 as __________________________ product

□ RUBISCO (ribulose bisphophate carboxylase) catalyzes carbon fixation

- Works slowly – so plants need a lot of it (most abundant protein on earth)

□ ATP and NADPH are used to generate more ribulose 1,5 bisphosphate (Step 3)

□ 3 CO2 makes one glyceraldehyde 3-phosphate ______________________________ 9 ATP and 6 NADPH

EXAMPLE: Overview of the Calvin Cycle



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● Once the glyceraldehyde 3-phosphate is created it can be used in a number of ways □ Converted into starch

□ Used in glycolysis to create ATP

□ Made into sucrose or other sugars

Carbon Fixation in C4 and CAM Plants

● Carbon fixation that occurs in C3 plants (most plants) is not efficient in ___________________ environments □ Stroma (pores) in the plant leaves __________________ when its hot to prevent loss of water

- Unfortunately, this prevents gas exchange (entering of CO2 into the plant) causing build up of O2

□ RUBISCO can bind to CO2 or O2 – each produces a different product

- CO2: Produces glyceraldehyde 3-phosphate – photosynthesis

- O2: Produces phosphoglycolate – photorespiration (big waste of plant energy)

□ ATP and NADPH are used to generate more ribulose 1,5 bisphosphate (Step 3)

EXAMPLE: Photorespiration in plant cells



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● C4 plants (corn, certain types of grasses) handle O2 build up by physically separating carbon fixation reactions □ Mesophyll cells – light-dependent reaction and fixation of CO2 to malate molecule

□ Bundle sheath cells – CO2 is released from malate and continues along the C3 Calvin cycle pathway

- RUBISCO is isolated from accumulation of O2 to prevent wasting energy on photorespiration

EXAMPLE: C4 photosynthesis pathway

● CAM plants (cacti) handle O2 build up by differentially controlling CO2 at different points in the day □ At night, when it is cool the stroma is open

- CO2 is fixed using RUBISCO and the C3 pathways

□ In daytime, when it is hot the stroma is closed

- CO2 is fixed to malate and stored in a vacuole

- When the stroma closes CO2-malates leaves the vacuole, is released and fixed by RUBISCO

EXAMPLE: Transition between day and night in CAM plants



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PRACTICE: 1. What is the function of RUBISCO in carbon fixation?

a. Catalyzes carbon fixation b. Convert carbon into starch c. Promoting gas exchange d. Opening and closing the stroma

2. Why does the Calvin cycle require light? a. Because light forms ATP through the light dependent reactions b. Because light forms NADPH through the light dependent reactions c. Because light forms CO2 through the light dependent reactions d. Because light forms O2 through the light dependent reactions



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3. How many molecules of CO2 are required to create one glyceraldehyde 3-phosphate? a. 1 b. 2 c. 3 d. 4

4. True or False: RUBISCO only binds to CO2. a. True b. False



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5. Which of the following plants handles O2 buildup by physically separating RUBISCO from O2? a. C3 Plants b. C4 Plants c. CAM Plants



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CELL BIOLOGY - CLUTCH CH. 12 - PHOTOSYNTHESISlightcat-files.s3.amazonaws.com/packets/admin_cell...5. A light photon enters into the light harvesting center of photosystem I and hits