BPSC 104 Class 10

Where does photosynthesis primarily occur

• Primarily in leaves (but any tissue that is green)

  • Within the chloroplasts

• Chloroplast structure and function are important for photosynthesis

Chloroplast structure (be familiar)

• Found in shoot system tissues

• Site of photosynthesis

• Contain chlroophyll, a green pigment

• Complex internal structure containing:

  • Thylakoids

  • Lumen

  • Grana

  • Stroma

  • Stroma thylakoids

chocolate part is the thylakoid membrane

mint is the lumen

Thylakoids (part of chloroplast internal structure)

internal membranes in which pigment molecules are embedded

Lumen (part of chloroplast internal structure)

liquid-filled cavity inside thylakoid

Grana (part of chloroplast internal structure)

stacks of thylakoids

Stroma (part of chloroplast internal structure)

fluid surrounding the thylakoids

Stroma thylakoids (part of chloroplast internal structure)

thylakoids that connect grana

Chloroplasts may also contain stored ____

starch

During:

Daytime: when a lot of glucose is being forme,d excess may be stored as starch in the chloroplast

Night: the starch will be broken down into sucrose

• Sugar is delivered through the phloem to other parts of the plant

• This supplies energy for metabolic processes

Light energy powers ___

photosynthesis

• Visible light makes up a small part of the electromagnetic spectrum

• Within the visible light spectrum

  • Violet has the shortest wavelength and highest energy

  • Red has the longest wavelength and lowest energy

Chromophore

Pigment + Proteins (combination of the two that allow for absorbtion)

Light energy must be __ to be useful for photosynthesis

Absorbed:

• Pigments

• Absorbtion spectrum

Pigments (related to light energy)

molecules that absorb light

• black appearance = if a pigment absorbs all wavelengths of visible light

• most pigments = absorb certain wavelength and reflect others

• Reflected - color that we see

Absorbtion spectrum

• the light absorption pattern of a pigment

• linked to action spectrum

Chlorophyll (absorbs and reflects ___)

• Absorbs violet and red light

• Reflects green light (why chlorophyll appears green to us)

• The action spectrum

• The absorption spectrum

The action spectrum (of photosynthesis)

shows the rate of photosynthesis

• similar to absorption spectrum of chlorophyll a and the action spectrum for photosynthesis (therefore linked)

Pigments involved in photosynthesis

• Chlorophyll a

• Chlorophyll b

• Cartenoids

Chlorophyll a (pigment in photosynthesis)

Essential for photosynthesis in plants

Chlorophyll b (pigment in photosynthesis)

Accessory (antenna) pigment

• not directly involved in photosynthesis

• Broadens the range of usable wavelengths

Cartenoids (pigment in photosynthesis)

• Accessory (antenna) pigments, broadens the range of usable wavelengths

• Protects chlorophyll from damage from light

Pigments absorbing light (electrons boosted to higher energy level, excited state)

Accessory (antennae) pigments

• expand wavelengths absorbed

• protect leaf from excess energy

• Transfer energy to reaction center - resonance energy transfer

  Reaction center chlorophyl a

  • Unique position

  • Initiates photosynthesis

  • Loses an electron to an acceptor

    think funnel

    funnel photons of light down to the reaction center

    change of form of the energy

Photosynthesis (2 sets of reactions)

1. Light reactions

   1. Require light energy

   2. Energy transduction reactions

2. Carbon fixation reactions

   1. Carbon dioxide in converted into organic compounds

   2. Also called the Calvin Cycle (think carbon)

(fixation means to take something inorganic and change it into CO2 and change it to sugar)

Photosynthesis reactions occur in different parts of the chloroplast

• Light reactions occur in thylakoid membranes

• Carbon fixation reactions occur in the stoma

photo = with light

lysis = to split

Light reactions occur in ___

• Thylakoid membrane

• Pigment molecules embedded in the thylakoid membranes absorb light energy

• Water in lumen (interior) of the thylakoid is split into oxygen gas and hydrogen atoms (electrons and protons

Carbon fixation reactions occur in the ___

Stoma

• sugar is produced

Photosynthesis (overview)

Light reactions

• Requires light energy

  • Split H₂O (PHotolysis)

  • Release O₂

  • Reduce NADP⁺

  • Generate ATP from ADP

  • Phosphorylation

Carbon fixation reactions

• Uses ATP and NADPH to convert CO2 to sugar

Two photosystems of light reactions

Photosystem - pigments embedded in thylakoid membrane are organized into discrete units called ___

Photosystems (in depth)

• 250-400 pigment molecules and two closely linked parts

  • Antennae Complex

  • Reaction center

• Pigments in antennae comp:

  • gather light energy and funnel it to the reaction center

• Proteins and chlorophyll a convert solar energy to chemical energy

Photosystems I and II are linked together by ___

an electron transport chain

Photosystem - numbered by order of discovery, not functional order

(not going to ask intermediate electron receptors in ps1

should know:

cytochrome b f complex connects ps2 to ps1

NADP+ gets reduced to NADPH - calvin benson cycle

Process:

electrons are being energized, dumping protons in the lumen, exciting the elecgtrons from ps2, lyssi in to nadp+ and reducing?

Photosystem I reaction center is P₆₈₀ (special pair)

Special pair - special pair of chlorophyll molecules in the reaction center is known as P680 (pigment 680 is the optimal absorbtion peak in nanometers)

Photosystem II reaction center is P₇₀₀ (special pair)

Special pair - special pair of chlorophyll molecules in the reaction center is known as P700 (pigment 700 is the optimal absorption peak in nanometers)

Photosystem I and II generally work ____

together simultaneously and continuously

Photosystem I and II are __ separated

Spatially separated in the thylakoid membranes

Structures of photosystems and other complexes in the photosynthetic apparatus

In photosystem II, water is ___ releasing __

oxidized; oxygen

• Light energy is absorbed by chlorophyll a of P₆₈₀ in reaction center

• Photosystem II has the unique ability to extract electrons from water - water photolysis

• Energized electrons are transferred to the cytochrome b6/f complex

• Protons are released into the thylakoid lumen

• Proton gradient - produced by protons released from water

  • needed for generation of ATP-

What complex links Photosystem I and Photosystem II

Cytochrome b6/f complex

How can photosystem I work independently of photosystem II

• Cyclic electron flow

Why have 2 system:

• The calvin cycle requires 3 ATP for every 2 NADPH

  • Noncyclic electron flow produces5 ATP and 6 NADPH

  • Cyclic electron flow produces additional ATP

The Calvin Cycle

• Present in all photosythetic plants

• Occurs in 3 stages

• 1st reaction catalyzed by RUBP carboxylase oxygenase = Rubisco

Rubisco

• most abundant protein on earth

• one of largest, most complex enzymes

• Balanced equation of photosynthesis

Clavin Cycle

need to know fixation step

need to know 3 PGA (1st detectable product, 3 carbon molecule)

pga gets reduced to pgal (6 carbon)

stage 3: extra 3 ATP

3 molecules of pgal is used to make the final part?

• count the carbons, understand why we need cyclic reaction/light rxn to produce the additional atp needed in reaction step (good test q)

why do we need to do three times:

• takes 3 molecules of co2 to make 1 pgal, which is what we use to make our sugars

why cyclic: requires more nadph than nadvadp?)