Bio346 week 2 Photosynthesis and Thylakoids reactions

How to dissect biology

Recall everything is a process, state, or thing. This is a principle you should use when looking at plants

Project

Go to google scholar or new articles about plants. Ask about later

How is energy held in an organism

Chemical Bonds + Electrochemical Gradients

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Chemical bonds releases most of energy as enthalpy and some entropy ask

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Electrical Gradients relation to entropy(maintained perhaps)

Combine these categories of energy

Enthalpy(Heat and Loss)

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Entropy(Disorder)

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Free Energy(Total amount of \n energy to do work)

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Free Energy Delta G, represents the amount of work a reaction can do

Predicts whether a reaction will occur

\- Delta G = spontaneous, free energy released to do work (exergonic)

reaction is energetically favorable

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\+ Delta G = non-spontaneous, free energy consumed

(endergonic)

reaction is energetically unfavorable

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When you talk about just the release of heat, then a reaction is called exothermic or endothermic

Energy is constantly needed in the cell

Mitosis

Exocytosis

Cell Wall biosynthesis

Ion Uptake/membrane homeostasis

Membrane synthesis

Gene expression

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Organisms require consistent energy input to avoid heading toward equilibrium (=Death!)

Green plants photosynthesize(synthesize sugars or other substances by means of photosynthesis)

The leaf is the primary photosynthetic machine

What is photosynthesis

a chemical process through which plants, some bacteria and algae, produce carbohydrates and oxygen from carbon dioxide and water, using light as a source of energy.

There is potential energy in chemical bonds

A molecule that gains high energy electron/s is said to be ‘reduced’ And contains more energy

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In photosynthesis the energy from light is used to ‘reduce’ the Carbon in CO2 to C6H12O

Photosynthesis can be divided into two phases

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Light

The shorter the wavelength - the more energy

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Violent on the left has the violent

Light interactions with matter

Plants eat light

Light absorbed for Photosynthesis

Red and Blue are absorbed

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Some violent and orange is absorbed

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Green and some yellow reflected is reflected and not absorbed

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The plant appears green because green light is reflected instead of absorbed.

Spectrophotometry

A spectrophotometer measures the amount of light that is absorbed by a sample at a given wavelength.

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Illuminate pigment with specific wavelengths

Measure absorbance

Repeat with different wavelengths

Plot absorbance vs. wavelength

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Each specific pigment has a spectrographic ‘fingerprint’

What light is used for photosynthesis?

Only a small amount of the wavelengths of electromagnetic radiation that hit earth are absorbed in photosynthesis

Common pigments of plants

Pigment means a colored compound

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Pigment are compound that absorb light

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1. Chlorophyll(a and b)
2. Carotenoids and Xanthophylls(carrots)
3. Phycobillins(in algae)

Chlorophylls

Large chlorophylls ring

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A glove or mit to absorb the light

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Chlorophyll a is the primary pigment inphotosynthesis

The first action spectum

places that had more photosynthesis produce more oxygen

Absorption vs action spectrum

Since both spectrums match this proves Chlorophyll is the primary pigment that feeds photosynthesis

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* An absorption spectrum shows all the light typically absorbed by a leaf. An action spectrum, meanwhile, shows all the light that is actually used for photosynthesis. The similarity of the action spectrum of photosynthesis and the absorption spectrum of chlorophyll tells us that chlorophyll is the most important pigments in the process.

Carotenoid also absorb light used in Photosynthesis

A. Carotenes

Orange to red-orange

Extremely hydrophobic (non-polar)

Functions: Antenna pigments

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B. Xanthophylls

Yellow

Hydroxylated (contain oxygen)

Moderately hydrophobic

Functions: Antenna pigments

Photoprotection

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The role of the antenna pigments is to collect light energy from the sun and transfer it to reaction centers.

Absorption of light by plant pigments

The total absorbance for the plant is the sum of the absorbances of all the pigments in the plant

Chloroplast structure

Leaf Cells

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Photosynthetic Pigments (Chlorophyll etc.) and Photosystems are located in the thylakoid membranes inside the chloroplast

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remember stroma

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thylakoid membrane should not be green they should be…

Chlorophyll Is anchored in the thylakoid membrane in Antenna Complexes

They can move laterally across the membrane

Antenna Complexes funnel light to the reaction center

Ultimately Chlorophyll a Passes on the energy to a Photosystem

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Photosystem convert the energy by passing it to other molecules as excited electrons

Chlorophyll Absorption of light

Chlorophyll - absorbs light in blue and red, radiates some energy as heat, and then releases the rest in a consistent “bite sized amount” with the same energy level as in red feeding the energy into photosynthetic reactions

If uncoupled chlorophyll will fluoresce red when exposed to blue or red light

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Absorbs blue= has to much energy; has to release

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Absorbs red= get bite sized energy

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Whatt happen with absorbed light

When light is absorbed by a molecule it moves an electron to a higher energy state

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Absorbed light energy can be:

radiated as heat

* re-emitted / fluoresced as light
* transferred to another molecule by resonance

used to reduce another compound (donates electrons)

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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.

Light harvesting

Energy transfer in the antenna complex is random but, because energy is lost during some of the transfers, it funnels the light to the reaction center(p680 here)

Ask

What is the point of this slide

Light harvesting

After the original light absorption the energy moves through the chlorophyll and carotenoid molecules in the Antenna Complex by Resonance transfer. Transfers occur as fast as femto seconds

Energy is transferred from antenna complexes to protein complexes in the membrane.

All cells have electron transport complexes in their membranes

Thylakoid reactions of Photosynthesis

There are TWO photosystems that receive energy from \n chlorophyll/antenna complexes - \n

Photosystem II, PS II or p680 \n Photosystem I, PS I or p700

The two photosystems act synergistically

Each Photosystem can absorb light to power photosynthesis but when both are activated they work synergistically - More then just the addition of the two parts

Energy + Electrons are required for photosynthesis

The chlorophyll a in the reaction center hands energy over to the Photosystem.

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The energy is carried in the photosystem as high energy electrons that are passed onto other molecules

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PS II takes electrons from water, H2O, to replenish the high energy electrons it releases.

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When electrons are taken from the water it leaves H+ ions and oxygen

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Oxygen is evolved as a ‘waste product’ of photosynthesis

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The purpose of this slide: That oxygen is a waste product of photosynthesis(thylakoid reaction). **Energy + Electrons are required**

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Oxygen becomes a free radical. Free radicals are bad because they are reactive and can cause cell damage.

Cellular energy review

Cells are constantly using energy to maintain organixation

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Reduced:

is gaining energy as high energy electrons

Energy in the cell \n Chemical Bonds

ATP is directly used to power enzymes but not safe to store in large quantities due to it reactivity

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Carbohydrates and lips contain lots of energy in their bonds but not directly used to power enzyme

The ATP cycle

atp adenosine triphosphate the primary energy carrier of life

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Cells maintain a constant level of ATP in the cytoplasm

The enzyme that makes (most) ATP is called ATP Synthase

There are versions of this ancient membrane bound molecular machine in all life - plants, animals (eukaryotes), Archaea and Bacteria.

Energy is Stored in Electrochemical gradients

A concentration gradient, where one side of a membrane has a high concentration of a molecule, is one of the ways a cell can store or convert energy (remember osmosis)

Biological Membranes

A concentration gradient, where one side of a membrane has a high concentration of a molecule, is one of the ways a cell can store (hold) energy High Potential energy!

Common Mechanism of ATP Synthesis

1. High Energy Electrons feed into an 2) Electron Transport Chain in the membrane which uses the power to create a 3) Hydrogen Ion gradient that flows back across the membrane to power 4) ATP synthesis

Energy Sources

Plants - Photosynthetic ATP Synthesis

Light provides the energy and electrons are taken from water, H2O. Oxygen is produced as a ‘waste’ by product

Electron Transport in Photosynthesis

Light energy enters the Electron Transport Chain in two places. Each energy entry point is called a Photosystem (or reaction center)

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Know what carries energy and know what is done in each step and where it gets the electrons from

Photosynthetic Electron Transport;Thylakoids reaction

Results:


1. H+ ions are created from water break down as well transport across the membrane into the thylakoid lumen. (creates a gradient that can do work!)
2. 2) Creates reduced NADPH (high energy)

\n Z scheme’energy diagram \n of Photosynthetic electron transport

Light increases the energy but each ‘hand off’ in the electron transportchain looses some energy

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After the second light entry the carriers are energized enough toreduce NADP+ to NADPH directl

Thylakoids reaction;Products of electron transport

1) Oxidize H2O to O2

2) Reduction of NADP+ to NADPH

3) Produce of NADP+ to NADPH

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H+ from 1) oxidizing H2O to O2 \n

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H+ transported to thylakoid Lumen by plastoquinone Q \n

H+ taken up by NADPH formation \n

Thylakoid reactions - summary

ATP synthesis is not part of electron transport. ATP synthesis is coupled to electron transport by the H+ gradient

Experiment to demonstrate that ATP is synthesized by Chemiosmosis

Scientists created an artificial gradient of H+ ions across the thylakoid membrane and were able to power ATP synthesis (light or dark)

Some Herbicides act to kill plants by blocking photosynthetic electron transport

DMCU blocks the transition

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Produces free radicals

Organization of thylakoid membranes

PSSII is concentrated in the grana stacks to helps make H+ gradient - less volume to fill means concentration increases with fewer H+ ions

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PSI and ATPase are concentrated in the stromal lamellae so products can diffuse away to be used

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Cytochrome and other carriers transport e- between photosystems