Photosynthesis Mechanisms

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Questions and Answers

Which part of chlorophyll is responsible for anchoring it within the membrane?

Reaction Center

Magnesium Ion

Hydrocarbon Tail (correct)

Porphyrin Ring Structure

What is the primary function of the photosystem's light harvesting complexes?

To release electrons

To generate ATP

To fix carbon dioxide

To collect light energy (correct)

Which of the following outcomes occurs when an excited electron returns to its ground state, releasing energy?

Fluorescence (correct)

Cyclic Flow

Resonance

Redox

What main role do ATP and NADPH play in the Calvin Cycle?

Energy source for carbon fixation Signup and view all the answers

Which of the following is characteristic of cyclic electron flow in photosystems?

It primarily produces ATP Signup and view all the answers

What enzyme is primarily responsible for carbon fixation in the Calvin Cycle?

RuBisCO Signup and view all the answers

Which factor can inhibit the efficiency of the Calvin Cycle during periods of high light incidence?

Low temperatures Signup and view all the answers

Which component of the photosystem consists of two special chlorophyll-A molecules?

Reaction Center Signup and view all the answers

What role do enzymes play in energy reactions?

They stabilize the transition state and reduce activation energy. Signup and view all the answers

What is the main difference between exergonic and endergonic reactions?

Exergonic reactions release energy while endergonic reactions absorb energy. Signup and view all the answers

What is one of the main products formed during glycolysis?

NADH Signup and view all the answers

During the Citric Acid Cycle, which of the following is produced?

Carbon Dioxide Signup and view all the answers

What does the light reaction of photosynthesis generate?

ATP and NADPH Signup and view all the answers

Which process is an endergonic reaction?

Photosynthesis Signup and view all the answers

Why is feedback inhibition important in metabolic pathways like glycolysis?

It helps maintain homeostasis by regulating metabolic activity. Signup and view all the answers

What is the primary function of ATP in cellular processes?

To serve as the main energy currency of the cell. Signup and view all the answers

What is the thylakoid space or lumen's role in photosynthesis?

It accumulates protons to create a gradient for ATP synthesis. Signup and view all the answers

What is the significance of measuring the change in free energy (ΔG) in chemical reactions?

It indicates whether the reaction is spontaneous or requires energy. Signup and view all the answers

Study Notes

Chlorophyll Structure

Composed of a long hydrocarbon tail and a porphyrin ring structure.
The porphyrin ring structure is similar to heme but contains a magnesium ion at its core.

Chlorophyll Excitation

Excited electrons have three possible outcomes:
- Fluorescence: electron returns to ground state with light and heat loss.
- Resonance: energy is transferred to other pigments and the reaction center.
- Redox: the reaction center loses an electron to an electron transport chain.

Photosystems

Photosystems have two parts:
- Light Harvesting Complexes: Collect light energy and transmit it through resonance to the reaction center.
- Reaction Center: Contains two special chlorophyll-A molecules centered around a reaction center.

Energy Flow Through Photosystems

Light reaction steps:
- Light energy is transferred to the PS-II reaction center.
- Energy is transferred through an electron transport chain (ETC), which pumps H+ ions to generate ATP.
- PS-I receives the electron.
- PS-I receives a second photon, and energy is transferred to reduce NADP+.

Cyclic Electron Flow

Electrons can flow backwards from PS-I to form a cycle instead of forward to NADP+.
This cycle generates ATP but not NADPH.
PS-I can switch between both paths.

Overview of the Light Reaction

Occurs in thylakoid membranes.
Enzymes are located with specific sides facing the thylakoid bi-layer.
Protons are pumped into the lumen, a small volume with a greater gradient.
ATP and NADPH are produced in the stroma.

Calvin Cycle ("Dark" Reaction)

Occurs in the stroma.
Divided into three main parts:
- Carbon Fixing by Rubisco.
- Reduction Phase.
- Regeneration of the starting molecule.
Occurs simultaneously with the light reaction.

Plant Response to Excess Light

Plants may have excess light but low temperatures.
Calving cycle may be slowed by temperature.

Cellular Energy Review

Enzymes lower activation energy by binding to and stabilizing the transition state.
Chymotrypsin binds to a substrate polypeptide at phenylalanine residues.
Other amino acids work together to push and pull electrons apart, breaking the peptide bond.

Cellular Energy Review II

Chemical reactions are categorized as exergonic (release energy) or endergonic (absorb energy).
Change in free energy (ΔG) determines if a reaction is exergonic or endergonic.
ΔG is related to heat released or absorbed (ΔH) and the change in entropy (ΔS).
Entropy is a representation of randomness or disorder in a system.

Cellular Energy Review III

Examples of entropy in biological systems:
- Glycogen, a structured molecule, burns to create smaller molecules and release heat (thermal energy).
- Thermal energy is the most unstructured form of energy.

Cellular Energy Review IV

Redox chemistry describes the movement of electrons from one molecule to another.
LEO (Lose Electrons = Oxidized)
GER (Gain Electrons = Reduced)

Cellular Energy Review V

Glucose breakdown occurs in three parts:
- Glycolysis breaks down a 6-carbon sugar into two 3-carbon intermediates (2 pyruvates, 2 NADH, net 2 ATP).
- Glycolysis consists of an investment phase and an energy recovery phase, involving phosphorylation of glucose followed by breaking it down into pyruvate.
- Phosphofructokinase, an enzyme involved in glycolysis, is highly regulated.

Cellular Energy Review VI

Citric acid cycle oxidizes glucose fully to CO2.
Linked to glycolysis by pyruvate oxidation.
Produces lots of NADH, 2 FADH2, and 2 ATP.
Phosphofructokinase is regulated by feedback.
The electron transport system is located on the inner membrane of the mitochondria.
The system converts energy from NADH to a proton gradient which drives ATP synthase to produce ATP.

Photosynthesis - Going Up the Energy Hill

Photosynthesis transfers energy from the sun to cellular molecules.
It is an endergonic process, storing energy in chemical bonds and reducing entropy.
This requires a large energy source, like the sun.

Photosynthesis Review

Occurs in chloroplasts of eukaryotes.
Found mainly in the mesophyll layer of leaves.
Chloroplasts contain specialized structures:
- Thylakoids are stacked in granum, a chloroplast "cytosol."
- Stroma is the chloroplast "cytosol."
- The thylakoid space (lumen) is the interior of the thylakoids.

Photosynthesis in Two Parts

Photosynthesis is divided into two parts:
- The light reaction captures light energy and converts it to chemical energy (ATP and NADPH).
- The dark reaction, which is not actually dark, converts redox chemistry to covalent bonds.

Pigments and Light Absorption

Electromagnetic radiation covers a wide spectrum of wavelengths and energies.
Only a narrow band of wavelengths is visible to humans.
Plants are selective in the wavelengths they absorb, which determines the energy they absorb..

Absorption Spectra

Chloroplasts contain multiple light-absorbing pigments, each with wavelengths of maximum absorption.
Few pigments absorb strongly in green light, which is why plants appear green.

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Description

This quiz explores the structure and function of chlorophyll in photosynthesis, covering excitation of electrons and the roles of photosystems. It delves into the light reactions and energy transfer processes involved in photosynthesis.