Photosynethisis - Lecture 7 Flashcards
What is photosynthesis
Plants only
Using light, responsible for almost all plants energy resources
6CO2 + 6H2O → C6H12O6 + 6O2
Where does photosynthesis happen and what are the 2 parts
In the chloroplast, this is an organelle that is found in plants and we can divide that into 2 parts
1- capturing light energy - this is a light reaction that produces ATP and NADPH, this is high energy and can take high energy electrons
2- Calvin cycle -this is where we take low energy ( CO2 ) into sugar molecules and we use ATP and NADH to do that, and in order to release that energy from sugar we use cellular respiration
Chloroplast structure
- 2 membranes, inner and outer
- thylakoid membrane, these are stacks of membrane for surface area to capture light energy
- storma - provides nutrients to the tissue or organ and removes waste and extra fluid, and this is also where carbon fixation occurs
- thylakoid space - help absorb sunlight in order for photosynthesis to occur
- intermembrane space
Explain light reaction
Photosystems capture light energy- these are proteins complexes that contain chlorophyll, these complexes are called photosystems, chlorophyll is a pigment that absorbs light, and due to the structure of the photosystem, the light energy absorbed by the chlorophyll results in movement of high energy electrons
What happens in the light reaction
The chlorophyll molecules and light energy comes in and gets absorbed by the chlorophyll molecules and then energy is transferred from one chlorophyll to another so energy is moving from in the photosystems until they reach the centre of the photosystems. And once the chlorophyll molecules are in the centre, the high energy electrons move away from the chlorophyll molecules due to the environment in the middle
In the light reaction where does the high energy electron move to
Through a photosynthetic electron transport chain
Explain the photosynthetic electron transport chain
Here’s a refined explanation of the photosynthetic electron transport chain:
Photosystem II (PSII), This is the first complex in the chain. Light energy is absorbed by chlorophyll, exciting electrons. Two high-energy electrons are then transferred to a series of proteins in the thylakoid membrane known as the electron transport chain (ETC) of PSII.
- Water Splitting: PSII also catalyzes the splitting of water molecules into oxygen, protons (H+), and electrons. This process, called photolysis, provides the electrons needed to replace those lost from chlorophyll.
- Electron Transport Chain (ETC): The high-energy electrons from PSII move through the ETC, losing energy as they are shuttled between proteins. This energy is used to pump protons from the stroma (low concentration) into the thylakoid lumen (high concentration), creating a proton gradient across the membrane.
- Photosystem I (PSI), Meanwhile, in PSI, light energy is absorbed, exciting electrons to a higher energy state. These high-energy electrons are then transferred to another ETC, where they eventually reduce NADP+ to NADPH, along with protons from the stroma.
- ATP Synthase, The proton gradient generated by the ETC drives protons back across the thylakoid membrane through ATP synthase, a protein complex that harnesses this flow to convert ADP and inorganic phosphate (Pi) into ATP, a process called chemiosmosis.
- NADPH and ATP, The products of the light-dependent reactions are ATP and NADPH, both of which are used in the light-independent reactions (Calvin cycle) to convert CO2 into glucose and other carbohydrates.
By splitting water, generating oxygen, and producing ATP and NADPH, the photosynthetic electron transport chain converts light energy into chemical energy, which is essential for the synthesis of organic molecules in plants and other photosynthetic organisms.
What is the second part of photosynthesis
Calvin cycle or carbon fixation
What happens in the Calvin cycle or the carbon fixation
- Carbon Fixation,
- The Calvin cycle starts in the stroma, the fluid-filled space inside chloroplasts.
- Three molecules of CO2 are fixed, meaning they are converted into a form that can be used to build sugars.
- Each CO2 molecule combines with a five-carbon compound called ribulose-1,5-bisphosphate (RuBP), with the help of an enzyme called RuBisCO. This forms an unstable six-carbon compound that immediately splits into two molecules of a three-carbon compound called 3-phosphoglycerate (3-PGA).
- Reduction Phase,
- The 3-PGA molecules are then converted into a more energy-rich form using ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are both energy carriers.
- ATP provides the energy needed for the conversion, while NADPH provides the electrons necessary to reduce (add hydrogen to) the 3-PGA molecules. This converts them into another three-carbon compound called glyceraldehyde-3-phosphate (G3P).
- Regeneration of RuBP,
- Some of the G3P molecules produced are used to regenerate RuBP, the five-carbon compound needed for carbon fixation to continue.
- This regeneration step requires ATP, as RuBP is regenerated through a series of reactions that rearrange the carbon atoms in the G3P molecules.
- Production of Glucose
- For every three molecules of CO2 fixed, six molecules of G3P are produced, but only one of these molecules exits the cycle to be used for glucose production.
- The other five G3P molecules continue in the cycle to regenerate RuBP and keep the cycle going.
- Overall Reaction
- The overall reaction for the Calvin cycle is: 3CO2 + 9ATP + 6NADPH + 6H+ → C6H12O6 + 9ADP + 8Pi + 6NADP+ + 3H2O
- This means that three molecules of CO2, along with ATP, NADPH, and H+, are used to produce one molecule of glucose, along with ADP, Pi (inorganic phosphate), NADP+, and water.
This cycle is crucial for the production of glucose, which can be used by plants for energy or converted into other molecules for growth and reproduction.
Is ATP generated in both plants and animals ?
Yes, generated in both respiration and photosynthesis
ATP synthase is responsible for ATP generation in both processes
This requires a protein gradient across a membrane in both chloroplast and mitochondrion
What are the similarities of chloroplast and mitochondria
( origin of chloroplast and mitochondria)
Mitrocondria and chloroplast both contain DNA, ribosomes and are able to make some proteins
Both have outer and inner membranes, however chloroplast have a third membrane
The DNA of chloroplasts and mitochondria is more similar to bacterial DNA than to nuclear DNA, providing further evidence of their bacterial origins.
