Photosynthesis and Carbon Assimilation Flashcards
Define metabolism
the totality of an organism’s chemical reactions
What does metabolism arise from?
Arises from interactions between molecules
A metabolic pathway has …
…many steps
What does the metabolic pathway begin with?
- Begin with a specific molecule and end with a product
Each step in the metabolic pathway catalysed by a _____ ______
- Each step in the metabolic pathway catalysed by a specific enzyme
Catabolic pathways break down…
…complex molecules into simpler compounds, releasing energy
Examples of catabolic pathways?
Glycolysis, Krebs Cycle
Examples of anabolic pathways?
Photosynthesis
Anabolic pathways build…
….complicated molecules from simpler ones.
- Consume energy
The capture of solar energy and its conversion to chemical energy is the …
…ultimate source of nearly all biological energy.
Photosynthetic organisms use …
…solar energy to form ATP and NADPH that are used to as energy sources to make carbohydrates and other compounds.
Photosynthesis takes place in:
higher plants
varieties of bacteria
algae
THe photosynthetic process in higher plants is shown in two processes which are…
- light-dependent reactions (light reactions)
- carbon-assimilation reactions (“dark reactions” – misleading, also take place in the light! sometimes called “light independent reactions”)
The photosynthesis process is similar in all organisms and based on the redox process:
CO2 + H2O –> O2 + (CH2O)
Where do Light dependent and carbon assimilation reactions take place?
In the chloroplast
Chloroplasts have their own…
…dna
CHloroplasts are surrounded by…
a double membrane (two membranes)
(an outer and inner membrane)
Chloroplasts contain…
….thylakoids
WHat are thylakoids?
Flattened membrane surrounded vesicles
What are thylakoids arranged in?
Arranged in stacks called GRANA
THe outer membrane of chloroplasts is permeable to…
…small ions
The inner membrane of chloroplasts ecloses a…
…compartment
In the thylakoids membranes (called lamellae) are the…
…photosynthetic pigments and enzyme complexes that perform light reactions and ATP synthesis
What makes us see a colour (EG: Green)?
White light is absorbed and only the green light is reflected by the pigment.
A pigment is a chemical (or cocktail of chemicals) that absorbs visible in all
Regions EXCEPT at 500-560 nm (see examples below).
The exact colour you see depends on…
…the precise wavelengths absorbed
What colour is not absorbed by plants for photosynthesis?
Green
Electromagnetic waves are made of …
…photons
What are photons?
(particles of energy - no mass)
electromagnetic waves travel at the…
…speed of light - but differ in frequency and wavelength
How does light absorption work?
A molecule struck by a photon with the right frequency and wavelength will absorb the photon´s energy and achieve an excited state
If the energy of the photon exactly matches the energy required to excite an electron to a higher energy level…
…it is absorbed and the electron moves to the excited state
The electron now possesses more energy.
The excited electron soon returns to the …
…ground state (it decays), giving off the absorbed energy as either light (fluorescence) or heat, but in photosynthesis, the energy released is captured by another energy absorbing molecule.
How is energy transferred across the antenna to the reaction center?
As energy
The energy irradiated (given off) is always…
…of a longer wavelength (lower energy) than the energy absorbed.
Pigments in the Thylakoids are arranged in functional arrays which are…
…PHOTOSYSTEMS
Each photosystem has…
~200 molecules of chlorophylls
~50 molecules of carotenoids
The majority of pigment molecules in the system are called:
LIGHT HARVESTING or
ANTENNA MOLECULES
What do LIGHT HARVESTING or
ANTENNA MOLECULES do?
absorb light energy and transmit it to the reaction centre
What occurs at the reaction center?
Photochemical reaction here converts the energy of a photon initiating electron flow.
An electron acts as an…
…energy store in each antenna molecule and reaction centre using its physical quantum state to define it
If we have a line of electrons in adjacent antenna molecules…
… the excited state passes not the electron
Chloroplasts have two different types of…
… photochemical reaction centres acting in tandem
Describe the Z Scheme
- Electrons that originate from water are fed into reaction centre P680 (photosystem II)
- They are excited by excitons, where they are passed via several electron carriers to photosytem I and its reaction centre P700
- Here they are excited again before being passed along more electron carriers eventually to NADP to form NADPH
The electron transport chains are located within the …
…thylakoid membrane
WHat happens within the thylakoid membranes in photosystems?
the energy of electron transport is used to pump protons across the membrane from the stroma to the inside of the thylakoid membrane.
ATP Synthesis by Photophosphorylation
- PS I and PS II move electrons from H2O to NADP+
- Energy from this process is conserved as:
- NADPH
- H+ gradient
(electrochemical potential)
How much ATP is synthesised by photophosphorylation?
O2 + 3 ATP + 2 NADPH
What is the difference between the number of protons required to make 1 ATP in mitochondria and chloroplasts?
None (no difference)
Is the light reaction strictly anabolic?
No
Is the calvin benson reaction strictly anabolic?
Yes
Describe Carbohydrate biosynthesis.
Plants are able to take the most oxidised form of carbon (CO2) and reduce it with water to make carbohydrates using the energy derived from the light-dependent reactions of photosynthesis
CO2 is the…
…SOLE source of carbon atoms required for biosynthesis of all other plant biomolecules
What is CO2 assimilation?
CO2 assimiliation where CO2 is incorporated into a three-carbon compound called 3-phosphoglycerate
Carbon Assimilation occurs in …
… 3 stages
What are the three stages of the Calvin-Benson Cycle?
1) CO2 –> biomolecules
2) Reduction of 3 Phosphoglycerate —> Glyceraldehyde 3-phosphate
3) Regeneration of Ribulose 1,5-bisphosphate
The light-dependent reactions (the Z-scheme) creates …
…equal amounts of NADPH and ATP.
- We need more ATP than NADPH!!
How can we obtain more ATP than NADPH?
This can be achieved by cyclic electron flow in the Z-scheme prevents NADPH formation and boosts ATP production to provide the relative proportions for glyceraldehyde 3-phosphate production.
Cyclic flow balances…
…ATP and NADPH production for carbon assimilation
What is produced in Cyclin electron flow?
Electrons are pumped continuously
around Photosystem I.
- ATP is generated (Cyt b6f)
- no O2 is produced
- no NADPH is produced
3:2 ratio of ATP:NADPH
