Lecture 10: Photosynthesis Flashcards
How many membranes does chloroplast have?
- 2
Explain the inner membrane/ thylakoid membrane
- define: lumen
- define: stroma
- define: granum
- lumen: inner space of the thylakoid
- stroma: space between thylakoid stacks
- granum: stack of thylakoids
Function of chloroplast (2)
- absorb visible light (violet-red and blue)
- contain photosynthetic pigments (chlorophylls, carotenes, xanthophylls) which absorb light from discrete wavelengths
The shorter the wave length, the _________
- higher the energy
What type of photons (2) excite electrons to a high energy state? Which one more than the other?
- blue and red
- blue more than red
How would you describe the excited state of an electron? How can it be utilised?
- unstable; lasts only ~10^-12 seconds
- energy released by an excited electron can be harnessed by photosynthesis
What are the 3 possible fates of excited electrons?
- fluorescence and/or heat
- resonance energy transfer
- reduction/oxidation
Explain one of the possible fates of excited electrons: fluorescence and/or heat
electron drops back down to lower energy level and emits fluorescence and/or heat
Explain one of the possible fates of excited electrons: resonance energy transfer
energy in electron is transferred to a nearby pigment; pigments absorb photons of slightly lower energy; specialized chlorophylls absorb photons and the excited electron leaves
Explain one of the possible fates of excited electrons: reduction/oxidation
- electron is transferred to a new compound (NADP+ –> NADPH)
Explain the process: photosystem 2
- first of the photosynthetic reactions (occurs before photosystem 1)
- function: uses energy from sunlight and the redox reactions in the ETC to make a proton gradient across thylakoid membrane. the proton gradient drives ATP synthesis
- the reaction centre becomes a strong oxidizing agent
- pheophytin (electron acceptor) is reduced and electrons from it are removed by plastoquinone (PQ)
- gains electrons from water splitting
Explain the process: photosystem 1; what is the difference in the product produced in photosystem 2 and 1
- see google doc
- p 2: ATP synthesis
- p 1: NADPH
How are PS2 and PS1 linked?
- plastocyanin (soluble electron carrier) accepts electrons from PS 2 and reduced PC diffuses through thylakoid lumen to PS 1
- see google doc
What is a by-product of photosynthesis?
- oxygen
Fact: PS1 can operate alone; how? What is produced instead? When is this useful?
- bypasses PS2
- Electrons are transferred from
ferredoxin to plastoquinone, and
then to plastocyanine - ATP is produced BUT not NADPH
- useful when additional ATP is required
Calvin cycle
- define it
- what are the 3 phases?
- chemical reactions that convert CO2 and other compounds into glucose phases 1. carbon fixation 2. reduction 3. regeneration
Briefly describe what happens in each of the calvin cycle phases
- carbon fixation: Rubisco (enzyme), speeds up CO2 and RuBP reaction. creates 2 molecules of 3PGA
- reduction: 3PGA is reduced to G3P (with the help of NADPH).
- regeneration: RuBP regenerated from G3P.
this occurs 6 times simultaneously and the cycle runs twice to form 1 ATP molecule
Map out the synthesis of carbs
- see google doc
sucrose vs starch
- sucrose: readily transported to other parts of plant for energy use; glucose/fructose reaction in the cytosol
- storage product; glucose/fructose reaction in chloroplast
Explain the enzyme Rubisco
- very large protein with 16 subunits and 8 catalytic centres
- the most abundant enzyme on earth
- very slow
- CO2 (carbon fixation) competes with O2 (photorespiration) to form a complex with rubisco
can you write out the photosynthesis reaction?
- see google doc
can you write out the photorespiration reaction?
- see google doc
what regulates photosynthesis (3)?
- light
- sugar
- CO2
What controls access to the leaf cells? What makes it open and close?
- stomata
- closes at night and during hot and dry conditions to prevent H2O loss
Many plants are coated in a waxy cuticle layer at their leaves. Why?
- prevents leaf dehydration
autotroph
self feeder
