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BIO201A Cell Biology Lecture 12 Monday 02/12/07
Important Announcements: • Exam on Friday, Feb 16th, 9AM in Knox20. • First exam will cover material up to and including today. Thirty four (34) multiple choice questions. • See next page for exam instructions. • Reading in Chapter 9 for upcoming lectures.
For the Exam • All you need are pencils (not pens), an eraser, your 8 digit Student Number, and Student ID. • Wait to enter the room until you are told. • Do not open your envelopes until you are told to do so. • The first thing you will do (when told to) is to put your name, Student Number, and exam form number in the correct spaces on the answer sheet. • The exam will end at 9:50 AM. No extra time will be given. • You must put your exam and answer sheet in your envelope and turn it in to get a grade • Do not seal the envelope.
Chloroplast Thylakoid membranes are high in protein and have no cholesterol 1. The envelope membrane is a double membrane. These membranes are not the photosynthetic membranes 2. Thethylakoid membranes are the photosynthetic membranes inside the chloroplasts. The light harvesting proteins (pigments), electron transport proteins and the ATP synthetase are all on or in the thylakoid membranes 3. The lumen is the aqueous area inside the thylakoids 4. The stroma is the aqueous area outside the thylakoids 5. No TCA cycle in chloroplasts. They are different than mitochondria. They do have their own DNA but 90% of their proteins come from nuclear-encoded genes
Chloroplast About how wide is this chloroplast?
Comparison of mitochondria and chloroplast Intermembrane space Mitochondria F1 faces the matrix High H+ outside of the inner membrane H+ Matrix ADP + Pi ATP H+ H+ H+ H+ H+ H+ H+ Inner membrane Chloroplasts are like inside-out mitochondria ADP + Pi ATP Stroma Chloroplast CF1 faces the stroma High H+ inside the thylakoid membranes lumen H+ H+ H+ H+ H+ H+ H+ Thylakoid membrane
In both mitochondria and chloroplasts, H+ flux is coupled to ATP synthesis In both, ATP is made when H+ flow from the low pH side to high pH side F1 of mitochondria CF1 of chloroplasts H+ ADP + Pi ATP H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Low [H+] High pH High [H+] Low pH Membrane
Chloroplasts H2O oxidized to O2 Energy required (light) Makes sugars from CO2 H+ high inside thylakoids CF1 faces out H+ efflux during ATP synthesis Mitochondria O2 reduced to H2O Energy produced (ATP) Makes CO2 from sugars H+ high outside inner membrane F1 faces in H+ influx during ATP synthesis
Overall scheme of photosynthesis: Light CO2 + H2O (CH2O)n + O2 Carbohydrates CO2 is reduced to make carbohydrates by reductive biosynthesis in the Dark Reactions. This requires ATP and NADPH from the light reactions
Light Reactions Convert light energy into chemical energy stored in NADPH and ATP Water is the initial e- donor to the electron transport chain. Water gets oxidized to O2 Dark Reactions* The NADPH and ATP made in the light reactions are used to make carbohydrates from CO2 *We will not discuss the dark reactions further in BIO201, we will focus on the light reactions
Pathway for electron transport in chloroplast thylakoids NADP+ + H+ NADPH e- e- H2O O2 + H+ H2O PSII PQ ctyb6/f PC PSI NADP+ PQ is plastoquinone. It is a lipid PC is Plastocyanin. It is a peripheral protein
Light Reactions of Photosynthesis Photophosphorylation produces NADPH and ATP. Why? To give to the Dark Reactions to help make carbohydrates 1. The energy from the sun is used to set up a H+ gradient with high H+ inside thylakoids 2. When H+ flow out (through the CFo/CF1), ATP is made in the stroma The initial e- donor is H2O and the final e- acceptor is NADP+
Stages of e- flow in photosynthesis: • Photolysis. PSII uses light energy to split water in the lumen. This produces three important products: H2O 2H+ + ½ O2 + 2e- 2. Pass e- from PSII to PSI. The energy generated helps to increase the [H+] in the lumen 3. Pass e- from PSI to NADP+. Produces NADPH For the H+ gradient For mitochondria, us and others things For e- transport Where do the electrons come from to start this e- transport? water