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

1. All you need are pencils (not pens), an eraser, your 8 digit Student Number, and Student ID.

2. Wait to enter the room until you are told.3. Do not open your envelopes until you are told to do so.4. 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.

5. The exam will end at 9:50 AM. No extra time will be given.6. You must put your exam and answer sheet in your envelope

and turn it in to get a grade7. Do not seal the envelope.

Chloroplasts and Photosynthesis

Chloroplast

1. The envelope membrane is a double membrane. These membranes are not the photosynthetic membranes

2. The thylakoid 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

Thylakoid membranes are high in protein and have no cholesterol

Chloroplast

About how wide is this chloroplast?

Comparison of mitochondria and chloroplast

Mitochondria

F1 faces the matrix

High H+ outside of the inner membrane

ADP + Pi ATPMatrix

Stroma

Intermembrane space

lumen

ADP + Pi ATP

H+H+ H+ H+

H+

H+H+

H+

H+ H+H+ H+H+

H+ H+

Chloroplast

CF1 faces the stroma

High H+ inside the thylakoid membranes

Thylakoid membrane

Inner membraneChloroplasts are like inside-out mitochondria

In both mitochondria and chloroplasts, H+ flux is coupled to ATP synthesis

H+

H+H+

H+H+

H+

H+H+

H+

H+H+

Membrane

ADP + Pi

ATP

High [H+]

Low pH

Low [H+]

High pH

F1 of mitochondria

CF1 of chloroplasts

In both, ATP is made when H+ flow from the low pH side to high pH side

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:

CO2 + H2O (CH2O)n + O2

Light

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

Dark Reactions*

The NADPH and ATP made in the light reactions are used to make

carbohydrates from CO2

Water is the initial e- donor to the electron

transport chain.

Water gets oxidized to O2

*We will not discuss the dark reactions further in BIO201, we will

focus on the light reactions

Pathway for electron transport in chloroplast thylakoids

H2O PSII PQ ctyb6/f PC PSI NADP+

H2O O2 + H+

e-

NADP+ + H+ NADPH

e-

PQ is plastoquinone. It is a lipid

PC is Plastocyanin. It is a peripheral protein

Photophosphorylation produces NADPH and ATP. Why?

Light Reactions of Photosynthesis

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:

1. 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