Biol 212- Unit 4: Photosynthesis

Front 1

What is photosynthesis:

Back 1

1. the combining of carbon dioxide in the atomosphere with existing sugars to make the carbon in the atom available to the plants.

2. Carbon dioxide is fixed into sugar

3. 6CO2 + 12H2O + light energy --> C6H12O2 + 6H2O
[happens in chloroplast, driven by light]

Front 2

Why is photosynthesis important?

Back 2

1. the only way to fix carbon atom into organic form

2. oxygen "waste" creates the oxygen in the atmosphere

3. oxygen in the atmosphere reacted to form ozone which then formed the ozone layer

Front 3

Do plants carry out oxidative respiration?

Back 3

Yes

since plants carry out both oxidative respiration and photosynthesis, that makes plants photoautotrophs.

Front 4

Photoautotrophs:

Back 4

feed themselves with light.

Front 5

Where does photosynthesis occur?

Back 5

1. occurs in the parenchymal cells of the mesophyll, epidermal cells of leaves and occasionally stems.

2. specifically it occurs in the chloroplasts of these cells

Front 6

Chloroplast:

Back 6

double membrane bound, giving rise to several sub-cellular compartments.

Front 7

functions of the outer membrane of the chloroplast?

Back 7

- barrier to cytoplast serves to retain chlorophyll content.

- does have transport proteins that move photosynthate to cytoplast for glycolysis.

Front 8

functions of the inner membrane of the chloroplast?

Back 8

- barrier to stroma, serves to retain chlorophyll contents

- has transport protein to move photoynthate to intermembrane space.

Front 9

function of the intermembrane space:

Back 9

function is still unknown

Front 10

stroma:

Back 10

is the site of carbon dioxide fixation

Front 11

thylakoid membrane (component of grana):

Back 11

is the site of embedded antenna chlorophyll molecules and light reaction components and ATP sythase.

Front 12

Thylakoid space:

Back 12

store of H+ (i.e. chemiosmotic potential) that is used to drive the ATP synthase of thylakoid.

Front 13

how chloroplast develop?

Back 13

1. preplastids (embroyonic plastids) are received form embryo.

2. preplastids develop along different developmental pathways in response to signals to become either chloroplasts or chromoplasts.

3. there are some interconversion as chloroplasts can become chromoplasts in the fall as leaves change color and are dropped.

Front 14

chromoplasts:

Back 14

pigment bearing plastids

Front 15

photosynthesis equation:

Back 15

[note glucose is not really the direct product of photosynthesis]

Front 16

during photosynthesis, the "waste" oxygen gas is derived from?

Back 16

the water, which reinforces the idea that photosynthesis is a redox reaction.

- reduction is adding electrons and oxidation is removal of electrons,

- when water is split, H+ and electrons are removed from O, the causes the O to bond with C making the sugar compound.

Front 17

Photosynthesis is really just the opposite of?

Back 17

oxidative respiration

Front 18

Light reactions:

Back 18

- uses light energy to make ATP and NADPH(the anabolic form of NADH)

- has similariites to the electron transport system

- Uses water as a source of electrons and releases oxygen gas as waste

Front 19

Calvin-Benson Cycle (aka: dark reactions):

Back 19

uses the ATP and NADPH from light reactions to fix carbon dioxide into sugar.

Front 20

Is light a wave or a particle?

Back 20

it has the properties of both

Front 21

Light is a form of?

Back 21

radiation

Front 22

The greater the wavelength, the ________ the energy level?

Back 22

lower

Front 23

Light radiation is radiation between what nm?

Back 23

~380nm - ~750nm

Front 24

different wavelengths of light have different colors

Back 24

Front 25

Why is the sunlight that you see white?

Back 25

because it is a mixture of all wavelengths

Front 26

Why do we say that light is like a particle too?

Back 26

the energy that light contains is quantized (energy acts as if it is in discrete packages [photons] and discrete quantities)

- we know the amount of energy in light is inversely related to wavelength.
(certain wavelengths have a certain energy)

Front 27

Why do substances absorb some light wavelengths and not others?

Back 27

- depends on the absorbing substance

- when a substance absorbs light, it is called a pigment and it interacts in a specific way with the light.

- For a specific wavelength of light to be absorbed, it must have the specific energy necessary to kick an electron from one specific orbital to a higher specific energy orbital in that substance.

Front 28

Light can be reflected, what does that mean?

Back 28

that it bounces off

Front 29

Light can be transmitted, what does that mean?

Back 29

it passes on through.

Front 30

Light can be absorbed, what does that mean?

Back 30

its energy is transferred to the substance. or its energy is transferred to the substance and partly re-emitted as fluorescent light.

Front 31

What is happening to the light when you see a green leaf?

Back 31

- green light (and yellow) is reflected and transmitted.

- red and blue are absorbed
(the colors you see are the colors that are reflected and transmitted. The colors you don't see are absorbed)

Front 32

Chlorophyll:

Back 32

most common are Chl(a) & Chl(b)
- very similar but have absorption max at slightly diff. wavelengths

Front 33

What happens to chlorophyll when struck by blue or red light?

Back 33

- specific electrons of the Mg are kicked up an energy level.

note:: blue light has more energy than red, but both can jump an electron of Mg up an energy level.

Front 34

What happens to the electron in the chlorphyll?

Back 34

very quickly, the electron drops back to the ground state

Front 35

What 4 things can happen to the energy released as the electron drops?

Back 35

1. energy can be given off as heat (helps keep plant from freezing)

2. energy can be given to another molecule (another chlorphyll)

3. energy can be given off as fluorescent light
(a) usually when there is no other molecule to pass the energy to
(b) photon emitted will be at a lower energy than the original photon due to heat loss

4. Energy can be transferred in a chemical reaction.

Front 36

Absorption spectrum:

Back 36

spectrum which shows all the light absorbed by the plant pigments.

Front 37

Does the plant use the other wavelengths of light?

Back 37

yes but use acessory pigments (Chl(b), carotinoids, xanophylls), to absorb light of different wavelengths and pass the energy to Chl(a).

happens at lower efficiency.

Front 38

Action Spectrum:

Back 38

the absorption wavelengths of light that will drive photosynthesis.

Front 39

Will the absorption spectrum match the action spectrum?

Back 39

- No, the absorption spectrum of chlorphyll a does not match the action spectrum,

- but the absorption spectrum of all the photopigments combined will more or less match the action spectrum.

Front 40

How was the action spectrum determined?

Back 40

By the Engelmann's Experiment:
- took a piece of filamentous algae and laid it out striaght.

- shined light through a prism to produce a spectrum and projected it along the length of the algal filament.

- billions of motile aerobic bacteria (need dioxide to carry out ox. resp) were added.

- bacteria moved to the red and blue regions, showing that red and blue are the wavelengths that drive photosynthesis.

Front 41

Photosystems:

Back 41

molecular systems in an organized array that absorbs light and transfers energy to other molecules that are useful for the system.

Front 42

Antenna Complexes:

Back 42

- composed of the antenna molecules, which are the photopigments [chl(a), chl(b), carotinoid, ...]

- molecules are arranged in an array embedded in the thylakoid membrane, and are spread out to maximize absorption.

Front 43

In the antenna complex, what energy transfers occurs?

Back 43

quantum energy transfer

Front 44

What happens when blue or red light strikes an antenna molecule?

Back 44

1. red/blue light is absorbed by an antenna molecule.

2. the energy is transferred as a quantum of energy to a neighbor antenna molecule (photopigment)

3. the neighbor antenna molecule passes the energy to another neighbor molecules until eventually the energy is passed to the reaction center molecule.

Front 45

Photosystem II:

Back 45

1. starts with an antenna complex with a reaction center containing a chl(a) called P680, along with electron transfer molecules.

2. light is absorbed by antenna molecules, energy is passed to other photopigment molecules by quantum transfer.

3. eventually the energy reaches chl(a) P680 where the quantized energy is absorbed.

4. energy is used to bump up the energy level of specific e- in Mg2+ of P680 by a specific amount.

5. the energized e- are donated to an acceptor molecule [ reduces the primary electron acceptor]

6. e- that the primary acceptor has accepted is high and unstable, the donated e- are easily passed to quinone [an e- transfer compound very similar to electron transport system]

7. e- are further transfered along an electron transfer sys. pathway until they are donated to P700 of photosystem I.

Front 46

how does photosystem II looks:

Back 46

Front 47

When e-'s are passed down the electron transport system of ox. resp. to dioxide, what is generated?

Back 47

a chemiosmotic potential

Front 48

what is a chemiosmotic potential?

Back 48

protons get pumped out.

Front 49

How does photosystem II actually produce a chemiosmotic potential?

Back 49

- PSII cytochromes are energized

- PSII cytochromose pump protons from the stroma, across the thylakoid membrane, and into the thylakoid space.

Front 50

What harnesses the chemiosmotic potential and how?

Back 50

The ATPases

- it allows the diffusion of protons back into the stroma and uses that energy to make ATP.

Front 51

Where do the electrons come from if plants keep removing electrons from P680 to feed the electron transport system?

Back 51

through photolysis of water

[the splitting or decomposition of a chemical compound by means of light energy or photons.]

- water is split into H+, oxygen, and electrons by an enzyme

- the electrons are used to replenish P680

- oxygen is generated. (how plants make oxygen)

Front 52

Photosystem I:

Back 52

- The e-s from PSII are donated to P700 of PSI.

- when a red or blue photon is captured by PSI antenna complex and then transferred to P700, the red or blue light elevates the energy level of e-s in Mg2+ in P700.

- high energy e-s are donated to an e- acceptor (Fd) in a process like PSII, -->but then the Fd donates the e-'s to an enzyme [NADP reductase]

- NADP reductase takes the e-'s and a stromal proton and combines them with NADP to make NADPH.

Front 53

Review of light reactions:

Back 53

products processed:
- ATP
- NADPH
- oxygen [waste product]

Front 54

Plants most commonly use light reactions to generate what? which fixes what?

Back 54

generates ATP and NADPH to fix carbon dioxide into a reduced form (sugar) that can be used in ox. phos. and biosynthesis.

Front 55

Where does the Calvin-Benson cycle occur? and does it use light directly?

Back 55

it doesn't use light directly and it occurs in the stroma.

Front 56

summary equation of the Calvin-Benson cycle:

Back 56

Front 57

Where does the carbon from carbon dioxide goes in the calvin-benson cycle?

Back 57

it goes to PGA

Front 58

What techniques were used in the discovery of the calvin-benson cycle?

Back 58

- TLC [ thin layer chromotography]
- autoradiography
- radioactive isotopes [ b/c radioactive elements are easily introduced into living things, and enzymes can't tell the difference between regular isotopes and readioactive isotopes.. can therefore be traced and tracked]

Front 59

Pulse-chase experiment [ the discovery of the calvin-benson cycle]:

Back 59

- placed algae in a flask and fed it carbon dioxide 14 for a very short period of time (pulse) and then gave it carbon dioxide 12 (chase)
[only products made when exposed to carbon dioxide 14 will have radioactive carbon incorporated.

- they extracted the organic chemicals from the algae, ran the extract out on the TLC sheet and autoradiographed the sheet.

- The largest spot on the autoradiogram turned out to be a C3 compound (3-PGA).

Front 60

C3 pathway:

Back 60

uses 5C + 1C= 3C x 2

reduction product: C3 compound.

Front 61

What is the enzyme that carries out the C3 pathway reaction:

Back 61

Rubisco

Front 62

What are some notes about carbon fixation?

Back 62

1. occurs without light

2. occurs in solution of the stroma

3. doesn't add carbon dioxide to a C2 to make a 3-PGA

4. Rubisco is the most abundant enzyme by weight in the world and possibly the most common protein.

Front 63

What are the 3 distinct phases the Calvin-Benson cycle is divided up into?

Back 63

1. the [carbon fixation] which is carried out by rubisco

2. the [reduction phase] which causes the carbon to be reduced further

3. the [regeneration phase] where RuBP is regenerated

Front 64

Phase 1: Carbon fixation:

Back 64

Front 65

Phase 2: Reduction phase:

Back 65

1. e-'s are added to a triose-P to generate GAP.

2. uses up NADPH and ATP

Front 66

What is GAP?

Back 66

- a compound that is an intermediate that can be shuttled among many pathways including oxidation phosphorelation.

Front 67

Phase 3: regeneration phase:

Back 67

1, RuBP is reformed so that the CO2 fixation steps can occur again.

2. uses ATP

[takes 5 GAPs & turning it into RuBP... 5 x 3C = 3 x 5C(RuBP)]

Front 68

What are some examples of plants that use the C3 pathway to fix carbon dioxide?

Back 68

- wheat
- rice
-soy