Transcript Photosynthesis

Topic:
Photosynthesis-Ch 6
Cellular Respiration-Ch 7
American biochemist and Nobel laureate Albert Szent-Gyorgyi, “What
drives life is thus a little electric current, set up by the sunshine.”
Light Absorption
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Occurs in chloroplasts
•VISIBLE LIGHT (roygbiv).
•Each
color = a specific wavelength
•Pigments:
compound that absorbs light
(specific pigments absorb specific wavelengths
in nanometers)
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Chloroplast Structure
Surrounded by a double membrane
Inside a chloroplast:
–Flattened membranes = thylakoid
–Stacks of thylakoids = grana
–Stroma = liquid
in the space
surrounding
the grana
Pigments
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Found in thylakoids
Chlorophyll a = Most important
pigment, absorbs the most light
(absorbs red, blue; reflects green)
Chlorophyll b = absorbs slightly
different wavelength
Carotenoids, Xanthophylls =
red, orange, and yellow absorb
additional wavelengths
Structure of Chlorophyll
Photosynthesis
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Converts inorganic compounds into
organic ones using the energy from
sunlight & biochemical pathways
2 Stages
1. Light Dependent (capturing light
energy or “Light”) stage
• releases oxygen for us to breathe
• makes ATP and NADPH to run Calvin Cycle
2. Calvin cycle (Light Independent or
“Dark") stage
• Makes organic cmpds (sugar for plant)
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Autotrophs: Make their own organic
compounds (food) ex. plants, algae
Heterotroph: cannot make their own
food
Photosystems
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Cluster of pigment molecules w/ a
specific job
Photosystem I
Photosystem II
Photosynthesis Equation
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6CO2 + 6H2O + light
C6H12O6 + 6O2
Light Reactions - a 5 step
process
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Occurs in the thylakoid membrane
Step 1
–Light energy (from sun) excites
electrons in chlorophyll a
molecules, these excited
electrons leave the chlorophyll a
molecule (photosystem II)
• This is oxidation reaction…..PS II lost an electron
Light Reactions - a 5 step
process
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Step 2
–Excited electrons leave the
chlorophyll a & go to the Primary
Electron Acceptor (2)
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This is reduction reaction…it gained electron
Step 3
–Primary electron acceptor gives the
electrons to the electron transport
chain
• Protons move INTO thylakoid from low
to high
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Light Reactions - a 5 step
process
Step 4
–In photosystem I electrons gets
excited again by light energy
(more sunlight)
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Oxidation reaction…lost electrons
–These electrons go to another
primary electron acceptor (1)
–These lost electrons are replaced by
the electrons that came from
photosystem II
Light Reactions - a 5 step
process
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Step 5
–Primary electron acceptor (I) gives
the electrons to another ETC (I).
–This ETC (I) moves electrons to the
stroma side of the memb.
–Electrons combine w/ a proton (H+) &
NADP+ this becomes NADPH
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Reduction…gains electrons
–NADPH is nicotinamide adenine
dinucleotide phosphate…..HOLDS
ENERGY
Replacing Electrons in PS II
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Where do the electrons come from?
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An enzyme splits 2
molecules of water
into 4 protons, 4
electrons and 1
molecule of oxygen
(O2)- this is where
oxygen is given off
in photosynthesis
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Chemiosmosis
The process by which ATP is made
in the light reaction
Happens in between PSII and PSI
More protons accumulate inside
the thylakoid than stroma = conc.
Gradient is high to low
Some protons came from water
splitting, others were pumped in
using energy generated by ETC
Chemiosmosis
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Protons flow out to
stroma through ATP
synthase enzyme in
membrane, this releases
energy
ATP synthase uses
released energy to
convert ADP to ATP
ATP synthase =
multifunction protein!
Chemiosmosis
Chemiosmosis
Components of the
light reaction
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Oxygen (given off)
ATP made (used in calvin
cycle/dark rxn)
NADPH made (used in calvin
cycle/dark rxn)
Water is consumed
Calvin Cycle
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Where CO2 is incorporated
Occurs in stroma of chloroplast
Makes 3C sugars (carbohydrate)
Calvin Cycle
Calvin Cycle
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Step 1
–3CO2 diffuses into stroma from
cytosol, CO2 gets added to
RuBP
by enzyme
Rubisco which is a 5 carbon
carbohydrate to equal a 6-Carbon
molecule that immediately splits
into 2 3-carbon molecules (PGA)
(ribulose biphosphate)
• phosphoglycerate
Calvin Cycle
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Step 2
–PGA converted into G3P
by adding P (from ATP) & H (from
NADPH) to the 3-carbon molecules.
(glyceraldehyde 3-
phosphate)
• Then the ADP, NADP and P are
used again in light reactions to
make more ATP and NADPH
– In other words…..Binds H carried by NADPH to Carbon from CO2,
with the help of ATP….all this was produced in light reactions…
Calvin Cycle
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Step 3
–Most G3P is converted back into
RuBP (keeps cycle going), but
some G3P leaves cycle & is used
to make organic compounds
–Plants using Calvin cycle are C3
plants (for the 3 Carbon
compound produced)
Calvin Cycle Requires
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ATP
NADPH
CO2
Stomata
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Pores on leaves through which CO2
enters & O2 exits
Low CO2 & High O2 stop calvin
cycle
Alternative Pathways, C4
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Hot dry climate
Partially close stomata during day
Make a 4 C compound first even
though CO2 is low and O2 is high
Lots of grasses do this + corn, sugar
cane
They lose about half as much water as
C3 plants when producing same
amount of carbs
Alternative Pathways, CAM
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Open stomata @ night and incorporate
C into a bunch of other compounds
they then use for photosynthesis
during the day…grow slowly; lose less
water
Ex: cactus, pineapple
–CAM stands for crassulacean acid
metabolism
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REVIEW
Light Dependent Reactions
– In thylakoid
– Collect light
– Produce ATP, NADPH
– Release Oxygen
– Consume water
Calvin Cycle/Dark Rxn/Light independent
– In stroma
– Take in Carbon dioxide
– Produce carbohydrate (G3P)
REVIEW
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Factors affecting
photosynthesis rate
Varies based on:
–amount of light (increase  level
off)
–amount of carbon dioxide
(increase  level off)
–Temperature (increase 
decrease)
How do you get the
energy out of the organic
compounds?
Cellular Respiration =
CH 7!
Cellular Respiration
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Energy is generated by a series of
reactions ultimately used to form
ATP from ADP
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C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
2 steps are:
1. Glycolysis
2. Aerobic Respiration
Glycolysis
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First Step in Respiration
Occurs in the cytosol
Splits ONE glucose into
TWO pyruvate
molecules
Does not require oxygen=
anaerobic
Uses 2 ATP process and 2
NAD+
Makes 4 ATP
Net yield = 2 ATP
After
Glycolysis:
If O2 present
= aerobic
resp.
If no O2 =
fermentation
Fermentation
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Glycolysis + an anaerobic pathway =
fermentation
Produces NAD+ which keeps glycolysis
going..w/out NAD+ then glycolysis
would stop and no ATP
would be made
Anaerobic process
Does not produce ATP
Lactic acid pathway
Ethyl alcohol pathway
Lactic Acid fermentation
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Pyruvic acid is converted into
lactic acid, forming NAD+
Yogurt, cheese, muscle cells
Produced when strenuous exercise
exceeds immediate demands of
muscle tissues
Alcoholic fermentation
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Pyruvic acid 
ethyl alcohol
Creates NAD +
Yeast, wine,
bread
Efficiency of anaerobic
pathways
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Not very efficient
Cannot sustain large multicellular
organisms
OK for bacteria & early life on Earth
Aerobic Respiration
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If oxygen is present, the pyruvic
acid from glycolysis undergoes
cellular respiration
Pyruvic acid still has a lot of
energy in it
Aerobic Respiration - 2
steps
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Step 1: Krebs cycle
Step 2: Electron transport chain &
chemiosmosis
In Eukaryotes these occur in
mitochondria
In Prokaryotes these occur in the
cytosol
Krebs Cycle
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Pyruvic acid diffuses into
mitochondria MATRIX & forms
acetyl CoA
Krebs Cycle
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4 carbon beginning product is
regenerated at the end of the cycle
Krebs Cycle
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If what you start with is the same
as what you end with, what is the
point of the Krebs cycle?
–It generates other “stuff” while
going through the cycle
Krebs Cycle
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Acetyl CoA does a bunch of stuff and generates:
(1 glucose = 2 turns of Krebs cycle)
– 4 molecules of CARBON DIOXIDE (is given off
as waste),
– 6 molecules of NADH,
– 2 molecules of FADH2
– 2 molecules of ATP
– Krebs still only makes
2 ATP like glycolysis…
So rest of products go into
Mitochondrial inner membrane to make more!
Electron Transport Chain
Electron Transport Chain
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Series of electron carriers accept
electrons from NADH and
FADH2
Electron Transport Chain
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Chemiosmosis creates ATP from ADP just like in photosynthesis!
The Role of Oxygen
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What does the end of the ETC do
with its electrons?
–Oxygen is “final electron
acceptor”
Oxygen combines with protons &
electrons that were part of NADH
and FADH2 to create water!!!!!!!!
Aerobic Respiration
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Much more efficient than anaerobic
Produces 38 ATP (glycolysis +
krebs + ETC)
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C6H12O6 + 6O2
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6CO2 + 6H2O + ATP
Summary of Cellular
Respiration
Cellular Respiration Summary
ETC and Chemiosmosis!