Energy Flow in the Biosphere
• Energy Transformations and Entropy
– 1st and 2nd Laws of thermodynamics
• 1st- Energy is neither created nor destroyed; it just changes
forms
• 2nd- Without energy input, systems will go towards higher
disorder (Entropy)
• Energy Flow
– …at the organsimal level- Autotrophs and Heterotrophs
– …at the organellar level: Photosynthesis and Cell
Respiration
Two energy strategies in the
biosphere…
• Autotrophs - Organisms that are capable of
synthesizing their own high energy organic
molecules (e.g., glucose) from simple inorganic
molecules (e.g., CO2 and H2O) and an external
energy source like the sun.
– Includes: all plants, some protists, cyanobacteria
• Heterotrophs - Organisms that are incapable of
synthesizing their own high energy organic
molecules and must therefore obtain them in premade form from their environment.
– Includes: all animals and fungi, some protists and bacteria
Endergonic
Exergonic
If ATP is in limited supply, and is continuously
being consumed, where does the energy to maintain
the cell’s level of ATP come from?
Photosynthesis
THE FLOW OF ENERGY IN NATURE
• The synthesis of organic compounds (sugars) from simple
inorganic compounds (CO2 and H2O) in the presence of
chlorophyll using light energy from the sun.
Autotrophs:
PS and CR
Heterotrophs:
only CR
– General Formula for PS
– The Organs of Photosynthesis - Leaves and
Chloroplasts
– Chloroplast Structure and Photosynthesis
• The Light Dependent Reactions
• The Light Independent Reactions (Dark Reactions
• Coupling the Light and Dark Reactions
– Photosynthetic Pigments and the Electromagnetic
Energy Spectrum
1
Cellulose
Fig. 6.7
What else happens
here?
6CO2 + 6H2O +
= C6H12O6 + 6O2
2
6CO2 + 6H2O +
= C6H12O6 + 6O2
Photosynthesis occurs in 2 stages:
• Light
dependent
reactions
on the
thylakoids
• Dark
reactions in
the stroma
Chlorophyll Absorption Spectrum
Accessory Pigments enhance
absorption and increase PS rates:
• Accessory pigments:
–
–
–
–
Other chlorophylls
Carotinoids
Xanthophylls
Phycobillins
• The Action Spectrum
– PS rate vs. wavelength
– The sum of all pigments
• How can this absorption system become more
efficient, i.e., collect more of the available energy?
Light Absorbing Molecules
3
The light reactions rely on two types of
photosystems that work together and
capture energy in two forms: ATP and
energized electrons (NADPH).
Electron Transport Chain
The production of NADPH and ATP
The Dark Reactions: Using ATP and
NADPH to help fix CO2 into sugars:
• ATP provides
the energy
• NADPH
provides the
electrons to
build sugar
molecules
4
The Production of Sugar
Photosynthesis: putting the light and
dark reactions together:
The ATP and NADPH are
used to make the sugar
Three Phases
1. CO2 fixation- Rubisco
2. Reduction of molecules
via NADPH electrons to
G3P
3. Regeneration of RuBP
For 1 G3P= used 9 ATP
and 6 NADPH
Other ways to get to the CO2
C3, C4, and CAM
Other ways to get to the CO2
C3, C4, and CAM
C4- adaptation to hot
and dry environments
CAM- adaptation to hot and
dry environments
Carbon goes into 4-carbon
molecule before Calvin.
Carbon goes into 4-carbon molecule
before Calvin.
Two different PLACES
Two different TIMES, night and day
Use 4-carbon as a reservoir
Use 4-carbon are reservoir
Ex. Sugarcane, Corn, grass
Ex. Pineapple, cacti, succulents
Why bother…?
Why bother…?
C4 and CAM
Photosynthesis converts energy from
the sun into fuel…now what?
• How do living things use this fuel?
• The fuel must be broken back down to
release the energy that was stored within.
5
THE FLOW OF ENERGY:
Aerobic Cellular Respiration
sunlight Æ photosynthesis Æ sugars
Æ cell respiration Æ ATP
• Glucose Oxidation
C6H12O6 + 6O2
6CO2 + 6 H2O + 686 kcal
– Spontaneous Combustion
– Aerobic Cellular Respiration
• Serves 3 important functions
– 2 ways to make ATP:
• Substrate level phosphorylation
• Oxidative phosphorylation
• 3 sets of enzymatically catalyzed reactions
– Glycolysis: cytosol
– The Krebs Cycle: mitochondrial matrix
– Oxidative Phosphorylation: mitochondrial cristae
membranes
• Anaerobic Respiration/Fermentation
Chemical Energy to Work
• Converting chemical energy into work.
• Lose most as heat
– Car 75%
– Us 60%
•
•
•
•
•
Calorie- raise 1g of H20 1ºC by burning
We really use Kilocalories
One peanut is 5 calories= Raise a quart by 5ºC!
Just a handful can boil water.
Lots of energy bound up in food.
Energy gain and cost
6
What causes Glucose to break
down?
Spontaneous Combustion
• Remember Oxygen's Electronegativity?
• Oxygen is an “electron grabber”
• Electrons naturally are pulled from glucose
to oxygen and release energy in the process.
• By controlling this release of electrons the
cell can use this energy
• “Controlled explosion”
Regulated “combustion”
ATP- The Energy Currency
Formation of ATP
Types of Cellular Work
7
Breathing and Cell Respiration:
Providing O2 for cell respiration
General Equation for
Aerobic Cellular Respiration
C6H12O6 + 6O2
It’s all about the
movement of electrons
6CO2 + 6H2O + 38ATP + HEAT
The Three Steps to ACR
An overview of cellular respiration
Overview of Aerobic Cell Respiration:
3 processes occurring in 3 parts of the cell
• Glycolysis: cytoplasm, anaerobic, 10 steps
• Transition Step: from glycolysis to Krebs
• Krebs Cycle (Citric Acid Cycle): aerobic,
mitochondrial matrix, 8 steps, completes the
oxidation of glucose
• Oxidative Phosphorylation: mitochondrial
cristae membranes
– The Electron Transport Chain
– Restoration of oxidized coenzymes
– Phosphorylation of ADP to ATP
8
An overview of cellular respiration
Energy Balance Sheet
C6H12O6 + 6O2
An overview of aerobic cellular respiration
2. Oxidative Phosphorylation:
6CO2 + H2O + 686Kcal energy
• Glycolysis:
– 4ATP - 2ATP = 2 ATP
– 2NADH = 4 or 6 ATP
• Transition step:
– 2NADH = 6 ATP
• Krebs Cycle:
– 6NADH = 18 ATP
– 2 FADH2 = 4 ATP
– 2 ATP
• Total: 36 or 38 ATP/glucose + HEAT
• The coenzymes NAD and FAD are used to transfer high
energy e- taken from glucose to an electron transport
chain where they can be used indirectly to make ATP.
• 34 out of 38 ATPs produced per glucose are formed this
way.
Glycolysis- “Sugar splitting”
The Ten Steps of
Glycolysis
Glyceraldehyde-3Phosphate (G3P); familiar??
9
Glycolysis Summary
1. Substrate-level phosphorylation
• The energy released
from breakdown of
glucose is
transferred directly
to the bonds of ATP.
• 4 out of 38 ATPs
produced per
glucose are formed
this way.
Transition into Mitochondria
Krebs Cycle Budget
The Three Steps to ACR
Carbon from Glucose
The
Krebs
Cycle
Carbon from
Glucose goes
into Krebs
Cycle
molecules,
and Krebs
Mol. Release
their Carbon
as CO2
Carbons
swap roles
Carbons from
Krebs
10
Tally Sheet- 90% of Energy locked in
NADH and FADH2…one more step to go
By third step of
Krebs Cycle, all
carbon from original
sugar is released as
CO2
ATP Synthesis…version 1
ATP Synthesis: Version 3
the Electron Transport Chain and
Oxidative Phosphorylation
NADH is Oxidized
ADP is
phosphorylated
ATP Synthesis… version 2
Electron Transport Chain
Version 4…
100x concentration
of H+
11
ATPs from Chemiosmosis and
Oxidative Phosphorylation
Oxidize NADH
to free H+ ions…
Choose your poison and learn a few
things about aerobic cellular respiration:
…and add
phosphate to
ADP = ATP
The ATP synthase:
a molecular mill
that uses the proton
gradient to
phosphorylate ADP
to ATP!
Energy Balance Sheet
ACR Summary
C6H12O6 + 6O2
6CO2 + 6H2O + 38 ATP + heat
• Glycolysis:
– 4ATP - 2ATP = 2 ATP
– 2NADH = 6 ATP
• Transition step:
– 2NADH = 6 ATP
• Krebs Cycle:
– 6NADH = 18 ATP
– 2 FADH2 = 4 ATP
– 2 ATP
• Total: 38 ATP/glucose + HEAT
We don’t just eat Glucose
Our bodies can use
other types of food
in the ACR cycle,
and can reverse
the arrows to
synthesize organic
molecules
Biosynthesis
• Our bodies
synthesize needed
molecules using
many of the same
pathways that
break them
down…just in
reverse!
12
Respiration without Oxygen
• Sometimes you can’t use Oxygen!
• Cells only have limited store of ATP and O2
can’t be delivered to cells fast enough.
Aerobic vs. Anaerobic Respiration: What
happens when there’s no O2 around to accept
electrons?
– No O2= no electron accepter for the Electron
Transport Chain…ACR can’t work!
• Our muscle cells can last about 5-15 sec.
• Anaerobic Respiration: Glycolysis w/out O2
– Alcoholic- yeast, bacteria
– Lactic Acid Fermentation
Lactic Acid-same amount of energy out
as alcoholic fermentation, but no CO2 released
Alcoholic Fermentation
Can only generate a small fraction of the ATP
that Aerobic respiration can (2/38)!
The control of cellular respiration
Negative feedbacks
control the rate of
cellular respiration
within a cell and in
the body as a
whole!
13
Anaerobic Respiration
• Produce only 2 ATP instead of 38! Is is
real worth it?
• So need to burn much more fuel to maintain
cells needs! Very inefficient, but…
• Can’t burn fatty acids without Oxygen.
• Acid or alcohol wastes are dealt with at a
later time.
• Facultative anaerobes
• Obligate anaerobes
14