Download Pathways that Harvest Chemical Energy (Cellular Respiration)

Energy: Cellular Respiration and
Photosynthesis
Wk4, Chapters 7,8
The Flow of Energy in Living Systems
To maintain their organization and carry out metabolic
activities, cells (and organisms) need a constant
supply of energy
Energy is defined as the capacity to do work
-kinetic energy: the energy of motion
-potential energy: stored energy
Food has potential energy because it can be converted
into various types of kinetic energy.
Food is specifically called chemical energy (energy is
stored in chemical bonds of carbohydrates,
proteins and fats).
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The use of energy by living organisms
Life is powered by sunshine
Land plants, some protists and cyanobacteria
harvest the energy of sunlight and convert
it into chemical energy (synthesis of organic
molecules) through the process of
photosynthesis.
These organisms are called autotrophs (selffeeders). Autotrophs can also use the
chemical energy from the organic
compounds to produce ATP through the
process of cellular respiration.
Animals, fungi and most protists and most
prokaryotes can not do photosynthesis and
only can do cellular respiration. They are
called called heterotrophs (fed by others).
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Photosynthesis versus respiration
All organisms do respiration to obtain energy from
organic compounds: Cellular Respiration involves
oxidation of organic compounds such as glucose
that releases energy that is utilized to synthesize
ATP. This process occurs in the mitochondria and
or the cytoplasm(glycolysis occurs in the
cytoplasm).
Only a few organisms can do photosynthesis:
Photosynthesis involves harvesting energy from
sunlight and converting it into chemical energy
(synthesis of organic molecules). This process
occurs in chloroplasts (in plants, algae, protists)
and in thylakoids (in cyanobacteria).
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Photosynthesis and Cellular Respiration
Energy Currency of Cells
ATP = adenosine
triphosphate
-the energy “currency”
of cells
ATP structure:
-ribose, a 5-carbon
sugar
-adenine
-three phosphates
High
Energy
bond
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Energy Currency of Cells
ATP stores energy in the bonds between the last
two phosphates.
When that bond breaks, high energy is released:
ATP
ADP + Pi + Energy
ADP = adenosine diphosphate
Pi = inorganic phosphate
The energy released when
ATP is broken down to ADP
can be used to fuel
endergonic reactions.
The energy
released from an
exergonic reaction
can be used to fuel
the production of
ATP from ADP + Pi.
Enzymes: Biological Catalysts
Enzymes: Molecules that catalyze (speed up) reactions
in living cells. Many are involved in the processes
leading to the production and use of energy
-most are proteins (except: ribozymes: RNA with
enzymatic abilities in the ribosome)
-are not changed or consumed by the reaction
Energy Units and Heat
During energy conversions, part of the energy is lost in the
form of heat.
The most convenient form to measure energy is in terms of
heat (all energy types can convert into heat).
The energy units are kilocalories.
1 kilocalorie (kcal) = 1000 calories
One Kilocalorie = the amount of heat required to raise the temp of
1 Kg of water by 1oC
“Food calories” listed on food packages are kilocalories of
energy.
Human Nutrition,Cellular Respiration, and Use
of ATP
Humans are heterotrophs. We need to take in food that
provides about 2,000-2500 kilocalories of energy per
day (“2000-2500 calories”).
75% is used for life sustaining activities (heart pumping,
to breath, to maintain body temperature…),
The rest is for voluntary activities (running, dancing,
sitting, walking).
About 40% of the energy provided by food is converted
into ATP by cellular respiration, the rest of the energy
is lost as heat (car engines converts about 25% of the
energy from gasoline to the kinetic energy of movement)
Walking at 3 mph, how far would you
have to travel to burn off the
equivalent of a slice of pizza that has
475 kcal (475 calories)?
How long would that take?
475/158
About 3 hours
3 mph x 3 h = About 9 miles
Food, such as
peanuts
Pathways that break down
various food molecules
Carbohydrates
4 Kcal
per gram
Fats
Glycerol
Sugars
9 Kcal
per gram
Fatty acids
Proteins
Amino acids
4 Kcal
per gram
DIGESTION
Amino
groups
Glucose
G3P
GLYCOLYSIS
Pyruvate
Acetyl
CoA
ATP
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
NADH
NAD+
+
ATP
2e–
Controlled
release of
energy for
synthesis
of ATP
H+
During cellular
respiration, electrons
from glucose or
other digested foods
are shuttled through
electron carriers in a
electron transport
chain to a final
electron acceptor
2e–
H+
H 2O
1

2
O2
Types of Cellular Respiration
The final electron acceptor is different in different types of
cellular respiration
aerobic respiration: final electron receptor is oxygen (O2)
fermentation: final electron acceptor is an organic molecule
(ethanol: in yeast/to make beer or wine, lactate:
bacteria/to make yogurt or cheese, muscle cells/intensive
exercise)
anaerobic respiration: final electron acceptor is an inorganic
molecule (not O2)
by methanogens: methanogens use CO2 that is reduced to CH4
(methane)
by sulfur bacteria: inorganic sulphate (SO4) is reduced to hydrogen
sulfide (H2S)
Aerobic Respiration
C6H12O6 + 6O2
6CO2+ 6H2O +Energy
A large amount of energy from
the electrons of food is
released in small steps by
being transferred from carrier
to carrier rather than all at
once.
Because of this, energy is not
released as heat but it is used
to produced ATP.
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Aerobic
respiration
The complete oxidation of
glucose proceeds in
stages:
1. glycolysis
2. pyruvate oxidation
(prep reaction)
3. Krebs cycle
4. electron transport chain
& chemiosmosis
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Mitochondrion: Structure & Aerobic Cellular
respiration
1. Glycolysis (@cytoplasm)
2. pyruvate oxidation
(prep reaction): @Matrix
3. Krebs cycle: @Matrix
4. electron transport chain
(cristae) & chemiosmosis
(intermembrane space, cristae,
mitochondrial matrix)
Glycolysis is common to all types of
cellular respiration
Glycolysis is the oxidation of glucose (6 carbons) into 2 molecules of
pyruvate (3 carbons each).
-occurs in the cytoplasm
-all organisms do glycolysis (the fate of pyruvate may differ)
-net production of 2 ATP molecules by substrate-level phosphorylation
-2 NADH produced by the reduction of NAD+
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Pyruvate fate
Pyruvate fate differs:
1. aerobic respiration – occurs when oxygen is used as the final
electron acceptor
When oxygen is present, pyruvate is oxidized to acetyl-CoA
which enters the Krebs cycle. NAD+ is recycled at the ETC.
2. fermentation – occurs when oxygen is not available; an
organic molecule is the final electron acceptor
When oxygen is not available, pyruvate is reduced in order to
oxidize NADH back to NAD+
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Aerobic Respiration
Fermentation
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Fermentation
In Fermentation: The final electron acceptor is an organic
molecule
Produces less ATP than in aerobic respiration
1. ethanol fermentation occurs in yeast
-glucose is transformed into CO2 and ethanol.
2. lactic acid fermentation
-occurs in animal cells (especially muscles under intensive
exercise),
-occurs in yeast and bacteria
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Glucose
2 NADH
2 Pyruvate
2 ADP
2 P
2 ATP
2 NAD+
GLYCOLYSIS
2 ATP
2 NAD+
GLYCOLYSIS
2 ADP
2 P
Glucose
2 NADH
2 Pyruvate
2 NADH
2 NADH
2 CO2
released
2 NAD+
2 NAD+
2 Lactate
Lactic acid fermentation
2 Ethanol
Alcohol fermentation
Aerobic respiration: Pyruvate Oxidation
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Electron Transport Chain and chemiosmosis
A proton gradient
is established by
the ETC
H+ will return back to
the matrix by diffusion through
ATP synthase to produce ATP
The higher negative charge in the
matrix attracts the protons (H+) back
from the intermembrane space to
the matrix.
The accumulation of protons in the
intermembrane space drives protons
into the matrix via diffusion.
Most protons move back to the matrix
through ATP synthase.
ATP synthase is a membrane-bound
enzyme that uses the energy of the
proton gradient to synthesize ATP
from ADP + Pi.
Electron Transport
Chain & ATP synthase
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Photosynthesis is a redox process, as is cellular
respiration
Photosynthesis, like respiration, is a redox
(oxidation-reduction) process
– Water molecules lose electrons along with hydrogen
ions (H+) to release O2
– Atmospheric CO2 is reduced to glucose as electrons
and hydrogen ions are added to it
Reduction
6 CO2 + 6 H2O
C6H12O6 + 6 O2
Oxidation
Photosynthesis Overview
Photosynthesis takes place in two stages
Light-dependent reactions
Pigments capture energy from sunlight (photons of
light) and electrons from pigments gain energy
Use of light/electron energy to make ATP and to reduce
NADP+ (an electron carrier) to NADPH
Light-independent reactions (Calvin cycle)
Using the ATP and NADPH to power the synthesis of
organic molecules from CO2 in the air.
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In
cyanobacteria
bacteria,
photosynthesis
takes
place in the
plasma
membrane, it
has thylakoids)
Photosynthetic bacteria
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In green plants and some algae, and some protists
(euglena, diatoms, kelp) photosynthesis
takes place in chloroplasts
In plants,
the mesophyll of
the leaves is
rich in chloroplasts
Stoma (stomata)
allows atmospheric CO2
to enter the
leave and allows O2 to be
released
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Photosynthesis Overview
Photosynthesis takes place in chloroplasts (many
of them are located in the mesophyll cells of
the leaf).
thylakoid membrane – internal membrane arranged in
flattened sacs
-contain chlorophyll and other pigments
-photosynthetic pigments are clustered together to
form photosystems
grana – stacks of thylakoid membranes
stroma – semiliquid substance surrounding thylakoid
membranes
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The light-dependent
reactions occur
on the thylakoid
membrane
The ATP and NADPH
Is then used to fuel
carbon fixation (CO2
Is converted into
organic molecules) via
the Calvin cycle
in the stroma
Photosynthesis is a redox process, as is cellular
respiration
• In photosynthesis, electrons gain energy by being
boosted up an energy hill (in cellular respiration
they went down)
– Light energy captured by chlorophyll molecules provides
the boost for the electrons
– As a result, light energy is converted to chemical energy,
which is stored in the chemical bonds of sugar molecules
The two stages of photosynthesis are linked by
ATP and NADPH
• NADPH produced by the light reactions provides
the electrons for reducing carbon in the Calvin
cycle
• ATP from the light reactions provides chemical
energy for the Calvin cycle
– The Calvin cycle is often called the dark (or lightindependent) reactions
– During the Calvin cycle carbon reduction occurs (CO2
into glucose)
H2O
CO2
Chloroplast
Light
NADP+
ADP
+ P
Photosystem II
Thylakoid
membranes
RuBP
Electron
transport
chains
Photosystem I
CALVIN
CYCLE
3-PGA
(in stroma)
ATP
NADPH
Stroma
G3P
O2
Sugars
LIGHT REACTIONS
CALVIN CYCLE
Cellular
respiration
Cellulose
Starch
Other organic
compounds
Visible radiation drives the light reactions
• Pigments, molecules that absorb light, are built
into the thylakoid membrane
– Plant pigments absorb some wavelengths of light
and reflect others
– We see the color of the wavelengths that are
reflected; for example, chlorophyll reflects green
– Pigments associated with photosynthesis absorb
light energy in the wavelengths that correspond to
red, blue and violet light.
Photosynthetic Pigments
Chlorophyll a – primary pigment in plants and
cyanobacteria. It absorbs violet-blue and red light and
reflects green light
Accessory pigments: secondary pigments absorbing light
wavelengths other than those absorbed by chlorophyll
a. -include: chlorophyll b and carotenoids
Clorophyll b absorbs violet-blue and red light and reflects green light
Carotenoids absorb blue and green light and reflect orange and
yellow light.
Light that is not absorbed by these pigments is reflected. The
reflected photons are absorbed by the retinal pigment of our eyes
(we see the reflected light). Chlorophylls reflect green light and
carotenoids reflect orange/yellow light.
Fall colors are produced by carotenoids and other accessory
pigments.
During the spring and summer, chlorophyll in leaves masks the
presence of carotenoids and other accessory pigments.
During the fall, cool temperatures cause the leaves to cease
manufacturing chlorophyll (so they do not reflect green light), and the
leaves reflect the orange/yellow light that carotenoids
and other pigments do not absorb.
+
Photosynthesis vs. Cellular Respiration
Cellular Respiration
Photosynthesis
O2
H2O
membranes
grana
ATP
NADP+
NAD+
enzymes
CO2
Carbohydrate
or other Organic
molecule
Which Organisms? Plants, photosynthetic protists (euglena, diatoms, kelp),
cyanobacteria (has thylakoids)
H2O
cristae
ADP
NADPH
O2
Carbohydrate
or other Organic
molecule
NADH
CO2
All organisms can do cellular respiration (aerobic, anaerobic, fermentation)
In Aerobic (presence of O2): pyruvate is oxidized
In the absence of O2 (anaerobic bacteria, yeast,
muscle/streneous exercise): pyruvate is reduced
Redox
CO2 is reduced to glucose, H2O is oxidized to O2
Energy conversion Sunlight into chemical energy (chemical bonds)
ATP production?
Yes, during light dependent/ Used in calvin cycle
Chemiosmosis
Yes, H+ move from thylakoid space to stroma/ATP synth.
Steps
Light dependent and Calvin cycle
ETC
On the thylakoid membrane
Enzymes
On the stroma (Calvin cycle)
Electron carriers NADPH/NADP+
Glucose is oxidized to CO2, O2 is reduced to H2O
Chemical energy (bonds) into ATP
Yes, during all the steps (that’s the goal)
Yes, H+ move from intermembrane space to matrix/ATP synth.
Glycolysis, pyruvate oxidation, krebs cycle, ETC/chemiosmosis
On the cristae (inner mitochondrial membrane)
On the matrix (Citric acid/Krebs cycle)
NAD+/NADH and FAD/FADH2
Photosynthesis and Cellular Respiration are
complementary Processes (Lab 4, Activity 1)
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