chapter 6: cellular respiration what did you eat for...
TRANSCRIPT
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Chapter 6: Cellular Respiration
• Why do we eat?
What did you eat for breakfast?
• What types of macromolecules were in your breakfast?
• Where did the macromolecules (carbs, protein, fat) in your breakfast come from?
• Producers and Consumers• Autotrophs and Heterotrophs
+ sugar
• Where do the producers get their ‘breakfast’?
• Plants take in carbon dioxide (CO2) at their leaves
• Plants absorb water (H2O) at their roots
• The simple molecules CO2 and H2O have all of the atomsneeded to form glucose (C6H12O6), if rearranged
CO2
CO2 and H2OBreakfast is served
Is glucose likely to form spontaneously from water (H2O) and
CO2?• Why or why not?
CO2 C6H12O6H2O
+
2
Fuel molecules are rich in Chemical Energy (a form of Potential Energy)
Glucose or Fuel Molecules
Where does the energy come from?
CO2 C6H12O6H2O
+ + O2 as ‘waste’
Photosynthesis is an uphill climb!
• The energy of the sun is captured, or harnessed at the chloroplasts, and used to do work!
• Reminder…What is work?• What has been ‘moved’ uphill in photosynthesis?
• There is more chemical energy in the products of photosynthesis than in the reactants!
A little, green sugar producing factory
• All plants, some bacteria and some protisis, trap energy from sunlight and use it to build sugars, which they need to live and grow. This process is called photosynthesis.
• Nearly all life on Earth depends on photosynthesis. If plants stopped photosynthesising, animals would have no food, and the world would eventually run out of oxygen.
Energy Flow and Chemical Cycling in Ecosystems
Do animals take in all of this glucose, or do plants keep some for themselves? Why or why not?
• Energy flows through the ecosystem, beginning as light energy from the sun
• Light energy is transformed into chemical energy
• Some used to do work, and some transformed into heat
• Why heat?
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POP QUIZ• Which living organisms have chloroplasts?
• All living things grow, and do cellular work, correct? We know that growth requires energy. All living things are capable of acquiring energy to do work.
• Hmm, then, do all living things undergo some form of cellular respiration. Yes or No?
Tomorrow we will learn that cellular respiration has 3 major steps. The first step,
glycolysis, occurs in the cytoplasm, and yields a little bit of ATP.
Cellular Respiration
• The process by which energy is harvested from the breakdown of food and converted into the energy of ATP
• This process is most efficient in the presence of oxygen (O2) but can occur in its absence– Aerobic respiration– Anaerobic respiration (fermentation)
Burning Fuel• Notice there are many arrows in this
equation.• Cellular Respiration breaks down glucose in a
highly regulated, multi-step process• Why not just one step? • Why not just light glucose on fire?
• During cellular respiration, the hydrogen from glucose (and an electron) is being transferred to oxygen
• This is also a transfer of electron(s), TO oxygen, from glucose.
• The electron(s) are moving to a MORE electronegative atom, Oxygen. Oxygen will hold on to these electrons(s) very tightly.
e-+
e-
H
• Recall that oxygen is a highly electronegative atom
• Energetically, it is much more difficult to move an electron (an electron and H) away from oxygen than it is to move an electron (and H) away from a carbon atom
• Thus, electrons held by oxygen are lower on the energy ‘hill’ than electrons associated with carbon in a fuel molecule
OXYGENH
O
H
4
H
H
Energy must be added to pull an electron away from an atom. The more electronegative the atom, the more energy is required to take an electron away from it
e-
O
C
e-Very stable bond
Less stable bond
Pot
entia
l E
nerg
y
H
H
H
How great is this potential energy difference? An electron equally shared between Hydrogen and Carbon vs. an electron being ‘hogged’ when bound to Oxygen?
e-
O
C
e-
Very stable bond
Less stable bond
Pot
entia
l E
nerg
y
H
A LOT! A rapid electron fall• A balloon is filled with
HYDROGEN GAS H2• This is similar to the
arrangement of C-H
• A match is touched to the balloon (a catalyst to get the reaction going)
• Hydrogen gas reacts with Oxygen in the air and causes an explosiong. All of the energy is given off as HEAT.
• (think Hindenburg, except on a smaller scale).
• Energy is released when electrons are transferred from a less electronegative atom to a more electronegative atom
• (like from glucose to oxygen-to make water)
• The electrons are now in a more ‘stable’environment, as more energy would be needed to pull them away from their current arrangement
Cellular Respiration is a collection of controlled Redox Reactions
•In cellular respiration, glucose is not burned in one step. Instead, the ELECTRONS from glucose are transferred, step-by-step to increasingly more electronegative atoms.
•The final electron (and H) acceptor is oxygen.
• Water is formed as a byproduct.
e-
e-
e-
e-
O2
e-
H2O
Cellular Respiration is a “Stepwise Energy Harvest”
“Stepwise Energy Harvest” via:
•Enzymes
• electron shuttlers (NADH)
• electron transport chain
e-
e-
e-
e-
O2
e-
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Electrons are passed in “short’’ energy steps, down to oxygen
•Electrons are passed in ‘short’ steps from food (glucose) to electron shuttlers, and then to an electron transport chain
•Energy is ‘harnessed’along the way
Coupled Chemical Reactions
Which picture is similar to the balloon experiment?
Which picture is analogous to an electron transport chain? Why?
Coupled Chemical Reactions
ATP
ADP P
Electron Transport Chain
ATP
The Regeneration of ATP
ATP synthesis requires Energy
ATP hydrolysis yields Energy
How do reactions yield energy?
• Transfer of electrons during chemical reactions
• Relocation of electrons releases energy stored in organic molecules
• This energy is ultimately used to synthesize ATP
NH2
e-
ATP
Redox Reactions are a form of Energy Transfer
• The term “Redox” is a combination and abbreviation of two words:1. Reduction2. Oxidation
• These two chemical reactions always happen together
• The coupled gain and loss of ELECTRONS (e-s) • Electrons are negatively charged
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LEO the lion goes GER
• Loss of• Electrons is• Oxidation
• Gain of• Electrons is• Reduction
LEO GEROIL RIG
Oxidation Is Loss
Reduction IsGain
Bush and Co.
Redox Reactions
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif
Redox Reactions: Follow the electrons (e-)
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif
Redox Reactions
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif
In this example,
Compound B is
transformed into a new compound with a more
negative charge. Its
overall charge has
been reduced.
A Redox Reaction
• Na + Cl → Na+ Cl-
• Which atom is reduced?• Which atom is oxidized?
– Follow the electrons!
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A Redox Reaction
• Na + Cl → Na+ Cl-
• Which atom is reduced? Cl-• Which atom is oxidized? Na+
becomes oxidized
becomes reduced
Redox Reactions
• Loss or gain of electrons does not need to be complete
Cellular Respiration is a collection of Redox Reactions
C6H12O6 + 6O2 → 6CO2 + 6H2O + E
becomes oxidized
becomes reduced
Cellular Respiration is a collection of Redox Reactions
C6H12O6 + 6O2 → 6CO2 + 6H2O + E
During cellular respiration: Glucose is oxidized and Oxygen is reduced. Glucose ‘lost’ electrons, while oxygen gained electrons as water.
Cellular Respiration: A 3-part story Cellular Respiration: A 3 part
story
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Glycolysis: the splitting of sugar• First step in cellular respiration
• Occurs in the cytoplasm– The enzymes involved are dissolved in cytoplasm!
• INPUT: glucose, a 6 carbon sugar• Small amount of ATP added to start reaction• OUTPUT:
– 2 molecules of pyruvic acid (a 3 carbon molecule) – small amount of ATP– NADH!
2 Pyruvic
Acid
ATP
NADH
C
C
C
C
C
C
Glycolysis splits a six-carbon glucose into 2 three-carbon molecules
Glucose is first ‘energized’ with a phosphate. It has become momentarily less stable, energized.
ATP
2
P
P
ADP
C
C
C
C
C
C
ATP
2
ADP
A high-energy 6 carbon, glucose-like molecule
Glycolysis splits a six-carbon glucose into 2 three-carbon molecules
C
C
C
C
C
C
P
P
C
C
C
C
C
C
P
C
C
C
P
C
C
C
enzyme
Small amount of energy INPUT
ATP
2
ADP
Glycolysis splits a six-carbon glucose into 2 three-carbon molecules
2 Pyruvic Acid
ATP
ATP
2
2
NADH
YIELDS:
C
C
C
C
C
C
P
P
C
C
C
C
C
C
P
C
C
C
P
C
C
C
enzyme
C
C
C
C
C
C
Small amount of energy INPUT
NADH
What is the cab
carrying?
2Pyruvic Acid
Glycolysis Occurs in the Cytosol and does not require oxygen!
ATP2
NADH
YIELDS:
Glycolysis
C
C
C
C
C
C
C
C
C
C
C
C
Glycolysis generates a small amount of ATP
Direct phosphate transfer, enzyme mediated
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Glycolysis generates NADHNADH
e-What is meant
by a ‘high energy
electron’?
If an electron was ‘swiped’ or transferred to NADH from
glucose, what happened to
glucose during glycolysis? Was
it oxidized or reduced?
Later!
Glucose
2 Pyruvic acid
The book’s version
High Energy Electrons in the form of NADH and FADH2
NAD+ reduced
NAD+ + 2 e- + 1 H+ →NADH
FADH2
Cellular Respiration
Part 2: Krebs Cycle
• Where is this occuring?• What is a cycle?
Scary picture!
Part 2: Krebs Cycle
• Focus on outputs!!
4 + 2 = 64
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Part 2: Krebs Cycle
• NUMEROUS OXIDATION STEPS
• 6 Carbon molecule is oxidized to 2 molecules of CO2 6
Part 2: Krebs Cycle• Oxidiation steps produce energy in the form of ATP,
NADH, FADH2
• And the starting material (4 carbon molecule) is regenerated
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Where are the cabs (with e- s) going??
• NADH and FADH2 shuttle high energy electrons to an Electron Transport Chain
Part 3: Electron Transport Chain
• Where is this located, EXACTLY??
• What molecule sits at the bottom of the ‘chain’? – Hint: the molecule at the bottom is waiting,
and is very hungry for electrons
?
Electron Transport Chain
in the Inner Mitochondrial
Membrane
e-e-
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• Why is oxygen so important for cellular respiration?
• What function does the oxygen we BREATHE in have in this process?
OXYGENe- High energy electrons
• When high energy electrons are obtained by a protein, the protein may become ‘energized’
• These energized proteins have the capacity to do work!
• The work they will do?• Transport H+ against its concentration
gradiente-
e-
Before receiving e-
I’m feeling low onenergy.
I couldn’t possiblydo any WORK
H+
H+H+
H+
H+
H+
H+H+
H+
H+
H+
H+H+
Mitochondrial matrix
Intermembrane Space
H+H+H+H+
H+H+
e-
AFTER receiving e-
I’m energized, and ready to do
some WORK
e-Mitochondrial matrix
Intermembrane SpaceH+
H+H+ H+
H+
H+ H+
H+
H+ H+
H+H+
H+H+
H+H+
H+
H+
empty
• The work that is done is the pumping of H+ ions across the inner mitochondrial membrane AGAINST a concentration gradient!
e-
As electrons are passed along the ETC, H+ is pumped into the intermembrane space
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• This cellular work, has set up a H+ gradientacross the inner mitochondrial membrane
• Which way (into the matrix, or into the inner membrane space) do the H+ ions NOW want to diffuse?
ATP Synthase• The hydrogen ions will diffuse (rapidly) down
their concentration gradient• H+ diffuses through ATP Synthase, a membrane
protein that functions like our paddle wheel
The paddle wheel, and Star of the show!!
ATP Synthase is a mini-machine!
ATP Synthasecaptures the kinetic energy of H+ diffusion, and transforms it to synthesize ATP from ADP and P.
http://www2.nl.edu/jste/electron_transport_system.htm
http://www.biologie.uni-osnabrueck.de/biophysik/junge/pics.html
MOVIE TIME
Energetic Summary of Cellular Respiration
Can we generate ATP under anaerobic conditions? How?
• Aerobic= oxygen present• Anaerobic= without oxygen
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Does glycolysis require oxygen?
Does glycolysis produce ATP? If so, how much?
Krebs Cycle
Without oxygen, NADH cannot drop off its high energy electrons at the ETCSince oxygen is not ‘pulling’ electrons down the ETC, NADH (the electron carrier) fills up
In the absence of oxygen, NADH donates its high energy electrons to alternate substrates
Anaerobic Respiration: Lactic Acid Fermentation
Why do we continue to breath heavily even after we’ve
STOPPED exerting ourselves?
Anaerobic Respiration: Alcohol Fermentation
Are you thankful for yeast now??
Anaerobic RespirationAerobic cellular respirationutilizes OXYGEN as the final electron acceptor
Anaerobic respiration can occur with an alternate electron acceptor!
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Evolutionary Implications of Anaerobic Respiration
• Glycolysis is the most widespread metabolic pathway on Earth
• Glycolysis evolved very early
3.5 bya= bacterial fossils
2.7 bya= O2 accumulates
Does glycolysis require membrane bound organelles? Eukaryotic cells? ?
People can’t live on glucose
alone!!
Carbon fuel can come from macromolecules other than glucose
OUT?
Food
Polysaccharides Fats Proteins
Sugars Glycerol Fatty acids Amino acids
Amino groups
Glycolysis Acetyl-CoA
KrebsCycle Electron
Transport
cyanide
• Why is cyanide poisonous?
• How does cyanide actually KILL people, at the molecular level??