Download Chapter 6: Cellular Respiration What did you eat for breakfast?

Chapter 6: Cellular Respiration
What did you eat for breakfast?
• What types of macromolecules were in
your breakfast?
• Why do we eat?
• Where did the macromolecules (carbs,
protein, fat) in your breakfast come from?
• Where do the producers get their
‘breakfast’?
+ sugar
• Producers and Consumers
• Autotrophs and Heterotrophs
Is glucose likely to form
spontaneously from water (H2O) and
CO2?
CO2
• Plants take in carbon dioxide
(CO2) at their leaves
• Plants absorb water (H2O) at
their roots
• Why or why not?
+
CO2
• The simple molecules CO2 and
H2O have all of the atoms
needed to form glucose
(C6H12O6), if rearranged
CO2 and H2O
H2 O
C6H12O6
Breakfast
is served
1
Fuel molecules are rich in Chemical
Energy (a form of Potential Energy)
Where does the energy come from?
Glucose or
Fuel Molecules
+
CO2
+ O2 as ‘waste’
H2 O
C6H12O6
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!
• 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.
A little, green
sugar producing
factory
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?
2
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.
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?
Cellular Respiration
Burning Fuel
• 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)
• 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?
H
e+
• During cellular respiration, the hydrogen from
glucose (and an electron) is being transferred to
oxygen
e-
• 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.
H
H
O
OXYGEN
• 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
3
How great is this potential energy difference?
An electron equally shared between Hydrogen and
Carbon vs. an electron being ‘hogged’ when bound to
Oxygen?
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- H
Less stable bond
e-
Very stable
bond
H
O
H
A LOT! A rapid electron fall
e-
H
O
H
Very stable bond
• Energy is released when
electrons are transferred
from a less
electronegative atom to a
more electronegative
atom
• A balloon is filled with
HYDROGEN GAS H2
• This is similar to the
arrangement of C-H
•
Less stable bond
C
Potential Energy
Potential Energy
C
e- H
A match is touched to
the balloon (a catalyst to
get the reaction going)
• (like from glucose to
oxygen-to make water)
• 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).
• 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
Cellular Respiration is a “Stepwise
Energy Harvest”
e-
“Stepwise Energy Harvest” via:
ee-
•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.
e-
• electron shuttlers (NADH)
eee-
O2
e-
•The final electron (and H) acceptor is
oxygen.
• Water is formed as a byproduct.
•Enzymes
H2 O
• electron transport chain
eO2
e-
4
Electrons are passed in “short’’ energy
steps, down to oxygen
Coupled Chemical Reactions
•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
Which picture is similar to the balloon experiment?
Which picture is analogous to an electron transport chain? Why?
The Regeneration of ATP
Coupled Chemical Reactions
ADP
ATP synthesis
requires Energy
ATP
ATP
ATP hydrolysis
yields Energy
P
Electron Transport Chain
Redox Reactions are a form of
Energy Transfer
How do reactions yield energy?
• The term “Redox” is a combination and
abbreviation of two words:
1. Reduction
2. Oxidation
• Transfer of electrons during chemical
reactions
e-
• Relocation of electrons releases energy
stored in organic molecules
• This energy is ultimately used to
synthesize ATP
NH2
• These two chemical reactions always happen
together
• The coupled gain and loss of ELECTRONS (e-s)
• Electrons are negatively charged
ATP
5
LEO the lion goes GER
LEO
GER
• Loss of
• Electrons is
• Oxidation
• Gain of
• Electrons is
• Reduction
Reduction
Is
Gain
Bush and Co.
Redox Reactions: Follow the
electrons (e-)
Redox Reactions
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif
Redox Reactions
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif
OIL RIG
Oxidation
Is
Loss
A Redox Reaction
In this
example,
Compound
B is
transformed
into a new
compound
with a more
negative
charge. Its
overall
charge has
been
reduced.
• Na + Cl → Na+ Cl• Which atom is reduced?
• Which atom is oxidized?
– Follow the electrons!
6
A Redox Reaction
Redox Reactions
becomes oxidized
• Na + Cl → Na+ Cl-
• Loss or gain of electrons does not need
to be complete
becomes reduced
• Which atom is reduced? Cl• Which atom is oxidized? Na+
Cellular Respiration is a collection
of Redox Reactions
Cellular Respiration is a collection
of Redox Reactions
becomes oxidized
C6H12O6 + 6O2 → 6CO2 + 6H2O + E
C6H12O6 + 6O2 → 6CO2 + 6H2O + E
becomes reduced
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
7
Glycolysis: the splitting of
First step in cellular respiration
sugar
Glycolysis splits a six-carbon glucose
into 2 three-carbon molecules
•
• 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!
ATP
2
Pyruvic
Acid
P
C
C
C
2
C
ATP
ADP
C
C
ATP
ADP
C
C
C
C
C
Glucose is first
‘energized’ with
a phosphate. It
has become
momentarily less
stable,
energized.
C
C
NADH
Glycolysis splits a six-carbon glucose into 2
three-carbon molecules
A high-energy
6 carbon,
glucose-like P
molecule
C
C
2
C
C
P
Glycolysis splits a six-carbon glucose into 2
NADH
three-carbon molecules
P
P
P
C
C
C
C enzyme
C
C
C
ATP
C
ADP
2
C
C
2
ATP
C
C
C
C
C
C enzyme
2 Pyruvic Acid
C
C
Small
amount of
energy
INPUT
C
C
C
C
P
C
C
C
P
C
C
C
C
Small
amount of
energy
INPUT
C
C
P
C
C
C
C
C
C
P
What is the
cab
carrying?
Glycolysis Occurs in the Cytosol and
does not require oxygen!
YIELDS:
2
NADH
ATP
Glycolysis generates a small
amount of ATP
2
Pyruvic Acid
C
C
C
C
C
C
Glycolysis
C
C
C
C
C
C
YIELDS:
2
NADH
ATP
Direct phosphate transfer, enzyme mediated
8
Glycolysis generates NADH
NADH
The book’s version
What is meant
by a ‘high
energy
electron’?
eLater!
If an electron
was ‘swiped’ or
transferred to
NADH from
glucose, what
happened to
glucose during
glycolysis? Was
it oxidized or
reduced?
High Energy Electrons in the form of NADH
and FADH2
2 Pyruvic acid
Glucose
Cellular Respiration
NAD+
reduced
NAD+ + 2 e- + 1 H+ →NADH
FADH2
Part 2: Krebs Cycle
• Where is this occuring?
• What is a cycle?
Part 2: Krebs Cycle
• Focus on outputs!!
6
2
Scary picture!
4
4+2=6
9
Part 2: Krebs Cycle
• NUMEROUS OXIDATION STEPS
• 6 Carbon molecule is oxidized to 2 molecules of
6
CO2
Part 2: Krebs Cycle
• Oxidiation steps produce energy in the form of ATP,
NADH, FADH2
• And the starting material (4 carbon molecule) is regenerated
4
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’?
Electron
Transport Chain
in the Inner
Mitochondrial
Membrane
e-
e-
– Hint: the molecule at the bottom is waiting,
and is very hungry for electrons
?
10
OXYGEN
e-
• Why is oxygen
so important for
cellular
respiration?
• What function
does the oxygen
we BREATHE in
have in this
process?
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
gradient
e-
I’m feeling low on
energy.
I couldn’t possibly
do any WORK
H+
H+
e-
Intermembrane Space
H+ H+
I’m energized,
and ready to do
H+
H+
some WORK
H+ H+
H+ H+
H+
H+
H+
H+
H+ H+ Intermembrane Space
H+
H+
eempty
eH+
H+
Before receiving e-
H+
H+
H+
H+ H+
H+
H+
H+ H+
H+
Mitochondrial matrix
H+
Mitochondrial matrix
AFTER receiving eH+
H+
H+ H+
H+ H+
• The work that is done is the pumping of
H+ ions across the inner mitochondrial
membrane AGAINST a concentration
gradient!
As electrons are passed along the ETC, H+
is pumped into the intermembrane space
e-
11
• This cellular work, has set up a H+ gradient
across 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 Synthase
captures the
kinetic energy of
H+ diffusion, and
transforms it to
synthesize ATP
from ADP and P.
Energetic Summary of Cellular
Respiration
http://www2.nl.edu/jste/electron_transport_system.
htm
http://www.biologie.uni-osnabrueck.de/biophysik/junge/pics.html
MOVIE TIME
Can we generate ATP under
anaerobic conditions? How?
• Aerobic= oxygen present
• Anaerobic= without oxygen
12
Does glycolysis require
oxygen?
Krebs
Cycle
Without oxygen,
NADH cannot drop off
its high energy
electrons at the ETC
Since oxygen is not
‘pulling’ electrons down
the ETC, NADH (the
electron carrier) fills up
Does glycolysis produce ATP? If so, how much?
Anaerobic Respiration: Lactic
Acid Fermentation
In the absence of
oxygen, NADH
donates its high
energy electrons to
alternate substrates
Anaerobic Respiration: Alcohol
Fermentation
Are you thankful
for yeast now??
Why do we continue
to breath heavily
even after we’ve
STOPPED exerting
ourselves?
Anaerobic Respiration
Aerobic cellular
respiration
utilizes OXYGEN
as the final
electron acceptor
Anaerobic
respiration can
occur with an
alternate electron
acceptor!
13
Evolutionary Implications of Anaerobic
Respiration
• Glycolysis is the most
widespread metabolic
pathway on Earth
• Glycolysis evolved very
early
People can’t
live on glucose
alone!!
OUT?
3.5 bya= bacterial fossils
2.7 bya= O2 accumulates
Does glycolysis require membrane bound
organelles? Eukaryotic cells?
?
Carbon fuel can come from
macromolecules other than glucose
Food
cyanide
Polysaccharides
Sugars
Glycerol
Fats
Fatty acids
Proteins
Amino acids
Amino groups
Glycolysis
AcetylCoA
Krebs
Cycle
Electron
Transport
• Why is cyanide
poisonous?
• How does cyanide actually
KILL people, at the
molecular level??
14