Transcript Respiration - Ms. Killikelly's Science Classes

2.2 Cellular Respiration: The Details
► Goals;
 Break the bonds b/w the 6 C atoms of glucose,
resulting in 6 CO2 molecules
 Move H atom electrons from glucose to oxygen,
forming 6 water molecules
 Trap as much of the free energy released in the
process as possible in the form of ATP
Overview of cellular respiration
►4
metabolic stages
 Anaerobic respiration
1. Glycolysis (substrate level
phosphorylation)
 respiration without O2
 in cytosol
 Aerobic respiration
 respiration using O2
 in mitochondria
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain and
chemiosmosis (oxidative
phosphorylation)
C6H12O6 +
6O2
 ATP + 6H2O + 6CO2 (+ heat)
Energy Transfer
►
1.
2.
How is the chemical potential energy in
glucose transformed into ATP?
Substrate-Level Phosphorylation
Oxidative Phosphorylation
Substrate-Level Phosphorylation
►A
molecule containing a phosphate transfers
it to ADP (with the aid of enzymes), forming
ATP. 31kJ/mol of free energy is also
transferred.
► For each glucose molecule, 4 ATP are made
this way in glycolysis (stage 1) and 2 ATP in
the Kreb’s cycle (stage 3)
Oxidative Phosphorylation
► ATP
is formed indirectly through a series of
enzyme-catalyzed redox reactions involving
oxygen as the final electron acceptor
► It begins when the compound NAD+ (nicotinamide
adenine dinucleotide), which is a coenzyme,
removes 2 H atoms (2 protons and 2 electrons)
from glucose.
► 2 electrons and 1 proton attach and reduce NAD+
to NADH, while the left over proton dissolves in
surrounding solution H+(aq)
Oxidative Phosphorylation
► NADH
is formed during glycolysis, pyruvate
oxidation and 3 times in the Kreb’s cycle
► A dehydrogenase enzyme catalyzes this rxn.
► FAD (flavin adenine dinucleotide) also acts like
NAD+ and is reduced by 2 H atoms from glucose
to form FADH2 (occurs in Kreb’s cycle)
► These reductions are both energy harvesting rxns
that will later transfer most of their free energy to
ATP
Oxidative Phosphorylation
► These
co-enzymes (reduced FADH2 and
NADH) function as energy carriers
► So, how does the free energy get
transferred to ATP? It occurs in Stage 4
(electron transport and chemiosmosis) and
requires oxygen…discussed later!
Aerobic respiration happens in 4
stages:
Stage 1 – Glycolysis
(10 step process occurring in cytoplasm)
glyco
glucose
lysis
splitting
► Stage
2-Pyruvate oxidation-1 step process
occurring in the mitochondrial matrix
► Stage 3-Kreb’s Cycle (citric acid cycle) 8
step cyclical process occurring in the
mitochondrial matrix
► Stage 4 Electron Transport and
chemiosmosis (oxidative phosphorylation)
multi step process occurring in the inner
mitochondrial membrane (cristae)
Mitochondria — Structure
►
Double membrane energy harvesting organelle
 smooth outer membrane
 highly folded inner membrane
► cristae
 intermembrane space
► fluid-filled
space between membranes
 matrix
► inner
fluid-filled space
 DNA, ribosomes
 enzymes
► free
in matrix &
What cells would have
a lot of mitochondria?
outer
intermembrane
membrane
inner
space
membrane-bound
membrane
cristae
matrix
mitochondrial
DNA
In glycolysis, a glucose molecule (6 carbon) is broken
down into two 3-carbon pyruvate (pyruvic acid)
molecules.
glucose
energy released to
make small
quantity of ATP
(2 molecules)
series of enzyme
controlled reactions
pyruvic acid
Glycolysis does not require oxygen
-ate or acid???
► -ate
replaces the word acid in organic acids
to indicate the ionized form of the acid
► E.g. pyruvic acid-pyruvate
► E.g. aspartic acid-aspartate
Fig 11 (p.98)
► The
overall chemical equation for glycolysis
glucose + 2ADP + 2Pi + 2NAD+
► The
2 pyruvate + 2ATP + 2(NADH + H+)
energy yield for glycolysis
4 ATP produced
2 ATP used
2 ATP produced net (can be used immediately)
2 NADH produced (used later to obtain more ATP)
Glycolysis
► Alone,
this process is not efficient in transferring
energy from glucose (only 2.2%)
► Some is lost as heat but most of the energy is
trapped in the pyruvate and NADH
► Glycolysis is thought to be the earliest form of
energy metabolism.
► Video -http://www.youtube.com/watch?v=xstLxqPt6E
► Songhttp://www.youtube.com/watch?v=6JGXayUyNVw
Your turn…
► Read
p.94-100 and note sheets
► Answer Q 1-10 on p.115
► Fill out glycolytic Pathway
► Quiz on Wednesday, October 13th (all 10
steps with enzymes)
Stage 2 – Pyruvate oxidation
The pyruvic acid made in glycolysis
(stage1) still contains a lot of energy
and are transported through the
mitochondrial membranes into the matrix
► A multi-enzyme complex catalyzes 3
changes
►
Pyruvate oxidation
1.
2.
3.
A carboxyl group is removed as CO (a
decarboxylation rxn using the enzyme pyruvate
decarboxylase)
NAD is reduced by 2 H atoms (food) to form
NADH. The NAD+ oxidizes the 2-C portion and
becomes acetic acid. This is a redox rxn as
pyruvate is oxidized and NAD+ is reduced
Coenzyme A (contains S) is attached to the
remaining acetic acid portion to form acetyl-CoA
in an unstable bond (sets it up for stage 3)
2
+
Pyruvate oxidation equation
2 pyruvate + 2 NAD+ + 2 CoA
2 acetyl-CoA + 2 NADH + 2 H+ + 2 CO2
Where do the products go?
► Acetyl-CoA
move to stage 3-Krebs Cycle
► NADH move to stage 4-Electron
Transport/Chemiosmosis (produce ATP by
oxidative phosphorylation)
► CO2 exits as waste
► H+ remain dissolved in the matrix
What exactly is Acetyl CoA?
► It
is multifunctional; If the body needs
energy it moves into the Kreb’s cycle, if not
it produces lipids (energy storing)
► Many nutrients catabolized for energy are
converted to acetyl-CoA and then channeled
toward fat or ATP production-depending on
energy needs.
Anaerobic Respiration
(in animals)
anaerobic = in the absence of oxygen
In low oxygen conditions or
during heavy exercise, when not
enough oxygen can be supplied,
muscle cells swap to anaerobic
respiration
glucose
glycolysis still
happens as it does
not require oxygen
pyruvic acid
in absence of
oxygen pyruvic
acid is turned
into lactic acid.
lactic acid
2 ADP + 2 Pi
2 ATP
A build up of lactic acid produces muscle fatigue.
Muscle fatigue makes muscles ache and contract
less powerfully.
A recovery period is needed. During this time more
oxygen is taken in to convert the lactic acid back
into pyruvic acid again.
The volume of oxygen needed is called the oxygen
debt.
Summary
glucose
pyruvic acid
oxygen debt
e.g. during hard
exercise
lactic acid
oxygen debt
repaid during
recovery time
Anaerobic Respiration
in plants
The same process occurs in plants
and yeast in low oxygen conditions,
e.g. muddy, flooded soils.
glucose
2 ADP + 2 Pi
glycolysis still
happens, producing
2 ATP molecules
2 ATP
pyruvic acid
This time in absence of
oxygen, pyruvic acid is
turned into carbon
dioxide and ethanol
This is irreversible
ethanol + carbon dioxide
Comparison of aerobic and
anaerobic respiration
Aerobic respiration
Anaerobic Respiration
in animals
in plants and yeast
Oxygen required?
yes
no
no
Glycolysis occurs
yes
yes
yes
ATP yield
38ATP
2ATP
2ATP
Glucose completely broke
down?
yes
no
no
End products
Carbon
Lactic acid
dioxide
and water
Ethanol and
carbon
dioxide
Fermentation (anaerobic)
► Bacteria,
yeast
pyruvate  ethanol + CO2
3C
2C
NADH
►beer,
NAD+
wine, bread
► Animals,
1C
back to glycolysis
some fungi
pyruvate  lactic acid
3C
3C
NADH
►cheese,
NAD+back to glycolysis
anaerobic exercise (no O2)
Alcohol Fermentation
pyruvate  ethanol + CO2
3C
NADH
2C
1C
NAD+ back to glycolysis
 Dead end process
 at ~12% ethanol,
kills yeast
 can’t reverse the
reaction
bacteria
yeast
recycle
NADH
animals
some fungi
Lactic Acid Fermentation
pyruvate  lactic acid

3C
NADH
O2
3C
NAD+ back to glycolysis
 Reversible process
 once O2 is available,
lactate is converted
back to pyruvate by
the liver
recycle
NADH
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
anaerobic
respiration
mitochondria
Krebs cycle
aerobic respiration
Stage 3: Kreb’s Cycle
► 8-step
process catalyzed by enzymes
► Considered cyclic b/c oxaloacetate (the
product of step 8) is the reactant in step 1
► Cycles through twice for every glucose
molecule as there are 2 molecules of acetyl
CoA.
► Equation;
Oxaloacetate + acetyl-CoA +ADP +Pi +3 NAD+ + FAD
NADH + 3H+ + FADH2 + 2 CO2 + oxaloacetate
CoA + ATP + 3
The Krebs Cycle
►
Occurs in the matrix of the mitochondrion. Transfers
energy from organic molecules to ATP, NADH, FADH2
and removes C atoms as CO2
►
Aerobic phase (requires oxygen). By the end of the
Kreb’s Cylce the original glucose molecule is entirely
consumed
Steps
1. 2-carbon acetyl CoA joins with a 4-carbon
compound (oxaloacetate) to form a 6- carbon
compound called Citrate. CoA is released
(recycled)
The Krebs Cycle
Steps
2. Citrate (6-C) is re-arranged to isocitrate
(6-C)
3. Isocitrate is converted to alphaketoglutarate (5-C) by losing a CO2 and 2
H atoms that reduce NAD+ to NADH
The Krebs Cycle
Steps
4. Alpha-ketoglutarate (5-C) is converted into
succinyl CoA (4-C). One CO2 is removed,
coenzyme A is added and 2 H atoms reduce
NAD+ to NADH.
5. Succinyl CoA (4-C) is converted to
succinate (4-C). ATP is formed by substrate
level phosphorylation and coenzyme A is
released
The Krebs Cycle
Steps
6. Succinate (4-C) is converted to fumarate
(4-C). Two H reduce FAD to FADH2
7. Fumarate (4-C) is converted to malate (4C). This is a hydrolysis rxn
8. Malate (4-C) is converted to oxaloacetate
(4-C). Two H reduce NAD+ to NADH
Highlights
► Video-
http://www.youtube.com/watch?v=XVWdeK
oiEOc
► Energy is harvested in steps 3 (NADH), 4
(NADH) , 5 (ATP-substrate-level
phosphorylation), 6 (FADH2), 8 (NADH)
► The last 4 C atoms of the original glucose
leave as CO2 (waste)
Grand Total so far…
► Glycolysis
(2 ATP, 2 NADH)
► Pyruvate oxidation (2 NADH, 2 CO2)
► Kreb’s Cycle (after 2 cycles)




6
2
2
4
► The
NADH
FADH2
ATP
CO2
12 reduced coenzymes (energy carriers) will
eventually be transferred to ATP in stage 4
Where did all the carbons go?
► 6-C
(glucose) at the end of glycolysis is
transformed into two 3-C pyruvate
► After pyruvate oxidation you are left with
two CO2 and two acetyl CoA (2 carbons
each)
► Once the Kreb’s Cycle is completed you
lose the last four original carbons as CO2
► Occurs
Cellular Respiration
Stage 4
ETC and Chemiosmosis
in the inner mitochondrial membrane
► Requires oxygen (final acceptor of electrons in the
ETC) without oxygen; Kreb’s, ETC and
chemiosmosis stop.
► Energy carriers (NADH and FADH2) transfer the H
atom electrons to a series of compounds (mostly
proteins) in the Electron Transport Chain (ETC)
ETC
Brief Overview
► Electrons
move through a series of redox
reactions that release the free energy used
to pump protons into the intermembrane
space (this creates an electrochemical
gradient-source of free energy)
Brief Overview
► During
chemiosmosis, protons move
through ATPase complexes (within the
membrane) releasing free energy (drives
the synthesis of ATP)
Videos
► Video-ETC
► http://www.youtube.com/watch?v=xbJ0nbzt5Kw
► Video-Chemiosmosis
► http://www.youtube.com/watch?v=3y1dO4nNaKY
► Video-Oxidative
Phosphorylation
► http://www.youtube.com/watch?v=Idy2XAlZIVA
ETC
► The
ETC is arranged in increasing
electronegativity (weakest attractor of
electrons at start to strongest at the end.)
► Each component is reduced (gaining 2
electrons from the component before) and
oxidized (losing 2 electrons from the
component after.)
► Electrons are shuttled through like a baton
from start to finish
► As they move they become more stable as they
get closer to the nuclei of the atoms they
associate with.
ETC
► Free
energy is used to pump out H+
protons into the intermembrane space
► At the last component of the ETC, oxygen
(highly electronegative) accepts (strips) the
last 2 electrons and together with 2 protons
from the matrix, forms water
Actual components of ETC
► NADH
dehydrogenase, ubiquinone (Q),
cytochrome b-c1 complex, cytochrome c,
cytochrome oxidase complex.
► The ETC is highly exergonic
► The free energy lost by the electron pair
during transport is used to pump out H +.
Energy converted
► Chemical
potential energy of electron
position is converted to electrochemical
potential energy of a proton gradient
(accumulation of charged protons).
► FADH2 passes on their electrons to complex
Q (Ubiqinone)
► 2 ATP are formed for every FADH2
► 3 ATP are formed for every NADH
Chemiosmosis and Oxidative
Synthesis
► The
electrochemical gradient (of H+) stores
free energy
► Creates a potential difference (voltage), like
that of a battery
► B/c they cannot pass through the
phospholipids bilayer, they must pass
through proton channels associated with
ATP-synthase.
Chemiosmosis and Oxidative
Synthesis
► The
free energy stored in the gradient produces a
PMF (proton-motive force) that moves protons
through ATPase complex.
► Free energy in gradient is reduced and is used to
create ATP from (ADP and Pi)
► It is called chemiosmosis b/c the energy that
drives the synthesis of ATP comes from the
“osmosis” of protons through a membrane.
Chemiosmosis and Oxidative
Synthesis
► Once
created ATP move into cytoplasm
through facilitated diffusion to do “work”
(movement, cell division etc)
Cellular Respiration Summary
► Table
3 p.114
How much ATP is really made?
► Theoretically
36 is made but as the
membrane is permeable (to protons) and
some energy is used for other endergonic
rxns, actual yield is about 30 ATP
► Efficiency of energy conversion is about
32%
Controlling Aerobic Respiration
► Phosphofructokinase
(enzyme at step 3 of
glycolysis) controls cellular respiration
► It is activated by ADP and citrate
► It is inhibited by ATP
► NADH inhibits pyruvate decarboxylase
(enzyme that converts pyruvate to acetyl
CoA).
Metabolic Rate
► Amount
of energy consumed at a given
time, and a measure of the overall rate at
which the energy-yielding rxns of cellular
respiration takes place.
► BMR (Basal Metabolic Rate) is the minimum
amount of energy for survival (breathing,
control temp.) Usually accounts for 60-70%
of daily energy
Metabolic Rate
► BMR
Calculator
► http://www.tlbc.ca/blog/index.php/bmrcalculator/
► Varies with age, sex, health
Looking back…
► ATP
is a high energy yielding nucleotide
that biological systems need to power rxns
(muscle contractions, cell division)
► Glucose is broken down during cellular
respiration (covalent bonds are split) to
provide energy for the synthesis of ATP.
By-product is CO2.
Looking back…
► The
role of oxygen is to “grab” the excess
H+ (don’t want the cell to be too acidic)
forming water.
► Glucose is oxidized (into CO2) and oxygen is
reduced to H2O
Practice
► Worksheets
► P.115
Q12-18