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Respiration• Cellular respiration is the process by which
cells transfer chemical energy from sugar molecules to ATP molecules.
• As this happens cells release CO2 and use up O2
• Respiration can be AEROBIC or ANAEROBIC
Breathing supplies oxygen to our cells and removes carbon dioxide
– Breathing provides for the exchange of O2 and CO2
Between an organism and its environment
CO2
CO2
O2
O2Bloodstream
Muscle cells carrying out
Cellular Respiration
Breathing
Glucose O2
CO2 H2O ATP
Lungs
Figure 6.2
.
The human body uses energy from ATP for all its activities. – ATP powers almost all cellular and body activities
CELLULAR RESPIRATION• Cellular respiration is an energy- releasing
process. It produces ATP• ATP is the universal energy source Making ATP
• Plants make ATP during photosynthesis
• Cells of all organisms make ATP by
breaking down carbohydrates, fats, and
protein
– The energy in an ATP molecule• Lies in the bonds between its phosphate groups
Phosphategroups
ATP
EnergyP P PP P PHydrolysis
Adenine
Ribose
H2O
Adenosine diphosphateAdenosine Triphosphate
++
ADP
Figure 5.4A
REDOX REACTIONS
– The loss of electrons is called oxidation.
– The addition of electrons is called reduction
Overview of Aerobic Respiration
C6H12O6 + 6O2 6CO2 + 6H2O +ATP
glucose oxygen carbon water
dioxide
– When glucose is converted to carbon dioxide• It loses hydrogen atoms, which are added to
oxygen, producing water
C6H12O6 6 O26 CO2 6 H2O
Loss of hydrogen atoms (oxidation)
Gain of hydrogen atoms (reduction)
Energy
(ATP)Glucose
+ + +
Figure 6.5A
STAGES OF CELLULAR RESPIRATION
Overview: Cellular respiration occurs in three main stages
1. Glycolysis
2. Krebs Cycle or Citric Acid Cycle
3. Electron Transport Chain or Phosphorylation
– Stage 1:
Glycolysis– No oxygen needed. It is universal
• Occurs in the cytoplasm
• Breaks down glucose into pyruvate, producing a small amount of ATP (2)
GLYCOLYSIS• Where?: In the cytosol of all cells.Both aerobic and anaerobic respiration begin with glycolysis.• What happens?: The cell harvests energy by oxidizing glucose
to pyruvate.• One molecule of glucose (6 carbons) is converted to two
pyruvate molecules (3 carbons) through a series of 10 reactions mediated by enzymes.
• Result: 2 pyruvate molecules (each with a 3 carbon backbone) 2 NADH molecules. Carrier that picks up hydrogens
stripped from glucose. 2 ATP molecules. 4 are made but cells use 2 to start
glycolysis so net gain is 2
An overview of cellular respiration
Preparatory steps to enter the Krebs cycle
• The 2 pyruvate molecules enter the mitochondrion and an enzyme strips one carbon from each pyruvate.
• This two carbon molecule is picked up by Co-enzyme A in preparation for the Krebs cycle.
• This is acetyl CoA. This is what enters the Krebs cycle: C-C-CoA (oxaloacetate)
Stage 2 :
The citric acid cycle or Krebs cycle
• Takes place in the mitochondria
• Completes the breakdown of glucose (catabolism), producing a small amount of ATP (2ATP)
• Pyruvate is broken down to carbon dioxide
• More coenzymes are reduced .Supplies the third stage of cellular respiration with electrons (hydrogen carriers such as NADH)
KREBS CYCLE or citric acid cycle • This cycle involves a series of 8 steps forming and
rearranging. Each time it releases CO2 and NADH carries hydrogen to the last step. 6 CO2 are given off as waste (this is the most oxidized form of Carbon)In total:
6 CO2
6 NADH are produced and
2 FADH and only
2 ATP
An overview of cellular respiration
Stage 3:
Oxidative phosphorylation or electron transport chain
• Occurs in the mitochondria (inner membrane)
• Uses the energy released by “falling” electrons to pump H+ across a membrane
• Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP
Chemiosmosis
Chemiosmosis is an energy coupling mechanism that uses energy stored on H+
Chemiosmosis is the coupling of the REDUX reactions of the electron transport chain to ATP synthesis
– NADH passes electrons to an electron transport chain
– As electrons “fall” from carrier to carrier and finally to O2
• Energy is released in small quantities
H2O
NAD
NADH
ATP
H
H
Controlled release of energy for synthesis
of ATPElectron
transport chain
2 O2
2e
2e
12
Figure 6.5C
ELECTRON TRANSPORT CHAIN
• Electron transport systems are embedded (protein
molecules) in inner mitochondrial membranes (cristae)
• NADH and FADH2 give up electrons that they
picked up in earlier stages to electron transport
system
• Electrons are transported through the system
• The final electron acceptor is oxygen. The
hydrogen combines with the oxygen to form water
Electron transport chain
Intermembrane space
Inner mitochondrial membrane
Mitochondrial matrix
Protein complex
Electron flow
Electron carrier
NADH NAD+
FADH2 FAD
H2OATPADP
ATP synthase
H+ H+ H+
H+
H+H+
H+
H+
H+
H+
H+
H+
H+
H+
P
O2
Electron Transport Chain Chemiosmosis
.
OXIDATIVE PHOSPHORYLATION
+ 212
Figure 6.10
An overview of cellular respiration (Layer 3)An overview of cellular respiration (Layer 3)
HOW MUCH TOTAL ATP(ENERGY) WAS PRODUCED?
• Glycolysis
2 ATP formed by substrate-level phosphorylation
• Krebs cycle and preparatory reactions
2 ATP formed by substrate-level phosphorylation
• Electron transport phosphorylation
32-34 ATP formed
2+2+34=38
Most ATP production occurs by oxidative phosphorylation or electron transport chain
WHY OXYGEN?
• Electron transport phosphorylation requires the presence of oxygen
• Oxygen withdraws spent electrons from the electron transport system, then combines with H+ to form water
Web site tutorials to check:
• http://www.sp.uconn.edu/~terry/Common/respiration.html
• http://www2.nl.edu/jste/electron_transport_system.htm
• http://www.wisc-online.com/objects/MBY2604/MBY2604.swf
An overview of cellular respiration
An overview of cellular respiration
An overview of cellular respiration (Layer 3)An overview of cellular respiration (Layer 3)
Animation: Cell Respiration OverviewAnimation: Cell Respiration Overview
How efficient is cellular respiration?
• Only about 40% efficient.
In other words, a call can harvest about 40% of the energy stored in glucose.
• Most energy is released as heat
Evolution of cellular respiration
• When life originated, atmosphere had little oxygen
• Earliest organisms used anaerobic pathways
• Later, photosynthesis increased atmospheric
oxygen
• Cells arose that used oxygen as final acceptor in
electron transport (without oxygen to act as the final
hydrogen acceptor the cells will die)
Fermentation
• Fermentation allows some cells to produce ATP without oxygen.
• This is Anaerobic respiration
ANAEROBIC RESPIRATIONFermentation is an anaerobic alternative
to cellular respiration• Do not use oxygen
• Produce less ATP( 2) than aerobic pathways
• Two types. One produces alcohol and the
other lactic acid as waste products
– Fermentation pathways
– Anaerobic electron transport
Fermentation– Under anaerobic conditions, many kinds of cells
can use glycolysis alone to produce small amounts of ATP
• Begin with glycolysis
• Do not break glucose down completely to carbon
dioxide and water
• Yield only the 2 ATP from glycolysis
• Steps that follow glycolysis serve only to regenerate
NAD+
Yeast
• Single-celled fungi
• Carry out alcoholic fermentation
• Saccharomyces cerevisiae– Baker’s yeast– Carbon dioxide makes bread dough rise
• Saccharomyces ellipsoideus– Used to make beer and wine
Our muscle cells…• In the absence of oxygen our muscles can
carry out fermentation, but the pyruvate from glycolysis is turned into lactic acid instead of alcohol
– In alcohol fermentation• NADH is oxidized to NAD+ while converting
pyruvate to CO2 and ethanol
NAD NADH NADH NAD2 2 2 2
GLYCOLYSIS
2 ADP 2 P ATP
Glucose 2 Pyruvate
releasedCO2
2 Ethanol
22
Figure 6.13B
Figure 6.13C
More details…
Two stages of glycolysis
• Energy-requiring steps
– ATP energy activates glucose and its six-
carbon derivatives
• Energy-releasing steps
– The products of the first part are split into
three-carbon pyruvate molecules
– ATP and NADH form
•Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
– In glycolysis, ATP is used to prime a glucose molecule
• Which is split into two molecules of pyruvate
NAD NADH H
Glucose2 Pyruvate
ATP2P2 ADP
22
2
2
+
+
Figure 6.7A
– In the first phase of glycolysis • ATP is used to energize a glucose molecule,
which is then split in two
ATP
Glucose PREPARATORY PHASE
(energy investment)
ADP
Step
Glucose-6-phosphate
Fructose-6-phosphate
P
P
Fructose-1,6-diphosphate
ATP
ADP
PP
Steps – A fuel molecule is energized, using ATP.
Step A six-carbon intermediate splits into two three-carbon intermediates.
1
2
3
44
1 3
Figure 6.7C
Pyruvate
ATP
ADP
ATP
ADP
P
ATP ATP
ADP ADP
P
2-Phosphoglycerate
P
H2O H2O
Phosphoenolpyruvate(PEP)
Steps – ATP and pyruvate are produced.
P 3 -Phosphoglycerate
P
P
9 9
6 6
7 7
8 8
6 9 Step A redox reaction generates NADH.
P
NADH NADHP
P P P P
P
+H+H
ENERGY PAYOFF PHASE
Glyceraldehyde-3-phosphate(G3P)
1,3 -Diphosphoglycerate
P
5
6 9
5 5
66
7 7
88
9 9
NAD NAD
– In the second phase of glycolysis• ATP, NADH, and pyruvate are formed
Net Energy Yield from Glycolysis
Energy requiring steps:
2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Glycolysis net yield is 2 ATP and 2 NADH
Preparatory reactions before the Krebs cycle
• Preparatory reactions– Pyruvate is oxidized into two-carbon acetyl units and
carbon dioxide– NAD+ is reduced
pyruvate + coenzyme A + NAD+
acetyl-CoA + NADH + CO2
• One of the carbons from pyruvate is released in CO2
• Two carbons are attached to coenzyme A and continue on to the Krebs cycle
CO2
Pyruvate
NAD NADH H
CoA
Acetyl CoA(acetyl coenzyme A)
Coenzyme A
Figure 6.8
Pyruvate is gets ready for the citric acid cycle– Prior to the citric acid cycle
• Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA
1
2
3
Krebs cycle– The acetyl units are oxidized to carbon dioxide– NAD+ and FAD are reduced
Products:• Coenzyme A
• 2 CO2
• 3 NADH
• FADH2
• ATP
The citric acid cycle (Krebs)completes the oxidation of organic fuel (glucose), generating many NADH and FADH2 molecules
– In the citric acid cycle• The two-carbon acetyl part of acetyl CoA is oxidized
CoA
CoA
CO2
NAD
NADHFAD
FADH2
ATP P
CITRIC ACID CYCLE
ADP
3
3
3 H
Acetyl CoA
2
Figure 6.9A
Krebs Cycle or Citric Acid Cycle
For each turn of the Krebs cycle
• Two CO2 molecules are released (All of the
carbon molecules in pyruvate end up in carbon dioxide)• Three NADH and one FADH2 (Coenzymes are
reduced, they pick up electrons and hydrogen)
• One molecule of ATP is formed for each turn so the net yield of ATP for the Krebs or Citric Acid cycle is 2 ATP molecules.
What happened to co-enzymes (NAD and FAD) during the first two stages?
Co-enzymes were reduced (gained electrons)
• Glycolysis 2 NADH• Preparatory
reactions 2 NADH• Krebs cycle 2 FADH2 + 6 NADH
• Total 2 FADH2 + 10 NADH
Most ATP production occurs by oxidative phosphorylation or electron transport chain
– Electrons from NADH and FADH2 • Travel down the electron transport chain to oxygen,
which picks up H+ to form water
– Energy released by the redox reactions• Is used to pump H+ into the space between the
mitochondrial membranes
ELECTRON TRANSPORT CHAIN OR PHOSPHORYLATION
• Takes place in the mitochondria• Coenzymes deliver electrons to electron
transport systems• Electron transport sets up H+ ion gradients• Flow of H+ down gradients powers ATP
formation• The net yield from oxidative
phosphorilation is 32 to 34 ATP molecules
Making ATP : Chemiosmotic model
– In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes
• Driving the synthesis of ATP
Intermembrane space
Inner mitochondrial membrane
Mitochondrial matrix
Protein complex
Electron flow
Electron carrier
NADH NAD+
FADH2 FAD
H2OATPADP
ATP synthase
H+ H+ H+
H+
H+H+
H+
H+
H+
H+
H+
H+
H+
H+
P
O2
Electron Transport Chain Chemiosmosis
.
OXIDATIVE PHOSPHORYLATION
+ 212
Figure 6.10
Certain poisons interrupt critical events in cellular respiration
– Various poisons• Block the movement of electrons
• Block the flow of H+ through ATP synthase
• Allow H+ to leak through the membrane
H+
H+
H+
H+
H+
H+ H+ H+ H+
H+
H+
H+
H+
O2
H2OP ATP
NADH NAD+
FADH2 FAD
Rotenone Cyanide, carbon monoxide
Oligomycin
DNP
ATPSynthase
2
ADP
Electron Transport Chain Chemiosmosis
1
2
Figure 6.11
•Review: Each molecule of glucose yields many molecules of ATP
– Oxidative phosphorylation, using electron transport and chemiosmosis
• Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration
NADHNADH
NADH NADH FADH2
Cytoplasm
Electron shuttleacross membrane Mitochondrion
GLYCOLYSISGlucose Pyruvate
by substrate-level phosphorylation
by substrate-level phosphorylation
by oxidative phosphorylation
OXIDATIVE PHOSPHORYLATION
(Electron Transport and Chemiosmosis)
2 AcetylCoA
CITRIC ACIDCYCLE
2 ATP 2 ATP about 34 ATP
Maximum per glucose:About
38 ATP
2
2 6 2
2 2
(or 2 FADH2)
Figure 6.12
Anaerobic Electron Transport
• Carried out by certain bacteria
• Electron transport system is in bacterial plasma membrane
• Final electron acceptor is compound from environment (such as nitrate), NOT oxygen
• ATP yield is almost as good as from aerobic respiration
INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND
SYNTHESIS
• Cells use many kinds of organic molecules as fuel for cellular respiration
– Carbohydrates, fats, and proteins can all fuel cellular respiration
• When they are converted to molecules that enter glycolysis or the citric acid cycle
OXIDATIVEPHOSPHORYLATION
(Electron Transportand Chemiosmosis)
Food, such aspeanuts
Carbohydrates Fats Proteins
Sugars Glycerol Fatty acids Amino acids
Aminogroups
Glucose G3P Pyruvate AcetylCoA
CITRICACID
CYCLE
ATP
GLYCOLYSIS
Figure 6.14
How is energy obtained from proteins?
• Proteins are broken down to amino acids
• Amino acids are broken apart
• Amino group is removed, ammonia forms, is
converted to urea and excreted
• Carbon backbones can enter the Krebs cycle
How do we get energy from fats?
• Most stored fats are triglycerides
• Triglycerides are broken down to glycerol and
fatty acids
• Glycerol is converted to PGAL, an intermediate of
glycolysis
• Fatty acids are broken down and converted to
acetyl-CoA, which enters Krebs cycle
LE 9-19
Citricacidcycle
Oxidativephosphorylation
Proteins
NH3
Aminoacids
Sugars
Carbohydrates
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
Fattyacids
Glycerol
Fats
• Food molecules provide raw materials for biosynthesis
– Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials
– This process of biosynthesis • Consumes ATP
ATP needed to drive biosynthesis
ATP
CITRICACID
CYCLE
GLUCOSE SYNTHESISAcetylCoA Pyruvate G3P Glucose
Aminogroups
Amino acidsFatty acids Glycerol Sugars
CarbohydratesFatsProteins
Cells, tissues, organisms
Figure 6.15
• The fuel for respiration ultimately comes from photosynthesis
– All organisms • Can harvest energy from organic molecules
– Plants, but not animals• Can also make these molecules from inorganic sources by the
process of photosynthesis
Figure 6.16
Electrons “fall” from organic molecules to oxygen during cellular respiration
• In cellular respiration, glucose and other fuels are oxidized, releasing energy.
• In the summary equation of cellular respiration: C6H12O6 + 6O2 6CO2 + 6H2O+ ATP
• Glucose is oxidized (loses electrons), oxygen is reduced ( gains electrons)
• Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time.
glucose is broken down gradually in a series of steps, each catalyzed by a specific enzyme