Respiration

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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

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• 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

Figure 6.2
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• The human body uses energy from ATP for all its
  activities.
• ATP powers almost all cellular and body activities

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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

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• The energy in an ATP molecule
• Lies in the bonds between its phosphate groups

Figure 5.4A
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REDOX REACTIONS

• The loss of electrons is called oxidation.
• The addition of electrons is called reduction

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Overview of Aerobic Respiration

• C6H12O6 6O2 ? 6CO2 6H2O ATP
• glucose oxygen carbon
  water
• dioxide

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• When glucose is converted to carbon dioxide
• It loses hydrogen atoms, which are added to
  oxygen, producing water

Figure 6.5A
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STAGES OF CELLULAR RESPIRATION
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• Overview Cellular respiration occurs in three
  main stages
• Glycolysis
• Krebs Cycle or Citric Acid Cycle
• Electron Transport Chain or Phosphorylation

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• 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)

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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

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An overview of cellular respiration
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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)

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• 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)

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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

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An overview of cellular respiration
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• 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

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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

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• 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

Figure 6.5C
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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

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Electron transport chain
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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
• 223438
• Most ATP production occurs by oxidative
  phosphorylation or electron transport chain

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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

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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

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An overview of cellular respiration
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An overview of cellular respiration
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Animation Cell Respiration Overview
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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

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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)

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Fermentation

• Fermentation allows some cells to produce ATP
  without oxygen.
• This is Anaerobic respiration

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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

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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

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Yeast

• Single-celled fungi
• Carry out alcoholic fermentation
• Saccharomyces cerevisiae
• Bakers yeast
• Carbon dioxide makes bread dough rise
• Saccharomyces ellipsoideus
• Used to make beer and wine

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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

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• In alcohol fermentation
• NADH is oxidized to NAD while converting
  pyruvate to CO2 and ethanol

Figure 6.13C
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More details
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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

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• 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

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Figure 6.7A
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• In the first phase of glycolysis
• ATP is used to energize a glucose molecule, which
  is then split in two

PREPARATORY PHASE (energy investment)
 Steps        A fuel molecule is
energized, using ATP.
Glucose
ATP
Step
1
ADP
Glucose-6-phosphate
P
2
Fructose-6-phosphate
P
ATP
3
ADP
Fructose-1,6-diphosphate
P
P
 Step      A six-carbon intermediate splits
into two three-carbon intermediates.
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Figure 6.7C
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• In the second phase of glycolysis
• ATP, NADH, and pyruvate are formed

P
P
Glyceraldehyde-3-phosphate(G3P)
 Step     A redox reaction generates NADH.
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6
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ENERGY PAYOFF PHASE
NAD
?
NAD
?
6
6
P
P
NADH
NADH
H?
H?
P
P
P
P
1,3 -Diphosphoglycerate
 Steps           ATP and pyruvate are
produced.
6
9
ADP
ADP
7
7
ATP
ATP
P
3 -Phosphoglycerate
P
P
P
8
8
2-Phosphoglycerate
H2O
H2O
P
P
Phosphoenolpyruvate(PEP)
9
9
ADP
ADP
ATP
ATP
Pyruvate
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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

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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

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• 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

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1
3
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Krebs cycle

• The acetyl units are oxidized to carbon dioxide
• NAD and FAD are reduced
• Products
• Coenzyme A
• 2 CO2
• 3 NADH
• FADH2
• ATP

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• 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

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Figure 6.9A
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Krebs Cycle or Citric Acid Cycle
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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.

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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

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• 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

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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

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Making ATP Chemiosmotic model
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• In chemiosmosis, the H diffuses back through the
  inner membrane through ATP synthase complexes
• Driving the synthesis of ATP

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Certain poisons interrupt critical events in
cellular respiration
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• Various poisons
• Block the movement of electrons
• Block the flow of H through ATP synthase
• Allow H to leak through the membrane

Figure 6.11
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• 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

Electron shuttleacross membrane
Mitochondrion
2
2
NADH
NADH
Cytoplasm
(or 2 FADH2)
FADH2
2
6
2
NADH
NADH
OXIDATIVE PHOSPHORYLATION (Electron Transport
and Chemiosmosis)
GLYCOLYSIS
2 AcetylCoA
CITRIC ACIDCYCLE
2
Glucose
Pyruvate
2 ATP
about 34 ATP
2 ATP
by substrate-level phosphorylation
by oxidative phosphorylation
by substrate-level phosphorylation
About38 ATP
Maximum per glucose
Figure 6.12
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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

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INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND
SYNTHESIS
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• Cells use many kinds of organic molecules as
  fuel for cellular respiration

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• Carbohydrates, fats, and proteins can all fuel
  cellular respiration
• When they are converted to molecules that enter
  glycolysis or the citric acid cycle

Figure 6.14
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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

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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

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LE 9-19
Proteins
Carbohydrates
Fats
Amino acids
Sugars
Glycerol
Fatty acids
Glycolysis
Glucose
Glyceraldehyde-3-
P
NH3
Pyruvate
Acetyl CoA
Citric acid cycle
Oxidative phosphorylation
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• 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

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Figure 6.15
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• 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

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Figure 6.16
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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