Cellular Respiration

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Cellular Respiration
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Objectives

• 3.6.0 Introduction to metabolism (review)
• 3.6.1 Review enzyme kinetics and ATP
  production.
• 3.7.1 Define cell respiration
• 3.7.2 State that, in cell respiration, glucose
  in the cytoplasm is broken down by glycolysis
  into pyruvate, with a small yield of ATP.
• 3.7.3 Explain that, during anaerobic cell
  respiration, pyruvate can be converted in the
  cytoplasm into lactate, or ethanol and carbon
  dioxide, with no further yield of ATP.

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Introduction to metabolism

• Energy needs of living things
• Autotrophs
• Get energy from the sun or chemicals
• Producers
• Heterotrophs
• Get energy from
  consuming food
• Consumers
• Herbivores
• Carnivores
• Detritivores
• Saprotrophs
• Get energy from consuming dead material
• Decomposers

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Introduction to metabolism

• Metabolic pathways alter molecules in a series of
  steps.
• Enzymes selectively accelerate each step.
• Catabolic pathways release energy by breaking
  down complex molecules to simpler compounds.
• Anabolic pathways consume energy to build
  complicated molecules from simpler compounds.

• Metabolism is the sum of chemical reactions in a
  body.
• Metabolic pathways alter molecules in a series of
  steps.
• Catabolic pathways release energy
  by breaking down complex mole-
  cules to simpler compounds.
• Anabolic pathways consume energy
  to build complicated molecules
  from simpler compounds.
• Enzymes selectively accelerate
  each step.

Metabolic pathway
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Introduction to metabolism

• Organisms transform energy.
• Energy is the capacity to do work - to move
  matter against opposing forces. Energy is also
  used to rearrange matter.
• Kinetic energy is the energy of motion - ex
  photons, heat.
• Potential energy is the energy matter
  possesses because of its location or
  structure.
• Chemical energy is a form of
  potential energy in molecules
  because of the arrangement of
  atoms.

ATP
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Introduction to metabolism

• Energy can be converted from one form to another.
• Ex as a boy climbs a ladder to the top of the
  slide he is converting his kinetic energy to
  potential energy.
• As he slides down, the potential energy is
  converted back to kinetic energy.
• It was the potential energy in the food
  he had eaten earlier that provided
  the energy that permitted him to climb up
  initially.

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Introduction to metabolism

• Cellular respiration and
  other catabolic pathways
  unleash energy stored in
  sugar and other complex
  molecules, which were
  created during photosyn-
  thesis, an anabolic path- way.
• CO2 H2O ? C6H12O6 O2

Anabolism
Photosynthesis ? ? ?
Catabolism
??? Respiration
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Introduction to metabolism

• Anabolic reactions (building molecules) are
  endergonic (or endothermic) ones that absorb
  energy.
• Ex the overall reaction of photosynthesis
• 6CO2 6H2O ? C6H12O6 6O2
• Through this reaction, energy from the sun
  has been put into the chemical bonds
  of a sugar molecule. The sugar has
  more energy than the CO2 and H2O.

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Introduction to metabolism

• Catabolic reactions (breaking molecules) are
  exergonic (or exothermic) ones that release
  energy.
• Ex the overall reaction of cellular respiration
• C6H12O6 6O2 ? 6CO2 6H2O
  
• Through this reaction energy in the sugar
  is been made available to do work in
  the cell. The products (CO2 and H2O)
  have less energy than the reactants.

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Introduction to metabolism

• Exergonic vs. endergonic reactions

Respiration - Photosynthesis -
energy released for work energy
gained from the sun
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Introduction to metabolism

• The energy created by respiration is used to do
  work.
• A cell does three main kinds of work
• Mechanical work beating of cilia, muscle
  contraction
• Transport work pumping substances across
  membranes
• Chemical work driving ender- gonic
  reactions such as the synthesis of
  polymers from monomers.

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Introduction to metabolism

• In most cases, the immediate source of energy
  that powers cellular work (coupling exergonic
  reactions to endergonic reactions) is ATP
  (adenosine triphosphate).

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Introduction to metabolism

• Energy from respiration (burning food with O2) is
  used to add a PO4- group to ADP.
• When energy is needed by a cell, the PO4- group
  is removed, and the energy is released.
• The energy traveled from the sun, to the plant,
  to the animal.

Exergonic ? ? Endergonic

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Enzyme review

• Most chemical reactions do not occur
  spontaneously in our bodies at 98.6o F were
  too cold.
• Enzymes are proteins that assist our metabolism.
• Substrates are held in the active site by weak
  hydrogen bonds and ionic bonds.

Within the active site, chemical bonds are
stressed, and ATP provides the little energy
needed to start the chemical reaction.
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Enzyme kinetics

• An enzyme is a catalytic protein.
• A catalyst is a chemical agent that changes the
  rate of a reaction without being consumed by the
  reaction.
• Enzymes speed up metabolic reactions by lowering
  energy barriers.
• Ex In a match head, S O2 ?
  SO2 energy, but the reaction is
  not spontaneous friction
  must be applied to give
  some initial energy for
  combustion.

friction
In a match head S O2 ? SO2 energy
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What is cell respiration?

• Cell respiration is the controlled release of
  energy from organic compounds in cells to form
  ATP.
• It encompasses different reactions under
  different circumstances.
• Anaerobic respiration no oxygen
• Glycolysis
• Fermentation
• Aerobic respiration with oxygen
• Citric acid cycle

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Glycolysis

• Glycolysis (Greek sugar destruction) is the
  first step in cell respiration.
• An ancient process - occurs in all cells on
  Earth.
• Takes place in the cytoplasm. ?
• Does not require oxygen.

Remember only eukaryotic cells have
mitochondria.
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Glycolysis

• Glucose is broken down into pyruvate.
• Yields a small amount of ATP only 2 molecules.

2 ATP must be used to activate the glucose
then 4 ATP are pro- duced enough to power
only a small cell. BUT without NAD, the
pathway stops.
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Fermentations

• Fermentation allows NAD to be
  regenerated, which
  allows glycolysis to
  continue.
• Two anaerobic pathways
• Alcoholic fermentation
• Lactic acid fermentation

Sole function of fermentation is to regenerate
NAD, but there are many side benefits.
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Alcoholic fermentation

• Pyruvate is converted in the cytoplasm into
  ethanol and CO2 no more ATP, but NAD is
  regenerated.
• The process is present in yeast and some
  bacteria.
• Humans use this process to make bread, wine,
  beer.
• CO2 makes bread rise.
• Ethanol forms when CO2 is removed from pyruvate.
• Also important now as a bio-fuel (gasoline
  substitute).

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Alcoholic fermentation

• Yeast are critical for bread, beer,
  and wine production.

Beer production line
Winery fermenters
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Alcoholic fermentation
Production of bio-fuels Ex from starch
in corn seeds
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Lactic acid fermentation

• Muscle cells switch from aerobic to lactic acid
  ferment-ation so ATP is still produced when O2 is
  scarce.
• Ex athletes such as those running a marathon.
• The NAD must be regenerated to make more ATP.
• The waste product, lactate, causes muscle
  fatigue, but ultimately it is converted back
  to pyruvate in the liver.

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Lactic acid fermentation

• Pyruvate is reduced directly by NADH to lactic
  acid.
• Lactic acid fermentation by some fungi and
  bacteria is used to make cheese yogurt.

The bite of these products is due to the
lactic acid.
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Aerobic Cell Respiration
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Objectives

• 3.7.4 Explain that, during aerobic cell
  respiration, pyru- vate can be broken down in
  the mitochondrion into CO2 and H2O with a large
  yield of ATP.
• C.3.3 Draw and label a diagram of a
  mitochondrion ex- plain the relationship
  between its structure and its function.
• C.3.7 Analyze data relating to respiration.

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Aerobic cell respiration

• Remember glycolysis is the first step in both
  aerobic and anaerobic respiration.
• Its an ancient process (gt3 byo),
• Its found in all cells (cytoplasm),
• It converts glucose into 2 pyru- vates with a
  net production of only 2 ATP.
• More than ¾ of the original energy
  in glucose is still present after glycolysis.
• This energy can be captured in the process of
  aerobic respiration.

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Aerobic cell respiration

• With oxygen, pyruvate can be broken down further
  to yield much more energy.
• In the mitochondria, pyruvate is completely
  oxidized to CO2 and H2O.
• There is a large yield of ATP 34 more than
  glycolysis.

Most of the energy within the bonds of sugar is
made available.
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Mitochondrial structure
Mitochondria have a double membrane membrane
ridges are called the cristae, and the soupy
space between them is called the matrix. They
also have their own DNA and ribosomes.
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Mitochondrial structure

• Mitochondrial structure is related to its
  function.
• They were once free-living bacteria (the theory
  of endosymbiosis).
• The outer membrane is thought to be the hosts,
  from the original endocytosis the inner is
  bacterial.
• They need a lot of membrane surface area since
  this is where the enzymes for respiration
  are located.
• More space for more energy production.

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Aerobic cell respiration

• The 3 stages of cell respiration
• Glycolysis occurs in the cytoplasm.
• Breaks 1 glucose into 2 molecules of pyruvate
  forms 2 NADH and 2 ATP.
• The Krebs cycle occurs in the mitochondrial
  matrix.
• Degrades pyruvate to CO2 forms 2 NADH 2 ATP.
• NADH passes electrons to the electron transport
  chain on the mitochondrial membrane.
• Electrons eventually combine with O2 to form
  water.
• In the process, 34 more ATP are produced, and
  NAD is regenerated to be used in glycolysis.

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Aerobic cell respiration

No oxygen
With oxygen
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Aerobic cell respiration

• In the Krebs cycle pyruvic
  acid from glycolysis is
  degraded to 3 CO2, which
  are breathed out.
• Two ATP and several NADH are made through
  enzyme actions from each pyruvate

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Aerobic cell respiration

• NADH, made in the Krebs cycle in the matrix of
  the mito-chondria (its cytoplasm) carries the
  electrons produced when pyruvate is broken down
  into CO2 to the inner mitochondrial membranes
  (the cristae).
• The electrons are passed from one molecule to
  another and give up some energy at each step.
• This energy is used to pump hydrogen (H) across
  the membrane, building up a high concentration
  inside.

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Aerobic cell respiration

• NADH, made in the Krebs cycle in the matrix of
  the mito-chondria (its cytoplasm) carries the
  electrons to the inner mitochondrial membranes
  (the cristae).
• The H can only exit by diffusion through a
  protein called ATP synthase.
• The protein is like a turbine in a dam the H
  spin the protein and ADP P ? ATP.

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Aerobic cell respiration

• The electron transfer chain
• Energy in the NADH (the electrons from glucose)
  pump H into the cristae, building up a
  thousand-fold concentration difference.
• These diffuse out through ATP synthase making
  ATP.
• Aerobic respiration yields 38 ATP vs. 2 from
  glycolysis alone.

The electrons eventually get picked up by
oxygen, hydrogens follow, making H2O (water).
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Respiration poisons

• Some poisons interrupt cell respiration.
• Cyanide decouples electron transport electrons
  cant reach oxygen and back-up. No NAD is
  available for glycolysis, and creatures run out
  of ATP and die.

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An Analysis of respiration data

• Biosphere 2, an enormous greenhouse built in the
  Arizona desert, has been used to study 5
  different ecosystems. It is a closed system, so
  measurements can be made under controlled
  conditions. The effects of different factors,
  including changes in CO2 concentration in the
  greenhouse, were studied. The data shown below
  were collected over the course of 1 day in
  January.
• Identify the time of day when the sun rose.
• Identify the time of minimal CO2 concentration.
• What was the CO2 concentration at that time?

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An Analysis of respiration data

• Determine the maximum difference in CO2 conc.
  over the 24-hr period.
• What is the relationship between CO2
  concentration and light intensity?
• Suggest reasons for changes in CO2 conc. during
  the 24-hr period.