Cellular Respiration: How Cells Harvest Chemical Energy

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Cellular RespirationHow Cells Harvest Chemical
Energy

• Chapter 6

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Organisms Must Use Energy

• When you do anything, you are using energy.
• Where does this energy come from?
• Your muscles use ATP in order to do their work.
• You break down sugars to make ATP.

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Photosynthesis and respiration give you all the
energy you need.
Photosynthesis grabs light energy.
Respiration takes light energy and makes ATP.
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Why do you breath oxygen?

• Your cells use oxygen get energy.
• Oxygen helps to break apart sugar.
• This is called aerobic respiration.
• Cellular respiration is the breakdown of sugars.
• Your respiratory system delivers oxygen to your
  cells.
• When you breath, you also get rid of carbon
  dioxide.
• CO2 is produced when sugar is broken down.

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Energy isnt magic, it is in the form of
molecules, and the main molecule used is ATP.

• Adenosine tri-phosphate
• The cells main energy currency.
• 3 parts of an ATP molecule
• Adenine
• This contains nitrogen.
• Ribose sugar
• This is a five-carbon sugar.
• 3 phosphate groups
• Hence the term tri-phosphate.
• Third phosphate bond is easily made and broken.
• ATP ? ADP P
• Phosphorylation?
• Any process that makes ATP.

ENERGY!
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Remember what energy is?Energy review!

• The capacity to do work.
• Kinetic energy is energy in motion.
• Potential energy is stored energy (usually in
  molecules).
• Energy can be transformed
• Kinetic to potential and kinetic to potential.
• This occurs in your bodies cells everyday.
• What is a calorie?
• It is a measure of how much energy a molecule
  has.
• One calorie is equal to the amount of energy
  needed to raise one gram of water 1 degree
  celcius, at ocean level.
• A calorie is a unit of measure.
• The calories in your food are actually
  kilo-calories. You do the math.

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How does the energy come from molecules?

• When you make or break chemical bonds, you
  actually shuttle electrons around.
• Redox reactions move electrons around.
• Oxidation (the removal of electrons).
• If a molecule is oxidized it has lost
  electrons.
• Reduction (the addition of electrons)
• If a molecule is reduced it has gained
  electrons.
• Imagine that electrons could be moved from a
  molecule with low potential energy, to a
  molecule with high potential energy.
• Which one would you rather have in your food?
• They are the same electrons, however.

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The Electron Transport Chain

• Remember our discussion on membranes?
• Membranes allow the cell to perform more work.
• These membranes are the basis of the ETC.
• This picture shows the inner membrane of a
  mitochondria, with its proteins, moving
  substances into and out of the inter-membrane
  space.

The folded membrane has proteins, which transport
electrons.
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What is cellular respiration?

• This is the process where energy is taken from
  food molecules.
• As you can see
• Nutrients are converted to sugars.
• Sugars get broken apart.
• Eventually food gets broken down to ATP.
• We will go through all of these steps.
• If you can describe how a sugar molecule gets
  broken down to ATP, you will understand this
  process!

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Cellular respiration has three main steps.

• 1. Glycolysis
• This is how sugar is initially broken apart.
• 2. The Citric Acid Cycle
• This occurs in the mitochondria.
• Sugar is completely broken down.
• 3. Electron Transport Chain
• Produces most of your bodys ATP.
• This is called oxidative phosphorylation.

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Glycolysis is the first step.

• Glycolysis takes place in the cytoplasm.
• Sugar is broken in half.
• After sugar is broken apart, then the cell needs
  to decide if there is enough oxygen present or
  not.
• You must break apart the sugar into smaller parts.

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Glycolysis is a two-step process.

• This initially breaks down sugar to two smaller
  molecules.
• There are two phases
• Energy investment
• Energy return
• These are shown on the right, but I will discuss
  them next.

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Glycolysis Energy Investment Phase

• This is a five-step process.
• You dont need to know the steps involved.
• Energy must be invested to break apart sugar.
• Here you can see two ATP molecules invested
  first.
• There is now a net loss of two ATP molecules so
  far.
• This may not make sense
• The idea of breaking apart sugar is to get ATP.
• Why invest ATP first?

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Glycolysis Energy Return Phase

• This is another five-step process that gives you
  ATP.
• You actually get more than you invested.
• In this step, you get a total of 4 ATP.
• You initially invested 2.
• This gives you a net of 2 ATP which is a profit.

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Glucose has now been broken in half.

• Follow the carbon atoms!
• Glucose has six carbon atoms.
• Each of these carbons has electrons.
• Remember that as you follow the flow of carbon
  atoms, you are actually following the flow of
  electrons to make ATP.
• Glucose (6C) is broken down into two independent
  Pyruvate (3C) molecules.
• You still have six carbon atoms, but two
  molecules.

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So far, so good

• Glucose was broken in half.
• One six-carbon molecule broken into two
  three-carbon molecules.
• You have produced 2 ATP so far.
• You still have to break down pyruvate molecules
  to get the rest of the energy.
• Remember, the cell must decide whether there is
  enough oxygen present or not.
• If yes, pyruvic acid is converted into Acetyl
  CoA.
• If no, pyruvic acid remains in the cytoplasm, and
  proceeds into anaerobic respiration.

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The Citric Acid Cycle

• If there is enough oxygen, pyruvic acid travels
  into the mitochondria and is chemically groomed
  before entering the citric acid cycle.
• It is converted into Acetyl Co-A.
• This is the molecule that enters the Krebs cycle.

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The Citric Acid Cycle

• Glycolysis occurred in the cytoplasm of the cell.
• Now pyruvate travels into the mitochondria.
• This is where the citric acid cycle occurs.
• Remember the mitochondria produces much of your
  cells energy.
• The mitochondria has folded membranes, giving it
  a lot of surface area.

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The Citric Acid Cycle

• You can see here that puruvate loses one carbon
  atom.
• This gives you one molecule of NADH.
• This will be used to make ATP later.
• Acetyl CoA then goes to the citric acid cycle.

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The Citric Acid Cycle

• Occurs in the matrix of the mitochondria.
• Completely breaks down the two remaining pyruvate
  molecules into CO2.
• When you breath out, 2/3 of the CO2 you expel
  comes from the Krebs Cycle.

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The Citric Acid Cycle

• Acetyl CoA enters the cycle.
• It has three carbon atoms.
• For each turn of the Krebs cycle
• Three NADH are produced.
• Two CO2 are produced.
• One ATP is produced.
• One FADH2 is produced.
• It takes two turns of the Krebs cycle to
  completely break down sugars, and release its
  stored energy.

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Summary of the Citric Acid Cycle

• One Acetyl CoA enters the cycle.
• What is produced
• One ATP molecule.
• Three NADH molecules.
• Two CO2 molecules.
• One FADH2
• Since there are two pyruvate molecules, each that
  has been converted you Acetyl CoA, you have to
  have two citric acid cycles to completely break
  down sugar.
• So, in order to find out what is made, double
  these numbers!
• 2 ATP
• 6 NADH
• 4 CO2
• 2 FADH2

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How much energy have we made so far?

• Glycolysis
• Two ATP (net).
• Production of Acetyl Co-enzyme A.
• Two NADH.
• Krebs Cycle
• Two ATP
• Six NADH
• One FADH2.
• The whole idea of breaking apart sugar is to get
  ATP. We have only made four so far. We need
  more!

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Oxidative PhosphorylationOccurs in the Electron
Transport Chain.

• Remember the term phosphorylation?
• This is any process that makes ATP.
• Oxidative means in the presence of oxygen.
• So what do you think oxidative phosphorylation
  does?
• This process makes most of your ATP, from the
  products of glycolysis and the citric acid cycle.

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The Electron Transport Chain

• On the inner membrane of the mitochondria, there
  are proteins.
• These proteins move electrons, and make ATP.
• This is how most of your ATP is made.

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The Electron Transport Chain

• This is the inner mitochondria membrane.
• NADH and FADH2 are broken apart.
• This puts H ions into the intermembrane space.
• These H ions form a concentration gradient.
• Concentration gradients are potential energy.
• ATP synthase, an enzyme, uses this potential
  proton energy to make ATP.

Outer mitochondrial membrane.
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The Electron Transport Chain

• Basically speaking
• On the inner membrane are proteins.
• A concentration gradient of H makes potential
  energy.
• This potential energy is like water behind a
  dam.
• This gradient (potential energy) causes H to go
  through (kinetic energy) the ATP synthase enzyme.
  This kinetic energy makes ATP, which is a form
  of potential energy.

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When studying

• Be able to draw and label a mitochondria, showing
  me where glycolysis, acetyl CoA production, and
  the Krebs cycle takes place.
• Be able to draw a chloroplast (discussed next
  lecture), label its parts and tell me where the
  light dependent and light independent reactions
  take place.
• Be able to draw the ETC, showing how ATP can be
  made through facilitated diffusion.

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Now you have broken down sugars.

• Glucose has six carbons.
• You have broken this down to six carbon dioxide
  molecules.
• You have also produced ATP.
• It may seem confusing, but draw the glucose
  molecule being broken apart. This will help.

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Look at the food you eat.

• We have only looked at sugars so far. But your
  food has more than sugars.
• Here is a brief overview of how other foods are
  broken down.
• You dont need to know these details, but
  hopefully it will help you understand the process.

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Poisons can interrupt the electron transport
chain.

• Take a look at
• Rotenone (a pesticide)
• Cyanide (poisons from plant materials)
• Carbon monoxide (cigarette smoke)
• Oligomycin (a fungal antibiotic)
• How do these stop the production of ATP?

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What happens if your cells dont have enough
oxygen?

• After glycolysis, your cells must determine if
  there is enough oxygen for the citric acid cycle.
• If there is enough oxygen, then aerobic
  respiration takes place.
• If there isnt enough oxygen, then fermentation
  will result.
• Fermentation is not as efficient it doesnt
  make near as many ATP.

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When plant and animal cells dont have enough
oxygen, they do different things.
Plant cells.
Animal cells.
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Plants undergo alcoholic fermentation.

• A plant makes ethyl alcohol, when there is not
  enough oxygen present.
• This is how beer, wine, and other alcohols are
  made.
• Animals (like you) dont do this.
• This is a good thing, or else you would be dead.
• This is still fermentation however, and only
  makes a little bit of ATP.

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Animals do lactic acid fermentation.

• If your cells dont have enough oxygen, you dont
  make very much ATP, and make lactic acid.
• Lactic acid can
• Destroy muscle tissue.
• Damage your brain.
• Your heart pumps oxygenated blood to counteract
  this lactic acid production.

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Your assignment.

• Complete the following questions, and turn them
  in at the beginning of your next lecture.
• 1, 2, 3, 6, 9, 10, 13.

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Wow that is a lot of information!

• Read the chapter.
• You may even want to do a chapter outline, and
  compare it to the next chapter.
• Pay attention in lecture.
• Ask questions.
• Good luck!