Energy in a Cell

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ATP

• Chapter 9
• Energy in a Cell

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9.1 The Need for Energy (p. 221-224)

• Energy is essential to life.
• Organisms are endergonic systems.
• What do we need E for?

• Active Transport
• Cell Division
• Transport
• Synthesis (proteins)
• others

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• ATP is the universal currency of energy exchange
  in biological systems.
• No matter what form of energy a cell uses as its
  primary source, the energy is ultimately
  transformed and conserved as ATP.

• adenosine monophosphate (AMP) nucleotide
• two phosphate groups
• pyrophosphate bonds (P).
• These two bonds are energy rich in the sense that
  their hydrolysis (breakage which releases water)
  yields a great deal more energy than a covalent
  bond of another molecule.

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• The ATP reaction is commonly written as
• ADP Pi energy? ATP
• The forming of ADP into ATP
• requires energy (endothermic) 8 kcal/mole
• is pH dependent.
• Note Forming ADP is like making a bank deposit
  or coiling a spring for each phosphate bond. (see
  figure 9.2 on p. 223)

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The Calorie

• Kcal kilocalorie
• equivalent to 1000 calories.
• When we say that a cup of milk has 120 calories
  we really mean 300 kilocalories or 300 000
  calories.
• Even though we use the word calorie it is, by
  definition, kilocalorie.

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The Mole
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9.2 Photosynthesis Trapping the Suns Energy p.
225-230

• Weve seen in our past learning that the cell
  uses energy during ACTIVE TRANSPORT. Where does
  this energy come from?

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RECALL FROM EARLIER GRADESAll animals are
heterotrophs - require food sources of energy.
i.e. trophic levels in a food chain
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• We do not make our own food for energy like
  plants, algae and some bacteria (autotrophs).
  This is summarized by the carbon-oxygen cycle
  below

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Photosynthesis The Energy Maker

• Autotrophs under go PHOTOSYNTHESIS to produce
  sugars (starches made up of glucose molecules)we
  say the suns energy is stored in a chemical
  bond.
• Recall
• UV energy CO2 6H2O ? C6H12O6 6 O2

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• In actuality, this reaction is elegant, but is
  not simple.
• MANY reactions occur inside the chloroplasts
  grana membrane.
• The chlorophyll in chloroplasts is one pigment (a
  green one, there are others) that absorbs sun
  energy (all colours except green) which excite
  electrons and cause a phosphate to attach to ADP
  molecules.

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LIGHT DEPENDENT-REACTIONS

• Energized electrons provide energy that
• Forms ATP.
• Releases oxygen molecules (from the splitting of
  H2O)
• See Fig. 9.5 p. 227
• Fig. 9.6 p. 228

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Light Independent Reactions/Dark Reactions

• At the same time (and more so at night when there
  is no sun) the Calvin cycle takes place in the
  stroma of the chloroplast.
• Powered by ATP
• from photosynthesis

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• Carbon dioxide gas (CO2) is taken in and used to
  form sugars (CH2O is short hand to represent many
  different types of sugar molecules, most
  importantly glucose).
• These are stored as starch granules in
  chloroplasts.
• They are also transported to other cells and
  accumulate in roots.
• See Fig. 9.7 p. 229

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The new summary of photosynthesis

• Light dependent reactions
• 12H2O 12NADP 18ADP ? 6O2 12NADPH 18ATP
• Light Independent reactions (Calvin cycle)
• 6CO2 12NADPH 18ATP?C6H12O612NADP18ADP6H2O
• Can you see how we get the overall Ps equation?
• The whole point of these reactions is to make a
  safe, energy rich molecule, glucose.

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9.3 Getting Energy to Make ATP

• Cellular Respiration
• When we consume the sugars from plants,
  (producers) or animals that have eaten plants
  (primary consumers), energy from the sugar bonds
  is released.
• The release of this energy is called respiration.
• Recall
• C6H12O6 6 O2 ? 6 CO2 6 H2O Energy (ATP)

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• Again, the reaction is elegant but far from
  simple!
• When animals and plants consume energy molecules
  like starch and glucose, many reactions occur.
• Glycolysis (anaerobic)
• Citric Acid Cycle (aerobic)
• Electron Transport Chain
• -also aerobic
• The last two occur
• inside the mitochondrion.

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Glycolysis

• Glycolysis is the only metabolic pathway shared
  by ALL organisms.
• Occurs in the cytoplasm.
• i.e. not in an organelle

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Glycolysis (contd)

• A process whereby glucose molecules are split in
  half (makes a 3-C compound called pyruvate) in a
  series of steps.
• Glycolysis releases a 2 ATP molecules per
  glucose molecule that are used to drive other
  reactions AND
• This process does not require O2
• Anerobic
• See Fig. 9.8 p. 232

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Aerobic vs. Anaerobic

• From here, pathways diverge in different
  organisms and in different situationsoxygen poor
  (anaerobic) and oxygen rich (aerobic).
• More about that later.

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• BUT more ATP is made inside the mitochondrion in
  two separate pathways
• The Citric Acid Cycle, CAC (KREBS CYCLE, KC)
• ELECTRON TRANSPORT CHAIN (ETC)
• CAC releases 1 ATP molecule
• ETC releases 30 ATP molecules!
• These reactions drive far more chemical reactions
  in our tissues because of it.

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Citric Acid Cycle (CAC)

• The CAC occurs inside the mitochondrial matrix.
• It is called a cycle, because one of its
  end-products is recycled in the cycle.
• Named because it forms citric acid
• an important intermediate molecule.

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Citric Acid Cycle (contd)

• The main outcome is the generation of a variety
  of energy intermediate molecules, not just ATP.
• GTP
• NADH
• FADH2.
• This cycle also releases 3 CO2 molecules per
  pyruvate (3-C).
• See Fig. 9.10 p. 233

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• A diagram shows the numbers of energy molecules
  generated
• animation

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The Electron Transport Chain (ETC)

• From the Krebs cycle (Citric Acid cycle) inside
  the mitochondrion, the ETC occurs inside the
  mitochondrial membrane.
• It causes a cascade of energy release by using
  the other energy molecules of NADH, FADH2 to cash
  in and make more ATP.
• See Fig. 9.11 p. 234

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• The specialized molecules that do this are called
  CYTOCHROMES and they pass excited electrons from
  one cytochrome to another stepwisethis releases
  even more ATP30 more ATP!in a controlled
  manner.
• This is where oxygen is consumed, and water
  formed.
• TOTAL ATP from 1 glucose molecule
• - 2 gly - 2 (Act T) 2 CAC 30 ETC 32 ATP

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• The schematic below shows how electrons
  transferred from the NADH in Krebs are
  transferred in a cascade of reactions in the
  ETCnote the need for flavin M (part of the group
  of riboflavins, or B vitaminsB2) and the role of
  iron ions (Fe).
• This releases a LOT of ATP molecules.

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Cellular Respiration Schematic
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In summary
www.goldiesroom.org
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In summary

• SO, back to our original reactionthe important
  component is the ENERGY
• C6H12O6 6O2 ? 6CO2 6H2O 32ATP
• We now know
• where oxygen is consumed,
• how CO2 is generated,
• where the H2O comes from
• and how many energy molecules are made.

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Anaerobic Respiration

• If no oxygen continues to be present or, in some
  organisms like yeast, where it is not used,
  fermentation occurs.
• This is also known as anaerobic respiration.
• uses the 3-C molecules (pyruvate) and makes
  lactic acid in our muscles or in yogurt) or
  ethanol (as in brewing).

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Anaerobic Respiration (contd)

• Only another 2 ATP molecules are made
• This occurs with some fungi, and with
  Lactobacillus acidophilus in yogurt, and in
  yeasts.
• This is the basis of cheese, yogurt, buttermilk,
  root beer (real root beer), breads, wines,
  spirits.

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Anaerobic Exercise

• In vigorous exercise, lactic acid builds up in
  our muscles when weve exhausted the oxygen
  supply in our haemoglobin
• i.e. We produce more lactic acid than our cells
  can remove and they begin to seize up creating
  pain.
• Athletes can increase their tolerance for lactic
  acid.

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Aerobic Respiration

• AEROBIC RESPIRATION occurs in our mitochondria
• these pathways occur when oxygen is required (as
  in us) and is present in sufficient amounts.
• Longer duration of exercise
• For these cycles to occur, active transport of
  pyruvate from glycolysis is needed this uses up
  the 2 ATP that were made.

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Metabolism

• METABOLISM refers to two contrasting cellular
  activities
• the total biochemical reactions required for
  energy making reactions called CATABOLISM
  (includes breaking down foods to store energy
  ATP - in our tissues)
• and
• the use of energy to synthesize cell material
  from small molecules in the environment, called
  ANABOLISM (energy consuming, using ATP to release
  energy).

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Catabolic Reactions

• Produce energy in the chemical bonds of a
  molecule called ATP (adenosine triphosphate).
• glycolysis
• CAC
• ETC
• lead to end products, which are "waste products"
  like water and CO2
• most importantthey generate ATP which is later
  used in anabolic reactions to build cell material
  from nutrients in the environment, like muscle
  tissue.

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Anabolic Pathways

• Lead to release of the energy to drive other
  reactions.
• These reactions make important molecules like
  proteins for our muscles, hair, nails, lipids for
  our fatty tissues, and so on.
• When energy is required during anabolism, it may
  be spent as the breaking of a high energy bond of
  ATP which has a value of about 8 kcal/mol of ATP
  molecules. This is like a withdrawal from your
  account.

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Role of Water
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• Breaking the ATP to make ADP releases 8 kcal/mol.
  The ATP reaction is commonly written as
• ATP ? ADP Pi 8 kcal/mol

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• The diagram showing the relationships between
  catabolism and anabolism is not to be memorized,
  but to help you understand the connections

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• IMP During catabolism, energy is changed from
  one form to another, but such energy
  transformations are never completely efficient,
  i.e., some energy is lost in the form of heat.
  This forms part of our body heat.
• In both catabolism and anabolism, energy is
  formed stepwise and broken down stepwise in a
  number of cycles.
• This controls the amount of energy stored or
  released.

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• The energy is passed along in two energy
  processes Exergonic reactions and Endergonic
  reactions.