Energy

1

• Energy the ability to do work or bring about a
  change
• Cells need energy to maintain their organization
• Cells need energy to carry out reactions used to
  grow, develop, and reproduce

2

• Forms of energy
• Kinetic energy energy of motion
• Ex you raise your arm
• Potential energy stored energy capable of
  producing energy, but not being used yet
• Ex food we eat has potential energy
• Chemical energy composed or organic molecules
  such as carbohydrates
• Ex food we eat, ATP

3

• First law of thermodynamics (the law of
  conservation of energy) energy cannot be
  created or destroyed, but it can be changed from
  one form to another
• Energy flows it does not cycle
• As materials change from one form of energy to
  another, some energy is given off as heat (a form
  of energy)

4

• Second law of thermodynamics energy cannot be
  changed from one form to another without a loss
  of usable energy
• Heat given off through the conversion of chemical
  energy to kinetic energy is not a usable form of
  energy
• For this reason, living things are dependent upon
  an outside source of energy the sun

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• Metabolic Pathways and Enzymes
• Cellular reactions are usually part of a
  metabolic pathway, a series of linked reactions
• Many reactions have molecules in common
• Energy can be released in small amounts rather
  than all at once
• Illustrated as follows
• E1 E2 E3 E4 E5 E6
  
• A ? B ? C ? D ? E ? F ? G
• Letters A-F are reactants or substrates, B-G are
  the products in the various reactions, and E1-E6
  are enzymes.

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http//highered.mcgraw-hill.com/sites/0072437316/s
tudent_view0/chapter8/animations.html
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• Enzyme - a protein molecule that functions as an
  organic catalyst to speed a chemical reaction.
• An enzyme brings together particular molecules
  and causes them to react.
• The reactants in an enzymatic reaction are called
  the substrates for that enzyme.
• For series of reactions below, A is substrate for
  E1 and B is product. B then becomes substrate
  for E2 and C is product. Continues to end of
  pathway.
• E1 E2 E3 E4 E5 E6
  
• A ? B ? C ? D ? E ? F ? G

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• Energy of activation (Ea) - the energy that must
  be added to cause molecules to react with one
  another
• Enzyme lowers the amount of energy required for
  reaction to occur
• Enzymes allow reactions to take place at lower
  temperatures otherwise, reactions would not be
  able to occur at normal body temperatures

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Energy of activation (Ea)
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When no enzyme is present more energy required
When an enzyme is added less energy required
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Enzyme-Substrate Complexes
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• Every reaction in a cell requires a specific
  enzyme.
• Enzymes are named for their substrates

Substrate Enzyme
Lipid Lipase
Ureas Urease
Maltose Maltase
Ribonucleic acid Ribonuclease
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• Active site part of enzyme that attaches to
  substrate
• Active site may undergo a slight change in shape
  in order to accommodate the substrate(s)
• The enzyme and substrate form an enzyme-substrate
  complex during the reaction.
• The enzyme is not changed by the reaction (active
  site returns to its original state), and it is
  free to act again.

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http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter2/animation__how_enzymes_work.
html
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Enzymatic reaction
Substrates are combined into a larger product
Substrate is broken down into smaller products
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Induced fit model
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• Because the enzyme must undergo a slight change
  in shape to fit with the substrate, this is known
  as the induced fit model.

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Factors Affecting Enzymatic Speed

• Substrate concentration
• Temperature and pH
• Enzyme concentration
• Enzyme inhibition
• Competitive inhibitors
• Non-competitive inhibitors
• Enzyme co-factors

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• Substrate concentration
• Enzyme activity increases as substrate
  concentration increases because there are more
  collisions between substrate molecules and the
  enzyme.
• When active sites on enzymes are filled almost
  continuously with substrate, rate of activity
  cannot increase further.

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• Temperature and pH
• As the temperature rises, enzyme activity
  increases because more collisions occur between
  enzyme and substrate.
• If the temperature is too high, enzyme activity
  levels out and then declines rapidly because the
  enzyme is denatured.
• When enzyme is denatured, its shape changes and
  it can no longer bind to substrate.
• Each enzyme has an optimal pH and temperature at
  which the rate of reaction is highest.

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Rate of an enzymatic reaction as a function of
temperature and pH
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• Enzyme Concentration
• A cell regulates which enzymes are present or
  active at any one time and the quantity of enzyme
  present by turning on of off genes
• Another way to control enzyme activity is to
  activate or deactivate the enzyme, such as
  through phosphorylation (removal of phosphate
  group).

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• Enzyme Inhibition
• Occurs when an active enzyme is prevented from
  combining with its substrate.
• When the product of a metabolic pathway is in
  abundance, it binds competitively with the
  enzymes active site, a simple form of feedback
  inhibition.
• Other metabolic pathways are regulated by the end
  product binding to an allosteric site (another
  area of enzyme).
• Poisons such as cyanide are often enzyme
  inhibitors penicillin is an enzyme inhibitor for
  bacteria.

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Feedback inhibition
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When there is a sufficient amount of the end
product, some of the product binds to the
allosteric site on the enzyme, the active site
changes shape, the reactant cannot bind, and the
end product is no longer produced.
http//highered.mcgraw-hill.com/sites/0072437316/s
tudent_view0/chapter8/animations.html
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• Competitive inhibitors
• Have a similar shape to the substrate fit into
  the active site of the enzyme
• Dont take part in the reaction
• Block active site so substrate cant enter

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Animation

• Non-competitive inhibitors
• Do not have the same shape as the substrate do
  not compete for the active site
• Bind at some other point on the enzyme molecule,
  which still changes the shape of the active site
  so enzyme-substrate complex cannot be formed.

http//www.stolaf.edu/people/giannini/flashanimat/
enzymes/allosteric.swf
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• Enzyme Cofactors
• Presence of enzyme cofactors may be necessary for
  some enzymes to carry out their functions.
• Inorganic metal ions, such as copper, zinc, or
  iron function as cofactors for certain enzymes.
• Organic molecules, termed coenzymes, must be
  present for other enzymes to function.
• Some coenzymes are vitamins certain vitamin
  deficiencies result in a lack of certain
  enzymatic reactions.

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The ATP cycle
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• ATP (adenosine triphosphate)
• The energy currency of cells.
• A nucleotide made of the following
• Adenine
• Ribose (a sugar)
• Three phosphate groups
• Constantly regenerated from ADP (adenosine
  diphosphate) after energy is expended by the
  cell.
• Pneumonic devices ATP a triple phosphate
• - ADP a double phosphate

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http//www.stolaf.edu/people/giannini/flashanimat/
metabolism/atpsyn2.swf
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Advantages of ATP 1) It can be used in many
types of reactions. 2) When ATP ? ADP P, energy
released is sufficient for cellular needs and
little energy is wasted. 3) ATP is coupled to
endergonic reactions (requires an input of
energy) in such a way that it minimizes energy
loss.
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• Overview of Cellular Respiration
• Makes ATP molecules
• Releases energy in several reactions
• Glycolysis
• Transition reaction
• Citric acid cycle (Krebs cycle)
• Electron transport system
• An aerobic process that requires O2

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• Cellular respiration takes the potential chemical
  energy in the bonds of glucose and transforms it
  into the potential chemical energy in the bonds
  of ATP.
• ATP molecules store usable chemical energy to
  drive life processes through coupled reactions.

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• It is an oxidation-reduction reaction, or redox
  reaction for short.
• Oxidation is the loss of electrons hydrogen
  atoms are removed from glucose.
• Reduction is the gain of electrons oxygen atoms
  gain electrons.
• Remember OIL RIG (oxidation is loss, reduction is
  gain)

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• Enzymes involved
• NAD
• Nicotinamide adenine dinucleotide
• Accepts 2 electrons 1 H to become NADH
• FAD
• Flavin adenine dinucleotide (sometimes used
  instead of NAD)
• Accepts 2 electrons 2 H to become FADH2

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The NAD cycle
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Phases of Cellular Respiration

• Four phases
• Glycolysis
• Transition reaction
• Citric acid cycle (Krebs cycle)
• Electron transport system
• (If oxygen is not available, fermentation occurs
  in the cytoplasm instead of proceeding to
  cellular respiration.)

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The four phases of complete glucose breakdown
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• Glycolysis
• Occurs in the cytoplasm (outside the
  mitochondria)
• Glucose ? 2 pyruvate molecules.
• Universally found in all organisms
• Does not require oxygen.

http//www.science.smith.edu/departments/Biology/B
io231/glycolysis.html
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• Energy-Investment Steps
• Requires 2 ATP to start process and activate
  glucose
• Glucose splits into two C3 molecules (PGAL)
• Each C3 molecule undergoes the same series of
  reactions.

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• Energy-Harvesting Steps
• PGAL is oxidized by the removal of electrons by
  NAD phosphate group is attached to each PGAL as
  well (phosphorylation)
• Removal of phosphate from 2 PGAP by 2 ADP
  produces 2 ATP, and 2 PGA molecules

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• Removal of water results in 2 PEP molecules
• Removal of phosphate from 2 PEP by 2 ADP produces
  2 ATP molecules and 2 pyruvate molecules

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Glycolysis summary

• Inputs
• Glucose
• 2 NAD
• 2 ATP
• 4 ADP 2 P

• Outputs
• 2 pyruvate
• 2 NADH
• 2 ADP
• 2 ATP (net gain)

• When oxygen is available, pyruvate enters the
  mitochondria, where it is further broken down
• If oxygen is not available, fermentation occurs

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• Inside the Mitochondria
• Structure of mitochondia
• Has a double membrane, with an intermembrane
  space between the two layers.
• Cristae are folds of inner membrane
• The matrix, the innermost compartment, which is
  filled with a gel-like fluid.
• The transition reaction and citric acid cycle
  occur in the matrix the electron transport
  system is located in the cristae.

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Mitochondrion structure and function
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• Transition Reaction
• Is the transition between glycolysis and the
  citric acid cycle.
• Pyruvate (made during glycolysis) is converted to
  acetyl CoA, and CO2 is released
• NAD is converted to NADH H
• The transition reaction occurs twice per glucose
  molecule.

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Transition reaction inputs and outputs per
glucose molecule

• Inputs
• 2 pyruvate
• 2 NAD

• Outputs
• 2 acetyl groups
• 2 CO2
• 2 NADH

http//www.science.smith.edu/departments/Biology/B
io231/krebs.html
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• Citric Acid Cycle (aka Krebs Cycle)
• Occurs in the matrix of the mitochondria.
• C2 acetyl group (produced during transition
  reaction) joins a C4 molecule, and C6 citrate
  results.
• Each acetyl group gives off 2 CO2 molecules.
• NAD accepts electrons in three sites and FAD
  accepts electrons once.
• Substrate-level phosphorylation results in a gain
  of one ATP per every turn of the cycle it turns
  twice per glucose, so a net of 2 ATP are
  produced.
• The citric acid cycle produces four CO2 per
  molecule of glucose.

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Citric acid cycle
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Citric acid cycle inputs and outputs per glucose
molecule

• Inputs
• 2 acetyl groups
• 6 NAD
• 2 FAD
• 2 ADP 2 P

• Outputs
• 4 CO2
• 6 NADH
• 2 FADH2
• 2 ATP

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• Electron Transport System (ETS)
• Located in the cristae of mitochondria
• Series of protein carriers pass electrons from
  one to the other.
• NADH and FADH2 carry electrons picked up during
  glycolysis, transition reaction, citric acid
  cycle
• NADH and FADH2 enter the ETS.

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• As a pair of electrons is passed from carrier to
  carrier, energy is released and is used to form
  ATP molecules by oxidative phosphorylation (term
  used to describe production of ATP as a result of
  energy released by ETS).
• Oxygen receives electrons at the end of the ETS,
  which combines with hydrogen to form water
• ½ O2 2 e- 2 H ? H2O

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Overview of the electron transport system
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• Organization of Cristae
• The ETS consists of 3 protein complexes and 2
  mobile carriers.
• Mobile carriers transport electrons between the
  complexes.
• Energy is released by electrons as they move down
  carriers
• H are pumped from the matrix into the
  intermembrane space of the mitochondrion.
• Produces a very strong electrochemical gradient -
  few H in the matrix and many H in the
  intermembrane space.

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• The cristae also contain an ATP synthase complex
• Hydrogen ions flow through ATP synthase complex
  down their gradient from the intermembrane space
  into the matrix.
• Flow of 3 H through ATP synthase complex causes
  the ATP synthase to synthesize ATP from ADP P.
• This process of making ATP is called
  chemiosmosis, because ATP production is tied to
  an electrochemical gradient (H gradient)
• Once formed, ATP molecules are transported out of
  the mitochondrial matrix.

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http//vcell.ndsu.nodak.edu/animations/atpgradient
/movie.htm
http//www.sp.uconn.edu/7Eterry/images/movs/synth
ase.mov
http//www.science.smith.edu/departments/Biology/B
io231/etc.html
http//highered.mcgraw-hill.com/sites/0072437316/s
tudent_view0/chapter9/animations.html
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• Energy Yield from Glucose Metabolism
• Per glucose molecule
• 10 NADH take electrons to the ETS ? 3 ATP from
  each
• 2 FADH2 take electrons to the ETS ? 2 ATP from
  each
• Electrons carried by NADH produced during
  glycolysis are shuttled to the electron transport
  chain by an organic molecule (mechanism of
  delivery may vary of ATP produced by ETS).

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Accounting of energy yield per glucose molecule
breakdown
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• Fermentation
• Occurs when oxygen is not available.
• During fermentation, the pyruvate formed by
  glycolysis is reduced to alcohol and CO2, or one
  of several organic acids, such as lactate.
• Fermentation uses NADH and regenerates NAD,
  which are free to pick up more electrons during
  early steps of glycolysis this keeps glycolysis
  going.
• Occurs in anaerobic bacteria, fungus, human
  muscle cells.

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http//instruct1.cit.cornell.edu/Courses/biomi290/
MOVIES/GLYCOLYSIS.HTML
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Fermentation

• Before fermentation, glycolysis produces 2
  pyruvate molecules.
• Then pyruvate is reduced by NADH into lactate or
  alcohol CO2.

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Advantages and Disadvantages of Fermentation

• Fermentation can provide a rapid burst of ATP in
  muscle cells, even when oxygen is in limited
  supply.
• For bacteria, glycolysis and fermentation is the
  main energy source
• Lactate, however, is toxic to cells.
• Initially, blood carries away lactate as it
  forms eventually lactate builds up, lowering
  cell pH, and causing muscles to fatigue.
• Oxygen debt occurs, and the liver must reconvert
  lactate to pyruvate.

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Efficiency of Fermentation

• Two ATP produced during fermentation are
  equivalent to 14.6 kcal complete oxidation of
  glucose to CO2 and H2O represents a yield of 686
  kcal per molecule of glucose.
• Thus, fermentation is only 2.1 efficient
  compared to cellular respiration (which is 39
  efficient).
• (14.6/686) x 100 2.1

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Glycolysis and Fermentation inputs and outputs
per glucose molecule

• Inputs (into glycolysis)
• Glucose
• 2 ATP
• 4 ADP 2 P

• Outputs
• 2 lactate (fermentation) or
• 2 alcohol 2 CO2 (fermentation)
• 2 ADP (glycolysis)
• 2 ATP (net gain) (glycolysis)