How Cells Work

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How Cells Work

• Chapter 5

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Energy Laws

• Energy is the capacity to do work
• The total amount of energy in the universe is
  constant (1st law)
• Energy is flowing from high-energy forms to forms
  lower in energy. This is called ENTROPY

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ENERGY

• Energy is the capacity to do work
• Energy exists in multiple forms
• Light
• Heat
• Electricity
• Chemical bond energy
• Etc.
• These various types of energy can be placed into
  two groups
• Kinetic energy
• Potential energy

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KINETIC ENERGY

• Energy of motion
• Anything that moves possesses kinetic energy
• e.g., Heat, light, balls on a pool table, flowing
  water, flowing electrons, etc.

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POTENTIAL ENERGY

• Energy of location or structure
• Stored energy
• Resting objects may still possess energy
• e.g., A rock at the top of a hill, chemical bond
  energy

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Adenosine triphosphate - ATP

• Main energy carrier in cells
• Can give up phosphate group to another molecule
• Phosphorylation primes a molecule to react
• Currency our cells use

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Adenosine triphosphate - ATP

• We take in large energy sources
• glucose, starch, lipids, etc.
• We break these down, take the energy that was
  stored in bonds, and store the energy as ATP

Not the only way we store energy
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• ATP couples energy inputs and outputs
• ATP/ADP cycle regenerates ATP

ATP ? ADP releases energy ADP ? ATP requires
energy
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The Cells Energy Currency

• ATP couples energy inputs and outputs
• ATP/ADP cycle regenerates ATP

Regeneration of ATP happens quickly 10
million/sec/cell in active muscle
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ATP
The high energy bond is not so high in,
energy, but very unstable.
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Energy Changes

• Endergonic reactions require energy
• Synthesis of glucose from carbon dioxide and
  water during photosynthesis
• Exergonic reactions release energy
• Breakdown of glucose to carbon dioxide and water
  by aerobic respiration

Energy 6H2O 6CO2 ? C6H12O6 6O2
C6H12O6 6O2 ? Energy 6H2O 6CO2
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Reactions
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Electron Transfers

• Extracting energy in small pieces/less waste
• Oxidation loss of an electron
• Reduction gain of an electron
• Electron transfer chains are vital to the
  formation of ATP during photosynthesis and
  aerobic respiration

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If the reaction slowed, we can extract energy in
more places
Vs.
All energy lost at once
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Participants in Metabolic Pathways

• Reactants starting substances (also called
  substrate)
• Intermediates substances formed during the
  reaction
• Products what remains at the end of the reaction

C6H12O6 6O2 ? Energy 6H2O 6CO2
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Participants in Metabolic Pathways

• Energy carriers provide energy to activate
  enzymes
• Enzymes speed reactions
• Cofactors assist enzymes with reactions
• Transport proteins help substances across cell
  membranes

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Metabolic Pathways

• Biosynthetic (anabolic) pathways
• Require energy inputs
• Assemble large molecules from subunits
• Photosynthesis
• Degradative (catabolic) pathways
• Release energy
• Breakdown large molecules to subunits
• Aerobic respiration

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Enzymes

• Catalyze (speed up) reactions
• Recognize and bind specific substrates
• Act repeatedly emerge unchanged
• Most are proteins

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Activation Energy

• Minimum amount of energy required to get a
  reaction started
• For a reaction to occur, an energy barrier must
  be surmounted
• Enzymes make the energy barrier smaller

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What are some reasons why it is a good thing that
enzymes lower the activation energy?
Why is it a good thing that enzymes usually
only bind to one type of substrate (reactant)?
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How do enzymes lower activation energy?
Tough question, but they put the reactants in an
environment more favorable for a reaction.
increases concentration of substrate reorients
excludes water
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ENZYME EXAMPLE
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Factors Influencing Enzyme Activity

• Coenzymes and cofactors
• Competitive and noncompetitive inhibitors
• Allosteric regulators
• Temperature
• pH
• Salt concentration

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Coenzymes and cofactors
Cofactor inorganic helpers that bind to
the active site or substrate that speed
reactions Coenzyme organic helpers that bind
to the active site or substrate that speed
reactions

• Many enzymes require non-protein helpers for
  catalytic activity
• e.g., DNAse requires Mg2 as a cofactor
• Removal of Mg2 inactivates the enzyme

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Competitive and noncomp. Inhibitor
Binds to active site and clogs
Allosteric site
Binds somewhere else and changes shape
Bio-warfare, toxins
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Allosteric or noncompetitive control

• Activator or inhibitor binds to an enzyme NOT in
  the active site, like non-competitive inhib.
• Binding changes enzyme shape
• Change hides or exposes active site
• Your body does this on purpose
• Feedback inhibition
• Product of pathway binds to and inhibits enzyme
  in the pathway

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Allosteric Control
inhibition
activation
Figure 4.8
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Effect of Temperature

• Small increase in temperature increases molecular
  collisions, reaction rates
• High temperatures disrupt bonds and destroy the
  shape of active site

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pH shifts and salts also denature proteins
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Concentration Gradient
TRANSPORT

• Means the number of molecules or ions in one
  region is different than the number in another
  region
• In the absence of other forces, a substance moves
  from a region where it is more concentrated to
  one where it is less concentrated down gradient

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Diffusion

• The net movement of like molecules or ions down a
  concentration gradient
• Although molecules collide randomly, the net
  movement is away from the place with the most
  collisions (down gradient)
• e.g. perfume open in a room

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Factors Affecting Diffusion Rate

• Steepness of concentration gradient
• Steeper gradient, faster diffusion
• Molecular size
• Smaller molecules, faster diffusion
• Temperature
• Higher temperature, faster diffusion
• Electrical or pressure gradients

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Transport Proteins

• Span the lipid bilayer
• Interior is able to open to both sides
• Change shape when they interact with solute, only
  let one type through
• Move water-soluble substances across a membrane

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Passive and Active Transport
Passive Transport
Active Transport

• Doesnt require energy inputs
• Solutes diffuse through a channel inside the
  proteins interior, or through cell membrane
• Net movement is down concentration gradient

• Requires ATP
• Protein is an ATPase pump
• Pumps solute against its concentration gradient

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Active Transport of Na and K
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Osmosis

• Diffusion of water across a selectively permeable
  membrane
• Hypotonic solution with a lower concentration
  of solute
• Hypertonic solution with a higher concentration
  of solute
• Water always moves from a hypotonic solution to a
  hypertonic solution

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Osmosis
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Hydrostatic Pressure

• Pressure that a fluid exerts against structure
  enclosing it
• Increases with increased solute concentration
• Influences the osmotic movement of water

Think of a water balloon
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Membrane Traffic

• Endocytosis
• Membrane sinks inward around a substance bringing
  it into the cell in a vesicle
• Exocytosis
• Vesicle carrying substance fuses with membrane
  releasing it into theintracellular fluid

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Types of Endocytosis

• Pinocytosis drinking fluids
• Phagocytosis eating particles
• Receptor-mediated endocytosis - specific

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Phagocytosis
Pinocytosis
Receptor mediated