how cells work chapter 5. energy laws energy is the capacity to do work the total amount of energy...
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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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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
Adenosine triphosphate - ATP
Not the only waywe store energy
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• ATP couples energy
inputs and outputs
• ATP/ADP cycle
regenerates ATP
ATP ATP ADP releases energy ADP releases energyADP ADP ATP requires energy ATP requires energy
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The Cell’s Energy Currency• ATP couples energy inputs and outputs
• ATP/ADP cycle regenerates ATP
Regeneration of ATP happens quickly10 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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Vs.
If the reactionslowed, we canextract energyin more places
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 thingthat enzymes lower the activation energy?
Why is it a good thing that enzymes usually onlybind to one type of substrate (reactant)?
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How do enzymes lower activation energy?
Tough question, but they put the reactantsin 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 theactive 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 siteand clogs
Binds somewhereelse and changesshape
Bio-warfare, toxins
Allosteric site
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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
• 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
TRANSPORT
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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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• 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
Transport Proteins
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Passive and Active Transport
• Doesn’t require energy inputs
• Solutes diffuse through a channel inside the protein’s interior, or through cell membrane
• Net movement is down concentration gradient
Passive Transport Active Transport
• 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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Pinocytosis Phagocytosis
Receptor mediated