Energy

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Chapter 5 The Working Cell

• Energy
• The capacity to do work
• What is work?
• Potential Energy
• Stored energy, eg. in chemical bonds
• Kinetic Energy
• Energy of motion
• What is the Law of Conservation of Energy?

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ATP and Cellular Work

• The chemical energy of organic molecules is
  released in cellular respiration to make ATP in
  the mitochondria

• Consists of adenosine plus a tail of three
  phosphate groups
• Is broken down to ADP, accompanied by the release
  of energy

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• ATP functions in what is called energy coupling,
  or the ATP cycle

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• Most enzymes are proteins with diverse structure.
• Enzymes are chemical catalysts that
• Increase the rate of a reaction.
• Are not permanently altered or used up by the
  reaction.
• Do not change the nature of the reaction.
• enzyme animation..

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• Reduce the required amount of activation energy
  required to initiate the reaction.
• Many enzymes work by orienting molecules so that
  they can better contact each other.
• Each type of enzyme has has a highly-ordered,
  characteristic 3-dimensional shape
  (conformation).
• Ridges, grooves, and pockets lined with specific
  amino acids.
• Pockets active in catalyzing a reaction are
  called the active sites of the enzyme..

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• The molecule affected by the enzyme is the
  substrate.
• Substrates have specific shapes to fit into the
  active sites (lock-and-key model)
• Better fit may be induced (induced-fit model)
• Enzyme undergoes structural change when substrate
  binds..

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• Enzyme names end with suffix -ase.
• Enzymes may be named according to their mode of
  action, e.g. kinase.
• May specify both the substrate of the enzyme and
  job category.
• Enzymes may be named for the substrate, e.g.
  lipase, maltase.
• Different organs may make different enzymes
  (isoenzymes) that have the same activity.
• Differences in structure do not affect the active
  sites..

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• Enzyme activity can be affected by several
  factors
• Changes in pH and/or temperature may denature the
  enzyme. These changes may break the H bonds
  stabilizing the molecule.

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• Small molecules or ions called cofactors alter
  the shape of the active site and/or is needed for
  the substrate to bind with the active site, e.g.
  Ca.
• Certain organic molecules called coenzymes are
  needed to transport small molecules or ions
  (especially H) from one enzyme to another, e.g.
  NAD..

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• Metabolic pathways are frequently regulated by
  inhibition. End-product inhibition occurs when
  one product binds with the enzyme and prevents it
  from binding with the substrate. The product may
  bind with the enzyme at the allosteric site. This
  is negative feedback.
• inhibition animation..

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• Competitive inhibition occurs when some other
  imposter molecule (similar to the substrate)
  binds with the enzyme. This prevents the
  substrate from participating in any metabolic
  pathway. This is typically how poisons work..

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Membrane Transport

• Working cells must control the flow of materials
• This is the primary function of the plasma
  membrane
• Transport proteins also help with this task
• Transport process may be categorized by the
  energy requirements
• Passive transport
• Net movement down a concentration gradient.
• Does not require metabolic energy (ATP).
• Active transport
• Net movement against a concentration gradient.
• Requires ATP..

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Diffusion

• Molecules/ions are in constant state of random
  motion due to their thermal energy.
• Diffusion is the movement of particles from an
  area of high concentration to and area of low
  concentration. Net diffusion indicates the final
  concentration changes.
• Diffusion Animation
• Diffusion of some substances through the plasma
  membrane requires carriers or channels (discussed
  later)..

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• Osmosis is the special term for the net diffusion
  of H20 across a selectively permeable membrane.
• Osmosis is the movement of H20 from a high H20
  to lower H20 until equilibrium is reached.
• Two requirements for osmosis
• Must be difference in solute on the 2 sides of
  the membrane.
• Membrane must be impermeable to the solute.

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• Hypertonic solution has a higher concentration
  of solute
• Hypotonic solution has a lower concentration of
  solute
• Isotonic solution has an equal concentration of
  solute

Osmosis Animation..
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Water Balance in Cells

• The survival of a cell depends on its ability to
  balance water uptake and loss Osmoregulation

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Carrier-Mediated Transport

• Molecules that are too large and/or polar to pass
  through the plasma membrane require protein
  carriers.
• Facilitated diffusion is passive transport
  utilizing carriers. Molecules move from high
  concentration to low concentration.
• e.g. GLUT carriers transport glucose into human
  cells..

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• Active transport required the expenditure of ATP.
  Molecules are moved from low concentration to
  high concentration.
• The most common primary active transport
  mechanism is the Na/K pump. In this case, the
  protein carrier is an ATPase that converts ATP to
  ADP Pi. The carrier transports 3 Na out of the
  cell and takes in 2 K.
• Na/K Pump Animation..

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Bulk Transport

• Movement of many large molecules, that cannot be
  transported by carriers, at the same time.
• Exocytosis
• Fusion of the membrane-bound vesicles that
  contains cellular products with the plasma
  membrane.

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• Endocytosis
• Exocytosis in reverse.
• Specific molecules can be taken into the cell
  because of the interaction of the molecule and
  protein receptor (receptor-mediated endocytosis).
• Endo/Exocytosis
  Animation

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• Phagocytosis
• Pinocytosis