Metabolism

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Metabolism
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Cell Energetics

• Metabolism total of all the chemical reactions
  taking place in an organism

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Metabolism

• Anabolism build up processes consume
  (store) energy by assembling macromolecules
  (photosynthesis)
• Catabolism break down reactions release
  energy by breaking down (lyse) molecules
  (digestion)

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• Concept 8.1 An organisms metabolism transforms
  matter and energy, subject to the laws of
  thermodynamics

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Metabolism

• Energy - the ability to do work
• Closed Systems - system without energy input
• Open systems system with energy input

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Types

• Potential capacity to do work
• Caused by POSITION
• Stored chemical energy (glucose, glycogen)
• Kinetic energy of motion
• Equilibrium energy runs out

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Thermodynamics

• Thermodynamics - the study of energy
  transformations
• 1st Law of Thermodynamics - energy cannot be
  created nor destroyed transformed

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• 2nd Law of
  Thermodynamics - in a
  closed system, when
  energy is
  transformed,
  some is lost as heat
• Entropy decreasing
  available energy of the
  universe is
  increasing
  (disorder)
• Energy systems become more disordered/random
• Total entropy increases stuff runs down

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Free Energy

• The energy in a system
  available for work
• A spontaneous change can cause free energy to
  flow
• System becomes more stable
• Less work capacity
• Free energy decreases (entropy)

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Biological Order and Disorder

• Organisms live at the expense of free energy
• Organisms are open systems with low entropy
• Use free energy to maintain order and
  organization
• Convert complex molecules into simpler ones
  digestion
• Trade organization for heat (increases randomness
  and entropy)

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Types of Reactions

• Exergonic reaction - net release of free energy
• Less stable, more work
• Fire, respiration
• Endergonic reaction - energy-requiring reaction
  energy is absorbed/stored
• Photosynthesis

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Concept 8.3 ATP Powers Cellular Work by Coupling
Exergonic Reactions to Endergonic Reactions

• Cells do three main kinds of work
• Mechanical - movement
• Transport of stuff
• Chemical polymerization, bioluminescence

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Coupled Reactions

• Coupled Reactions - endergonic reactions are
  coupled with exergonic reactions
• Energy from an exergonic reaction (respiration)
  is stored in phosphate bonds
• Phosphate group is added to a molecule
• Phosphorylation
• Molecule works

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ATP

• Adenine ribose phosphate group
• Phosphate bond is easily broken/formed
• Controlled by enzymes

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Uses of Energy

• Mechanical - beating of cilia/flagella, muscle,
  cytoplasmic flow, movement of chromosomes
  (mitosis)
• Transport - H pump, receptors
• Chemical polymerization, bioluminescence

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Enzymes
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Concept 8.4 Enzymes speed up metabolic reactions
by lowering energy barriers
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Enzymes

• Enzymes - biological catalysts
• Accelerate reactions without being changed
• Proteins (700)
• Catabolic or anabolic
• All chemical reactions require activation energy
• Activation energy, EA - the initial amount of
  energy needed to start a chemical reaction
• Often supplied as heat from the environment
  (spontaneous)

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Enzymes

• Cellular T needs to remain low, but metabolism is
  too slow at low T
• Enzymes reduce activation energy
• Transition state - reactants have absorbed energy

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Enzymes

• Substrate substance enzyme acts upon
• Active site area on the enzyme which the
  substrate binds to (attaches)
• Verryyy specific
• Groove, pocket 3d shape

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Enzymes

• 2 mechanisms describe how enzymes function
• Lock and Key
• Induced Fit - enzyme may change shape to allow
  better reaction on substrate

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Chemical bonds broken
Active site
Induced fit
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Enzymes

• Enzymatic action is reversible
• E S P E
• Enzyme unaffected by reaction
• Dependent upon concentration of reactants vs
  products
• Reaction rate of 1000s per second
• Speeding up enzyme reactions
• Add more substrate until saturated with
  substrate
• Add more enzyme
• DNA controls cells activities by storing the
  code for protein synthesis (enzymes)

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Factors That Affect Enzyme Activity

• Temperature and pH
• Inorganic salts disrupt H, ionic bonds,
  hydrophobic interactions
• Cofactors
• Inhibitors

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Cofactors

• Cofactors - nonprotein enzyme helpers
• Metals Fe, Zn, Cu
• Coenzymes - organic
• Vitamins
• Inhibitors substances that inhibit the actions
  of enzymes (2 kinds)
• Competitive inhibitors
• Noncompetitive inhibitors

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Competitive inhibitors - resemble substrate,
block active site Neurotoxin, Disulfiram
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Enzymes

• Noncompetitive inhibitors - causes enzyme to
  change shape
• Destroys conformation (active site)
• DDT, nerve gas (DSF)
• May be allosteric regulation

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Concept 8.5 Regulation of enzyme activity helps
control metabolism

• A cells metabolic pathways must be tightly
  regulated

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Allosteric Regulation of Enzymes

• Allosteric regulation - a proteins function at
  one site is affected by binding of a regulatory
  molecule at another site
• Receptor site located away from the active site
  (quaternary structure)
• Allosteric site has to be activated, (may be
  inhibited)

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Allosteric activator
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Allosteric inhibitor
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Enzymes

• Cooperativity - one substrate molecule can
  activate all other subunits of an enzyme
• Only requires a small concentration of substrate
  to activate enzyme
• Hemoglobin

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Feedback Inhibition
Isoleucine allosteric inhibitor

• Metabolic pathways series of enzymes creates
  small steps to a final product
• Controlling the enzymes (activity or production)
  controls the pathway and product(s)
• Feedback Inhibition - end product of the pathway
  inhibits the pathway

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Enzymes

• Feedback inhibition prevents cells from wasting
  resources
• dont need gas if you dont have a car.

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Structure and Metabolism

• Cells are organized
• Enzymes are grouped into complexes or
  incorporated into membranes
• Multi-enzyme complex enzymes are assembled in
  correct physical position for a sequence of
  events to happen
• Mitochondria, chloroplasts