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Summary BIOL 151 Exam 2 Study Guide

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Biol 151

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Virginia Commonwealth University

This is a comprehensive and detailed summary on Exam 2 that covers key topics like;Energy for Life: Chemical Reactions and Enzymes Energy for Life Part 2: Enzyme Regulation Getting Energy from Food: Basics of Cellular Respiration Photosynthesis for this course. *Essential!! *For effective exam ...

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Bio 151 Study Guide #2
Energy for Life: Chemical Reactions and Enzymes
 Organisms need energy for all cellular activity
o Movement, building macromolecules, cell division
o Energy must be replenished often to meet these demands
 Energy comes from the sun
o Producers: Convert CO2 and water into sugars and O2 through photosynthesis
 Sun gives energy via photosynthesis
 CO2 + H2O  C6H12O6 + O2
o Consumers: Eat producers (or each other) and break down their molecules to obtain energy
 And building blocks for their macromolecules!
o Breaking down stuff into energy our cells can use
 Producers aren’t only plants – produce material that can be consumed by consumers and
decomposers
o Not a cycle – energy isn’t cycled; nutrients are cycled
o One way process because the steps aren’t energy efficient
 Energy gets lost as heat at every step
 This energy can’t be regained or used for anything else
 Why more energy is constantly needed
 Energy used by organisms to power metabolism
o Metabolism: Sum total of all chemical reactions inside our cells
o 2 groups – anabolic and catabolic
 Anabolic: Building up, require energy stored in chemical bonds
 Catabolic: Breaking apart, releases energy in bonds
 Energy – 2 categories
o Kinetic: Energy associated with movement; direct way to do work in cells
 Heat = molecular movement
 Can break bonds
 Light has movement
 Mechanical Energy = direct movement, like muscles
o Potential: Stored energy; has potential to do work
 Stored through energy bonds, concentration gradient, electric charge imbalance
o Potential and kinetic can be converted into each other
 Breaking bonds releases energy
 Laws of Thermodynamics: Rules we assume the whole universe operates by; physical laws that
govern energy
o First Law of Thermodynamics: Energy can’t be created or destroyed. The total amount of
energy in the universe is constant
 Can be converted into different forms/released as heat
 Plants take light  chemical energy
o Second Law of Thermodynamics: Converting energy isn’t efficient; heat energy increases
entropy
 Entropy: Measure of disorder in a system
 Higher degree of disorder = higher entropy
 Naturally increases, becomes more disorderly without energy input
 Energy must be invested to maintain order
 Old cells must be replaced
 All things tend to chaos, including cells
 Energy is lost as heat during conversions
 Some energy is used to increase entropy/disorder
o Contributes to the thermal motion of particles (heat) and increases the
entropy of the surroundings
o Heat can’t be used as energy
 The energy lost as heat must be replaced
o This is why organisms need a constant supply of energy
 Energy lost at each level as we move up ecological pyramid
o Why there are less organisms as you go up pyramid
o Nutrients are recycled
 Gibb’s Free Energy: Energy available to the cell, needed to run reactions
o Unusable energy = entropy, S x T

, o Total Energy = enthalpy (H)
o Can’t measure absolute energy levels, only changes in energy
 Measured in calories (cal) or joules (J)
 Change is represented by the symbol delta (Δ)
 ΔG = ΔH – T ΔS
 Useful (free) energy = total energy - wasted energy
 +ΔG = energy came in, more energy the cell can use
o Endergonic
o Anabolic reaction – requires energy inputs stored in chemical bonds
 -ΔG = losing energy, energy released, can be used for other things
o Energy left the system
o Exergonic and catabolic
 Free energy = energy used by the cell
o Requires energy to be put in or released
 Anabolic = endergonic  end up with more energy than you started with
 Catabolic = exergonic  end with less energy than you started with
 ATP = adenosine triphosphate; main energy currency for cell
o A base in DNA or RNA +3 phosphates
o Linked by high energy bonds
o It picks up free energy from exergonic reactions
 It stores it, and releases it elsewhere to help run endergonic reactions
o Endergonic reaction to link bonds
 Energy stored in phosphate bonds
 Lots of energy released when bond breaks (hydrolysis)
 Energy used on endergonic reaction elsewhere
 Usually only one phosphate broken off  ADP
 Last one broken off, energy is coupled to endergonic reaction
o ATP cycles between ATP and ADP
 Tons are made and broke down in seconds
 Enzymes make biochemical reactions happen
o Activation Energy: Input of energy required to get a reaction going
 Both exergonic and endergonic reaction require this
 Used to destabilize reactants  makes them more reactive
 Transition State Intermediates: Reactants in their unstable state
o Once the transition state is reached, the reaction will proceed on its own
without further E input
 Can come from random molecular movement
 More movement  more energy
 If a molecule moves fast enough, it can enter its transition state and react
 Doesn’t affect ΔG b/c the invested energy is re-gained during the reaction
o Enzyme: Catalyst, speeds up reaction by lowering activation energy
 Help bring reactants together, put them in an orientation to work optimally
 Enzyme = substrate
 Each enzyme is specific to a specific reaction
 Binds to specific reactant
 Active Site: Where reactant binds
o Forms enzyme-substrate complex
 Enzymes = very specific; usually only bind one set of substrates,
and catalyze one specific reaction
 Reaction takes place, products are released
o The enzyme is not changed or used up during the reaction
 Why shape and polarity = important
 Overcomes activation energy in 3 ways
 Enzymes move substrates into the right orientation to react
 Enzymes strain substrate bonds, putting them in an unstable transition state
 Enzymes can temporarily add chemical groups to the substrate, destabilizing its
bonds
o Not all enzymes will use all 3 methods to lower activation energy
 Induced Fit: Enzyme changes shape after substrate binds

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