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.
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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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