Metabolism & Free Energy Flashcards
Metabolism
All the chemical reactions occurring in an
organism
Metabolic Pathways
a molecule is altered through a series of steps resulting in a specific product
-Catalyzed by enzymes
Catabolic Pathways
release energy by breaking down molecules (exergonic)
Anabolic Pathways
consume energy to build complicated molecules from simpler ones (endergonic)
Energy
the capacity to cause change
Types of Energy
kinetic, heat (thermal), potential, chemical
Kinetic Energy
energy due to motion
-molecules move due to kinetic energy (ie passive transport)
Heat (thermal) energy
affects the speed of molecular movement
-type of kinetic energy
Potential Energy
based on position/location in surroundings
-stored energy
Chemical Energy
potential energy stored in chemical bonds
1st Law of Thermodynamics
Energy of the universe is constant so it can be transferred or transformed but not created or destroyed
2nd Law of Thermodynamics
Every energy transformation leads to increased entropy
Free Energy: definition
The portion of energy within a system that is free to do work (symbolized by G)
Free Energy: equation
ΔG = ΔH – TΔS
If ΔG is a negative value…
the process is spontaneous and exergonic & decreases the system’s free energy
– The final state of energy is less likely to change & is
more stable
If ΔG is a positive value…
the process requires energy input (endergonic) & increases the system’s free energy
Exergonic Reactions
Release energy (ΔG is negative) – Spontaneous (this doesn’t indicate the required time) – Ex: Cellular Respiration
Endergonic Reactions
Absorbs energy (Δ G is positive)
– Nonspontaneous
– Ex: Photosynthesis
Types of Cellular Work
mechanical, transport, chemical
Mechanical Work
– Beating cilia
– Contracting muscles
– Moving chromosomes (by spindle fibers during mitosis/meiosis)
Transport Work
Pumping substances across the cell membrane
and up the concentration gradient
Chemical Work
– Pushing endergonic reactions
– Creating polymers
To manage energy resources, cells use
energy coupling
Energy Coupling
Exergonic processes drive endergonic ones
– ATP is responsible for most coupling in cells and
acts as the immediate power source for work
How does ATP release energy?
The bonds between the phosphate groups are broken by hydrolysis creating an inorganic phosphate (Pi), ADP, and a release of energy
– The energy released from ATP is greater than most other molecules due to the high negative charge on the phosphate tail
ATP & Energy Coupling
When ATP is hydrolyzed the free phosphate will be used to phosphorylate other molecules through use of an enzyme
• The phosphorylated molecule is less stable & more reactive & this change allows it to perform work
• This ties together an endergonic reaction with an exergonic one
– Used in cellular work
Regeneration of ATP
ATP is a renewable resource…just add a phosphate group to ADP
– Requires energy from exergonic reactions in the cell
– Creating and breaking down ATP is known as the ATP Cycle
– performed during cellular respiration
Enzyme
Catalytic proteins that speed up reactions without being consumed
– Without these many metabolic pathways would
be stuck for years (ex. sucrose hydrolyzed into
fructose and glucose)
How do you recognize an enzyme?
• It will usually end with –ase
• Conveniently, its name will usually indicated
its substrate
Activation Energy
Energy input required to start a metabolic process or chemical reaction (EA)
• Determines the rate of reaction
– Many EA are very high & transition states are rarely reached without assistance
– EA is directly proportional to the difficulty of breaking
apart bonds in the substrate
Enzyme Action Curves
Enzymes lower EA, allowing molecules to absorb enough energy to transition at moderate temperatures & reasonable time frames
• They do NOT change the overall reaction (ΔG)
Why isn’t heat used to speed up chemical reactions?
- Heat would increase the rate of all chemical reactions, wasting energy
- Proteins within cells can be denatured
- Enzymes are specific, reusable, and energy-efficient
Enzymes-Substrate Interaction
While the enzyme and substrate are joined the
catalytic action converts the substrate to the
product(s)
Enzyme specificity:
Each enzyme only catalyzes a specific substrate
Active Site
the region of the enzyme that binds to the
substrate is the active site
Induced fit
means active sites are not rigid but change shape slightly once chemical interactions occurs with the substrate to ensure a snug fit
(ie handshake)
substrate
The molecule an enzyme will act upon
How do enzymes lower activation energy?
- Acting as a template for substrate orientation
- Stressing the substrate by bending critical bonds
- Providing a favorable mini environment, such as
a pH pocket - Participating directly in the catalytic reaction by
providing temporary covalent bonding
point of saturation
A point of saturation can be reached by
enzymes & the only way to speed up creation
of the product is to create more enzymes
temperature
– Reaction rates increase with higher temperatures because substrates collide with active sites more frequently (greater kinetic/heat energy)
– Only works to a point because too high of a temperature will cause enzyme denaturation
pH
There are optimal pH range because too acidic an environment will cause denaturation
– Example: Pepsin works at pH 2 because functions in
our stomach & trypsin works at pH 12 works in the alkaline environment of the small intestine
Cofactors
Non protein that all function in various ways to increase enzymatic productivity
– Inorganic cofactors examples are Cu, Fe, Zn
– Organic cofactors (coenzymes) such as vitamins
Inhibitors
Chemicals that selectively inhibit the actions of enzymes
– Are reversible if bond with a weak bond, but can be irreversible if covalently bonded
Many inhibitors are naturally occurring in the cell
Competitive Inhibitors
Resemble the normal substrate & compete for admission into active site
ex. penicillin
Noncompetitive Inhibitors
Molecules that bind to a portion of the enzyme away
from the active site (allosteric site)
– Cause the enzyme to change shape & the active site becomes unreceptive
– Ex. DDT
Feedback Inhibition:
A metabolic pathway is switched off by its end product
• Product inhibits an enzyme in its own pathway by noncompetitive inhibition
– Prevents unnecessary waste from excess products
enthalpy
total energy (H) or a system in a spontaneous reaction, enthalpy decreases
entropy
(S)
the measure of the disorder/randomness of a system
in spontaneous reactions, entropy increases
how does ΔG decrease?
decrease in enthalpy (H) or increase in entropy (S) and/or temperature
