Summary of Units 5,6 and 7. The full scope of Semester test 2. These notes have been made using the book BIOLOGY by Raven and are in line with the study outcomes. Diagrams are included, great for visual learners.
Biology 8e Raven Chapter 1 Questions and Answers Graded A+ 2024 Reviewed
MLB111 Units 8-10 Semester test 3 (updated 2024)
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Semester Test 2 Notes
ENERGY, ENZYMES AND METABOLISM IN THE CELL
Energy: The capability to do work.
Kinetic energy: energy of motion
Potential energy: stored energy (have the capacity to move but are not moving)
Potential energy is released as kinetic energy.
1st Law of Thermodynamics concerns the amount of energy in the universe.
States: Energy cannot be created or destroyed; it can only change from one form to another (eg: potential to
kinetic). The total amount of energy in the universe remains constant.
2nd Law of Thermodynamics addresses the efficiency of energy transformations.
States: Energy cannot be transformed from one form to another with 100% efficiency, some energy is
always unavailable.
The unavailable energy manifests as an increase in the random motion of molecules, therefore increasing in
the disorder of the system. We measure this as an increase in entropy (S). Entropy = a measure of disorder.
Disorder is more likely than order (eg: pile of bricks. A pile with entropy is more stable than a column.)
Free energy:
The energy available to do work in any system.
This energy is available to break and subsequently form other chemical bonds.
Energy is needed to break bonds. Heat energy makes it easier to pull atoms apart.
G = H – TS (For constant temp. pressure and volume)
G = Gibbs free energy
H = energy contained in chemical bonds
S = entropy / disorder
T = absolute temperature in degrees Kelvin (K =℃ + 273)
When reactions take place, the free energy changes.
We can use the change in free energy to predicts spontaneity.
,Change in free energy G = energy of products minus energy of reactants.
• If G is positive, then non-spontaneous. (Require input energy) = Endergonic reactions.
• If G is negative, then the reaction is spontaneous. = Exergonic reactions.
Remember, chemical reactions are reversible therefore, one direction is exergonic, and the other is
endergonic. Equilibrium is reached when the rate of the forward reaction = rate of reverse.
Equilibrium constant (Keq) = a ratio of the concentrations of products divided by concentrations of
reactants.
Endergonic reactions, G will be positive and Keq will be <1 meaning equilibrium favours the reactants.
Exergonic reactions, G will be negative and Keq will be >1 meaning equilibrium favours products.
Activation Energy: The extra energy needed to destabilize existing chemical bonds and initiate a
chemical reaction.
The rate of an exergonic reaction depends on activation energy required for the reaction to begin.
Larger activation energy reactions tend to proceed more slowly because fewer molecules will collide with
sufficient energy.
Rate if reaction can increase by:
(1.) increasing the energy of reacting molecule.
(2.) lowering activation energy.
Catalysts accelerate reactions by lowering the
amount of activation energy required to initiate the
reaction.
The process of influencing chemical bonds in a way that lowers activation energy is called Catalysis.
Catalysts stabilize the intermediate transition state, hereby lowering the activation energy and accelerate
rates of both forward and reverse reactions – Therefore, they do not alter the ratio of reactant to product.
G does not change (can be seen on graph)
, ATP: (Adenosine triphosphate) The Energy Currency of Cells
Structure: 3 smaller components:
• 5-carbon sugar Ribose (framework to which 2 other subunits are
attached)
• Adenine (organic molecule composed of 2 carbon-nitrogen
rings)
• Chain of 3 phosphates
Storage of energy:
Phosphate groups are highly negatively charged and repel each other.
This repulsion makes the covalent bonds joining with the phosphates
unstable.
These unstable bonds holding the phosphates together have a low
activation energy and are easily broken by hydrolysis.
The reaction is exergonic therefore hydrolysis of ATP has a negative G.
The energy released can be used to preform work.
In most reactions, only the outermost high-energy phosphate bond is hydrolysed, the ATP becomes ADP
plus an inorganic phosphate (Pi) and energy is released.
ATP and Endergonic Processes:
Cells use ATP to drive endergonic processes (non-spontaneous reactions)
Energy released by the hydrolysis of ATP can supply the energy needed by the endergonic reaction.
The ATP Cycle:
The instability of phosphate bonds makes ATP an effective energy donor, but a poor long-term energy
storage molecule.
Therefore, cells use ATP cyclically: This is an example of a Coupled reaction where the energy released
from an exergonic reaction is used to drive an endergonic reaction.
The (exergonic) hydrolysis of ATP with water provides energy to drive them (endergonic) synthesis of ATP
from ADP + Pi.
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