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Biology 2112 Exam 2 Study guide
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Biology 2112 Exam 2 Study guide
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Study Guide: Examination 2Chapter 8
- The cell is a miniature chemical factory where thousands of reactions occur. The cell
extracts energy and applies energy to perform work.
- Metabolism is the totality of an organism’s chemical reactions. It is a property of life that
arises from interactions between molecules inside the cell.
- A metabolic pathway starts with a specific molecule and ends with a product. Each step
along the way is catalyzed (sped up) by a specific enzyme.
- A catabolic pathway releases energy by breaking down complex molecules into simple
compounds. An example of this is cellular respiration (breakdown of glucose in the
presence of oxygen).
- An anabolic pathway consumes energy to build a complex molecule from a simpler one.
An example of this is the synthesis of protein from amino acids.
- Energy is the capacity to cause change. It exists in different forms, and some can
perform work. Some types of energy include …..
- Kinetic energy - energy associated with motion.
- Heat or (Thermal energy) - kinetic energy linked to random movement of atoms
or molecules.
- Potential energy - energy that matter has because of its location or structure.
- Chemical energy - potential energy available for release in a chemical reaction.
- Exergonic reactions have a net release of free energy and are spontaneous
- Endergonic reactions absorb free energy from their
surroundings and are non-spontaneous.
- A cell does three main types of work which are…..
- 1. Chemical
- 2. Transport
- 3. Mechanical
In order to do work, cells manage energy resources energy coupling (using an exergonic
process to drive an endergonic one. Most energy coupling in cells is mediated by ATP.
- ATP (adenosine triphosphate) is the cell’s energy ‘shuttle’ (it drives reactions in the cell).
It is composed of ribose (a sugar), adenine (a nitrogenous base) and three phosphate
groups.
, - The bonds between the phosphate groups of ATP can be broken by hydrolysis (the
chemical break down of a compound as a result of a reaction with water) Energy is
released from ATP when the phosphate bond is broken. This is caused by the chemical
change to a state of lower free energy and not from the phosphate bonds themselves.
The result of this is ADP (adenosine diphosphate). Di = 2 phosphates Tri = 3 phosphates
- How ATP performs work: The three
types of cellular work which are
mechanical, transport and chemical
(as mentioned above) are all
powered by the hydrolysis of ATP.
In the cell, the energy from the
exergonic reaction of ATP
hydrolysis is used to drive an
endergonic reaction. Overall, the
coupled reactions are exergonic.
- ATP drives endergonic reactions by phosphorylation (the transfer of a phosphate group
to some other molecule like a reactant) the molecule that receives the phosphate group
is deemed, phosphorylated.
- This all can be reversed as well. ATP is a
renewable resource that is regenerated
when a phosphate group is added to ADP
(adenosine diphosphate). This energy to
phosphorylate ADP comes from catabolic
reactions in the cell. The chemical
potential energy that is temporarily stored
in ATP drives most cellular work.
- A catalyst is a chemical agent that speeds up a reaction without being consumed by the
reaction. An enzyme is a catalytic protein. Hydrolysis of sucrose by the enzyme sucrase
is an example of an enzyme-catalyzed reaction.
- Every chemical reaction between molecules involves bond breaking and bond forming.
The initial energy that is needed to start a chemical reaction is called the free energy of
activation, or as most people call activation energy (EA). Activation energy is often
supplied in the form of heat from the surroundings.
- Enzymes catalyze reactions by lowering the EA barrier. Enzymes do not affect the change
in free energy (ΔG) but instead they speed up reactions that would occur eventually
anyways.
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