BIO1022 Chapter Notes - Chapter Prescribed: Integumentary System, Cellular Respiration, Vasodilation
30 May 2018
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BIO1022 – Readings – Week 5
concept 8.2
- the free energy change of a reaction tells us whether or not the reaction occurs
spontaneously
- free energy change
• gibes free energy of a system - G
• free energy is the portion of a system’s energy that can perform work
when temperate and pressure are uniform through the system, as in a
living cell
• value of delta G enable a prediction of withered the process will be
spontaneous - more energetically favourable
• only processes with a negative delta G are spontaneous
• every spontaneous process decreases the system’s free energy
• processes that have a positive or zero delta g are never spontaneous
- free energy, stability and equilibrium
• delta G represents the difference between the free energy of the final state
and the free energy of the initial state
• thus delta G can be negative only when the process involves a loss of free
energy during the change from initial state to final state
• - free energy - measure of a system’s instability -
• unstable systems - positive delta G become stable when then change to a
lower G
• equilibirum - maximum stability
• a process is spontaneous and can perform work only when it is moving
towards equilibrium
- free energy and metabolism
• exergonic and endergonic reactions in metabolism
•
o exergonic - energy outwards
o
▪ proceeds with a net release of energy
▪ loses free energy - delta G decreases
▪ negative delta G
▪ occur spontaneously
o endergonic - energy inward
o
▪ absorbs free energy from its surroundings
▪ usually stores free energy in molecules
▪ delta g is positive
▪ delta g is quantity of energy required to drive the reaction
- equillbrium and metabolism
• reactions in an isolated system eventually reach equilibrium and can then
do no work
• systems at equilibrium are at a minimum of G and can do no work
8.3
- ATP powers cellular work by coupling exergonic reactions to endergonic
reactions
- a cell does three main kinds of work
• chemical work
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• transport work
• mechanical work
- energy coupling - the use go an exergonic process to drive an endergonic one
- the structure and hydrolysis of ATP
• with the help of specific enzymes, the cell is able to use the energy
released by ATP hydrolysis to drive chemical reactions that by themselves
are endergonic
• If the ΔG of an endergonic reaction is less than the amount of energy
released by ATP hydrolysis, then the two reactions can be coupled so that,
overall, the coupled reac- tions are exergonic.
• This usually involves phosphorylation, the transfer of a phosphate group
from ATP to some other molecule, such as the reactant. The recipient
molecule with the phosphate group covalently bonded to it is then called
a phosphorylated intermediate.
- the regeneration of ATP
8.4
- enzymes speed up metabolic reactions by lowering energy barriers
- an enzyme is a macromolecule that acts as a catalyst - a chemical
agent that speeds up a reaction without being consumed by the reaction
- the activation energy barrier
• activation energy - initial investment of energy for starting a reaction
- how enzymes speed up reactions
- substrate specificity of enzymes
• the reactant an enzyme acts on is referred to as the enzyme’s substrate
• the enzyme binds to its substrate when there are two or more reactants -
forming an enzyme substrate complex
• while enzyme and substrate are joined - the catalytic action of the enzyme
converts the substrate to the products of the ration
• only a restricted region of the enzyme binds to the substrate - called the
active site
- catalysis in the enzyme’s active site
- effects of local conditions on enzymatic activity
• temperature and pH
•
o up to a point - the rate of an enzymatic reaction increases with
increasing activity - partly because substrates collide with active
sites more frequently when the molecules move rapidly
o above that temp - enzymatic activity drops sharply
o optimal pH that it is most active at
• cofactors
•
o many enzymes require nonprotein helpers for catalytic activity -
called cofactors
o some are inorganic - called a coenzyme
• enzyme inhibitors
•
o certain chemicals selectively inhibit the action of specific enzymes
o competitive inhibitors - resemble the normal substrate molecule
and compete for admission into the active site
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o
▪ reduce the productivity of enzymes by blocking substrates
from entering active sites
o noncompetitive inhibitors
o
▪ do not directly compete with the substrate to bind to
the enzyme at the active site
▪ they impede enzymatic reactions by binding to another part
of the enzyme - causing the enzyme molecule to change
shape - in such a way that the active site becomes
less effective at catalysing the conversion of substrate
to product
8.5
- regulation of enzyme activity helps control metabolism
- allosteric regulation of enzymes
• allosteric regulation - term used to describe any case in which a protein’s
function at one site is affected by the binding of a regulatory to a separate
site
• allosteric activation and inhibition
•
o interaction of subunits - a single activator or inhibitor molecule
that binds to one regulatory site will affect the active sites of all
subunits
- feedback inhibition
• a metabolic pathway is halted by the inhibitory binding of its end product
to an enzyme that acts early in the pathway
- localisation of enzymes within the cell
9.6
- glycolysis and the citric acid cycle connect to many other metabolic pathways
- the versatility of catabolism
- biosynthesis - anabolic pathways
• in addition to calories - food must also provide the carbon skeletons that
cells require to make their own molecules
- regulation of cellular respiration via feedback mechanisms
- body temperature
concept 40.2
- feedback control maintains the internal environment in many animals
• animals manage their internal environment by either regulating or
conforming
- regulating and conforming
• an animal is a regulator for an environmental variable if it uses internal
mechanisms to control internal change in the face of external fluctuation
•
o body temp independent of outside temp
• an animal is a conformer if it allows its internal condition to change in
accordance with external changes
• an animal may regulate some internal conditions while allowing others to
conform to the environment
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find more resources at oneclass.com
Document Summary
Bio1022 readings week 5 concept 8. 2. The free energy change of a reaction tells us whether or not the reaction occurs spontaneously. Equillbrium and metabolism reactions in an isolated system eventually reach equilibrium and can then do no work systems at equilibrium are at a minimum of g and can do no work. Atp powers cellular work by coupling exergonic reactions to endergonic reactions. A cell does three main kinds of work chemical work transport work: mechanical work. Energy coupling - the use go an exergonic process to drive an endergonic one. The structure and hydrolysis of atp: with the help of specific enzymes, the cell is able to use the energy released by atp hydrolysis to drive chemical reactions that by themselves are endergonic. The recipient molecule with the phosphate group covalently bonded to it is then called a phosphorylated intermediate. Enzymes speed up metabolic reactions by lowering energy barriers.
