Chapter 6 An Introduction To Metabolism. Metabolism/Bioenergetics. Metabolism : The totality of an organism’s chemical processes; managing the material and energy resources of the cell Catabolic pathways : degradative process such as cellular respiration; releases energy
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E transferred/transformed, not created/destroyed
Organisms live at the expense of free energy.
The amount of energy available to do work.
G = H - TS
G = free energy
H = enthalpy or total energy
T = temperature in 0K
S = entropy (disorder/randomness)
Indicates whether a reaction will occur spontaneously
In a spontaneous reaction, G decreases, DG<0 (negative)
EXERGONIC REACTIONENDERGONIC REACTION
Products have less G Products have more G
Reaction is ‘downhill’ Reaction is ‘uphill’
Spontaneous Require energy input
DG is negative DG is positive
Many metabolic reactions are reversible and reach
At equilibrium a cell is dead!
Disequilibrium is maintained by the continual use/removal
of products e.g. respiration
e.g. zinc, iron, copper
Allosteric enzymes have two conformations, one
catalytically active, the other inactive.
Binding of an activator to the allosteric site stabilizes
the active conformation of the enzyme
Binding of an inhibitor to the allosteric site stabilizes
the inactive form of the enzyme (non-competitive)
Binding at one site enhances binding at other sites
Each enzyme is specific for the reaction it will catalyze. In this laboratory,Enzyme = catalase Substrate = hydrogen peroxide (H2O2)Products = water and oxygen H2O2 H2O + O2
If a small amount of catalase is added to hydrogen peroxide, you will be able to observe bubbles of oxygen forming.
In such a titration, you slowly add a chemical (KMnO4) that will cause a color change until a target is achieved.
To determine how much hydrogen peroxide (substrate) has been broken down by catalase at varying times, you measure the amount of peroxide remaining in each flask.
We can calculate the rate of a reaction by measuring, over time, either the disappearance of substrate or the appearance of product.
For example, on the graph above, what is the rate, in moles/second, over the interval from 0 to 10 seconds?
Rate = Dx = 7-0 moles = 7 = 0.7 mols/sec
Dy 10-0 seconds 10
During what time interval is the enzyme working at its maximum velocity?
a. 0–30 seconds
b. 60–120 seconds
c. 120–180 seconds
d. Over the entire time course
In order to keep the rate constant over the entire time course, which of the following should be done?
Which of the following graphs represents the rate of the reaction shown above? Notice that in the graphs below, the y-axis is number of molecules/sec.
a. It is the substrate on which catalase acts
b. It binds with the remaining hydrogen peroxide during titration
c. It accelerates the reaction between enzyme and substrate
d. It blocks the active site of the enzyme
e. It denatures the enzyme by altering the active site
A student was performing a titration for this laboratory, and accidentally exceeded the endpoint. What would be the best step to obtain good data for this point?
a. Estimate the amount of KMnO4 that was in excess, and subtract this from the result
b. Repeat the titration using the reserved remaining sample.
c. Obtain data for this point from another lab group
d. Prepare a graph of the data without this point, and then read the estimated value from the graph.