AP Bio Chapter 8
Catabolic
destructive metabolism; the breaking down in living organisms of more complex substances into simpler ones, with the release of energy
Enzyme
catalysts that speed up chemical reactions
enzyme
catalysts that speed up chemical reactions
Potential energy
energy matter possesses because of location or structure
The value of ^G can be used to determine
if a reaction will be spontaneous or will require additional energy to take place
Which type of energy does water behind a dam have? A mole of glucose?
potential energy; chemical energy
Which reactions are considered uphill?
anabolic
Enzymes are encoded by
genes
List the three main kinds of work that a cell does.
-Chemical work, the pushing of endergonic reactions that would not occur spontaneously, such as the synthesis of polymers from monomers -Transport work, the pumping of substances across membranes against the direction of spontaneous movement; possible examples include the sodium-potassium pump and proton pump -Mechanical work, such as the beating of cilia, the contraction of muscle cells, and the movement of chromosomes during cellular reproduction
Enzymes use a variety of mechanisms to lower activation energy. Describe four of these mechanisms.
-In reactions involving two or more reactants, the active site provides a template on which the substrates can come together in the proper orientation for a reaction to occur between them. -As the active site of an enzyme clutches the bound substrate, the enzyme may stretch the substrate molecules toward their transition-state form, stressing and bending critical chemical bonds that must be broken during the reaction. -The active site may also provide a microenvironment that is more conducive to a particular type of reaction than the solution itself would be without the enzyme. -Direct participation of the active site in the chemical reaction is another mechanism of catalysis.
List four ways in which the energy of activation can be lowered due to the substrate binding to the active site of an enzyme.
-orienting substrates correctly so a reaction can take place -straining substrate bonds that must be broken during the reaction -providing a favorable microenvironment -amino acids in the enzyme can participate in the chemical reactions by briefly bonding covalently to the substrate; enzymes are not permanently changed or used up during a reaction
What is a catalyst?
A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction.
What is meant by a spontaneous process?
A process that occurs without an overall input of energy; a process that is energetically favorable.
Explain the name ATP by listing all the molecules that make it up.
ATP contains the sugar ribose, with the nitrogenous base adenine and a chain of three phosphate groups bonded to it, forming adenosine triphosphate.
Describe the picture on page 159
After the threonine binds to the enzyme and passes through four more enzymes, isoleucine is produced. When the isoleucine binds to the allosteric site the active site of enzyme 1 is no longer able to catalyze the conversion of theorine to intermediate A and the pathway is halted.
What effect does an enzyme have on EA?
An enzyme catalyzes a reaction by lowering EA barrier
temperature
As temperature increases, so does the rate of enzymatic reaction. Above the temperature, the speed of enzymatic reaction drops sharply.
How do enzymes catalyze reactions?
Be lowering Ea level. Enzymes don't affect ^G but they speed up reactions that would occur eventually
What is meant by induced fit? How is it shown in the figure in question 20?
Caused by entry of the substrate, the change in shape of the active site of an enzyme so that it binds more snugly to the substrate. In Figure 8.14 on page 154, when the substrate enters the active site, it forms weak bonds with the enzyme, inducing a change in the shape of the protein. This change allows additional weak bonds to form, causing the active site to enfold the substrate and hold it in place.
Energy
capacity to cause change, do work, or move matter against opposing forces
The second law of thermodynamics is sometimes called the "you always lose rule" Why is that an appropriate expression?
During every energy transfer or transformation, some energy becomes unavailable to do work.
According to the first law of thermodynamics, wha can and cannot happen to energy?
Energy can be transferred and transformed, but it cannot be created or destroyed.
Explain how protein structure is involved in enzyme specificity.
Enzymes are proteins, and proteins are macromolecules with unique three-dimensioal configuration. The specificity of an enzyme results from its shape, which is a consequence of its amino acid sequence. The specificity of an enzyme is attributed to a compatible fit between the shape of its active site and the shape of the substrate.
What is free energy? What is its symbol?
Free energy is the portion of a system's energy that can perform work when temperature and pressure are uniform throughout the system, as in a living cell. Triangle G is the symbol.
Although it is not an enzyme, hemoglobin shows cooperativity in binding O2. Explain how hemoglobin works at the gills of a fish.
Hemoglobin is made up of four subunits, each of which has an oxygen-binding site. The binding of an oxygen molecule to one binding site increases the affinity for oxygen of the remaining binding sites. Thus, where oxygen is at high levels, such as in the lungs or gills, hemoglobin's affinity for oxygen increases as more binding sites are filled.
Is cellular respiration an endergonic or an exergonic reaction? What is ∆G for this reaction?
It is exergonic, G is negative
For an exergonic reaction, is ∆G negative or positive?
It is negative due to the release of free energy
How is allosteric regulation somewhat like noncompetitive inhibition? How might it be different?
It may inhibit enzyme activity, but it may also simulate enzyme activity.
If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur?
Nothing; the reaction will stay at equilibrium.
Name a human enzyme that functions well in pH 2. Where is it found?
Pepsin, stomach
Is photosynthesis endergonic or exergonic? What is the energy source that drives it?
Photosynthesis is an endergonic reaction. Plants get the required energy from the environment by capturing light and converting its energy into chemical energy.
Many toxins and poisons cause irreversible enzyme inhibition. Select one and explain why its so deadly.
Sarin-nerve gas. The molecule binds covalently to the R group on amino acid serine.
Explain the difference between an allosteric activator and an allosteric inhibitor.
The binding of an activator to a regulatory site stabilizes the shape that has functional active sites, whereas the binding of an inhibitor stabilizes the inactive form of the enzyme.
What is activation energy (EA)?
The initial energy needed to start a chemical reaction.
Initial concentration of substrate
The more substrate molecules that are available, the more frequently they access the active sites of the enzyme molecules.
What is energy coupling?
The use of an exergonic process to drive an endergonic one.
Recall that enzymes are globular proteins. Why can extremes of pH or very high temperatures affect enzyme activity?
Three-dimensional structures of proteins are sensitive to their environment. As a consequence, each enzyme works better under some conditions than other conditions, because these optimal conditions favor the most active shape for their enzyme molecule
If you could not regenerate ATP by phosphorylating ADP, how much ATP would you need to consume each day?
We would need to consume our body weight.
Catalyst
a chemical agent that speeds up a reaction without being consumed by the reaction
Cooperativity
a form of allosteric regulation that can amplify enzyme activity; one substrate molecule primes an enzyme to act on additional substrate molecules more readily.
Reactant
a substance that takes part in and undergoes change during a reaction
The binding of an activator stabilizes the ____ form of the enzyme
active
Optimal conditions favor the most ____ ____ for the enzyme molecule. ____ can also influence the actions of an enzyme
active shape; chemical
If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to
add more of the enzyme
What type of reaction is photosynthesis?
anabolic
Which reactions build up larger molecules?
anabolic
Which reactions consume energy?
anabolic
Which reactions require enzymes to catalyze reactions?
anabolic
Kinetic energy
associated with the relative motion of objects
Noncompetitive Inhibitor
bind to another part of an enzyme, causing the enzyme to change shape and make the active site less effective
Noncompetitive Inhibitors
bind to another part of an enzyme, causing the enzyme to change shape and make the active site less effective
Induced fit
brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction.
How does the cell regulate enzyme activity or provide feedback inhibition?
by switching the genes that encode specific enzymes on and off. Feedback inhibition increases the efficiency of the pathway by turning it off when the end product accumulates in the cell
What type of reaction is cellular respiration?
catabolic
Which reactions break down molecules?
catabolic
Which reactions release energy?
catabolic
Anabolic
constructive metabolism; the synthesis in living organisms of more complex substances from simpler ones
Catabolism is to anabolism as _____ is to _______
exergonic is to endergonic
By what process will the bond in ATP break?
hydrolysis
The binding of the inhibitor stabilizes the _____ form of the enzyme
inactive
Allosteric Regulation
it may either inhibit or stimulate an enzyme's activity; a molecule binds to a protein at one site and affects the protein's function at another site
products
material resulting from a chemical reaction
If energy is released ∆G must be positive or negative?
negative
Cofactors
nonprotein helpers for catalytic activity (inorganic: zinc, iron, copper)
pH
optimal pH ranges from 6-8
Coenzymes
organic molecule serving as a cofactor (vitamins)
In many cellular reactions, a phosphate group is transferred from ATP to some other molecule in order to make the second molecule less stable. The second molecule is said to be
phosphorylated intermediate
Most allosterically regulated enzymes are made from two or more ____ _____
polypeptide subunits
Competitive Inhibitors
reduce the productivity of enzymes by blocking substrates from entering active sites, and they function by binding to the active site of an enzyme, competing with the substrate
Competitive Inhibitor
reduces the productivity of enzymes by blocking substrates from entering active sites
When the terminal phosphate bond is broken, a molecule of inorganic phosphate Pi is formed, and energy is
released
Most cells cannot harness heat to perform work because
temperature is usually uniform throughout a cell
What factors affect the optimal functioning of an enzyme?
temperature, pH, substrate concentration, and enzyme concentration
What is allosteric regulation?
the binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site
Feedback inhibition
the end product of a metabolic pathway shuts down the pathway and it prevents a cell from wasting chemical resources by synthesizing more product than is needed.
Energy of Activation
the initial energy needed to start a chemical reaction
Gibbs free energy
the portion of the system's energy that can perform work when temperature and pressure are uniform in a system
Substrate
the reactant that an enzyme acts on
substrate
the reactant that an enzyme acts on
active site
the region on the enzyme where the substrate binds
Some bacteria are metabolically active in hot springs because
their enzymes have high optimal temperatures
Examples of inhibitors
toxins, pesticides, poisons, antibodies
How is ∆G affected by the enzyme?
unaffected
enzyme-substrate complex
when an enzyme binds to a substrate