Unit 2 Practice Questions Flashcards
Catabolism is to anabolism as ____________ is to ____________.
exergonic; endergonic
Most cells cannot harness heat to perform work because
temperature is usually uniform throughout a cell.
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.
Some bacteria are metabolically active in hot springs because
their enzymes have high optimal temperatures.
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.
______ pathways synthesize more complex organic molecules using the energy derived from ______ pathways.
Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.
The synthesis of complex molecules in _____ pathways requires an input of energy from _____ pathways.
The synthesis of complex molecules in anabolic pathways requires an input of energy from catabolic pathways.
_____ systems are those in which energy and materials can be exchanged between the system and its surroundings.
Open systems are those in which energy and materials can be exchanged between the system and its surroundings.
_____ Systems: Organisms acquire energy from and lose energy to their surroundings.
Open
_____ Systems: The metabolism of an organism is isolated from its surroundings.
Closed
organisms constantly lose _____ to their environment as a consequence of being open systems.
Heat
Growth of plants requires an input of ____. It is a ______ processes.
energy, non-spontaneous
The growth of plants represents a ______ in entropy, which by the second law requires a corresponding _____ in entropy of the plant’s surroundings (the universe).
The growth of plants represents a decrease in entropy, which by the second law requires a corresponding increase in entropy of the plant’s surroundings (the universe).
For plants, Energy is NOT produced by _______; it is converted from energy in the form of sunlight into energy in the form of ______.
Energy is NOT produced by photosynthesis; it is converted from energy in the form of sunlight into energy in the form of chemical bonds (sugars).
According to the second law of thermodynamics, The ____ in entropy associated with life must be compensated for by _____ entropy in the environment in which life exists.
The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists.
The second law of thermodynamics demands that total entropy _____ with any reaction.
increase
If the entropy of a living organism is decreasing,
Energy input into the organism must be occurring to drive the decrease in entropy.
If the entropy is decreasing, this would tend to make the free energy change associated with this positive. Thus, an input of energy would be required to make this decrease in entropy occur.
If the entropy is decreasing, this would tend to make the free energy change associated with this positive. Thus, an input of energy would be required to make this decrease in entropy occur.
Which part of the equation ΔG = ΔH – TΔS tells you if a process is spontaneous?
ΔG
In any spontaneous process, the free energy of a system decreases. The change in free energy equals the change in total energy minus the change in entropy times the temperature.
a decrease in the system’s total energy will increase the probability of spontaneous change, increasing the entropy of a system will increase the probability of spontaneous change, and increasing the temperature of a system will increase the probability of spontaneous change
a decrease in the system’s total energy will increase the probability of spontaneous change, increasing the entropy of a system will increase the probability of spontaneous change, and increasing the temperature of a system will increase the probability of spontaneous change
An exergonic (spontaneous) reaction is a chemical reaction that __________.
releases energy when proceeding in the forward direction
_______ reactions proceed with a net release of free energy, and they occur spontaneously.
Exergonic
Molecules A and B contain 110 kcal/mol of free energy, and molecules C and D contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded?
The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants.
By subtracting the free energy of the reactants from the free energy of the products, the _____can be calculated, and the difference in these values determines the sign of the difference.
ΔG
Metabolic pathways can be displaced from equilibrium either by adding_____ or by removal of the ______ of the pathway by other reactions.
free energy, products
In general, the hydrolysis of ATP drives cellular work by __________.
releasing free energy that can be coupled to other reactions
With the help of specific enzymes, the cell can couple the energy of ATP hydrolysis directly to _______ processes.
With the help of specific enzymes, the cell can couple the energy of ATP hydrolysis directly to endergonic processes.
Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because __________.
the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP
When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell.
In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.
***The coupling of ATP to other endergonic processes in cells means that less of the free energy is released as heat. When ATP is hydrolyzed without this coupling, all of the energy is released as heat.
The role of ATP in cellular metabolism:
The free energy released by ATP hydrolysis may be coupled to an ______ process via the formation of a phosphorylated intermediate.
The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.
This is one way a cell can use an exergonic reaction to drive an endergonic reaction.
A chemical reaction is designated as exergonic rather than endergonic when __________.
the potential energy of the products is less than the potential energy of the reactants
If a reaction is _____, the formation of new bonds releases more energy than was invested in breaking the old bonds.
exergonic
What is changed by the presence of an enzyme in a reaction?
The activation energy
An enzyme lowers the amount of energy required to get the reactants to the transition state.
What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction?
Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction.
The speed of a reaction is determined by the activation energy barrier of the reaction and the temperature (which determines how many reactants have the energy to overcome the barrier).
Enzymes speed up reactions by lowering the activation energy barrier for the reaction. Enzymes cannot change the DG for the reaction.
Enzymes speed up reactions by lowering the activation energy barrier for the reaction. Enzymes cannot change the DG for the reaction.
Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.
Enzymes lower the activation energy barrier of a reaction but do not change the free energy of the products.
The environment usually supplies activation energy in the form of ____. The lower the temperature, the less energy that is available to overcome the activation energy barrier.
heat
Enzyme facts:
An enzyme ____ the activation energy of a chemical reaction.
Most enzymes are ____.
Enzymes can be used to accelerate both ____ and ____ reactions.
An enzyme is very specific in terms of the ____ to which it binds.
*An enzyme lowers the activation energy of a chemical reaction.
*Most enzymes are proteins.
*Enzymes can be used to accelerate both anabolic and catabolic reactions.
*An enzyme is very specific in terms of the substrate to which it binds.
The ____ site for an enzyme may resemble a groove or pocket in the surface of a protein into which the _____ fits.
The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.
What is meant by the “induced fit” of an enzyme?
the enzyme changes its shape slightly as the substrate binds to it.
**The enzyme changes slightly to bind to the substrate and catalyze the reaction.
The role or roles of heat in biological reactions?
Heat from the environment is necessary for substrates to get over the activation energy barrier.
The kinetic energy of the substrates is increased as the amount of heat in the system is increased.
Heat from the environment is necessary for substrates to get over the activation energy barrier.
The kinetic energy of the substrates is increased as the amount of heat in the system is increased.
As the heat energy in a system increases, so does the _____ energy of the reactants. As the ____energy of the reactants increases, the reactants are more likely to interact (with each other directly, or with the active site of an enzyme). Subsequently, the reaction rate would increase.
kinetic
Changes in temperature, substrate concentration, and pH are all likely to affect enzyme activity.
Changes in temperature, substrate concentration, and pH are all likely to affect enzyme activity.
Each enzyme has an optimal pH at which it is most active, and variations in pH can alter the enzyme’s structure, changing activity.
Each enzyme has an optimal pH at which it is most active, and variations in pH can alter the enzyme’s structure, changing activity.
A _______ competes with the substrate for binding at the active site.
competitive inhibitor
The action of competitive inhibitors may be reversible or irreversible.
Competitive inhibitors that bind covalently to the enzyme would be irreversible, and those that bind weakly would be reversible.
Competitive inhibitors that bind covalently to the enzyme would be irreversible, and those that bind weakly would be reversible.
The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule outside the active site is an example of __________.
allosteric activation
Binding of a ______ inhibitor would stabilize the enzyme in a form that is less active
Binding of a noncompetitive inhibitor would stabilize the enzyme in a form that is less active, not more active
a molecule similar to the substrate blocks the active site.
competitive inhibition
In _____ inhibition, accumulating product inhibits one of the early enzymes in the metabolic pathway.
In feedback inhibition, accumulating product inhibits one of the early enzymes in the metabolic pathway.
allosteric proteins is/are:
*They are sensitive to environmental conditions.
*They exist in active and inactive conformations.
*They are acted on by inhibitors.
The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Why?
The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.
What does the term “fluid mosaic” refers to?
The fluid aspect of the membrane is due to the mobility of phospholipids, and embedded proteins account for the mosaic aspect.
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found?
In the interior of the membrane
The steroid cholesterol, wedged between phospholipid molecules in the plasma membranes of animals, helps stabilize the membrane.
According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly
embedded in a lipid bilayer.
Which of the following factors would tend to increase membrane fluidity?
a greater proportion of unsaturated phospholipids
a greater proportion of saturated phospholipids
a lower temperature
a relatively high protein content in the membrane
a greater proportion of unsaturated phospholipids
Which of the following processes includes all the others?
osmosis
diffusion of a solute across a membrane
passive transport
transport of an ion down its electrochemical gradient
passive transport
Functions of membrane proteins? (Concept 7.1)
*Intercellular joining
*Cell-cell recognition
*Transport
*Enzymatic activity
Present in biological membranes to act as stores of energy, carbon, and nitrogen.
Lipids
Plasma Membrane carbohydrates function primarily in
cell-cell recognition.
Variations in carbohydrate structure distinguish one species from another, one individual from another, and even one cell type from another.
The primary location of carbohydrates is on the ______ of the plasma membrane, where they can contribute to cell-cell recognition.
outer surface
The carbohydrates on cell surfaces are generally branched chains of fewer than 15 sugars.
The carbohydrates on cell surfaces are generally branched chains of fewer than 15 sugars.
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found?
On the outside (external) surface of the membrane
Membrane ________ are covalently bonded to lipids or proteins and extend out from the external side of the plasma membrane as a means of cell identification.
Membrane carbohydrates are covalently bonded to lipids or proteins and extend out from the external side of the plasma membrane as a means of cell identification.
Which statement about the sidedness of the plasma membrane is correct?
Every integral membrane protein has a specific orientation in the plasma membrane.
Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane.
The two lipid layers may differ in specific lipid composition.
The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed.
All is correct
Which of the following molecules is most likely to passively diffuse across the plasma membrane?
Sodium ion
DNA
Glucose
Hemoglobin
Carbon dioxide
Hydrophobic molecules, such as hydrocarbons, carbon dioxide, and oxygen, can dissolve in the membrane and cross it with ease.
What would be least likely to diffuse through a plasma membrane without the help of a transport protein?
A large, polar molecule
The combination of being polar and large means that this molecule will be the slowest one from the choices to move across the membrane.
Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs _______ concentration gradient of the molecule.
down the
_____ is the tendency of molecules to spread out in the available space. A substance will ____ from an area of higher concentration to an area of lower concentration without energy input.
It is a ______ process.
Diffusion, diffuse, passive
A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition?
Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease
The added salt makes the solution hypertonic compared to the cell. Water will leave the cell by osmosis.
Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?
Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall.
**Hypertonic: more solutes outside of the cell than inside
Facilitated diffusion of solutes may occur through ________ in the membrane.
channel or transport proteins
The passageways for facilitated diffusion may be either protein pores or carrier proteins.
- can move ions across membranes.
- requires a concentration gradient.
-can occur by means of transport proteins. - can occur through protein channels.
Facilitated diffusion
Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?
A hypertonic sucrose solution
When a cell is placed in a hypertonic environment, water will leave the cell, causing it to shrink.
Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives?
A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis.
If a cell is placed in a hypertonic solution, it will lose water to its environment, shrivel, and probably die.
If a cell is placed in a _____ solution, it will lose water to its environment, shrivel, and probably die.
If a cell is placed in a hypertonic solution, it will lose water to its environment, shrivel, and probably die.
Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane.
This is how the sodium-potassium pump generates voltage across the cell membrane.
Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient.
To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.
What is the difference between active transport and facilitated diffusion?
Active transport requires an input of energy, and facilitated diffusion does not.
Both systems depend on specific membrane transport proteins.
______ allow a single ATP-powered pump to drive the active transport of many different solutes.
Cotransport proteins
The electrochemical gradient created by a single ATP-dependent pump can drive the transport of many different solutes using cotransport proteins.
In receptor-mediated_____, only a specific molecule, called a ligand, can bind to the receptor. Without receptor binding occurring first, _____ does not proceed.
endocytosis
In ______, vesicles derived from the endomembrane system fuse with the plasma membrane, thus increasing the number of phospholipids in the plasma membrane and increasing its surface area. The smooth ER is largely responsible for production of ____ destined for the membrane, and the rough ER produces _____ destined for the plasma membrane.
In exocytosis, vesicles derived from the endomembrane system fuse with the plasma membrane, thus increasing the number of phospholipids in the plasma membrane and increasing its surface area. The smooth ER is largely responsible for production of lipids destined for the membrane, and the rough ER produces proteins destined for the plasma membrane.
A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother’s milk. These molecules probably enter the cells lining the baby’s digestive tract via which process?
Endocytosis is the procedure that cells use to import large molecules across their plasma membrane.
______: the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane
Pinocytosis is the uptake of liquid and the solutes dissolved in the liquid.
_____: secretion of large particles from the cell by fusion of vesicles with the plasma membrane
Phagocytosis is a type of endocytosis, so it involves bringing material into the cell by englufing solid particles, forming pockets, enclosing it forming a vesicle within the cell
_____: passive diffusion of water and small solutes across a membrane
Osmosis
