BIOL 105 Practice test questions ch 5-7

A chemical reaction that occurs spontaneously ____.

must proceed without an input of external energy Spontaneous chemical reactions run in the direction that lowers the free energy of the system. Exergonic reactions are spontaneous and release free energy; endergonic reactions are nonspontaneous and require an input of energy to proceed

Compared to FAD, FADH2 is ____.

reduced and has more potential energy FADH2 has two electrons more than FAD and, due to the position of those electrons, has more potential energy

The predominant form of glucose dissolved in an aqueous solution is _____.

the ring configuration In aqueous solutions, almost all glucose molecules will bend into a ring structure.

A protein that has an ER signal sequence will produce a protein destined for secretion only when ____________.

the signal recognition particle (SRP) directs the ribosome to a translocon and allows translation to occur into the rough ER Proteins destined for secretion must first be made into the lumen of the rough ER.

ATP hydrolysis is an exergonic reaction because _______.

there is a large drop in enthalpy Releasing the negative charged phosphate group allows for a much more relaxed (low potential energy) state in the ADP

Polysaccharides probably did not play an important role in the origin of life because ____.

they cannot serve as a template for replication The first living molecule needed to catalyze self-replication, requiring it to both catalyze reactions and serve as a template for copies. Carbohydrates can perform neither of these functions.

What is the major difference between amylose and amylopectin?

Amylose is a straight-chain polymer of glucose, whereas amylopectin is highly branched. A major difference between amylose and amylopectin is that amylose is made up of glucose linked through a-1,4 bonds, and amylopectin contains both a-1,4- and a-1,6-glycosidic linkages.

In most instances, enzymes do not work alone. What is a type of enzyme "helper"?

-Prosthetic groups -Cofactors -Coenzymes Cofactors, coenzymes and prosthetic groups can all aid in enzymatic function.

Which of the following statements describes a fundamental difference between plant cells and animal cells?

Animal cells do not have chloroplasts. Chloroplasts are only found in photosynthetic organisms such as plants and algae.

Both starch and cellulose are glucose polymers. Why can animals easily degrade starch, but not cellulose?

Animals have enzymes that can degrade a-1,4-glycosidic bonds, but not b-1,4-glycosidic bonds. Cellulose and starch are both glucose polymers. However, in cellulose the glucose molecules are linked through b-1,4-glycosidic bonds. Few organisms have the capability to degrade these bonds.

When detergents are added to the solution surrounding a lipid bilayer, _____.

-the hydrophilic regions of the detergent molecules orient toward the polar solute (water) -the hydrophobic tails of the detergent molecules interact with the hydrophobic tails of the lipids -membrane proteins can be isolated so they can be purified and studied in detail -the hydrophobic tails of the detergent molecules interact with the hydrophobic portions of transmembrane proteins Detergents are amphipathic molecules that form micelles in water. Detergents break apart membranes by coating the hydrophobic tails of the phospholipids and dissolving them in water. This action is similar to how dish and laundry detergents break up grease on dishes and clothes

What type of chemical interactions do phospholipids have with their environment?

Amphipathic Phospholipids are amphipathic, which means they have both hydrophobic and hydrophilic regions. The phosphate and glycerol head of a phospholipid are hydrophilic, and the fatty acid tail is hydrophobic.

Which of the following is true of cell membranes?

Amphipathic proteins can span the membrane. The cell membrane consists of a phospholipid bilayer interspersed with transmembrane proteins.

How can an individual cell increase the total reaction rate of a reaction?

Adding more enzyme catalyst Cells can control the amount of enzyme within the cytosol as they can increase transcription and translation of the enzyme.

In graphs of enzyme activity versus temperature, activity increases up to a certain temperature and then decreases again. What is the mechanism that explains this pattern?

As temperatures increase, substrates collide with the enzyme more, but even higher temperatures cause too much enzyme movement and the enzyme denatures. Higher temperatures will initially speed up reactions, but even higher temperatures can denature enzymes

Enzyme-catalyzed reactions increase in rate very rapidly at low substrate concentrations but plateau at higher substrate concentrations. What is the reason for the plateau?

At high substrate concentrations, all available enzyme molecules are working at maximal speed and are unable to further increase the rate of reaction. Once you reach a substrate concentration at which all enzymes are actively working, adding additional substrate cannot further increase the rate of reaction.

Which chemical formula could represent a monosaccharide?

C3H6O3 Carbohydrates contain carbon, hydrogen, and oxygen, usually in the ratio of 1:2:1.

Which of the following bonds found in carbohydrates have the lowest potential energy?

Carbon-oxygen (C-O) bonds The electrons in the C-O bonds of carbohydrates are held very tightly because of oxygen's high electronegativity and therefore have very low potential energy.

Prokaryotic cells' intracellular fluid is often hypertonic to the habitat they find themselves in. What cellular feature prevents the prokaryote from expanding and lysing under these conditions?

Cell wall The cell wall is a fibrous outer layer that acts as an exoskeleton.

Which of the following polysaccharides contains a modified monosaccharide?

Chitin The N-acetyl-glucosamine units that make up chitin are composed of modified glucose monomers.

Which of the following statements accurately compares the different polysaccharides?

Chitin, cellulose, and peptidoglycan consist of long, parallel strands linked to one another. This structure is characteristic of the structural polysaccharides, as it gives them the ability to withstand pushing and pulling forces.

As a defense mechanism, the barley plant produces an enzyme called chitinase that breaks down the polysaccharide chitin found in certain pathogens. Which of the following statements describes the protective action of chitinase?

Chitinase disrupts the cell walls of fungal plant pathogens. Chitin is used for structural support in the cell walls of fungi. These cell walls are disrupted by the hydrolysis of chitin by chitinase.

Which method of inactivating an enzyme could most likely be overcome by adding high levels of substrate?

Competitive inhibition Because the competitor and the substrate are competing for the same site, high substrate levels can outcompete the inhibitor and help restore enzyme activity.

___________________ is a technique that allows researchers to separate cellular components based on their relative size and density.

Differential centrifugation Centrifugation involves the separation of cell components by their size or density.

In what important way does competitive inhibition differ from allosteric inhibition?

During competitive inhibition, a regulatory molecule binds to the active site, whereas during allosteric inhibition, a regulatory molecule binds to a site other than the active site. During competitive inhibition, a regulatory molecule looks like the substrate and competes with the substrate for binding at the active site. During allosteric inhibition, a regulatory molecule binds to a site other than the active site, which changes the enzyme's shape and makes the active site unavailable to the substrate.

Which statement best describes results of an experiment designed to test whether the protein cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel?

Electric current flowed across membranes only in the presence of CFTR, indicating the movement of chloride ions. Ions carry a charge, so the electric current flowing only with the CFTR in place in the membrane indicated a flow of chloride ions.

In a metabolic pathway, A is converted to B via enzyme one, B to C via enzyme two, and C to D via enzyme three. According to the retro-evolution hypothesis for metabolic pathway evolution, which enzyme evolved first?

Enzyme three The retro-evolution hypothesis predicts that latter steps evolved first and that earlier steps were added on later as substrates became limiting

Which of the following is true of enzyme phosphorylation?

Enzymes (kinases) catalyze phosphorylation. Phosphorylation is a covalent modification and it takes enzymes to create the new bonds. The levels of phosphorylation and dephosphorylation enzymes in cells help regulate protein activity.

The fluid mosaic model describes the structure of the cellular membrane in which proteins are embedded in a lipid bilayer. Which of the following statements describes evidence that supports the fluid-mosaic model of plasma membrane structure?

Freeze fracture followed by scanning electron microscopy showed pits and mounds. During the freeze fracture, transmembrane proteins remained with either the upper layer or the lower layer of the bilayer. Scientists observed either pits (where proteins had left) or mounds where proteins now protruded above the single lipid layer

What is an important function of glycoproteins in animal cells?

Glycoproteins are important in cell-cell recognition. The carbohydrates found on the external surface of a cell membrane are important in cell-cell recognition and immune function.

Which of the following statements regarding polysaccharide polymerization is false?

Glycosidic linkages form between the same locations of monomers giving polymers a standard backbone structure. The location and geometry of glycosidic linkages can vary widely among different polysaccharides because glycosidic linkages form between hydroxyl groups and every monosaccharide contains at least two hydroxyl groups. Consequently, polysaccharides do not have a standard backbone structure as found in proteins and nucleic acids.

How do high temperatures speed chemical reactions?

Heat causes the reactants to move faster and collide more often. Reactants must be in physical contact for chemical reactions to occur. Heat speeds molecular motion and energy level of the reactants.

When researchers analyzed the effects of temperature and reactant concentration on reaction rates (Figure 8.4), why were temperature and concentration examined separately?

If higher temperatures and reactant concentrations were combined, researchers couldn't tell which factor led to an increase in reaction rate. A good experiment manipulates just a single factor and holds other variables constant

From the molecular formula, what would indicate that a six-carbon sugar was a disaccharide composed of two trioses and not a hexose?

In the disaccharide the molecular formula would be C6H10O5. Disaccharides are formed via a condensation reaction, which results in the loss of a water molecule.

How does concentration of substrate and product change the rate of chemical reactions?

Increased concentration of substrate will increase a chemical reaction rate. Increased availability allows for greater rate of reaction

Which of the following would decrease membrane fluidity?

Increased level of saturation of fatty acids An increase in saturation rate will decrease fluidity because phospholipids will be able to pack together more tightly. Saturated fatty acids are solid at room temperature.

Which of the following statements regarding ion channels is false?

Ion channels consume ATP to move ions against a concentration gradient. Ion channels do not perform active transport, the process of consuming ATP to move ions against a concentration gradient. Instead, ion channels allow ions to cross the plasma membrane by facilitated diffusion down an electrochemical gradient.

What is a feature that is exclusive to eukaryotic plant cells?

It is impossible to determine. The presence of these listed features does not allow for the classification of this cell as a eukaryotic plant cell. It is the presence of all these features and a nucleus that would define this as a eukaryotic plant cell.

Which of the following is true of the mitochondrion?

It is surrounded by a double membrane. The mitochondrion is surrounded by two membranes. Each one consists of a phospholipid bilayer.

The mixing of purified microtubules with transport vesicles and ATP does not result in movement of the vesicles. Why?

Kinesin is missing. Kinesin is a motor protein that mediates the interaction between microtubules and transport vesicles and converts the chemical energy of ATP into the kinetic energy of movement.

A large carbohydrate is tagged with a fluorescent marker and placed in the extracellular environment surrounding a eukaryotic cell. The cell ingests the carbohydrate via endocytosis. Which of the following cellular structures is most likely to be the one fluorescently labeled?

Lysosomes Lysosomes are organelles that can degrade material enclosed in endocytic vesicles.

Considering the reaction CH4 (methane) plus O2 yields CO2 plus H2O plus energy, which of the following is true?

Methane acts as an electron donor. Methane donates electrons and becomes oxidized to carbon dioxide. The electrons in the C-H bonds were held equally by carbon and hydrogen, but in CO2 the electrons have moved away from carbon (carbon is an electron donor). Also, oxygen is nearly always an electron acceptor, so methane must be the electron donor

Gold particles below a certain size limit that are injected into the cytoplasm can later be observed in the nucleus. This suggests which of the following?

Molecules below a certain size can diffuse nonselectively through the nuclear pore complex. Although large proteins require a nuclear localization signal to enter the nucleus, many small molecules can simply diffuse into and out of the nucleus through the nuclear pores.

Carbohydrates are made up of which of the following subunits?

Monosaccharides Carbohydrates are sugars and their polymers. They are composed of carbon, hydrogen, and oxygen. The individual subunits have a characteristic carbon skeleton, are either aldoses or ketoses, and have hydroxyl functional groups associated with them.

Which type of molecules moves across a cell membrane most easily?

Nonpolar molecules such as oxygen and carbon dioxide To pass readily through the lipid bilayer without a transport protein, the molecule must be lipid soluble. Furthermore, those molecules that move most readily through membranes also have a relatively small molecular weight.

Glycoproteins are important in cell-cell recognition. Where are the carbohydrate portions of these molecules normally found?

On the exterior surface of the cell membrane To fulfill their role in cell-cell recognition, the carbohydrates must be oriented to the exterior surface of the cell membrane.

Which of the following accurately represents how intermediate filaments differ from actin filaments and microtubules?

Only intermediate filaments play a purely structural role. In addition to their structural role, actin filaments and microtubules are also involved in cell movement.

What is the difference between peptidoglycan, found in the cell walls of prokaryotes, and chitin, found in the exoskeletons of insects?

Parallel strands of glucosamines in chitin are cross-linked by hydrogen bonds, whereas parallel strands of peptidoglycan are linked by peptide bonds. The structural integrity of the glucosamine polymers of both peptidoglycan and chitin are maintained by extensive cross-linking. The constituent glucosamines are different between peptidoglycan and chitin, as is the manner in which parallel strands are cross-linked.

Which organelle is a fluid-filled vessel responsible for the detoxification of the cell?

Peroxisomes Peroxisomes contain enzymes and oxidizing molecules such as hydrogen peroxide.

Which of the following is a covalent modification that can affect enzyme activity?

Phosphorylation Enzymes can catalyze the covalent addition of phosphate groups onto proteins to regulate their activity.

There are hundreds, if not thousands, of proteins that are specifically localized to the cell nucleus. What is likely to be true about transport of these proteins into the nucleus?

Proteins specifically localized to the nucleus must have the same or a similar nuclear localization signal that directs them to the nucleus. Nuclear localization signals are molecular "zip codes" that interact with proteins associated with the nuclear pore complex. This interaction allows proteins with a nuclear localization signal to be actively transported into the nucleus.

How does a pump differ from a channel or a carrier?

Pumps require energy for transport, but channels and carriers do not use energy. Pumps move materials against an electrochemical gradient and thus require energy. Channels and carriers only facilitate diffusion down a molecule's or ion's electrochemical gradient.

Researchers supplied a short pulse of radioactively labeled leucine, followed by a long chase of unlabeled leucine, to cells that secrete digestive enzymes. The bulk of the radioactive label was initially found in the rough endoplasmic reticulum (ER), then in the Golgi apparatus, then in secretory vesicles, and finally outside the cell. These results support which of the following hypotheses?

Secreted proteins are synthesized in the rough ER and travel through the Golgi apparatus to be packaged into secretory vesicles that fuse with the plasma membrane. This experiment is tracking the path of secreted proteins from the site of their synthesis to their secretion outside the cell.

A certain eukaryotic cell type specializes in synthesizing lipids. Which organelle would be found in greater abundance in this cell type than in other cell types that don't synthesize lipids?

Smooth endoplasmic reticulum The smooth endoplasmic reticulum contains proteins necessary for lipid synthesis

Suppose that the plasma membrane around a eukaryotic flagellum is opened to reveal the axoneme inside. The radial spokes connecting the peripheral microtubule doublets to the central pair are then broken by chemical treatment and ATP is added. What is the expected observation?

The axoneme will elongate. Microtubules will slide past each other, elongating rather than bending the axoneme, because of the lack of anchors provided by the radial spokes.

Suppose that a transmembrane protein destined for the plasma membrane is labeled with a fluorescent dye on the part of the protein exposed on the outer face of the endoplasmic reticulum (ER) membrane. If the protein distributes among cellular compartments, where would you expect the dye to be located?

The dye will be on the outer face of the ER, on the outer face of the Golgi apparatus, and on the intracellular face of the plasma membrane. The orientation of membrane components will be the same in the Golgi apparatus and the plasma membrane as in the ER. The part that faces the cytoplasm will remain cytoplasmic throughout the journey

Which of the following most accurately describes feedback inhibition?

The end product of a metabolic pathway inhibits an early enzyme in the pathway. As the end product builds up, it inhibits an early step, saving the initial substrate for other pathways.

Proteins are amphipathic molecules that contain nonpolar (hydrophobic) amino acids and polar (hydrophilic) amino acids. Where would you expect to find the hydrophobic and hydrophilic amino acid residues of a transmembrane protein?

The hydrophobic amino acids would come into contact with the hydrocarbon tails of the phospholipid bilayer, whereas the hydrophilic amino acids would interact with the intracellular and extracellular environment. The bilayer interior is hydrophobic and nonpolar, so the hydrophobic amino acid residues would come into contact with this area. Hydrophilic amino acids would be oriented toward intracellular fluid or toward extracellular fluid, or toward the interior of the protein.

Which of the following transport processes is an example of active transport across a plasma membrane?

The movement of potassium across the plasma membrane through a channel protein Facilitated diffusion involves use of transmembrane proteins such as potassium channel proteins to assist the passive transport of substances across a plasma membrane.

The degree of saturation of phospholipids in a membrane will affect which of the following functions of phospholipids?

The permeability of the membrane Carbon-carbon double bonds create kinks in the hydrocarbon tails of the fatty acids. The more saturated the fatty acid tails of phospholipids, the more tightly they can be packed into the membrane, resulting in a decrease in permeability.

Which of the following statements best describes the fluid-mosaic model of membrane structure?

The phospholipid bilayer contains diverse proteins, including some embedded amphipathic proteins that span the bilayer. This statement best explains the fluid-mosaic model. First described in 1972 by Singer and Nicolson, this model is based on freeze-fracture preparations. It replaced the Davson-Danielli sandwich model.

Suppose that the plasma membrane around a eukaryotic flagellum is opened to reveal the axoneme inside. The dynein sidearms between the peripheral microtubule doublets are removed by chemical treatment and ATP is added. What is the expected observation?

There will be no movement because the ability to use ATP is lost. Dynein is the protein that converts ATP energy to movement of the microtubule doublets in cilia and flagella.

What do myosin, dynein, and kinesin all have in common?

They all hydrolyze ATP to provide energy for movement. All three are motor proteins that convert the chemical energy of ATP to the kinetic energy of movement.

Which is usually true of catabolic pathways?

They break large molecules into smaller parts and produce energy. Glucose oxidation into carbon dioxide and water is an example of a catabolic pathway.

Simple sugars can differ from one another in which of the following ways?

They can differ in the location of their carbonyl group. Each monosaccharide contains a carbonyl group, but the placement of that group varies between sugars.

What happens when phospholipids are placed into water?

They form liposomes. Liposomes are water-filled vesicles, with phospholipids forming a bilayer that encloses the vesicle. Lipid bilayers are composed of two aligned layers of phospholipids with the tails pointing to the inside.

You have discovered a new type of animal cell and are viewing it under an electron microscope. You discern a large amount of rough endoplasmic reticulum (ER) and protein-filled vesicles, more than in other cell types. Which of the following is a reasonable assumption?

This cell type secretes a lot of proteins. Cells that secrete a lot of proteins will be enriched with rough endoplasmic reticulum.

In the model of enzyme action, which state is responsible for lowering the activation energy of a reaction?

Transition state facilitation It is here when interactions between substrate and enzyme lower the activation energy.

Region A has a low solute concentration. Region B has a high solute concentration. They are separated by a selectively permeable membrane that is impermeable to the solute but allows passage of water. Which of the following is true?

Water moves from region A to region B via osmosis. Osmosis refers specifically to the diffusion of water across a selectively permeable membrane down its concentration gradient from regions of high water concentration (low solute) to regions of low water concentration (high solute).

Unlike animal cells, bacteria have a porous cell wall surrounding their plasma membrane. The cell wall may help bacteria survive in _____ environment.

a hypotonic In a hypotonic environment, water will enter the cell via osmosis. The cell wall can prevent bursting of the cell as could occur in an animal cell in a hypotonic environment.

If a monosaccharide's carbonyl group is on an internal carbon, then the monosaccharide is ____.

a ketose In ketoses the carbonyl group is on an internal carbon and not on an end carbon.

The three types of lipids found in cells (fats, steroids, and phospholipids) are insoluble in water because they all possess _____.

a significant component of hydrocarbons All lipids contain a significant proportion of hydrocarbons. Hydrocarbons are nonpolar, which makes them hydrophobic

The extensive hydrogen bonding found among parallel glucose polymers of cellulose enables it to function in plants as _____.

a structural polysaccharide Cellulose makes up the bulk of the cell walls of plants. The rigidity of the molecule imparts a great deal of tensile strength to the structure. Cellulose is one reason plant stems can support the rest of their structures

Across all of cellular life, there are three conserved structures. Those structures are______________.

chromosomes, ribosomes, and a plasma membrane All cells are surrounded by a plasma membrane, have one or more DNA-containing chromosomes, and need ribosomes to synthesize proteins.

Molecules that move down a concentration gradient and require transport proteins to cross a membrane use _____.

facilitated diffusion Transport proteins permit molecules such as sugars to move across membranes down a concentration gradient.

Sperm identify an ovum by interacting with a glycoprotein called ZP3 in the gelatinous extracellular matrix that surrounds the ovum. Predict the outcome of the experimental removal of sugars from these glycoproteins. When sugars are removed from ZP3, _____.

fertilization is prevented Experimental removal of sugars from ZP3 glycoproteins in the zona pellucida, a gelatinous extracellular matrix surrounding the ovum, prevents fertilization as sperm can no longer recognize the ovum.

A red blood cell that is placed in distilled water (pure water lacking solutes) will _____.

gain water and expand Red blood cells have dissolved solutes, and distilled water has no dissolved solutes. Therefore, distilled water has a higher concentration of water molecules relative to the red blood cell. Water would move down its concentration gradient via osmosis into the cell.

Monosaccharides differ from one another in ____.

whether they contain an aldose or a ketose group Sugars are aldoses or ketoses with multiple hydroxyl groups.

A reaction will be spontaneous at all temperatures under which set of conditions?

∆H is negative and ∆S is positive. Under these conditions, ∆G will be negative and spontaneous at all temperatures.